The diversity of secondary metabolites in amaranth.
Abstract
Cultivated amaranths are crops with an unrealized agronomical potential despite their high nutritional value and nutraceutic properties of their seeds and/ or leaves. They tolerate growing conditions unsuitable for cereals, and are tolerant to biotic aggressors. Several Amaranthus species are abundant of sources of secondary metabolites, mostly phenylpropanoids, predominantly in seeds and leaves, many of which may confer health benefits associated with their antioxidant properties. They could also act as defensive compounds against predators or pathogens. Recent biochemical and molecular approaches partly defined the mechanisms responsible for grain amaranth´s tolerance against biotic stress. However, the role played by secondary metabolites in (a)biotic stress amelioration in amaranth is practically unknown. Our group has identified several genes coding for enzymes involved in secondary metabolism pathways in A. hypochondriacus, in addition to related regulatory transcription factors. More than 50% of these genes involve the phenylpropanoid pathway. In this chapter, the role played by this pathway in (a)biotic stress amelioration in plants will be briefly reviewed, followed by an examination of its involvement in the conferral of nutraceutic properties to amaranth plants. A description of the progress obtained so far regarding the characterization of phenylpropanoid genes in grain amaranth will close this chapter.
Keywords
- (a)biotic stress
- grain amaranth
- phenylpropanoids
1. Introduction
Species belonging to the Amaranthaceae compose a diverse and interesting family of plants. They can develop in highly contrasting habitats, from arid and semi-arid zones, where they can survive in sandy alkaline and/ or serpentine soils, to disturbed tropical forests. A minority are found in aquatic, semi-aquatic or marine environments. Their high affinity to saline conditions stems, in part, from to the weedy nature of most of the species that constitute the
The
In this chapter, we shall first review the role played by phenylpropanoid pathway in the amelioration of both biotic and abiotic stress in plants. Then, we shall proceed to describe the state of the art with regard to the phenylpropanoid pathway in
2. Reactive Oxygen Species (ROS)
2.1. Brief description of their ubiquitous and malignant role in plant stress and the antioxidant defense mechanisms induced for their control — What is known regarding amelioration of ROS-related damage in amaranth plants during stress?
The abundance of reactive oxygen species (ROS) tends to increase in the tissues of plants exposed to diverse environmental challenges including contact with heavy metal contaminants in soil, water or salinity stress, which is often accompanied by high light and temperature, and nutrient deficiency [16]. Most stress conditions in plants cause an accumulation of ROS, such as superoxide ion, hydrogen peroxide, oxygen-containing radicals, and others. These chemical entities can produce extensive oxidative damage in the apoplastic compartment and may also harm cellular membranes by lipid peroxidation. Additionally, they can have an impact on ion homeostasis mechanisms, which are crucial for many stress tolerance mechanisms, by interfering with ion fluxes [17]. ROS detoxification frequently involves the combined action of both antioxidant metabolites such as ascorbate, glutathione, tocopherols, and ROS-detoxifying enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) [18,19]. In this sense, overproduction of antioxidants in response to drought-induced oxidative stress has been frequently found to be associated with the drought stress tolerance of different plant species [20,21]. Also, enhanced drought tolerance has been generated in several different transgenic plants transformed with genes encoding diverse types of antioxidant-related enzymes or metabolites (e.g., SOD, APX, monodehydroascorbate reductase, and tocopherol cyclase, a key enzyme of tocopherol biosynthesis, [22]). Regarding grain amaranth, a series of proteomic studies performed in plants exposed to drought and saline stress detected the accumulation of various antioxidant enzymes, similar to those mentioned above [23,24]. In addition, the participation of antioxidant genes, such as
Glycine betalaine (GB) is a quaternary ammonium compound that acts as an osmolite with protective functions in plants subjected to the osmotic stress normally produced under drought, high temperature and/ or excessive salinity conditions. GB accumulation in the cytoplasm reduces ion toxicity, and ameliorates the highly damaging effects caused by the usually simultaneous presence of dehydration, salinity, and extreme temperature stresses. The protective effect is proposed to be exerted by the stabilization of macromolecular structures, and/ or by the protection of chloroplasts, particularly the photosystem II complex. The latter is believed to involve the thermodynamic stabilization of the indirect interaction of extrinsic photosystem II complex proteins with membrane phosphatidylcholine moieties [25]. GB is synthesized by the two-step oxidation of choline. The first step is catalyzed by choline monooxygenase, followed by the action of betaine aldehyde dehydrogenase. Both genes have been described in different amaranth species [12,26,27], whereas the presence of GB has been reported in all Amaranthaceae species examined so far, with the exception of
2.2. Betacyanins in amaranth: More than pigments?
Betalains are water-soluble, nitrogen-containing pigments that are found only in one group of angiosperms, the Caryophyllales. For reasons that remain unresolved, they have never been found jointly with anthocyanins in the same plant [29,30]. This particular trait has been employed for chemo-taxonomical purposes. These pigments can be divided into the red-violet betacyanins and the yellow betaxanthins. Both are immonium conjugates of betalamic acid covalently bonded with cyclo-dihydroxyphenylalanine (cDOPA) glucosides, which can undergo further acylations [31–33]. These pigments are possibly needed for the optical attraction of pollinators and seed dispersers. Regarding stress, a protective role against accumulating ROS has been inferred from a number of studies [34–36] whereas the betacyanin amaranthine has also been proposed to exert protective effects against photo-oxidative damage in
Recently, an analysis of key genes/ enzymes of the betacyanin biosynthetic pathway in
In addition to pigments, diverse phytochemical studies have shown that amaranth plants are capable of synthetizing a notable diversity of secondary metabolites [3,38,39]. Although many of these compounds are not considered to be essential for the primary needs of the plant, they are certainly required for survival in and/ or adaptation to challenging environmental conditions. Many of these compounds may be employed in amaranth and other plants as signaling compounds, in defense and/ or for communication with other organisms, such as pollinators [40–44].
The most commonly found secondary metabolite families found in amaranth and related species are phenylpropanoids, including flavonoids, phenolic acids, and their related amides, followed by alkaloids and terpenoids. From an anthropocentric perspective, some of these chemicals, including betacyanins, flavonoids polyphenols, and phenolic acids, are responsible for conferring amaranth and quinoa tissues with the bioactive antioxidant activity associated with their well-documented health benefit effects [3,38,45–49].
3. Phenylpropanoid secondary metabolites
Plants have accumulated a great diversity of phenolic compounds as a result of their long process of evolutionary adaptation. Approximately 40% of these compounds are derived from the highly diverse phenylpropanoid metabolism. The phenylpropanoid compounds constitute a highly diverse assortment of phenylalanine-derived secondary metabolites. These include flavonoids, which are generally sub classified into the anthocyanins, proanthocyanidins, flavonols, isoflavonoids, phlobaphenes, flavanones, and flavones subgroups, which are found in the majority of higher plants, in addition to the aurone subgroup, which is widespread, but not ubiquitous. Also included are monolignols, lignans, coumarins, phenolic acids, quinines, stilbenoids, and xanthones. Other phenolics include alkylmethoxyphenols, alkylphenols, curcuminoids, furacoumarins, hydroxybenzaldehydes, hydroxybenzoketones, hydroxycinnamaldehydes, hydroxycoumarins, hydroxyphenylpropenes, methoxyphenols, naphthoquinones, phenolic terpenes, and tyrosols.
Most of the flowers and fruits pigments employed for pollinator attraction and seed dispersal are water-soluble anthocyanins [50]. Proanthocyanidins, or condensed tannins, are colorless flavonoid polymers produced by the condensation of flavan-3-ol units [51]. Similarly colorless are the abundant flavonols which are usually found in the form of mono-, di-, or triglycosides [52]. Isoflavonoids and phlobaphenes are groups of flavonoids characterized by being predominantly found in the Papilionoideae family [53] or by their red pigmentation which results from the polymerization of flavan-4-ols [54], respectively. Based on their carbon skeleton, the ubiquitous phenolic acids can belong to the hydroxycinnamic acid type (chlorogenic, ferulic, rosmarinic, and sinapic acids) or to the hydroxybenzoic acid type (p-hydroxybenzoic, vanillic, and protocatechuic acids). Finally, the stilbenes represent a small family of phenylpropanoid metabolites dispersed in over 70 unrelated plant species [55–57]. Interestingly, the latter compounds are induced in response to several biotic and abiotic stimuli or by functionally related elicitors, such as methyl jasmonate (MeJA), and ethylene. Flavonoids are also involved in the regulation of auxin transport [58–60] and participate in the chemical dialog established between the plant roots and nitrogen-fixing bacteria and in signaling pathways designed to modulate ROS levels in plant tissues [61,62]. These compounds are also determining factors of male fertility and precursors for the synthesis of lignin [63–65]. The latter is an aromatic heteropolymer that confers mechanical strength to the cell wall and rigidity to plant stems, whose synthesis involves the assembly of p-coumaryl, coniferyl, and sinapyl alcohol monolignols. Lignin is also a waterproof insulator for cell walls and, as such, facilitates the transport and assimilation of water through the vascular system. It also provides protection against wounding, UV light, and pathogen attack [66].
As noted, phenylpropanoids have notable structural and biological function diversity. In terms of defense in plants, phenylpropanoids can be classified into three broad categories according to their function. Those having signaling activity, those known as phytoanticipins, which are part of the basal defensive arsenal of the plant and constitutively accumulate in certain plants tissues, and those whose
3.1. Phenylpropanoid biosynthesis: A profusely branched pathway
Phenylpropanoids contain at least one aromatic ring with one or more hydroxyl groups, and are synthesized via the shikimate pathway alone or in combination with the mevalonate pathway. The first three steps in the synthesis of phenylpropanoid-derived compounds are catalyzed by phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate coenzyme A ligase (4CL), collectively referred to as the general phenylpropanoid pathway (GPP). GPP products then serve as precursors for phenylpropanoid-derived compounds [71,72].
The deamination of phenylalanine to cinnamic acid catalyzed by phenylalanine ammonia lyase (PAL, EC 4-3.1-5) is the initial step shared by all phenylpropanoid secondary metabolites. PAL is a conserved homotetrameric protein that is a key enzyme in the phenylpropanoid pathway of higher plants [73–76]. PAL enzymes are grouped as families having many isoforms that are responsive to different developmental and environmental stimuli [77,78].
Cinnamate is the basic structure from which simple phenylpropanoids with the basic C6–C3 carbon skeleton of phenylalanine are produced, via a series of hydroxylation, methylation, and dehydration reactions. This group includes compounds such as p-coumaric, caffeic, ferulic, and sinapic acids and simple coumarins, which rarely accumulate as free acids inside plant cells, being usually conjugated to sugars, cell wall carbohydrates, or organic acids. Salicylic, benzoic, and other acids are uncharacteristic phenylpropanoids that lack the three-carbon side chain, even though they originate from cinnamate and p-coumarate, whereas a large number of stress-induced phenylpropanoids are derived from the C15 flavonoid skeleton, which is synthesized via the chalcone synthase (CHS)-catalyzed condensation of p-coumaroyl-coenzyme A (COA) and three molecules of malonyl-COA. The tetrahydroxychalcone product resulting from the CHS-catalyzed step in most plants is further converted to other flavonoids, such as flavones, flavanones, flavanols, anthocyanins, and 3-deoxyanthocyanidins (Figure 1) [67,68]. Lignin and suberin represent an increased level of complexity, since they are large polymers, constructed from monolignol phenylpropanoid precursors, whose composition varies from species to species.
3.2. Regulation of phenylpropanoid biosynthesis: A complex scenario
The biosynthesis and accumulation of secondary metabolites, including phenylpropanoids, are usually tissue- and developmental-stage-specific. As mentioned above, phenylpropanoids can be present as pigments in leaves, flowers, fruits, and seeds or participate in the establishment of mutualistic or detrimental interactions either with beneficial fungi or bacteria or with pathogenic oomycetes [79]. They can participate in the synthesis of lignins and related fibrous materials associated with changes in the cell wall occurring concomitantly with development, in response to stress [66], or in the determination of pollen function. The latter involves the conjugation of polyamines with hydroxycinnamic acid [63–65,80–82]. Numerous factors mediate the expression of phenylpropanoid genes, including sugar levels, transcription factor (TF) regulation, and diverse types of stress. Sucrose, for instance, has a dual function, first by providing carbon for phenylpropanoid metabolism, and second, by modulating transcriptional and post-translational regulation of many pigment-related genes [83,84]. Recently, a sugar-related regulatory loop was described in which the induction, by sucrose, of AN1, a MYB TF that activates the phenylpropanoid biosynthetic pathway, was self-regulated by the increased sucrolytic activity induced in parallel by the action of AN1 [85]. Structural variability in secondary metabolism is also determined by post-translational chemical modifications of the primary chemical structure by diverse reactions. This is a mechanism that profoundly alters the biological activity of phenylpropanoid compounds via its ability to modify various critical biochemical parameters, including stability, solubility, and/or localization within the cell. For instance, the glycosylation of hydroxycinnamic acids was found to have an important participation during N-limiting stress conditions in
Controlled transcription of biosynthetic genes is one major mechanism regulating secondary metabolite production in plant cells. Several TFs involved in the regulation of metabolic pathway genes have been isolated and studied. Synthesis of more than one class of phenylpropanoid-derived compounds is predominantly under the control of V-myb myeloblastosis viral oncogene homolog (MYB) proteins of the R2R3-MYB class that can act both as transcriptional activators and repressors [92]. The participation of these TFs in many phenylpropanoid-related processes has been extensively recorded in various plant species. In Arabidopsis, several R2R3-MYB members have been implicated as positive regulators of lignin synthesis. For instance, the secondary cell wall-associated AtSND1 protein, in association with related proteins, starts a cascade of events that regulate secondary cell wall formation by inducing the expression of the
Complex formation, initiated by the activation of R2R3-MYB genes can be induced by environmental stress conditions or in response to developmental cues. Known targets of this complex are genes encoding dihydroflavonol 4-reductase (DFR), bHLH2, and, curiously, two MYB repressors whose activation leads to a self-regulatory feedback repression loop [105]. The AtDOF4-2, BrMYB4, and AtMYB4 TFs have been reported also as negative regulators of flavonoid and lignan biosynthesis [80,106,107]. In Arabidopsis, anthocyanin biosynthesis via the MBW complex has been demonstrated to be stimulated in response to light, sucrose, nitrogen, and JA [83,108–110].
In addition, anthocyanin patterning and spatial localization are mainly determined by R2R3-three subgroups of MYB activators, many of which have been identified in plants [92]. The MYB, bHLH, and WDR transcription factors have also been shown to be prevalent in the regulation of proanthocyanidin genes [105,111]. Conversely, the regulation of the flavonol pathway is species-specific, and diverges from the above regulatory mechanisms by its diversity, which may require the action of either a single MYB TF, the formation of an MYB-bHLH dimer or an MBW complex. Additionally, augmented flavonol content in Arabidopsis has been found to result from the association of members of the plant-specific teosinte branched1, cycloidea, and proliferating cell nuclear antigen factor, or TCP TF family that interact with AtMYB12 and AtMYB111 [112]. Additionally, the expression of
3.3. Phenylpropanoid and other less abundant secondary metabolites in amaranth: Nutraceutical properties and suggested defensive roles
Several chemical analyses of diverse tissues of
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Flavonoids |
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Betacyanins |
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Phenolic acids |
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Tannins |
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Steroids and triterpenoids |
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Saponins |
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Coumarins |
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Alkaloids |
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Amarantholidosides |
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Polyhydroxylated nerolidols |
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Carotenoids |
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Chlorophylls |
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Phytate |
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Resinols |
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Tocopherols and tocotrienols |
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A recent study reported a significantly variable content of bioactive substances and phenolic contents in leaves of various cultivars of
In this study, the levels of 11 different polyphenols, including three flavonoids, i.e. rutin, isoquercitrin, and nicotiflorin, and 8 phenolic acids, i.e., protocatechuic, vanillic, 4-hydroxybenzoic, p-coumaric, syringic, caffeic, ferulic, and salicylic acids, were analyzed in mature seeds of 18
Once more, PCA clearly identified that samples from one location (i.e., in Argentina) differed from all other experimental sites by having a higher content of most compounds analyzed. Phenolic acids were, once again, a key group of compounds since their analysis permitted the separation of the different experimental groups, while separation of both amaranth genotypes could be performed primarily by the higher contents of trigonelline and the two hydroxycinnamyl amides present in
The influence of other experimental effects on polyphenol levels, such as tissue type, ripeness, or time of harvest was demonstrated by results obtained from a two-year field study performed with various grain and foliar amaranth species, in addition to two amaranth hybrids [120]. The tissue-type effect was clearly demonstrated by results that showed a more than 300-fold difference in rutin content between seeds and leaves. This study also showed that rutin was predominantly found in mature amaranth leaves, in accordance with previous reports describing a progressive accumulation of rutin in maturing amaranth and other rutin-accumulating plants, such as common buckwheat. Genotype-dependent effects were again observed, since noticeable variations between the species and even between the varieties belonging to the same species were detected. For instance, the highest rutin contents found in
Other environmental factors, such as light, or the lack of it, have been also found to selectively influence the level of certain phenolic compounds. Thus, growth of
Aside from expected genotype- and tissue-related variations, the differences observed were also suggested to be caused by the analytical methods employed for tannin content determination. Posterior processing procedures (e.g., roasting of seeds, cooking, or blanching of leaves, etc.) were also found to be significant factors affecting tannin content in amaranth seeds or leaves. Subsequently, a pertinent study assessed that the nutraceutical value of leaves of
Two recent reports focused on direct or indirect changes in polyphenolic content in grain amaranth plants exposed to different stress conditions. The first one determined changes in the abundance of 3 flavonoid glucosides (rutin, nicotiflorin, and isoquercitin), 9 phenolic compounds (coumaric, vanillic, caffeic, syringic, ferulic, sinapic, protocatechuic, salicylic, and 4-hydroxybenzoic acid) and 3 betalains (amaranthine, iso-amaranthine, and betanin) in leaves of five varieties of three grain amaranth species subjected to insect folivory, in a one-year field trial [44]. Multivariate regression analysis revealed significant and predictable differences in the chemical composition of the leaves between grain amaranth genotypes. A similar analytical approach indicated that 8 of the 15 compounds analyzed in the plants, including all 3 flavonoid glucosides, 2 betalains, and 3 phenolic acids, had significant linear relationships with insect herbivory in the field. However, the experiment was not designed to determine biological relevance of the herbivory-induced accumulation of some of these metabolites in amaranth leaves. Thus, the possibility that phenolics could have been acting as feeding deterrents, phagostimulants, digestion inhibitors, digestion stimulants, toxins, toxicity reducers, signal inhibitors, and/or signal transducers in damaged grain amaranth remained unanswered [130]. In potato (
In a related proteomic study, the upregulation of transcription factors (i.e., DOF and MIF) was found to be coupled with the downregulation of caffeic acid O-methyltransferase, an isoflavone reductase-like protein, and two different S-adenosylmethionine synthetases, which are enzymes related to secondary metabolism associated with flavonoid and lignin synthesis [23]. Based on these results, the authors suggested that repressed root growth in grain amaranth plants subjected to severe drought is an adaptive response occurring in response to decreased root lignification. This proposal is in accordance to other reports showing that roots of plants exposed to different stresses may change their lignin content and composition [132]. One possible advantage derived from reduced lignification of the roots, particularly in the elongation zone, is that it may facilitate growth recovery once drought stress has been alleviated [133].
3.4. Secondary metabolism biosynthetic pathways and related genes in amaranth: Wandering into unknown territory?
The information provided above indicates that a potentially high nutritive and medicinal benefit may be derived from the consumption of amaranth seeds and foliage, which are high in antioxidant phenolic compounds, among other health-enhancing constituents. Until recently, information about the biosynthesis of these bioactive compounds and of the genes coding for the respective biosynthetic enzymes was practically null in amaranth. However, a recent transcriptomic study of grain amaranth leaves subjected to various stress treatments [14] revealed the presence of several genes involved in secondary metabolism, mostly in the phenylpropanoid biosynthetic pathway. The rest of this chapter will concentrate on the description of their characteristics and possible functions.
The transcriptomic study permitted the identification of 95 genes that code for the enzymes that most probably form part of the secondary metabolite biosynthetic flow in
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ID1 | Indole 3-glycerol phosphate lyase ( |
1 | Emission of volatile compounds related to defense [169]. |
ID1 | Anthranilate synthase ( |
2 | Production of tryptophan pathway metabolites as part of an Arabidopsis defense response (e.g., camalexin) [170, 171]. |
ID1 |
|
1 | Pathogen-induced transcription factor; camalexin biosynthesis [172]. |
A2 | Berberine bridge enzymes ( |
3 | Upregulation of these genes was observed at specific stages of development and in response to osmotic stress and pathogens attack [173,174]. |
A2 | Strictosidine synthase like ( |
The four SSL-coding genes in Arabidopsis are regulated individually, suggesting specific roles in basal (SSL4) and inducible (SSL5-7) plant defense mechanisms [175]. | |
A2 | Tropinone reductase ( |
4 | The |
A2 | Hyoscyamine 6-hydroxylase ( |
2 | The overexpression of |
T3 | Acetoacetyl-CoA thiolase ( |
2 | The AACT is a regulatory enzyme in isoprenoid biosynthesis involved in abiotic stress adaptation [178]. |
T3 | 3-Hydroxy-3-methyl-glutaryl-CoA reductase ( |
3 | HMGR activity induced by wounding, elicitor, or pathogen challenge is correlated with increased |
T3 | 1-Deoxy-xylulose 5-phosphate synthase ( |
1 |
|
T3 | Sesquiterpene synthase ( |
2 | Involved in indirect defense of maize against herbivore attack [183]. |
T3 | Squalene synthase ( |
1 | The downregulation of |
T3 | Squalene epoxidase ( |
4 | The synthesis of saponins and expression of respective genes ( |
T3 |
|
1 | The orthologous genes, |
In this respect, the phenylpropanoid pathway is the best represented, with more than 69.5% of the above 95 biosynthesis-related genes coding for enzymes related to their biosynthesis [14]. Their position in the intricate phenylpropanoid biosynthetic reaction pathway is shown in Figure 1. Many of these genes have been amply characterized in other plant species. However, those described below code for enzymes that should be highly active, considering that, as mentioned in previous sections of this chapter, amaranth plants have been frequently found to be unusually rich in these compounds (Table 4). Thus, these particular grain amaranth enzymes and/or genes could have attractive biochemical and/or regulatory properties that could offer potentially important biotechnological applications. In addition, four TFs similar to those described above as key regulators of this biosynthetic pathway are described.
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Catequin | 0.15-0.23 | 0.07-0.22 | - |
Rutin | 0.38-0.47 | 0.17-0.30 | 4.0-10 (4798-15531)* |
Quercetin/isoquercetin | - | 0.1-0.65 | 0.3-0.5 (27.8-279.5)* |
Nicotiflorin | - | - | 4.8-7.2 (141-1281)* |
As already mentioned, PAL catalyzes the first committed step of the phenylpropanoid pathway, which is shared by all compounds produced by downstream ramifications of the pathway (Figure 1). It also represents a bifurcation point between primary and secondary metabolism. Diverse environmental stimuli and developmental programs regulate PAL. It is induced by lignin demands for cell wall fortification and by both biotic (e.g., pathogen and insect damage) and abiotic stresses (e.g., UV irradiation, low temperatures, and nutrient deficiency) [134,135]. PAL activity has been found in all the higher plants analyzed so far, and in some fungi and a few bacteria, but not in animals. In all species studied,
A number of R2R3 MYB transcription factors are known to be able to transactivate
Correspondingly, the
Cinnamate 4-hydroxylase (C4H) is the second key enzyme in the phenylpropanoid pathway and catalyzes the hydroxylation of
The enzyme 4-coumaric acid CoA ligase (4CL) plays an important role in the biosynthesis of lignin precursors such as hydroxycinnamate-CoA thioesters. The
Chalcone synthase (CHS) is another key enzyme of the flavonoid/ isoflavonoid biosynthesis pathway. Besides being part of the plant developmental program,
Flavanone 3-hydroxylase (EC 1.14.11.9), F3H, is a key enzyme in the flavonoid biosynthetic pathway, catalyzing the 3-hydroxylation of (2S)-flavanones, such as naringenin to dihydroflavonols. In soybean seeds the downregulation of
Tolerance to UV radiation and severe water deprivation in the extremophyte
Flavonol synthase (EC 1.14.11.23), FLS, is another relevant enzyme due to its crucial participation in the conversion of several precursors needed for different branches of the flavonoid biosynthesis. For instance, the biosynthesis of flavonols from dihydroflavonols is catalyzed by FLS, a soluble 2-oxoglutarate-dependent dioxygenase (2-ODD) (Figure 6). The expression is tissue- and organ-specific organ and is regulated by various light intensities, pathogen infection, and herbivore attack [134,161–163]. Silencing of the
Dihydroflavonol 4-reductase (DFR, EC 1.1.1.219), DFR, is a pivotal enzyme in the flavonoid biosynthetic pathway that plays a crucial role in producing simple and condensed anthocyanins. This enzyme catalyzes the production of flavan-3, 4-diols (leucoanthocyanidins) via the reduction of three colorless dihydroflavonols, i.e., dihydrokaempferol, dihydroquercetin, and dihydromyricetin. These compounds are also intermediates of flavonol biosynthesis, occurring through the flavonol synthase reaction. These leucoanthocyanidins are subsequently converted to pelargonidin, cyanidin, and delphinidin, respectively. DFR can accept wide range of substrates, although substrate specificity of DFR has been shown to vary depending on the specific types of anthocyanins that accumulate in a given plant species. In plants, DFR can be either present as a single gene or as a multicopy gene family. Single DFR genes have been found in
Leucoanthocyanidin dioxygenase (LDOX: 1.14.11.19), also called 2-oxoglutarate iron-dependent dioxygenase (2-ODD) or anthocyanidin synthase (ANS), is also involved in anthocyanin biosynthesis and catalyzes the conversion of colorless to colored leucoanthocyanidin. Expression of
As mentioned, lignin is the generic term for a large group of aromatic polymers that result from the oxidative combinatorial coupling of 4-hydroxyphenylpropanoids (Figure 7). These polymers are deposited predominantly in the secondary walls of thickened cells, making them rigid and impermeable. In addition to developmentally programmed deposition of lignin, its biosynthesis can also be induced upon various biotic and abiotic stress conditions, such as wounding, pathogen infection, metabolic stress, and perturbations in cell wall structure. Activation of the monolignol precursor biosynthesis in the apoplast requires the combined activity of enzymes such as peroxidases (POX), laccases (LAC), or other polyphenol oxidases that transfer electrons from monolignols to electron receptors. These apoplastic enzymes interact with ROS such as hydrogen peroxide or superoxide, which act as electron receptors or modulators of POX and LAC enzymes through their signaling function. Once oxidized, monolignol radicals can bind to other similarly formed radicals to form the three-dimensionally cross-linked structures that characterize lignin. This polymerization process constitutes the final step of lignin biosynthesis.
Contrary to lignin, lignans represent a structurally diverse class of plant-specialized metabolites that are ubiquitously distributed in all land plants. They are presumed to have a predominantly defensive role
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Cinnamoyl-CoA- reductase ( |
1 | In wheat, this gene is involved in pathogen defense signaling. In tomato and other plants, the repression of this gene produced severe development-related phenotypes. | [189,190] |
Cinnamyl alcohol dehydrogenase ( |
16 | The silencing |
[189,191,192] |
Caffeoyl CoA 3-O-methyltransferase ( |
3 | This gene can be highly induced by drought and cold stress, suggesting a possible role in plant abiotic stress resistance. In maize and wheat, |
[193–195] |
4-Coumaroyl shikimate 3-hydroxylase/ p-coumarate 3-hydroxylase ( |
1 | C3H downregulation led to a dramatic accumulation of several glucosides of |
[196] |
Caffeic acid O-methyltransferase ( |
3 | In wheat, silencing of this gene is linked to increased susceptibility to fungal pathogens, such as |
[193,197] |
Ferulic acid hydroxylase ( |
2 |
|
[198–201] |
Hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase ( |
2 | Downregulation of the HCT gene in alfalfa plants exhibited constitutive activation of defense responses, triggered by release of bioactive cell wall fragments and production of hydrogen peroxide generated as a result of impaired secondary cell wall integrity. | [202] |
Coumarins may be subclassified as simple coumarins (benzo-α-pyrones syn 1, 2-benzopyrone), 7-oxygenated coumarins (furanocoumarins syn. furobenzo-α-pyrones or furocoumarins) or pyranocoumarins (benzodipyran-2-ones). Simple coumarins, furanocoumarins, and pyranocoumarins share the same biosynthetic pathway, whereas the most common phenylcoumarins (i.e., coumestans) originate from isoflavone. Coumarin is characterized for its pleasant vanilla-like odor. The presence of this metabolite has been reported in a diversity of plants, including members of the Fabaceae, Lauraceae, Lamiacea, Apiaceae, Asteracea, Rutaceae, and Amaranthaceae (
Finally, many stress-induced phenylpropanoids are classified as phytoalexins. These are antimicrobial compounds synthesized in response to pathogen attack. They include pterocarpans (e.g., glyceollin), isoflavans, prenylated isoflavonoids (e.g., kievitone), stilbenes, psoralens, coumarins, 3-deoxyanthocyanidins, flavonols (e.g., quercetin, kaempferol), and aurones. Most of these compounds have trivial names, such as the coumarins umbelliferone (7-hydroxycoumarin), esculetin (6, 7-dihydroxycoumarin), scopoletin (6-methoxy-7-hydroxycoumarin), and others. No phenylpropanoid phytoalexins have been reported in amaranth. Findings from a recent report [15] suggested, however, that they could be participating as part of the induced defense responses against bacterial pathogens produced by the application of defense-related inductors, such as BTH, JA, or the exposure to avirulent pathogens. This proposal is supported by the induced expression of
4. Conclusion
The several hypotheses raised by the discovery of the numerous stress-related phenylpropanoid genes in grain amaranth represents a strong incentive for the initiation and subsequent deepening of secondary metabolite studies in
Acknowledgments
Paula A. Castrillón-Arbeláez was supported financially by a one-year Post-Doctoral Fellowship awarded by the Autonomous National University of México (UNAM).
References
- 1.
Sánchez-del Pino I, Flóres-Olvera H, Valdés J. La familia Amaranthaceae en la flora halófita y gipsófila de México. Anales del Instituto de Biología Universidad Autónoma de México 1999;70:29–135. - 2.
Caselato-Sousa VM, Amaya-Farfan J. State of knowledge on amaranth grain: a comprehensive review. J Food Sci 2012;77:R93–104. - 3.
Venskutonis PR, Kraujalis P. Nutritional components of amaranth seeds and vegetables: a review on composition, properties, and uses. Compr Rev Food Sci Food Saf 2013;12:381–412. - 4.
Kauffman CS, Weber LE. Grain amaranth. In: Janick J, Simon JE. (Eds.) Advances in New Crops, Timber Press, Portland, OR; 1990. pp. 127–139. - 5.
Johnson BL, Henderson TL. Water use patterns of grain amaranth in the northern Great Plains. Agron J 2002;94:1437–43. - 6.
Omami EN, Hammes PS, Robbertse PJ. Differences in salinity tolerance for growth and water-use efficiency in some amaranth ( Amaranthus spp. ) genotypes. New Zea J Crop Horticult Sci. 2006;34:11–22. - 7.
Espitia-Rangel E, Ed. Amaranto: Ciencia y Tecnología, vol 2. Celaya, Guanajuato, México; 2012. 354 p. - 8.
Brenner D, Baltensperger D, Kulakow P, Lehmann J, Myers R, Slabbert M, Sleugh B. Genetic resources and breeding of Amaranthus . Plant Breed Rev 2000;19:227–85. - 9.
Castrillon-Arbelaez PA, Martinez-Gallardo N, Arnaut HA, Tiessen A, Delano-Frier JP. Metabolic and enzymatic changes associated with carbon mobilization, utilization and replenishment triggered in grain amaranth ( Amaranthus cruentus ) in response to partial defoliation by mechanical injury or insect herbivory. BMC PlantBiol 2012;12:163. - 10.
Vargas-Ortiz E, Espitia-Rangel E, Tiessen A, Delano-Frier JP. Grain amaranths are defoliation tolerant crop species capable of utilizing stem and root carbohydrate reserves to sustain vegetative and reproductive growth after leaf loss. PLoS ONE 2013;8:e67879. - 11.
Niveyro S, Salvo A. Taxonomic and functional structure of phytophagous insect communities associated with grain amaranth. Neotrop Entomol 2014;43:532–40. - 12.
Délano-Frier JP, Martínez-Gallardo NA, Martínez-de la Verga O, Salas-Araiza MD, Barbosa-Jaramillo ER, Torres A, Vargas P, Borodanenko A. The effect of exogenous jasmonic acid on induced resistance and productivity in amaranth ( Amaranthus hypochondriacus ) is influenced by environmental conditions. J Chem Ecol 2004;30:1001–34. - 13.
Sánchez-Hernández C, Martínez-Gallardo N, Guerrero-Rangel A, Valdés-Rodríguez S, Délano-Frier J. Trypsin and a-amylase inhibitors are differentially induced in leaves of amaranth ( Amaranthus hypochondriacus ) in response to biotic and abiotic stress. Physiol Plant 2004;122:254–64. - 14.
Délano-Frier JP, Avilés-Arnaut H, Casarrubias-Castillo K, Casique-Arroyo G, Castrillón-Arbeláez PA, Herrera-Estrella L, Massange-Sánchez J, Martínez-Gallardo NA, Parra-Cota FI, Vargas-Ortiz E, Estrada-Hernández MG. Transcriptomic analysis of grain amaranth ( Amaranthus hypochondriacus ) using 454 pyrosequencing: comparison withA. tuberculatus , expression profiling in stems and in response to biotic and abiotic stress. BMC Genomics 2011;12:363. - 15.
Casarrubias-Castillo K, Martinez-Gallardo NA, Delano-Frier JP. Treatment of Amaranthus cruentus with chemical and biological inducers of resistance has contrasting effects on fitness and protection against compatible Gram positive and Gram negative bacterial pathogens. J Plant Physiol 2014;171:927–39. - 16.
Gill SS, Tuteja N. Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants. Plant Physiol Biochem 2010;48:909–30. - 17.
Baier M, Kandlbinder A, Golldack D, Dietz KJ. Oxidative stress and ozone: perception, signalling and response. Plant Cell Environ 2005;28:1012–20. - 18.
Mittler R. Oxidative stress, antioxidants and stress tolerance. Trend Plant Sci 2002;7:405–10. - 19.
Neill S, Desikan R, Hancock J. Hydrogen peroxide signalling. Curr Opin Plant Biol 2002;5:388–95. - 20.
Pastori GM, Foyer CH. Common components, networks, and pathways of cross-tolerance to stress. The central role of "redox" and abscisic acid-mediated controls. Plant Physiol 2002;129:460–8. - 21.
Sunkar R, Kapoor A, Zhu JK. Posttranscriptional induction of two Cu/Zn superoxide dismutase genes in Arabidopsis is mediated by downregulation of miR398 and important for oxidative stress tolerance. Plant Cell 2006;18:2051–65. - 22.
Noreen S, Ashraf M. Modulation of salt (NaCl)-induced effects on oil composition and fatty acid profile of sunflower ( Helianthus annuus L.) by exogenous application of salicylic acid. J Sci Food Agric 2010;90:2608–16. - 23.
Huerta-Ocampo JA, Leon-Galvan MF, Ortega-Cruz LB, Barrera-Pacheco A, De Leon-Rodriguez A, Mendoza-Hernandez G, de la Rosa AP. Water stress induces up-regulation of DOF1 and MIF1 transcription factors and down-regulation of proteins involved in secondary metabolism in amaranth roots ( Amaranthus hypochondriacus L.). Plant Biol 2011;13:472–82. - 24.
Huerta-Ocampo JA, Barrera-Pacheco A, Mendoza-Hernández CS, Espitia-Rangel E, Mock HP, Barba de la Rosa AP. Salt stress-induced alterations in the root proteome of Amaranthus cruentus L. J Proteome Res 2014;13:3607–27. - 25.
Slama I, Abdelly C, Bouchereau A, Flowers T, Savoure A. Diversity, distribution and roles of osmoprotective compounds accumulated in halophytes under abiotic stress. Ann Bot 2015;115:433–47. - 26.
Meng YL, Wang YM, Zhang B, Nii N. Isolation of a choline monooxygenase cDNA clone from Amaranthus tricolor and its expression under stress conditions. Cell Res 2001;11:187–93. - 27.
Bhuiyan NH, Hamada A, Yamada N, Rai V, Hibino T, Takabe T. Regulation of betaine synthesis by precursor supply and choline monooxygenase expression in Amaranthus tricolor . J Exp Bot 2007;58:4203–12. - 28.
Chen TH, Murata N. Glycinebetaine protects plants against abiotic stress: mechanisms and biotechnological applications. Plant Cell Environ 2011;34:1–20. - 29.
Brockington SF, Walker RH, Glover BJ, Soltis PS, Soltis DE. Complex pigment evolution in the Caryophyllales. New Phytol 2011;190:854–64. - 30.
Gandia-Herrero F, Garcia-Carmona F. Biosynthesis of betalains: yellow and violet plant pigments. Trend Plant Sci 2013;18:334–43. - 31.
Cai YZ, Sun M, Corke H. Identification and distribution of simple and acylated betacyanins in the Amaranthaceae. J Agric Food Chem2001;49:1971–8. - 32.
Strack D, Vogt T, Schliemann W. Recent advances in betalain research. Phytochemistry 2003;62:247–69. - 33.
Tanaka Y, Sasaki N, Ohmiya A. Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids. Plant J 2008;54:733–49. - 34.
Sepulveda-Jimenez G, Rueda-Benitez P, Porta H, Rocha-Sosa M. A red beet ( Beta vulgaris ) UDP-glucosyltransferase gene induced by wounding, bacterial infiltration and oxidative stress. J Exp Bot 2005;56:605–11. - 35.
Chang-Quan W, Min C, Ji-Qiang Z, Bao-Shan W. Betacyanin accumulation in the leaves of C3 halophyte Suaeda salsa L. is induced by watering roots with H2O2. Plant Sci 2007;172:1–7. - 36.
Shao L, Li Y, Wu X, Peng C. Comparison on antioxidative capability in leaves of red and green amaranth ( Amaranthus tricolor L.) under high temperature stress. Plant Physiol Commun 2008;44:923–6. - 37.
Casique-Arroyo G, Martinez-Gallardo N, Gonzalez de la Vara L, Delano-Frier JP. Betacyanin biosynthetic genes and enzymes are differentially induced by (a)biotic stress in Amaranthus hypochondriacus . PLoS ONE 2014;9:e99012. - 38.
Kraujalis P, Venskutonis PR, Kraujaliene V, Pukalskas A. Antioxidant properties and preliminary evaluation of phytochemical composition of different anatomical parts of amaranth. Plant Food Human Nutr 2013;68:322–8. - 39.
Viswa Preeth GP, Paul Das M. Comparative study on phytochemical parameters of Amaranthus caudatus andAmaranthus hybridus . J Chem Pharm Res 2014;6:1462–5. - 40.
Simmonds MS. Flavonoid-insect interactions: recent advances in our knowledge. Phytochemistry 2003;64:21–30. - 41.
Lattanzio V, Lattanzio VM, Cardinali A. Role of phenolics in the resistance mechanisms of plants against fungal pathogens and insects. Phytochem Adv Res 2006;661:23–67. - 42.
Carlsen S, Fomsgaard I. Biologically active secondary metabolites in white clover ( Trifolium repens L.)-a review focusing on contents in the plant, plant-pest interactions and transformation. Chemoecology 2008;18:129–70. - 43.
Falcone Ferreyra ML, Rius SP, Casati P. Flavonoids: biosynthesis, biological functions, and biotechnological applications. Front Plant Sci 2012;3:222. - 44.
Niveyro SL, Mortensen AG, Fomsgaard IS, Salvo A. Differences among five amaranth varieties ( Amaranthus spp.) regarding secondary metabolites and foliar herbivory by chewing insects in the field. Arthropod-Plant Interact 2013;7:235–45. - 45.
Alvarez-Jubete L, Arendt EK, Gallagher E. Nutritive value of pseudocereals and their increasing use as functional gluten-free ingredients. Trend Food Sci Technol 2010;21:106–13. - 46.
Arif T, Mandal TK, Dabur R. Natural products: anti-fungal agents derived from plants. J Asian Nat Prod Res 2011;11:621–38. - 47.
Nana FW, Hilou A, Millogo JF, Nacoulma OG. Phytochemical composition, antioxidant and xanthine oxidase inhibitory activities of Amaranthus cruentus L. andAmaranthus hybridus L. extracts. Pharmaceuticals 2012;5:613–28. - 48.
Pannu J, Thalwal S, Gupta A. Comparison of antimicrobial activity and phytochemical constituents of in vivo andin vitro grownAmaranthus spinosus plant. Int J Pharm Pharm Sci 2013;5:703–7. - 49.
Khanam UKS, Oba S. Bioactive substances in leaves of two amaranth species, Amaranthus tricolor andA. hypochondriacus . Can J Agricult Sci 2013;93:47–58. - 50.
Zhang Y, Butelli E, Martin C. Engineering anthocyanin biosynthesis in plants. Curr Opin Plant Biol 2014;19:81–90. - 51.
Xie DY, Sharma SB, Paiva NL, Ferreira D, Dixon RA. Role of anthocyanidin reductase, encoded by BANYULS in plant flavonoid biosynthesis. Science 2003;299:396–9. - 52.
Stracke R, Ishihara H, Huep G, Barsch A, Mehrtens F, Niehaus K, Weisshaar B. Differential regulation of closely related R2R3-MYB transcription factors controls flavonol accumulation in different parts of the Arabidopsis thaliana seedling. Plant J 2007;50:660–77. - 53.
Yi J, Derynck MR, Chen L, Dhaubhadel S. Differential expression of CHS7 and CHS8 genes in soybean. Planta 2010;231:741–53. - 54.
Grotewold E, Drummond BJ, Bowen B, Peterson T. The myb-homologous P gene controls phlobaphene pigmentation in maize floral organs by directly activating a flavonoid biosynthetic gene subset. Cell 1994;76:543–53. - 55.
Sotheeswaran S, Pasupathy V. Distribution of resveratrol oligomers in plants. Phytochemistry 1993;32:1083–92. - 56.
Yu CK, Springob K, Schmidt J, Nicholson RL, Chu IK, Yip WK, Lo C. A stilbene synthase gene ( SbSTS1 ) is involved in host and nonhost defense responses in sorghum. Plant Physiol 2005;138:393–401. - 57.
Counet C, Callemien D, Collin S. Chocolate and cocoa: new sources of trans-resveratrol and trans-piceid. Food Chem 2006;98:649–57. - 58.
Brown DE, Rashotte AM, Murphy AS, Normanly J, Tague BW, Peer WA, Taiz L, Muday GK. Flavonoids act as negative regulators of auxin transport in vivo in Arabidopsis. Plant Physiol 2001;126:524–35. - 59.
Wasson AP, Pellerone FI, Mathesius U. Silencing the flavonoid pathway in Medicago truncatula inhibits root nodule formation and prevents auxin transport regulation by rhizobia. Plant Cell 2006;18:1617–29. - 60.
Peer WA, Murphy AS. Flavonoids and auxin transport: modulators or regulators? Trend Plant Sci 2007;12:556–63. - 61.
Taylor LP, Grotewold E. Flavonoids as developmental regulators. Curr Opin Plant Biol 2005;8:317–23. - 62.
Agati G, Azzarello E, Pollastri S, Tattini M. Flavonoids as antioxidants in plants: location and functional significance. Plant Sci 2012;196:67–76. - 63.
Winkel-Shirley B. Flavonoid biosynthesis. A colorful model for genetics, biochemistry, cell biology, and biotechnology. Plant Physiol 2001;126:485–93. - 64.
Al-Ghazi Y, Bourot S, Arioli T, Dennis ES, Llewellyn DJ. Transcript profiling during fiber development identifies pathways in secondary metabolism and cell wall structure that may contribute to cotton fiber quality. Plant Cell Physiol 2009;50:1364–81. - 65.
Schilmiller AL, Stout J, Weng JK, Humphreys J, Ruegger MO, Chapple C. Mutations in the cinnamate 4-hydroxylase gene impact metabolism, growth and development in Arabidopsis. Plant J 2009;60:771–82. - 66.
Boerjan W, Ralph J, Baucher M. Lignin biosynthesis. Annu Rev Plant Biol 2003;54:519–46. - 67.
Dixon RA, Paiva NL. Stress-induced phenyl-propanoid metabolism. Plant Cell 1995;7:1085–97. - 68.
Naoumkina MA, Zhao Q, Gallego-Giraldo L, Dai X, Zhao PX, Dixon RA. Genome-wide analysis of phenylpropanoid defence pathways. Mol Plant Pathol 2010;11:829–46. - 69.
Mattila P, Hellstrom J. Phenolic acids in potatoes, vegetables, and some of their products. J Food Comp Anal 2007;20:152–60. - 70.
Habauzit V, Morand C. Evidence for a protective effect of polyphenols-containing foods on cardiovascular health: an update for clinicians. Ther Adv Chronic Dis 2012;3:87–106. - 71.
Winkel BS. Metabolic channeling in plants. Annu Rev Plant Biol 2004;55:85–107. - 72.
Vogt T. Phenylpropanoid biosynthesis. Mol Plant 2010;3:2–20. - 73.
Bowles DJ. Defense-related proteins in higher plants. Annu Rev Biochem 1990;59:873–907. - 74.
Bate NJ, Orr J, Ni W, Meromi A, Nadler-Hassar T, Doerner PW, Dixon RA, Lamb CJ, Elkind Y. Quantitative relationship between phenylalanine ammonia-lyase levels and phenylpropanoid accumulation in transgenic tobacco identifies a rate-determining step in natural product synthesis. Proc Natl Acad Sci USA 1994;91:7608–12. - 75.
Reichert AI, He XZ, Dixon RA. Phenylalanine ammonia-lyase (PAL) from tobacco ( Nicotiana tabacum ): characterization of the four tobaccoPAL genes and active heterotetrameric enzymes. Biochem J 2009;424:233–42. - 76.
Rawal HC, Singh NK, Sharma TR. Conservation, divergence, and genome-wide distribution of PAL andPOX A gene families in plants. Int J Genom 2013;2013:678969. - 77.
Shang QM, Li L, Dong CJ. Multiple tandem duplication of the phenylalanine ammonia-lyase genes in Cucumis sativus L. Planta 2012;236:1093–105. - 78.
Hemmati S. Phenylalanine ammonia-lyase through evolution: a bioinformatic approach. Trend Pharm Sci 2015;1:10–14. - 79.
Badri DV, Weir TL, van der Lelie D, Vivanco JM. Rhizosphere chemical dialogues: plant-microbe interactions. Curr Opin Biotechnol 2009;20:642–50. - 80.
Skirycz A, Jozefczuk S, Stobiecki M, Muth D, Zanor MI, Witt I, Mueller-Roeber B. Transcription factor AtDOF4;2 affects phenylpropanoid metabolism in Arabidopsis thaliana . New Phytol 2007;175:425–38. - 81.
Hassan S, Mathesius U. The role of flavonoids in root-rhizosphere signalling: opportunities and challenges for improving plant-microbe interactions. J Exp Bot 2012;63:3429–44. - 82.
Sinha R, Rajam MV. RNAi silencing of three homologues of S-adenosylmethionine decarboxylase gene in tapetal tissue of tomato results in male sterility. Plant Mol Biol 2013;82:169–80. - 83.
Teng S, Keurentjes J, Bentsink L, Koornneef M, Smeekens S. Sucrose-specific induction of anthocyanin biosynthesis in Arabidopsis requires the MYB75/PAP1 gene. Plant Physiol 2005;139:1840–52. - 84.
Yan J, Wang B, Jiang Y, Cheng L, Wu T. GmFNSII -controlled soybean flavone metabolism responds to abiotic stresses and regulates plant salt tolerance. Plant Cell Physiol 2014;55:74–86. - 85.
Payyavula RS, Singh RK, Navarre DA. Transcription factors, sucrose, and sucrose metabolic genes interact to regulate potato phenylpropanoid metabolism. J Exp Bot 2013;64:5115–31. - 86.
Babst BA, Chen HY, Wang HQ, Payyavula RS, Thomas TP, Harding SA, Tsai CJ. Stress-responsive hydroxycinnamate glycosyltransferase modulates phenylpropanoid metabolism in Populus . J Exp Bot 2014;65:4191–200. - 87.
Kylli P, Nousiainen P, Biely P, Sipila J, Tenkanen M, Heinonen M. Antioxidant potential of hydroxycinnamic acid glycoside esters. J Agric Food Chem 2008;56:4797–805. - 88.
Meissner D, Albert A, Bottcher C, Strack D, Milkowski C. The role of UDP-glucose:hydroxycinnamate glucosyltransferases in phenylpropanoid metabolism and the response to UV-B radiation in Arabidopsis thaliana . Planta 2008;228:663–74. - 89.
Rivas-San Vicente M, Plasencia J. Salicylic acid beyond defence: its role in plant growth and development. J Exp Bot 2011;62:3321–38. - 90.
Zheng XY, Zhou M, Yoo H, Pruneda-Paz JL, Spivey NW, Kay SA, Dong X. Spatial and temporal regulation of biosynthesis of the plant immune signal salicylic acid. Proc Natl Acad Sci USA 2015;112:9166–73. - 91.
Schwab W. Metabolome diversity: too few genes, too many metabolites? Phytochemistry 2003;62:837–49. - 92.
Liu J, Osbourn A, Ma P. MYB Transcription factors as regulators of phenylpropanoid metabolism in plants. Mol Plant 2015;8:689–708. - 93.
Zhong R, Richardson EA, Ye ZH. The MYB46 transcription factor is a direct target of SND1 and regulates secondary wall biosynthesis in Arabidopsis. Plant Cell 2007;19:2776–92. - 94.
Zhong R, Lee C, Zhou J, McCarthy RL., Ye ZH. A battery of transcription factors involved in the regulation of secondary cell wall biosynthesis in Arabidopsis. Plant Cell 2008;20:2763–82. - 95.
McCarthy RL, Zhong R, Ye ZH. MYB83 is a direct target of SND1 and acts redundantly with MYB46 in the regulation of secondary cell wall biosynthesis in Arabidopsis. Plant Cell Physiol 2009;50:1950–64. - 96.
Zhou J, Lee C, Zhong R, Ye ZH. MYB58 and MYB63 are transcriptional activators of the lignin biosynthetic pathway during secondary cell wall formation in Arabidopsis. Plant Cell 2009;21:248–66. - 97.
Legay S, Lacombe E, Goicoechea M, Briere C, Seguin A, Mackay J, Grima-Pettenati J. Molecular characterization of EgMYB1, a putative transcriptional repressor of the lignin biosynthetic pathway. Plant Sci 2007;173:542–9. - 98.
Fornale S, Shi X, Chai C, Encina A, Irar S, Capellades M, Fuguet E, Torres JL, Rovira P, Puigdomenech P, Rigau J, Grotewold E, Gray J, Caparros-Ruiz D. ZmMYB31 directly represses maize lignin genes and redirects the phenylpropanoid metabolic flux. Plant J 2010;64:633–44. - 99.
Legay S, Sivadon P, Blervacq A S, Pavy N, Baghdady A, Tremblay L, Levasseur C, Ladouce N, Lapierre C, Seguin A, Hawkins S, Mackay J, Grima-Pettenati J. EgMYB1 , an R2R3 MYB transcription factor from eucalyptus negatively regulates secondary cell wall formation in Arabidopsis and poplar. New Phytol 2010;188:774–86. - 100.
Shen H, He X, Poovaiah CR, Wuddineh WA, Ma J, Mann DG, Wang H, Jackson L, Tang Y, Stewart CN, Chen F, Dixon RA. Functional characterization of the switchgrass (Panicum virgatum ) R2R3-MYB transcription factor PvMYB4 for improvement of lignocellulosic feedstocks. New Phytol 2012;193:121–36. - 101.
Omer S, Kumar S, Khan BM. Over-expression of a subgroup 4 R2R3 type MYB transcription factor gene from Leucaena leucocephala reduces lignin content in transgenic tobacco. Plant Cell Rep 2013;32:161–71. - 102.
Zhu L, Shan H, Chen S, Jiang J, Gu C, Zhou G, Chen Y, Song A, Chen F. The heterologous expression of the chrysanthemum R2R3-MYB transcription factor alters lignin composition and represses flavonoid synthesis in Arabidopsis thaliana . PLoS ONE 2013;8:e65680. - 103.
Goff SA, Cone KC, Chandler VL. Functional analysis of the transcriptional activator encoded by the maize B gene: evidence for a direct functional interaction between two classes of regulatory proteins. Gene Develop 1992;6:864–75. - 104.
Baudry A, Heim MA, Dubreucq B, Caboche M, Weisshaar B, Lepiniec L. TT2, TT8, and TTG1 synergistically specify the expression of BANYULS and proanthocyanidin biosynthesis inArabidopsis thaliana . Plant J 2004;39:366–80. - 105.
Albert NW, Davies KM, Lewis DH, Zhang H, Montefiori M, Brendolise C, Boase MR, Ngo H, Jameson PE, Schwinn KE. A conserved network of transcriptional activators and repressors regulates anthocyanin pigmentation in eudicots. Plant Cell 2014;26:962–80. - 106.
Jin H, Cominelli E, Bailey P, Parr A, Mehrtens F, Jones J, Tonelli C, Weisshaar B, Martin C. Transcriptional repression by AtMYB4 controls production of UV-protecting sunscreens in Arabidopsis. EMBO J 2000;19:6150–61. - 107.
Zhang L, Wang Y, Sun M, Wang J, Kawabata S, Li Y. BrMYB4 , a suppressor of genes for phenylpropanoid and anthocyanin biosynthesis, is down-regulated by UV-B but not by pigment-inducing sunlight in turnip cv. Tsuda. Plant Cell Physiol 2014;55:2092–01. - 108.
Qi T, Song S, Ren Q, Wu D, Huang H, Chen Y, Fan M, Peng W, Ren C, Xie D. The Jasmonate-ZIM-domain proteins interact with the WD-repeat/ bHLH/ MYB complexes to regulate jasmonate-mediated anthocyanin accumulation and trichome initiation in Arabidopsis thaliana . Plant Cell 2011;23:1795–814. - 109.
Zhou LL, Shi MZ, Xie DY. Regulation of anthocyanin biosynthesis by nitrogen in TTG1-GL3/TT8-PAP1-programmed red cells of Arabidopsis thaliana . Planta 2012;236:825–37. - 110.
Maier A, Schrader A, Kokkelink L, Falke C, Welter B, Iniesto E, Rubio V, Uhrig JF, Hulskamp M, Hoecker U. Light and the E3 ubiquitin ligase COP1/SPA control the protein stability of the MYB transcription factors PAP1 and PAP2 involved in anthocyanin accumulation in Arabidopsis . Plant J 2013;74:638–51. - 111.
Schaart JG, Dubos C, Romero De La Fuente I, van Houwelingen AM, de Vos RC, Jonker HH, Xu W, Routaboul JM, Lepiniec L, Bovy AG. Identification and characterization of MYB-bHLH-WD40 regulatory complexes controlling proanthocyanidin biosynthesis in strawberry ( Fragaria x ananassa ) fruits. New Phytol 2013;197:454–67. - 112.
Li S, Zachgo S. TCP3 interacts with R2R3-MYB proteins, promotes flavonoid biosynthesis and negatively regulates the auxin response in Arabidopsis thaliana . Plant J 2013;76:901–13. - 113.
Stracke R, Favory JJ, Gruber H, Bartelniewoehner L, Bartels S, Binkert M, Funk M, Weisshaar B, Ulm R. The Arabidopsis bZIP transcription factor HY5 regulates expression of the PFG1/MYB12 gene in response to light and ultraviolet-B radiation. Plant Cell Environ 2010;33:88–103. - 114.
Scalbert A, Manach C, Morand C, Remesy C, Jimenez L. Dietary polyphenols and the prevention of diseases. Crit Rev Food Sci Nut 2005;45:287–306. - 115.
Klimczak I, Malecka M, Pacholek B. Antioxidant activity of ethanolic extracts of amaranth seeds. Nahrung/ Food 2002;46:184–6. - 116.
Ogrodowska D, Czaplicki S, Zadernowski R, Mattila P, Hellstrom J, Naczk M. Phenolic acids in seeds and products obtained from Amaranthus cruentus . J Food Nutr Res 2012;51:96–101. - 117.
Steffensen SK, Rinnan A, Mortensen AG, Laursen B, de Troiani RM, Noellemeyer EJ, Janovska D, Dusek K, Délano-Frier J, Taberner A, Christophersen C, Fomsgaard IS. Variations in the polyphenol content of seeds of field grown Amaranthus genotypes. Food Chem 2011;129:131–8. - 118.
Steffensen SK, Pedersen HA, Labouriau R, Mortensen AG, Laursen B, de Troiani RM, Noellemeyer EJ, Janovska D, Stavelikova H, Taberner A, Christophersen C, Fomsgaard IS. Variation of polyphenols and betaines in aerial parts of young, field-grown Amaranthus genotypes. J Agric Food Chem 2011;59:12073–82. - 119.
Pedersen HA, Steffensen SK, Christophersen C, Mortensen AG, Jorgensen LN, Niveyro S, de Troiani RM, Rodriguez-Enriquez RJ, Barba-de la Rosa AP, Fomsgaard IS. Synthesis and quantitation of six phenolic amides in Amaranthus spp. J Agric FoodChem 2010;58:6306–11. - 120.
Kalinova J, Dadakova E. Rutin and total quercetin content in amaranth ( Amaranthus spp.). Plant Food Human Nutr 2009;64:68–74. - 121.
Pasko P, Sajewicz M, Gorinstein S, Zachwieja Z. Analysis of selected phenolic acids and flavonoids in Amaranthus cruentus andChenopodium quinoa seeds and sprouts by HPLC. Acta Chromatograph 2008;20:661–72. - 122.
Ali MB, Khandaker L, Oba S. Comparative study on functional components, antioxidant activity and color parameters of selected colored leafy vegetables as affected by photoperiods. J Food Agric Environ 2009;7:392–8. - 123.
Ali MB, Khandaker L, Oba S. Changes in pigments, total polyphenol, antioxidant activity and color parameters of red and green edible amaranth leaves under different shade levels. J Food Agric Environ 2010;8:217–22. - 124.
Khandaker L, Akond AS MGM, Ali MB, Oba S. Biomass yield and accumulations of bioactive compounds in red amaranth ( Amaranthus tricolor L.) grown under different colored shade polyethylene in spring season. Sci Hort 2010;123:289–94. - 125.
Gorinstein S, Lojek A, Číž M, Pawelzik E, Delgado-Licon E, Medina OJ, Moreno M, Salas IA, Goshev I. Comparison of composition and antioxidant capacity of some cereals and pseudocereals. Int J Food Sci Technol 2008;43:629–37. - 126.
Kunyanga CN, Imungi JK, Okoth M, Momanyi C, Biesalski HK, Vadivel V. Antioxidant and antidiabetic properties of condensed tannins in acetonic extract of selected raw and processed indigenous food ingredients from Kenya. J Food Sci 2011;76:C560–7. - 127.
López-Mejía OA, López-Malo A, Palou E. Antioxidant capacity of extracts from amaranth ( Amaranthus hypochondriacus L.) seeds or leaves. Ind Crop Prod 2014;53:55–9. - 128.
Bunzel M, Ralph J, Steinhart H. Association of non-starch polysaccharides and ferulic acid in grain amaranth ( Amaranthus caudatus L.) dietary fiber. Mol Nutr Food Res 2005;49:551–9. - 129.
Hartley RD, Harris PJ. Phenolic constituents of the cell walls of dicotyledons. Biochem Sys Ecol 1981;9:189–203. - 130.
Johnson MTJ, Ives AR, Ahern J, Salminen J-P. Macroevolution of plant defenses against herbivores in the evening primroses. New Phytol 2014;203:267–79. - 131.
Kroner A, Marnet N, Andrivon D, Val F. Nicotiflorin, rutin and chlorogenic acid: phenylpropanoids involved differently in quantitative resistance of potato tubers to biotrophic and necrotrophic pathogens. Plant Physiol Biochem 2012;57:23–31. - 132.
Moura JC, Bonine CA, de Oliveira Fernandes Viana J, Dornelas MC, Mazzafera P. Abiotic and biotic stresses and changes in the lignin content and composition in plants. J Integ Plant Biol 2010;52:360–76. - 133.
Vincent D, Lapierre C, Pollet B, Cornic G, Negroni L, Zivy M. Water deficits affect caffeate O-methyltransferase, lignification, and related enzymes in maize leaves. A proteomic investigation. Plant Physiol 2005;137:949–60. - 134.
Ali MB. Secondary metabolites and environmental stress in plants: biosynthesis, regulation, and function. In: Ahmad P, Wani MR. (Eds.) Physiological Mechanisms and Adaptation Strategies in Plants Under Changing Environment, vol 2. Springer Science Business Media, New York; 2012. pp. 55–85. - 135.
Zhang X, Liu CJ. Multifaceted regulations of gateway enzyme phenylalanine ammonia-lyase in the biosynthesis of phenylpropanoids. Mol Plant 2015;8:17–27. - 136.
Kim DS, Hwang BK. An important role of the pepper phenylalanine ammonia-lyase gene ( PAL1 ) in salicylic acid-dependent signalling of the defence response to microbial pathogens. J Exp Bot 2014;65:2295–306. - 137.
Lu B, Sun W, Zhang S, Zhang C, Qian J, Wang X, Gao R, Dong H. HrpN Ea-induced deterrent effect on phloem feeding of the green peach aphid Myzus persicae requiresAtGSL5 andAtMYB44 genes inArabidopsis thaliana . J Biosci 2011;36:123–37. - 138.
Persak H, Pitzschke A. Dominant repression by Arabidopsis transcription factor MYB44 causes oxidative damage and hypersensitivity to abiotic stress. Int J Mol Sci 2014;15:2517–37. - 139.
Song S, Qi T, Fan M, Zhang X, Gao H, Huang H, Wu D, Guo H, Xie D. The bHLH subgroup IIId factors negatively regulate jasmonate-mediated plant defense and development. PLoS Genet 2013;9:e1003653. - 140.
Nguyen HN, Kim JH, Hyun WY, Nguyen NT, Hong SW, Lee H. TTG1-mediated flavonols biosynthesis alleviates root growth inhibition in response to ABA. Plant Cell Rep 2013;32:503–14. - 141.
Whitbred JM, Schuler MA. Molecular characterization of CYP73A9 andCYP82A1 P450 genes involved in plant defense in pea. Plant Physiol 2000;124:47–58. - 142.
Betz C, McCollum TG, Mayer RT. Differential expression of two cinnamate 4-hydroxylases in ‘Valencia’ orange ( Citrus sinensis Osbeck). Plant Mol Biol. 2001; 46: 741-748. - 143.
Lu S, Zhou Y, Li L, Chiang VL. Distinct roles of cinnamate 4-hydroxylasegenes in Populus . Plant Cell Physiol 2006;47:905–14. - 144.
Bell-Lelong DA, Cusumano JC, Meyer K, Chapple C. Cinnamate-4-hydroxylase expression in Arabidopsis. Regulation in response to development and the environment. Plant Physiol 1997;113:729–38. - 145.
Raes J, Rohde A, Christensen JH, Van de Peer Y, Boerjan W. Genome-wide characterization of the lignification toolbox in Arabidopsis. Plant Physiol 2003;133:1051–71. - 146.
Lillo C, Lea US, Ruoff P. Nutrient depletion as a key factor for manipulating gene expression and product formation in different branches of the flavonoid pathway. Plant Cell Environ 2008;31:587–601. - 147.
Sadeghi M, Dehghan S, Fischer R, Wenzel U, Vilcinskas A, Kavousi HR, Rahnamaeian M. Isolation and characterization of isochorismate synthase and cinnamate 4-hydroxylase during salinity stress, wounding, and salicylic acid treatment in Carthamus tinctorius . Plant Signal Behav 2013;8:e27335. - 148.
Ehlting J, Büttner D, Wang Q, Douglas CJ, Somssich IE, Kombrink E. Three 4-coumarate: coenzyme A ligases in Arabidopsis thaliana represent two evolutionarily divergent classes in angiosperms. Plant J 1999;19:9–20. - 149.
Lindermayr C, Möllers B, Fliegmann J, Uhlmann A, Lottspeich F, Meimberg H, Ebel J. Divergent members of a soybean ( Glycine max L.) 4-coumarate: coenzyme A ligase gene family. Eur J Biochem 2002;269:1304–15. - 150.
Lindermayr C, Fliegmann J, and Ebel J. Deletion of a single amino acid residue from different 4-coumarate: CoA ligases from soybean results in the generation of new substrate specificities. J Biol Chem 2003;278:2781–6. - 151.
Hectors K, Van Oevelen S, Guisez Y, Prinsen E, Jansen MAK. The phytohormone auxin is a component of the regulatory system that controls UV-mediated accumulation of flavonoids and UV-induced morphogenesis. Physiol Plant 2012;145:594–603. - 152.
Sun C, Huang H, Xu C, Li X, Chen K. Biological activities of extracts from Chinese bayberry ( Myrica rubra Sieb. et Zucc.): a review. Plant Food Human Nutr 2013;68:97–106. - 153.
Xu Q, Yin XR, Zeng JK, Ge H, Song M, Xu CJ, Li X, Ferguson IB, Chen KS. Activator- and repressor-type MYB transcription factors are involved in chilling injury induced flesh lignification in loquat via their interactions with the phenylpropanoid pathway. J Exp Bot 2014;65:4349–59. - 154.
Yu O, Shi J, Hession AO, Maxwell CA, McGonigle B, Odell JT. Metabolic engineering to increase isoflavone biosynthesis in soybean seed. Phytochemistry 2003;63:753–63. - 155.
Liu M, Li X, Liu Y, Cao B. Regulation of flavanone 3-hydroxylase gene involved in the flavonoid biosynthesis pathway in response to UV-B radiation and drought stress in the desert plant, Reaumuria soongorica . Plant Physiol Biochem 2013;73:161–7. - 156.
Zuker A, Tzfira T, Ben-Meir H, Ovadis M, Shklarman E, Itzhaki H, Forkmann G, Martens S, Neta-Sharir I, Weiss D, Vainstein A. Modification of flower color and fragrance by antisense suppression of the flavanone 3-hydroxylase gene. Mol Breed 2002;9:33–41. - 157.
Jiang F, Wang JY, Jia HF, Jia W-S, Wang H-Q, Xiao M. RNAi-mediated silencing of the flavanone 3-hydroxylase gene and its effect on flavonoid biosynthesis in strawberry fruit. J Plant Growth Regul 2013;32:182–90. - 158.
Oh DH, Dassanayake M, Bohnert HJ, Cheeseman JM. Life at the extreme: lessons from the genome. Genome Biol 2012;13:241. - 159.
Buhmann A, Papenbrock J. An economic point of view, secondary compounds in halophytes. Funct Plant Biol 2013;40:952–67. - 160.
Wang A-R, Song H-C, An H-M, Huang Q, Luo X, Dong J-Y. Secondary metabolites of plants from the genus Chloranthus : chemistry and biological activities. Chem Biodivers 2015;12:451–73. - 161.
Mohanta TK, Occhipinti A, Atsbaha Zebelo S, Foti M, Fliegmann J, Bossi S, Maffei ME, Bertea CM. Ginkgo biloba responds to herbivory by activating early signaling and direct defenses. PLoS ONE 2012;7:e32822. - 162.
Xu F, Li L, Zhang W, Sun N, Cheng S, Wang Y. Isolation, characterization, and function analysis of a flavonol synthase gene from Ginkgo biloba . Mol Biol Rep 2012;39:2285–96. - 163.
Cheng S, Zhang W, Sun N, Xu F, Li L, Liao Y, Cheng H. Production of flavonoids and terpene lactones from optimized Ginkgo biloba tissue culture. Notulae Botanicae Horti Agrobot Cluj-Napoca 2014;42:88–93. - 164.
Mahajan M, Joshi R, Gulati A, Yadav SK. Increase in flavan-3-ols by silencing flavonol synthase mRNA affects the transcript expression and activity levels of antioxidant enzymes in tobacco. Plant Biol 2012;14:725–33. - 165.
Kumar V, Nadda G, Kumar S, Yadav SK. Transgenic tobacco overexpressing tea cDNA encoding dihydroflavonol 4-reductase and anthocyanidin reductase induces early flowering and provides biotic stress tolerance. PLoS ONE 2013;8:e65535. - 166.
Ahmed NU, Park JI, Jung HJ, Yang TJ, Hur Y, Nou IS. Characterization of dihydroflavonol 4-reductase (DFR) genes and their association with cold and freezing stress in Brassica rapa . Gene 2014;550:46–55. - 167.
Lacy A, O'Kennedy R. Studies on coumarins and coumarin-related compounds to determine their therapeutic role in the treatment of cancer. Curr Pharm Design 2004;10:3797–811. - 168.
Bourgaud F, Hehn A, Larbat R, Doerper S, Gontier E, Kellner S, Matern U. Biosynthesis of coumarins in plants: a major pathway still to be unravelled for cytochrome P450 enzymes. Phytochem Rev 2006;5:293–308. - 169.
Frey M, Stettner C, Pare PW, Schmelz EA, Tumlinson JH, Gierl A. An herbivore elicitor activates the gene for indole emission in maize. Proc Natl Acad Sci USA 2000;97:14801–6. - 170.
Zook M. Biosynthesis of camalexin from tryptophan pathway intermediates in cell-suspension cultures of Arabidopsis. Plant Physiol 1998;118:1389–93. - 171.
Niyogi KK, Fink GR. Two anthranilate synthase genes in Arabidopsis: defense-related regulation of the tryptophan pathway. Plant Cell 1992;4:721–33. - 172.
Birkenbihl RP, Diezel C, Somssich IE. Arabidopsis WRKY33 is a key transcriptional regulator of hormonal and metabolic responses toward Botrytis cinerea infection. Plant Physiol 2012;159:266–85. - 173.
Daniel B, Pavkov-Keller T, Steiner B, Dordic A, Gutmann A, Nidetzky B, Sensen C. W, van der Graaff E, Wallner S, Gruber K, Macheroux P. Oxidation of monolignols by members of the berberine bridge enzyme family suggests a role in cell wall metabolism. J Biol Chem 2015;290:18770–81. - 174.
Gonzalez-Candelas L, Alamar S, Sanchez-Torres P, Zacarias L, Marcos JF. A transcriptomic approach highlights induction of secondary metabolism in citrus fruit in response to Penicillium digitatum infection. BMC Plant Biol 2010;10:194. - 175.
Sohani MM, Schenk PM, Schultz CJ, Schmidt O. Phylogenetic and transcriptional analysis of a strictosidine synthase-like gene family in Arabidopsis thaliana reveals involvement in plant defence responses. Plant Biol 2009;11:105–17. - 176.
Kushwaha AK, Sangwan NS, Trivedi PK, Negi AS, Misra L, Sangwan RS. Tropine forming tropinone reductase gene from Withania somnifera (Ashwagandha): biochemical characteristics of the recombinant enzyme and novel physiological overtones of tissue-wide gene expression patterns. PLoS ONE 2013;8:e74777. - 177.
Palazón J, Moyano E, Cusidó RM, Bonfill M, Oksman-Caldentey KM, Piñol MT. Alkaloid production in Duboisia hybrid hairy roots and plants overexpressing theh6h gene. Plant Sci 2003;165:1289–95. - 178.
Soto G, Stritzler M, Lisi C, Alleva K, Pagano ME, Ardila F, Mozzicafreddo M, Cuccioloni M, Angeletti M, Ayub ND. Acetoacetyl-CoA thiolase regulates the mevalonate pathway during abiotic stress adaptation. J Exp Bot 2011;62:5699–711. - 179.
Yang Z, Park H, Lacy GH, Cramer CL. Differential activation of potato 3-hydroxy-3-methylglutaryl coenzyme A reductase genes by wounding and pathogen challenge. Plant Cell 1991;3:397–405. - 180.
Suzuki M, Kamide Y, Nagata N, Seki H, Ohyama K, Kato H, Masuda K, Sato S, Kato T, Tabata S, Yoshida S, Muranaka T. Loss of function of 3-hydroxy-3-methylglutaryl coenzyme A reductase 1 (HMG1 ) in Arabidopsis leads to dwarfing, early senescence and male sterility, and reduced sterol levels. Plant J 2004;37:750–61. - 181.
Phillips MA, Walter MH, Ralph SG, Dabrowska P, Luck K, Uros EM, Boland W, Strack D, Rodriguez-Concepcion M, Bohlmann J, Gershenzon J. Functional identification and differential expression of 1-deoxy-D-xylulose 5-phosphate synthase in induced terpenoid resin formation of Norway spruce ( Picea abies ). Plant Mol Biol 2007;65:243–57. - 182.
Okada A, Shimizu T, Okada K, Kuzuyama T, Koga J, Shibuya N, Nojiri H, Yamane H. Elicitor induced activation of the methylerythritol phosphate pathway toward phytoalexins biosynthesis in rice. Plant Mol Biol 2007;65:177–87. - 183.
Schnee C, Kollner TG, Held M, Turlings TC, Gershenzon J, Degenhardt J. The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores. Proc Natl Acad Sci USA 2006;103:1129–34. - 184.
Manavalan LP, Chen X, Clarke J, Salmeron J, Nguyen HT. RNAi-mediated disruption of squalene synthase improves drought tolerance and yield in rice. J Exp Bot 2012;63:163–75. - 185.
Jenner H, Townsend B, Osbourn A. Unravelling triterpene glycoside synthesis in plants: phytochemistry and functional genomics join forces. Planta 2005;220:503–6. - 186.
Suzuki H, Reddy MS, Naoumkina M, Aziz N, May GD, Huhman DV, Sumner LW, Blount JW, Mendes P, Dixon RA. Methyl jasmonate and yeast elicitor induce differential transcriptional and metabolic re-programming in cell suspension cultures of the model legume Medicago truncatula . Planta 2005;220:696–707. - 187.
Tholl D. Terpene synthases and the regulation, diversity and biological roles of terpene metabolism. Curr Opin Plant Biol 2006;9:297–304. - 188.
Pandey SP, Somssich IE. The role of WRKY transcription factors in plant immunity. Plant Physiol 2009;150:1648–55. - 189.
Thevenin J., Pollet B., Letarnec B., Saulnier L., Gissot L., Maia-Grondard A., Lapierre C., Jouanin L. The simultaneous repression of CCR and CAD, two enzymes of the lignin biosynthetic pathway, results in sterility and dwarfism in Arabidopsis thaliana . Mol Plant 2011;4:70–82. - 190.
Van der Rest B, Danoun S, Boudet AM, Rochange SF. Down-regulation of cinnamoyl-CoA reductase in tomato ( Solanum lycopersicum L.) induces dramatic changes in soluble phenolic pools. J Exp Bot 2006;57:1399–411. - 191.
Barakat A, Bagniewska-Zadworna A, Choi A, Plakkat U, DiLoreto DS, Yellanki P, Carlson JE. The cinnamyl alcohol dehydrogenase gene family in Populus : phylogeny, organization, and expression. BMC Plant Biol 2009;9:26. - 192.
Preisner M, Kulma A, Zebrowski J, Dyminska L, Hanuza J, Arendt M, Starzycki M, Szopa J. Manipulating cinnamyl alcohol dehydrogenase (CAD) expression in flax affects fibre composition and properties. BMC Plant Biol 2014;14:50. - 193.
Bhuiyan NH, Selvaraj G, Wei Y, King J. Gene expression profiling and silencing reveal that monolignol biosynthesis plays a critical role in penetration defence in wheat against powdery mildew invasion. J Exp Bot 2009;60:509–21. - 194.
Tatout C, Grezes-Besset B, George P. Maize with enhanced tolerance to fungal pathogen. 2012; US Patent App. 12/447,023. - 195.
Liu SJ, Huang YH, HE CJ, Fang C, Zhang YW. Cloning, bioinformatics and transcriptional analysis of caffeoyl-coenzyme A 3- O -methyltransferase in switchgrass under abiotic stress. J Integr Agric 2015; Doi:10.1016/S2095-3119(15)61038-3 - 196.
Coleman HD, Park JY, Nair R, Chapple C, Mansfield SD. RNAi-mediated suppression of p -coumaroyl-CoA 3'-hydroxylase in hybrid poplar impacts lignin deposition and soluble secondary metabolism. Proc Natl Acad Sci USA 2008;105:4501–6. - 197.
Quentin M, Allasia V, Pegard A, Allais F, Ducrot PH, Favery B, Levis C, Martinet S, Masur C, Ponchet M, Roby D, Schlaich NL, Jouanin L, Keller H. Imbalanced lignin biosynthesis promotes the sexual reproduction of homothallic oomycete pathogens. PLoS Pathog 2009;5:e1000264. - 198.
Landry LG, Chapple CC, Last RL. Arabidopsis mutants lacking phenolic sunscreens exhibit enhanced ultraviolet-B injury and oxidative damage. Plant Physiol 1995;109:1159–66. - 199.
Kim YJ, Kim DG, Lee SH, Lee I. Wound-induced expression of the ferulate 5-hydroxylase gene in Camptotheca acuminata . Biochim Biophys Acta 2006;1760:182–90. - 200.
Kim J, Choi B, Park YH, Cho BK, Lim HS, Natarajan S, Park SU, Bae H. Molecular characterization of ferulate 5-hydroxylase gene from kenaf ( Hibiscus cannabinu s L.). Sci World J 2013;2013:1-11. - 201.
Maruta T, Noshi M, Nakamura M, Matsuda S, Tamoi M, Ishikawa T, Shigeoka S. Ferulic acid 5-hydroxylase 1 is essential for expression of anthocyanin biosynthesis-associated genes and anthocyanin accumulation under photooxidative stress in Arabidopsis. Plant Sci 2014;219–20:61–8. - 202.
Gallego-Giraldo L, Jikumaru Y, Kamiya Y, Tang Y, Dixon RA. Selective lignin downregulation leads to constitutive defense response expression in alfalfa ( Medicago sativa L.). New Phytol 2011;190:627–39. - 203.
Ferrer JL, Jez JM, Bowman ME, Dixon RA, Noel JP. Structure of chalcone synthase and the molecular basis of plant polyketide biosynthesis. Nat Struct Biol 1999;6:775–84.