Open access peer-reviewed chapter

Genetic Engineering for Oil Modification

Written By

Muthulakshmi Chellamuthu, Kokiladevi Eswaran and Selvi Subramanian

Submitted: 26 September 2021 Reviewed: 29 November 2021 Published: 18 May 2022

DOI: 10.5772/intechopen.101823

From the Edited Volume

Genetically Modified Plants and Beyond

Edited by Idah Sithole Niang

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Abstract

Genetic manipulation is a strong tool for modifying crops to produce a considerably wider range of valuable products which gratifies human health benefits and industrial needs. Oilseed crops can be modified both for improving the existing lipid products and engineering novel lipid products. Global demand for vegetable oils is rising as a result of rising per capita consumption of oil in our dietary habits and its use in biofuels. There are numerous potential markets for renewable, carbon-neutral, ‘eco-friendly’ oil-based compounds produced by crops as substitutes for non-renewable petroleum products. Existing oil crops, on the other hand, have limited fatty acid compositions, making them unsuitable for use as industrial feedstocks. As a result, increasing oil output is necessary to fulfill rising demand. Increasing the oil content of oilseed crops is one way to increase oil yield without expanding the area under cultivation. Besides, the pharmaceutical and nutraceutical values of oilseed crops are being improved by genetic engineering techniques. This chapter addresses the current state of the art gene manipulation strategies followed in oilseed crops for oil modification to fulfill the growing human needs.

Keywords

  • oil quality
  • yield
  • essential fatty acids

1. Introduction

During India’s green revolution in the mid-twentieth century, the use of agrochemicals and high-yielding crop types established through traditional plant breeding procedures resulted in a major increase in crop productivity [1]. Conventional plant breeding can no longer meet the ever-increasing global food demand. Food insecurity and malnutrition are two of the most major threats to human health today, claiming the lives of millions of people in poor countries. To stay healthy, we need to eat a range of meals that contain all of the needed nutrients, as well as those that provide health advantages beyond basic nutrition [2]. It is now way to encourage sustainable farming approaches for increasing crop output while preserving all natural resource to the greatest extent possible [3]. Agricultural biotechnology is proven to be a valuable addition to traditional ways for addressing the global need for high-quality food. We now have access to large gene pools that may be utilized to confer desirable characteristics in economically significant crops thanks to modern plant biotechnology technologies. Crop varieties that are genetically modified (GM) can help us satisfy the demand for high-yielding, nutritionally balanced, biotic and abiotic stress tolerant crops [4]. Oilseed crop adoption has increased significantly in recent decades as a result of high demand for human consumption and industry interest. The composition of the seed oils, which are composed of a broad group of fatty acids with six predominant types and other unusual fatty acids produced by wild plant species with chain lengths ranging from 8 to 24 carbons, such as 16 or 18 carbon palmitic, stearic, oleic, linoleic, and linolenic acids, and 12 carbon lauric acid. In this study, a review of the major advances in genetic improvement of oilseed crops is provided, beginning with omics to understand metabolic routes and identify key genes in seed oil production and progression to use modern biotechnology. Genetic engineering is a new breeding technique (NBT) that has enabled the functional study of genes with potential applications. The important advancements in plant genetic improvement using current biotechnology, with an emphasis on oilseed crops such as Sesamum indicum, Arachis hypogaea, Carthamus tinctorius and Jatropha curcas are discussed in the following sections.

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2. Genetic modified crops vs conventional breeding

In several countries, GM crops created by adding genes for greater agronomic performance and/or enhanced nutrition are commercially grown. The source of the DNA utilized to develop the GM crop has a significant impact on the rigor of the food safety assessment. If the DNA comes from an edible plant, the regulatory process prior to commercialization will be streamlined, and customer acceptance will improve [5]. Crops that have been traditionally bred and those that have been genetically modified through various methods of gene transfer technologies are the results of genetic changes. Both conventional breeding and GM technologies have the potential to alter an organism’s genetic makeup in terms of DNA sequences and gene order. However, compared to traditional breeding, where thousands of uncharacterized genes of an organism may be involved, the quantity of genetic modifications brought about by GM technology is limited and clearly documented. Furthermore, GM crops are the result of very specific and targeted gene modifications, with well-defined end products like as proteins, metabolites, and phenotypes [6].

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3. Sesamum indicum

The genus of Sesamum belongs to the clade eudicots; order Lamiales and Pedaliaceae family and broadly grown species around the world [7]. The genus Sesamum contains 36 species including 22 species from African continent, seven is found commonly in Asia and Africa, five in Asia and one species in Brazil and Greek island. Most of the wild species of Sesamum originated in the African continent however the crop has been domesticated from its wild relative species S. malabaricum native to south Asia [8]. Sesame harbors a vast range of diversity and adaptation to various environments and it was recorded with long-term natural and artificial selections [9]. The percentage content of other fatty acids like oleic acid, linoleic acid, palmitic acid, erudic acid are 36%, 30%, 9%, 0.8% respectively. These are the major fatty acids present in sesame. Linolenic acid (omega 3 fatty acid) content is in very trace amounts in sesame seeds. The percentage content of poly unsaturated fatty acids ranges from 30.9 to 52.5%, it shows very large variation in their germplasm (Figure 1) [10].

Figure 1.

Future directions and strategies for enhancing sesame oil yield and improvement.

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4. Nutritional value of sesame

Sesame not only contains protein, carbohydrates, poly unsaturated fatty acids, it also contains the lignans, phytosterols, phytates and tocopherols. They keep on maintaining the oil quality level in long shelf life time by preventing the oxidative rancidity [11]. The combination of these compounds is mainly responsible for the good oxidative stability of the sesame seed oil [12]. The antioxidant property of the oil aids in preventing the degenerative diseases like cancer, cardiovascular disease, atherosclerosis and the process of aging [13].

The major desmethylsterols present in sesame seed oil are β-sitosterol, campasterol, stigma sterol, Δ-5 and avenasterol [14]. Sesame oil also contain some enzymes such as Protex 7 L, Alcalase 2.4 L, Viscozyme L, Natuzyme and kemzyme. Among those enzymes Alcalase is found in large amounts in sesame [15]. These enzymes are mainly used for aqueous oil extraction process which is an alternative for solvent extraction. An Enzyme-assisted aqueous extraction (EAAE) process which is used to recover the high-quality protein for human consumption [16].

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5. Sesame breeding

Plant breeding allows the successful management of existing genetic diversity as well as the development of new ones in order to achieve desired traits. There is different type of breeding approaches which is employed for genetic improvement of sesame varying from plant selection, hybrid development and molecular breeding. In conventional breeding the choice of parental lines and development of sesame types with desired characters is attained through pedigree selection from segregating generations [17]. Plant selection is vital for increasing seed yield and development of novel sesame varieties [18]. Several phenotypic traits are useful for determining selection criteria such as number of capsules, branching, biomass, harvest index which reveals positive correlation with sesame seed yield [19]. Hybridization is one of the frequently used techniques in conventional breeding technique. Combination of desired traits with different plant lines can be achieved through cross-pollination. Cytoplasmic male sterility lines in sesame were developed by hybridizing S. indicum with its wild relative S. malabaricum. Many hybrids exhibited high heterosis for oil content, seed yield and number of capsules per plant [20]. Mutation breeding involves induction of new genetic variability through spontaneous or artificial mutagens either chemical or physical. Sesame mutants have been developed for desirable traits for quality, seed color, higher yield, plant architecture and larger seed size [21]. The gamma ray induced mutants were developed with improved plant growth having determinate growth habit, resistance to Fusarium blight, improved oil quality with higher oleic acid and low linoleic acid content [22].

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6. Genetic improvement of sesame

Sesame breeding uses a variety of novel ways, including genetic engineering, to overcome the disadvantages of traditional breeding. Sesame’s resistance to current biotechnology makes it difficult to use. Furthermore, various researchers have tried a variety of ways and media to create callus tissue [23]. Cotyledons, root, hypocotyl segments and sub apical hypocotyl of seedlings were all successful in somatic embryogenesis [24]. In addition, the efficient micro propagation mechanism for sesame conservation and multiplication has been upgraded. This is useful for genetic transformation, reproductive growth, and other tissue culture research. The genetic transformation of sesame by Agrobacterium has been reported, however the transformation frequency is low. High-frequency sesame transformation techniques recently yielded high regeneration and transformation frequency of 57.33% and 42.66%, respectively, for sesame [25, 26, 27, 28]. Current crop breeding approaches will not be sufficient to meet the ever-increasing population’s demands for food security and nutrition. To speed agricultural genetic improvement, 5G breeding tactics such as genome assembly, germplasm characterization, gene function identification, genomic breeding methodologies, and gene editing technologies have been proposed [29]. Genomic tools and methodologies for phenotype discovery and molecular breeding are provided by genome assembly. A gene expression, proteome, metabolome, and epigenome maps are essential. Researchers from the Chinese Academy of Agricultural Science’s Oil Crops Research Institute and other institutions have successfully created a high-quality sesame genome. Two landraces (S. indicum cv. Baizhima and Mishuozhima) and three modern cultivars (S. indicum var. Zhongzhi 13, Yuzhi 11, and Swetha) have genome assembly presently available, providing a significant tool for comparative genomic analysis and gene identification [30]. In seeds of Nicotiana tabacum, expression of sesame plastidial FAD7 desaturase modified with endoplasmic reticulum targeting and retention signals increases a-linolenic acid accumulation. The expression of the modified sesame ω-3 desaturase raises the a-linolenic acid concentration in the seeds of transgenic tobacco plants by 4.78–6.77%, while lowering the linoleic acid level. The findings suggested that the engineered plastidial ω-3 desaturase from sesame has the potential to influence the profile of a-linolenic acid in tobacco plants by shifting the carbon flux away from linoleic acid, and thus it could be used in a genetic engineering strategy to increase a-linolenic acid levels [31]. Increases in oil content and seed weight were seen when sesame DGAT1 was overexpressed in many lines of Arabidopsis thaliana ‘Col 0’ [32]. Through a genetic engineering technique, the Fusarium moniliforme 12/15 bifunctional desaturase gene was used to increase the omega 3 fatty acid content of sesame (Unpublished data). Yeast is a great model for studying lipid production. The oil accumulation and functional characterization of the sesame DGAT and PDAT genes were studied using a yeast H1246 oil synthesis defective mutant [33]. In order to improve the oil quality, another study examined the co-expression of DGAT1 and PDAT1 genes with omega 3 desaturase genes in a yeast expression system (Unpublished data). Sesame transformation research using Agrobacterium to assess the biodiesel potential of transgenic sesame plants showed an increased TAG content by 10% when PDAT1 and FAD3 were combined in a transgenic construct [34].

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7. CRISPR/Cas system for oil production and quality improvement in sesame

Although some of the candidates for oil characteristics are extremely suggestive, they are still suspected causal genes. The creation of several biparental populations from well-designed crosses will increase mapping resolution, allow epistatic interactions to be identified, and allow the development of new germplasm with improved phenotypic performance. To validate the impacts of these candidate genes and their functional variations for the connections underpinning oil characteristics, functional genomics approaches such as genetic transformation and genome-editing technologies using the CRISPR/Cas system are needed. Sesame genes for oil production and quality are likely to play major roles in other closely related oilseed species (for example, sunflower), allowing researchers to search for genes with similar functions. This work in sesame may provide unique knowledge and guiding examples for continuing genetic investigations for oilseed crops with more complicated genomes [35].

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8. Arachis hypogaea

Groundnut (A. hypogaea), often known as peanut, is a major oil, food, and feed legume crop farmed in more than a hundred nations. Groundnut is prized for its high calories content, which comes from oil (48–50%) and protein (25–28%) in the kernels. From 100 g of kernels, they supply 564 kcal of energy. Furthermore, groundnut kernels are high in mono-unsaturated fatty acids and contain several health-promoting substances such as minerals, antioxidants, and vitamins. They include antioxidants such as p-coumaric acid and resveratrol, as well as Vitamin E and a variety of B-complex vitamins and minerals such as thiamin, pantothenic acid, vitamin B-6, folates, and niacin. Groundnut is a good source of bioactive polyphenols, flavonoids, and isoflavones in the diet. Groundnut and groundnut-based products can be promoted as nutritional foods to combat energy, protein, and micronutrient deficiency among the poor due to their high nutritional value [36].

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9. Genetic manipulation in peanut

Genetic transformation can make it easier to introduce possible candidate genes into plants for controlling a variety of crop-improvement features. Transformation technology paved the way for key genes to be transferred into the peanut genome for improved resistance to fungal, viral, and other pests, drought, and salinity, as well as the silencing of undesired genes and improved nutrient uptake. Transgenic peanuts with the human Bcl-xL gene expressed in their genome demonstrated high tolerance to oxidative and salt stresses [37]. By compartmentalizing Na+ ions in the vacuoles, overexpression of the AtNHX1 gene in peanut (a vacuolar Na+/H+ antiportar) increased resistance to extreme salinity and water deprivation [38]. Under field settings, PDH45, a pea DNA helicase similar to eiF4A, displayed abiotic stress tolerance and increased peanut productivity at T3 generation [39]. In another study, transgenic peanuts expressing the AtNAC2 and MuNAC4 (NAM, ATAF, and CUC) transcription factors conferred drought, moisture stress, and salinity tolerance, as well as increased crop output [40, 41]. The list of genetically modified traits were shown in Table 1.

Trait EvaluationReference
Abiotic stress tolerance
Empirical approach for drought tolerance[39]
Transpiration efficiency[40]
SPAD chlorophyll meter reading (SCMR), specific leaf area (SLA), carbon isotope discrimination [and thus water-use efficiency (WUE)][41, 42]
High temperature[43, 44]
Salinity[45, 46]
Aluminum toxicity[47, 48]
Biotic and abiotic stress[34]
Photosynthetic rate, stomata conductance and higher transpiration rate under limited water conditions[49]
Resistant to higher salt and water[35]
Drought stress tolerance[50, 51, 52]
Salt and oxidative stress[53]
Improved water/drought stress tolerance[37]
Drought and salinity tolerance[38]
Water deficit stress[54]
Nitrogen fixation tolerant to soil drying[55]
Fungal resistant varieties
Resistance against C. personata[56]
Resistance against the late leaf spot disease[57]
Resistance against three fungal pathogens[58]
Late leaf spot disease[59]
Resistance towards C. arachidicola and A. flavus[60]
Virus resistant varieties
Resistance to TSV infection[61]
Resistance to PBNV[62]
Resistance to PStV[63]
Resistance to TSWV[64]
Insect/pest resistance varieties
Resistance against S. litura[65]
Insecticidal activity against H. parallela[66]
S.minor resistance[67, 68]
S. litura resistance[69]
Resistance against lepidopteron insect larvae of lesser crosstalk borer[70]
Tomato spotted wilt virus (TSWV)[71]
Vaccine producing varieties
Edible vaccine against Helicobacter pylori[72]
Blue tongue outer coat protein that comprises the neutralizing the epitopes[73]
Allergen silencing varieties
Produced hypo allergenic peanut by silencing Arah 2 and Arah 6 genes[34]
Alleviated peanut allergy[74]
Genome editing technology
CRISPR/Cas9 mutagenesis of FAD2 genes[75]
TALEN mutagenesis of fatty acid desaturase 2[76]

Table 1.

List of genetically modified peanut traits.

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10. Genome editing in peanut

The CRISPR/Cas9 system is based on the prokaryotic type II CRISPR system, which was derived from a gene editing mechanism in bacteria. It’s a relatively new technique that allows researchers to change the DNA of an organism for the sake of research. Breeders can use this technique to add, remove, or modify genetic materials at a precise point in the genome. In comparison to ZFNs and TALENs, the CRISPR/Cas9 system stands out for its ease of use, efficiency, and low cost, as well as its capacity to target multiple genes [77]. Gene-editing technology has a lot of potential for improving peanut oleic acid. The first gene editing in the model plants Arabidopsis thaliana and Nicotiana benthamina using CRISPR/Cas9 was reported in 2013 [71, 78]. Since then, it has been widely used in many plant species for gene function research, and its current widespread use in crop breeding shows promise for future breeding programmes. The limited specificity of sgRNA in CRISPR/Cas9 may result in off-target DNA sequences. An unanticipated or undesirable mutation will occur in the organism’s genome as a result of this consequence. Despite the fact that cas9 nickase was developed to decrease the off-target effect, improvement is still required [79]. The use of gene editing techniques makes the creation of double-strand breaks in chromosomes much faster than using conventional breeding techniques. Double stranded breaks (DSBs) can be utilized to deliver targeted disease resistance and genome alterations to improve agronomic parameters such as yield and nutritional content by harnessing the natural cellular DNA repair process [80, 81]. To characterize the functions of peanut AhNFR1 and AhNFR5 genes in the nodulation symbiosis, researchers used hairy root-mediated CRISPR knockout. The findings not only confirmed that using CRISPR/Cas9 in combination with a hairy root transformation system is a quick way to characterize gene functions in roots, but they also improved our understanding of the role of the NFR genes in peanut nodulation [82].

11. Carthamus tinctorius

Safflower (C. tinctorius) is a versatile crop that can be grown in the tropics and subtropics in semi-arid climates [83]. Safflower seed cakes provide a high protein source, feed for animals and birds, and traditional medicine. Safflower oil is rich in oleic as well as linoleic acid [84]. In addition to these traditional applications, safflower is increasingly being used to synthesize transgenic goods, including pharmaceutical ginseng, human insulin, and apolipoprotein [85]. Safflower has evolved into a platform for industrial food production due to its low outcrossing rate and weediness, distinctive appearance from other oilseed crops, and excellent agronomic characteristics, such as the taproot architecture that allows it to access subsoil water reserves [86]. It has been commercially successful to genetically modify safflower, but there is no detailed description of how to generate and analyze transgenic T1 plants in the public domain. The lack of reliable regeneration of transgenic T1 progeny in safflower has enormous implications for this economically-important plant’s capacity to be used as a high yielding industrial crop. Safflower is undoubtedly a challenging crop to genetically engineer, and there is substantial literature that describes limitations of tissue culture techniques for safflower [87, 88].

12. Crop improvement of safflower

Although safflowers produce some of the healthiest oils for human consumption, their agronomical features of drought resistance and arid region adaptation prevent them from becoming a major crop. The lack of oil and yield is due to its low oil content and susceptibility to diseases and insect pests as compared to other oilseed crops like canola and cotton. Plant breeding has produced a range of cultivars that have different fatty acid profile oils, quantities, and quality, with the primary use being edible and industrial oils, along with a minor use as bird seed. This comprises specialized oils with high -linoleic acid (gamma-linoleic acid, GLA) and higher tocopherol content, which are thought to offer health benefits. Safflower oil offers potential in the biofuel industry as well as foundation for pharmaceutical manufacture in GM safflower seed [85, 89, 90, 91]. Current Australian varieties contain up to 42% oil whereas in United States have developed cultivars with oil content levels ranging from 45 to 55% [92]. In India, the most prevalent breeding approach for safflower cultivar production is choice from indigenous varieties, and multiple germplasm lines with required qualities have been created. Through selection and/or hybridization with local lines, this material can then be used for breeding in other countries. Safflower cultivars were produced in the twentieth century in the United States, Canada, and Argentina, using material imported from India, Russia, and Turkey [93]. The most complicated variables in safflower are seed yield and oil content, and selection for these traits is impeded by substantial genetic-environmental interactions. For the production of hybrid safflower plants, dominant and recessive genetic male sterility (GMS), cytoplasmic male sterility (CMS), and temperature sensitive genetic male sterility (TGMS) systems have been established. In India, GMS safflower lines (including spiny and non-spiny flowered lines) with a 20–25% increase in seed and oil output are available. In India, CMS and TGMS lines are also commercially accessible. Despite the development of hybrid safflower production technologies and the testing of hybrids, practical production of hybrid safflower is still a long way off [94, 95].

13. Fatty acid modification in safflower

Oil seed crops like safflower are primarily grown for their high-quality edible oil. All safflower seeds contain fatty acids including linoleic acid, stearic acid, and palmitic acid. Safflower lines had improved fatty acid compositions comprising reduced palmitic acid, reduced stearic acid, and high to very high linoleic and oleic acids with reduced saturated fatty acids such as palmitic and stearic acids [96]. In research published by [97], the al allele has been linked to a defective fatty acid desaturase (FAD2-1) (fatty acid desaturase) enzyme in microsomes. These vegetable oils contain a higher level of oleic acid and are more nutritionally beneficial [98, 99]. Saffola 517, a high-oleic-oil type, and Saffola 555, a linoleic-oil variant, were both introduced to Australia from the United States. Traditional breeding and genetic modification were used to create HO cultivars. Biodiesel, lubricants, and hydraulic oils are all items that require strong oxidative stability; therefore HO vegetable oils with high oxidative stability have non-food applications or prospective industrial usage [100]. GLA is a crucial fatty acid needed by the body, derived from linoleic acid by means of delta-6-desaturase in the endoplasmic reticulum. The oil content, viability, or fitness of high GLA lines is invariable and heritable across generations. SonovaTM 400, a nutritional supplement containing GLA extracted from GM safflower, has received FDA approval for use. It has been shown in clinical trials that GLA can be useful to treat eczema and various types of cancer [85]. The high level of oleic acid (75–85%) found in some safflower cultivars is ideal for food use but not for industrial use due to the extremely high level of purity required. Potential industrial applications for high oxidative stability HO vegetable oils include biodiesel, lubricants, hydraulic oils, and oleo chemical applications. The oxidative stability of oil extracted from super high oleic (SHO) safflower was significantly improved when compared to the high oleic acid cultivar S317, which contained over 93% and 75.4% oleic acid, respectively. The seed-specific RNAi-silencing of the FATB and FAD2.2 genes, which are responsible for the release of saturated medium-chain fatty acids and the desaturation of oleic acid to linoleic acid, respectively, was used to create the SHO safflower [101]. Bio fortification of safflower, an oil seed crop was genetically modified to improve the ALA content. In safflower, accumulation of Linoleic acid is higher which an immediate precursor of ALA. Hence, FAD3 isolated from A. thaliana driven under seed specific promoter isolated from Glycine max is transformed through agrobacterium mediated transformation to increase the ALA content. The vector used for cloning is pCAMBIA2300. The transformed seeds contained about 1.34–18.2 mg of ALA per gram dry weight of the seeds. Thus, it proves that fatty acid desaturase can increase the accumulation of ALA content in plants [102].

14. Jatropha curcas

Jatropha is a second-generation biofuel resource that is prized for its high oil content, low seed cost, ease of land reclamation, and adaptability to a variety of marginal and semi-marginal areas [103]. The extensive potential of this plant, as well as the many uses of different plant components, has made cultivation of this species highly profitable [104]. Because fossil fuels constitute a significant danger to energy security and have negative environmental consequences, efforts are underway to partially replace fossil fuels with biofuels. The high oil content of up to 50% of its seeds, which can be easily processed to partially or completely replace petroleum-based diesel fuel, has recently attracted interest [105, 106]. Jatropha is a non-food crop, which distinguishes it from the fuel vs. food debate. It has a flash point of 235°C and a calorific value of 39.63 MJ kg−1, making it appropriate for use as a biofuel. Jatropha oil has a similar composition as peanut, palm, and corn oil, with 45.79% oleic acid (18:1), 32.27% linoleic acid (18:2), 13.37% palmitic acid (16:0), and 5.43% stearic acid (18:0). Jatropha is second only to oil palm in terms of oil production per hectare, which encourages its planting around the world. To mitigate financial risk, jatropha farmers have reportedly avoided cultivating the crop on marginal and ruinous lands, but this is no longer possible [107, 108, 109]. Because jatropha is widely available in India, it can be used as an alternative energy source to ensure the country’s energy security. By 2020, India plans to increase biodiesel production and replace 20% of diesel usage. Depending on the potential yield of the plant types and additional improvement projects, the area required to accomplish this substitution aim ranges from 4.24 to 66.98 million hectares (Mha). Because of the vast amount of open wastelands in India, this goal is achievable. The CSIR-CSMCRI is well-known around the world for its work on Jatropha elite accessions selection, cultivation, genetic enhancement, and biodiesel production (Figure 2) [110, 111].

Figure 2.

Future perspectives of Jatropha for oil improvement.

15. Targeting enhanced oil production in Jatropha curcus

Various plant breeding strategies are employed in the last few decades to increase oil yield and quality, as well as resistance to biotic and abiotic challenges in edible and non-edible oil plants. Marker-aided selection, next-generation sequencing, “omics” technologies, and genetic engineering are some of the new biotechnological methods that have sped up the breeding process for such features in these plants. The use of omics technologies to identify and isolate important genes involved in lipid biosynthesis pathways, as well as their transfer to edible and non-edible oil plants is predicted to result in cost-effective oil production as a feedstock for biodiesel generation [112]. Biodiesel production from non-edible oil plants would be far more realistic if new varieties/hybrids of oil plants could be developed that contain more oil, are resistant to biotic and abiotic challenges, and do not contain harmful proteins. Through various breeding techniques, oil plants that produce edible and non-edible oils have increased these properties over recent decades. In the field of plant breeding, development, selection, target trait evaluation, multiplication, and distribution are the major objectives [113, 114]. Breeding targets for various crops have been rapidly accelerated by genetic and metabolic engineering techniques over the last few decades. Genetic engineering can be used to increase the amount of oil found in seeds of nonedible plants by engineering lipid biosynthesis pathways [115]. It is the simplest and most efficient way to increase oil yields in nonedible plants. Furthermore, the expression of genes encoding fatty acyl carrier thioesterase A (FatA), glycerol-3-phosphate dehydrogenase (GPD), and lysophosphatidyl-acyltransferases (LPAT) has enhanced the oil production pathway and therefore could be regarded as key genes to boost oil content in bioenergy plants [113, 116]. Engineering other genes involved in agronomical traits such as seed, fruit, and leaf size, plant growth and biomass, root architecture, and vegetative/reproductive transition, in addition to the genes involved in TAG biosynthesis. Genetic engineering for oil content has a significant impact on the potential of bioenergy plants as a source of biodiesel production. Because seed size plays such an essential role in Jatropha oil yield, it has been prioritized as a breeding target to improve oil yields. In Jatropha, a candidate gene (CYP78A98) with the potential to increase seed size has just been discovered [117, 118]. Improvement of Jatropha through genetic engineering was listed in Table 2. The growing demand for biofuels has prompted plant scientists to develop plant feedstocks specifically for biodiesel production, using either traditional or modern breeding techniques to develop oilseed varieties with higher oil content and optimal fatty acid composition. Biodiesel is a fuel made up of mono-alkyl esters of long-chain fatty acids derived from plant oils, with the majority of the fatty acids being triacylglycerols (TAGs) and short-chain alcohols (>95%). Waste vegetable oils and non-edible crude vegetable oils are another source of biodiesel that reduces its price. Jatropha, castor bean, cotton, Pongamia, tobacco, mahua, neem, and Camelina are currently used as non-edible oil yielding plants for second-generation biodiesel production [131]. Gene editing techniques like CRISPR can be used in precision breeding to improve yield, disease resistance, herbicide resistance, induce haploids, fix hybrid vigor, solve self-incompatibility, and help de novo domesticate oil crops. While it will likely be a long time before genome-edited oil crops become commercially available, we anticipate that regulatory constraints on them will gradually be eased in the near future [132].

Trait evaluationTargeting geneReference
Inhibition of TAG degradationSugar-dependent protein 1 triacylglycerol lipase (SDP1) in Jatropha[119]
Improving morphological and developmental traitsAuxin response factor 19 (JcARF19) in Jatropha[120]
Flowering locus T (JcFT)[121]
Increased oleic acid contentFatty acid desaturase (FAD2) in Jatropha[122]
Acyl-ACP thioesterase (FATB)[123]
Reduction of toxins and inhibitorsCurcin precursor gene[124]
JcCASA: casbene synthase gene[125]
Drought tolerancePPAT; phosphopantetheine adenylyltransferase
NF-YB: The subunit of the NF-Y transcription factor
GSMT/DMT genes
[126]
Salinity tolerancesbNhx1: encoding vacuolar Na+/H+ antiporter (NHX1)[127]
Pest resistancecry1Ab/1Ac: Bacillus thuringiensis dendotoxin[128]
Disease resistanceChitinase[129]
Hairpin dsRNA[130]

Table 2.

Genetic manipulation strategies used to improve Jatropha.

Acknowledgments

The authors thank Department of Biotechnology, PSG College of Technology for providing infrastructural facilities and we thank Tamil Nadu Agricultural University for providing sesame seed varieties for our research purpose.

Conflict of interest

The authors declare no conflict of interest.

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Written By

Muthulakshmi Chellamuthu, Kokiladevi Eswaran and Selvi Subramanian

Submitted: 26 September 2021 Reviewed: 29 November 2021 Published: 18 May 2022