Development of Better Wheat Plants for Climate Change Conditions

Abstract

Wheat is a staple food of about 40% of the world population, and continuous improvement is vital to meet the increasing demands of the world population. Climate change, a serious concern of the present time, could strongly affect the wheat crop. To mitigate the climate change effects on wheat, scientists are developing wheat germplasm tolerant to the number of stresses and for this purpose different strategies have been adopted. In this chapter, the effect of climate change on wheat and strategies to develop a better wheat plant for climate change using advance breeding and molecular techniques have been discussed. Conventional breeding including hybridization, mutation breeding and shuttle breeding are some classical approaches which have led to the development of some high yielding wheat varieties but it’s a time taking task, the advancement in science has opened the new window for making a better crop for changing climate. Recent achievements in genetic engineering are expected to augment conventional breeding to further increase production. Advances in genome sequencing and molecular breeding have increased the rate of gene discovery. The use of advance genomic technique is a key to overcome the food security issue related to climate change.

1. Introduction

Wheat (Triticum aestivum), an important commodity since always, is the central pillar of food security like Plato said that ‘A true statesman is never ignorant of wheat’. This crop is staple food of about 40% of the world’s population and a source of daily protein for about 2.5 billion people in less-developed countries [1]. It is ranked top in terms of area and 2nd in terms of production globally [2, 3]. Wheat is a rich source of carbohydrates: the whole wheat grain and flour contain 60–70% and 65–75% starch respectively [4, 5]. Additionally, it also contains an appreciable amount of protein (20%), dietary fibers and vitamins [5, 6]. It is a multifaceted crop normally used as food, in the guise of bread, macaroni and because of the elasticity of gluten, it is very popular in Asian countries for chapatti making.

Wheat is one of the most widely cultivated cereal crops with the production of 760.93 million tons and an area of 219.01 million hectares of farmland worldwide [7] which is a 15.4% arable area globally. Its production has increased since green revolution in 1961 from 222.35 million tons to an estimated 775.3 million tons in 2021 [8]. In 2017, the global production of wheat was 751.99 million metric tons however it was increased by 8 million tons in 2018 with the total estimated production of 758.02 million metric tons. A similar trend was observed in 2019 where wheat production was 765.76 million metric tons however the global consumption of wheat assessed by World Agricultural Supply and Demand Estimates (WASDE), was 791.1 million tons for the year 2021 [9]. It has been projected that the wheat demand in developing countries will be increased up to 60% by 2050 which is a stern concern related to food security [10]. Wheat is the main rabi crop in Pakistan covering 38% of the cultivated area and accounts for 13.1% of value agricultural products and because of its staple food status, it occupies a central position in agricultural policies. Pakistan ranks 8th in terms of wheat area and production and 58th in terms of average yield (2805.9 kg ha⁻¹) [11]. Wheat productivity is globally increasing only at 1.1% per annum (p.a.) which is not enough to reach the predicted increase in wheat demand at 1.7% (p.a.) rate until 2050, and even in some regions, the productivity is stagnant [12].

Global wheat demand is skyrocketing in recent years because of many factors; change in eating habits, population trends, socio-economic conditions, especially in Asia and Africa. Among these, population explosion and climate change are the most pressing challenges to food availability in the present and future eras. Fast-rising population levels are putting pressure on land due to urbanization and fuelling global food demand [13]. Economic growth and access to food are important factors in alleviating poverty and hunger (hidden and chronic), although mere access to food is not enough to accelerate the reduction in malnutrition and hidden hunger [14]. Another most important factor is the changing climate and extreme weather conditions which are reshaping the whole picture of food security.

To overcome the drastic effects of climate change there is a need to develop such a plant type that can fight the battle against climate change. In this review, we will through light on some classical and advanced techniques which can be helpful to develop a better wheat plant that can win the war against climate change.

2. Threat of climate change on suitable crop production

According to the Intergovernmental Panel on Climate Change (IPCC) climate change refers to “any change in climate over time, whether due to natural variability or as a result of human activity”. However, according to the United Nations Framework Convention on Climate Change, it is referred to as a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere [15]. Climate change cause very harsh direct, indirect and socio-economic effect on environment, more importantly on crop grown under this type of environment. Different stresses including high temperature, drought, increased salinity level and flooding arise as the result of climate change. These stresses are the most influencing factors which affect the natural system, human health and agricultural production, especially in developing countries [16]. The expeditious increase in world population indirectly affects the demand and supply chain of food which is a great concern for global environment stability [17].

Climate change is a global phenomenon; however, the noticeable changes in rainfall and temperature in recent years have had an impact on wheat productivity. The elevated temperature will change the plant life cycle by inducing early flowering and fruit sets which will shorten the growth period and the developed seeds would be deficient in nutrients due to increased respiration rate. For each °C rise in temperature 6–13% reduction in the potential yield of wheat will happen. Although the exact consequences of climate change are impossible to predict, the general view is that global crop production will be negatively affected [18, 19]. To overcome this pressure and to meet the future demand for wheat international initiatives were taken [20]. Different international policy-making organizations “The Agricultural Ministers of G20” and “the Consultative Group for International Agricultural Research (CGIAR) research centers” keep climate change and food security a key priority area and motivate the need to further see the sights how one key staple food may be influenced by efforts to make the food system more resilient [21, 22].

Adverse effects may happen through increasing levels of CO₂, temperature, pests and diseases [23], and deteriorating quality and yield attributes [24]. The frequency of extreme weather events such as droughts and floods also increase in the response to changing climate [25]. One of the main reasons for changing climate and continuous elevation of CO₂ is deforestation; the level of CO₂ elevated from 280 μmol⁻¹ to 400 μmol⁻¹ and the prediction tells that might grow into two folds (800 μmol⁻¹) up to the end of this century [26].

Food insecurity is an emerging issue of today’s era that is a result of climate change. Almost 815 million people around the globe are facing hunger and malnutrition, hampering viable development programs to accomplish the worldwide goal of stamping out hunger by 2030 [27]. The adverse climatic conditions, mainly elevated temperature, is causing a threat to food security and agricultural yield [28]. The inhabitants are likely to grow up to 9 billion by 2050 and food supplies are expected to accelerate by about 85% [29]. Environmental supremacy is going from bad to worse comprising low variation and high application of inputs, and unbalanced output due to climatic variations in crops [30]. The escalated spells of drought and heavy precipitation, elevation in temperature, salinity, and disease attacks are expected to decrease crop production and leads to higher threats of famine [31]. The best possible way to tackle this problem is the development of climate-smart cultivars.

3. Stresses as an outcome of climate change

In recent years, the environment has been significantly affected due to climate change, the most expected area is agriculture, or the agriculture crops grown in these environments. As a result of climate change, the elevation in CO₂ and temperature was observed by different scientists [32]. These are major limitations that develop a gap between the supply and demand of food and lead most researchers into looking for good adaptation strategies for plants under these conditions [33], by developing climate-smart crops that are resilient against climate change [34]. Sensitivity to this kind of stress causes a serious effect on the plants; like disruption in the plant metabolism processes, thereby resulting in the reduction in felicity and quality of agricultural crop production [35]. There are two types of stresses: biotic and abiotic. Biotic stress in plants occurs by the infestations of living entities like viruses, bacteria, nematodes, fungi, insects and weeds, however, abiotic stresses include drought, eminent CO₂, temperature (low and high) [36], waterlogging, high precipitation, increased sunshine intensity and chemical factors (heavy metals and pH).

3.1 Biotic stresses

When we talk about the wheat crop, different biotic factors (including diseases and pests) come under consideration which limits wheat production. These insect pests and diseases are distributed worldwide and some of these exist in major wheat-growing areas which are destructive for wheat production. Karnal bunt and Russian wheat aphid are more dangerous and cause a heavy loss in yield in their hotspot [37]. Main wheat diseases include yellow rust/stripe rust, tan spot and leaf rust/brown rust caused by Puccinia striiformis west, Pyrenophora tritici-repentis (Died.) and Puccinia triticina respectively. Leaf rust causes considerable yield losses in wheat by disrupting the photosynthesis process of leaves which ultimately result in stunted growth, decreased number of grain per spike, shrined seeds and eventually a huge loss in production [38]. When the onset of the disease is early in the growth cycle of the plant the loss increases up to 50% [39]. Stripe rust is also a major disease prevalent in temperate regions and results in 10–70% yield losses [40]. Different chemical treatments and agronomic practices are available to overcome these diseases, but the development of resistant cultivars is the most economical and effective strategy.

3.2 Abiotic stresses

Abiotic stresses like drought [41], heavy metal stress [42], and salinity significantly affects the average yield of crops including wheat [43]. Approximately 9% area of the globe is under cultivation and 91% of that is affected by different stresses. Statistical models predict that a 10% reduction in wheat yield is due to extreme weather, global warming, resulting in increased evaporation rate and reduction in precipitation [44], and more specifically because of drought [45]. Abiotic stresses contribute 50% loss in yield of different crops which includes temperature (20%), salinity (10%), drought (9%), cold (7%), and other stresses (4%) [46]. Water scarcity is a global issue that takes place in any wheat-growing region which causes osmotic stress. In United states, the losses due to drought reached up to $6–8 billion per year which is a threat to global food security [44, 47]. The most frequent spells of drought are the result of global warming, which is a serious concern for wheat yield [44]. Temperature plays a key role in balancing normal crop growth and development which ultimately regulates the crop yield [48]. Wheat survives in a broad range of temperatures, the upper and lower limits of temperature for wheat survival are −17 ± 1.2°C to 47.5 ± 0.5°C, respectively [49]. The daily high surge in temperature is 25–35°C crossways the world wheat-growing areas [50]. The most affected growth stage by temperature stress is flowering followed by germination which is delayed under heat stress due to the alternation in metabolic activities of nearby soil temperature [51]. The result of a delay in germination is low crop density. The most adverse effect of heat stress occurs during the anthesis and seed setting stage and leads towards significant yield loss [52]. An increase in salt accumulation in soil cause physiological drought which decreases the ability of plants to take up water from the soil, [53]. Similarly, heavy metals also affect wheat plants from germination to growth as well as biochemical mechanism and ultimately the reduction of yield. All above-mentioned stresses in wheat-growing areas bring decisive yield loss of wheat.

4. Impact of climate on wheat productivity

Climate change is a major challenge for wheat productivity, which includes declining water availability, increased temperature and different insect pests which cause a serious reduction in the crop. The first step to mitigate climate change is to assess the possible damages and adaptation strategies to accomplish the size and nature of these effects on crop productivity. As wheat is the staple food of many countries its importance is amplified concerning food security, so, it is a need of time to measure the response of wheat to changing climate. The response of wheat plants to changing climate is different with different stages of growth and development including germination, growth and maturity. High temperature is an imperative variable to study which affects the wheat crop throughout the growth cycle. Similarly, rainfall also has an important positive effect if it occurs at proper time with a proper amount at critical stages of growth. Therefore, the estimation of the effect of climate change on wheat productivity can provide important visions for adaptation [54].

4.1 Germination

Germination is the most sensitive stage in the whole wheat life cycle which affects crop density and uniform maturation, which eventually expedite an important role in yield. Extreme alternation in the immediate environment of a germinating seed can inhibit germination processes, eventually leading to possible yield loss due to a drop in cropping density [52]. Different studies suggested that under salt-affected soil, the germination rate of wheat decreased and the seed took more time than normal to germinate. The scientific reason behind that phenomenon is the reduction in osmotic potential of germination media, which restrict seed imbibition. Salinity also destroys the food reserve of the seed by imbalancing the hormonal status of the seed [55]. Other factors impelling germination include seeds’ dormancy, age, seed coat hardness, vigor, polymorphism, temperature, light and gases [56]. The delay in germination may leave crops vulnerable to heat stress at the end of growing seasons or promote uneven maturation of crops [57]. Wheat seed is also sensitive to different chemical and physical conditions such as the presence of heavy metals in the rhizosphere which cause a reduction in germination and affects seedling vigor [58]. Recent studies have documented that heavy metals inhibit the storage of food mobilization, stunt the radical formulation, disrupt the cellular osmoregulation and degrade the proteolytic activities, eventually causing inhibition of seed germination and seedling development [59].

4.2 Physiology

Physiology plays an important role in the growth of any plant. Photosynthesis is an important physiological process for plant development and survival that is greatly affected by environmental conditions. Higher accumulation of salts resulting from climate change primarily lessens the water potential and store Na⁺ and Cl⁻ ions in the chloroplast, which inhibit the photosynthesis process [55]. According to Arfan et al. [60] transpiration rate, stomatal conductance, net CO₂ assimilation and sub stomatal CO₂ concentration were decreased by salinity stress at 150 mM NaCl. Similar to the salt stress, drought/osmotic stress disrupt the photosynthesis process of wheat plants, can damage sugar synthesis essential to drive yield in wheat crops but also leads to stomata closure by turgor loss through reduction of internal water contents. It leads to death of plant by disturbing metabolism [61, 62]. Plant physiological processes are also sensitive to a higher temperature, heat stress cause the deactivation of Rubisco enzyme, reduced photosynthetic capacity, assimilated translocation reduces, brings premature leaf senescence, decrease chlorophyll content and ultimately decrease in yield [63]. High temperature also affects the starch and protein content in grain and induce the production of reactive oxygen species (ROS) which cause a change in membrane stability along with lipid peroxidation, protein oxidation and damage to nucleic acids [64]. Thus, all the stresses are significant variables that emphasis the scientific community to develop climate-smart wheat varieties to tackle food security issues.

4.3 Yield

All the biotic and biotic stresses such as high temperature, water scarcity and frost abate the wheat yield by reducing grain number, grain size and single grain weight. However, how and which yield component will get affected by certain stress depends upon its duration, intensity and timing [65]. For example; if the stress occurs before and during anthesis it reduces the number of grains per ear due to an increased seed abortion. However, when stress occurs after anthesis it does not influence the grain number but effect grain size by shrinking the grain and single grain weight by inhibiting grain filling [66]. Wheat grain yield and number of tillers decreased 53.57% and 15.38% respectively under heat stress [67]. The influence of heat stress is highly significant during the reproductive phase. The increase of 1°C average temperature during the reproductive stage may lead to a higher loss in grain yield [64]. It is also important to note the importance of the flag leaf when looking at yield and grain filling [68]. The flag leaf contributes approximately 30–50% of seed carbohydrates; therefore, any damage to the flag leaf would negatively impact yield [69]. When we talk about the wheat yield loss due to biotic stresses, then the leaf rust (LR) is the main widely spread biotic stress. In the United States, economic losses of $350 million were attributed to LR between 2000 and 2004. In China, annual yield losses due to LR are estimated at 3 million tons [39]. According to a recent estimation, annual yield reductions of 5.47 million tons of wheat are attributable to yellow rust disease, which is equivalent to annual losses of $979 million [70]. A detailed analysis of wheat grain yield and its yield component is crucial to identify genomic regions responsible for grain yield and stress tolerance [71].

5. Approaches to scrimmage against climate change

The fluctuation in climatic conditions directly affects morphology, phenology and physiology of plants and indirectly affects the productivity by alteration in soil biota, fertility, and water and nutrients availability. Keeping in view the current status of wheat production, it is predicted that the wheat productivity will be 1 t/ha short to meet the global demand by 2050. Variation in climate, change in pest and a pathogens life cycle and new variants will further aggravate the situation by threatening global food security. Thus, in future, food security will face a four-fold challenge: upward pressure on demand with downward pressure on supply and the need for sustainable production [72]. All these factors are interlinked and their collective reinforcement will amplify the burden on food demand and require a revolutionized food system [73]. Climate change in short affects plants, their environment and society at large. Breeding for disease-resistant, climate stress-tolerant and potentially high yielding wheat will improve productivity to meet future demands.

5.1 Conventional approaches

Conventional breeding achieves incremental yield gains by recombining alleles mainly from within elite materials and selecting among thousands of progeny per cross for expression of appropriate agronomic traits, resistance to a spectrum of prevalent diseases and yield based on multi-location trials [1]. Crossbred through conventional breeding is only possible between the same or closely related species. The absence of gene of interest (GOI) in the natural gene pool puts limitations on the introgression for the creation of varieties with desirable traits. Therefore, hunting for an alternate source of GOIs in distantly related plant species and even in microorganisms is necessary [74]. Plant breeding programme’s success strongly depends on the climate, market demand and trends. Genomic selection helps in multiple quantitative traits prediction in genotypes from breeding pipelines [75] and by attaining historical phenotypes and adding high-density genotypic information.

5.1.1 Hybridization

In wheat, hybrid cultivar and commercial seed production are still limited to a specific sector as compared to other cereal crops like rice or maize [76]. Conventional breeding by backcrossing is a method to improve an elite line by adding a new trait. An F₁ hybrid is obtained by crossing a donor line carrying GOI with an elite line and then F₁ hybrid is recurrently back-crossed with the elite line until 5-8th generation. The final genotype will be a product of characteristics of the elite line and will carry the introgressed GOI [77]. Wheat is a self-pollinated crop with an out-crossing rate of <1%, so, execution of effective cross-pollination techniques between the wheat elite lines that can overcome the autogamous mode is needed. This can be achieved by crossing between a male-sterile female plant with good pollen recipient properties and a male plant with good pollen shedding properties. Efforts have been made to develop maternal plants with cytoplasmic male-sterility (CMS) for wheat breeding e.g. CMS systems were identified in wheat (i.e. Triticum timopheevii) (Angus, 2001) e.g. four new alien CMS (Ae. kotschyi, Ae. uniaristata, Ae. mutica and Hordeum chilense) were discovered [78]. Due to the Bottleneck effect in bread wheat, a potent source of genetic diversity is required. The gene pools of Triticeae, which includes the primary, secondary, and tertiary gene pools are a rich source of genes that can be used to improve traits such as; abiotic and biotic stress tolerance including disease, herbicides and extreme climatic conditions. The plasticity of the wheat genome is depicted by the fact that novel alleles from 52 species have been introgressed into wheat [79]. Landraces, another crucial gene pool, are also reported to contribute genes for yield improvement in irrigated environments or, in drought and heat-stressed environments [80]. Rht dwarfing gene is one of the best examples which originated from a Japanese landrace “Shiro Daruma” and was introgressed into the first dwarf wheat variety “Norin10” [81]. These same genes were utilized by the famous Dr. Norman E. Borlaug to develop the semi-dwarf and high-yielding wheat varieties that triggered the Green Revolution. Breeding efforts to cope with the upcoming foreseeable future and the speeding up of the genetic gain from the current rate of <1% per year will depend on the following four strategies: 1) use of germplasm from exotic sources to broaden the gene pool and overcome the bottleneck effect due to conventional breeding [82]; 2) strategic hybridization to combine Radiation use efficiency (RUE) associated; 3) empirical methods and skill to identify individual plants with desirable traits and extrapolate the observation to increase the efficiency of conventional breeding; 4) advance techniques like molecular-assisted breeding, genome-wide assisted selection (GWAS) and high-throughput phenotyping to permit the efficient utilization of trait-linked markers as they are identified through gene discovery and GWAS modeling [83].

5.1.2 Mutation

Ever since the epoch-making discoveries made by Muller and Stadler [84], the application of mutation techniques by using different chemical and physical agents have played a significant role in modern plant breeding and genetic studies by generating a vast amount of genetic variability [85]. The narrow genetic diversity of the cultivars imposes the prime challenge in the development of varieties with high yield, stress tolerance, and improved traits like early maturity, seed size and nutrition value [86]. Hugo De Vries coined the term mutation, to indicate a sudden change in the genotype that is heritable [87] and these genetic variations provide the raw material for evolution. The rate of spontaneous mutation is relatively very low i.e. 10⁻⁶ or one out of a million for an individual gene [88], therefore, artificial mutations are necessary to increase the percentage of genetic diversity. The process of inducing desirable mutations and exploiting them for crop improvement is called mutation breeding, which comprises three main steps; using mutagens, screening of mutant candidates for desirable traits, and official release of the new variety [89]. The widespread use of induced mutants in plant breeding programmes across the globe has led to the official release of 265 wheat plant mutant varieties in more than 24 countries throughout the world (Figure 1).

Figure 1.

Wheat mutant varieties released during 1960–2018 [90].

According to [82], mutation breeding has a major advantage over other methods is that in this process no genetic material is lost, rather only mutation is induced in the preexisting genome. It offers the possibility of inducing such unique desired traits that were either lost during evolution or do not exist naturally.

5.1.3 Shuttle breeding

The shuttle breeding concept was originally developed by the International Maize and Wheat Improvement Center’s (CIMMYT) wheat breeding program and was popularized by Nobel laureate Dr. Norman Borlaug. This system allowed an extra generation to be advanced each year by using different field locations. CIMMYT used two contrasting locations with diverse environmental conditions in Mexico for wheat shuttle breeding: Ciudad Obregón, an irrigated dessert located in Northern Sonora Valley and Central Mexican highlands (2249 m altitude). Since the beginning of this programme in Mexico, segregating populations have been “shuttled” about 130 times representing 200,000 crosses. Off-season breeding activities through shuttle breeding has the advantages of screening segregating material in contrasting locations for developing high yielding, disease-resistant, widely adapted and photoperiod insensitive genotypes of wheat within a limited period [91]. Additionally, Borlaug and his team noticed two more advantages of shuttle breeding: first, breeding in locations with different environmental conditions, soil types and stresses allow selection of breeding materials for broad range disease resistance; secondly, photoperiod-sensitive material is screened and eliminated. In this way, the resulting photoperiod-insensitive germplasm permitted CIMMYT’s semi-dwarf high yielding and disease resistant lines to adapt in multi-range environmental conditions worldwide. Shuttle breeding was the foundation of the success of what we today call “the Green Revolution” [92].

5.2 Chromosome doubling

In the second half of the twentieth century, the emergence of doubled haploid (DH) technology revolutionized the generation of genetically pure and homozygous lines and led to the direct production of completely homozygous lines from heterozygous plants in a single generation. Double haploids production by chromosome doubling, spontaneous or by using colchicine, of haploid cells like pollen grains, which greatly shortens the line fixation stage, at least three to four generations of self-pollination, is a means of accelerating the wheat breeding for development of true breeding lines with desirable traits [93]. This technique includes two main steps: haploid induction and chromosome doubling. Haploid induction attempts to regenerate haploids or spontaneous DH plants, which can be achieved by gynogenesi, androgenesis or parthenogenesis, depending on the species. Antimitotic compounds are used for the chromosomal doubling step, which is mandatory if spontaneous doubling does not occur in haploid plants [94].

This process is performed in tissue-culture laboratories and applies to species that are responsive to tissue culturing this technique could complement the conventional breeding programs to accelerate the release of new varieties. In wheat various methods are employed to develop DHs including; isolated microspore culture (IMC), haploid gene inducer, meiotic restitution genes, doubling chemicals, ovule culture, chromosome removal using hybridization, wide hybridization and anther culture [95]. AC and wide hybridization methods are frequently used in applied research and breeding programs [96] while IMC is still under development [97].

5.3 The genetic and genomic course of action

5.3.1 Omics approaches for amelioration of wheat

Omics approaches are useful in deciphering the whole mechanism and thus providing insight into modification at the molecular level which results from changes in environmental conditions. Omics is a diverse branch that includes genomics, transcriptomics, proteomics, metabolomics, and their interactions with each other. The period of omics has been commenced with the advent of automated sequencing approaches which lead to the first whole-genome sequencing of model plant i.e., Arabidopsis thaliana. Advancement in sequencing techniques led to high throughput next-generation sequencing (NGS) followed by a new era of genome-scale molecular analysis with modeling of various molecular and physiological parameters and their correlation provides an accomplished move to deal with different stresses due to climate change. Bread wheat (Allohexaploid, 2n = 6x = 42, AABBDD genomes) has one of the most intricated genomes. The homologous chromosomes containing similar genes mess up the whole biological network. A total of 124,000 gene loci in the wheat genome covering all the three sub-genomes (A, B and D) are involved in a diverse network of biological approaches. Furthermore, transcriptomics (RNA level) and proteomics (protein level) helped in understanding the functions of RNA and proteins respectively. All genes are not transcribed at the same time; therefore, phenotype cannot be fully understood by genomic studies. Thus, the successful combination of genomics (genes), transcriptomics (RNA), proteomics (proteins), and metabolomics (metabolite) will assist in the decoding of diverse metabolism in plants and facilitate breeders to select potential and best traits to improve crop productivity under different stresses due to climate change [42].

5.3.2 Genomics Progress in wheat

Genomics aims at exploring the genome physical structure, studying the whole constitution of the genome including genes and regulatory network. A major milestone in the wheat genome has been achieved in 2012 with the complete de-novo sequencing of bread wheat. Sequencing revealed that A, B and D wheat genomes consist of 28,000, 38,000, and 36,000 genes respectively [98].

5.3.3 Marker assisted breeding perspective in wheat

Upon the advancement in genomics and the advent of the molecular markers era, myriads of shortcomings of conventional breeding approaches are resolved as they are not impacted by environmental factors and can expose variations at the DNA level. Classical breeding is based on the phenotypic selection of genotypes. Genotype X Environment (GE) interaction is the main constraint including the time-consuming and costly procedure of phenotypic selection. By employing molecular markers, desirable genotypic selection can be done at the early generation of the breeding program without the influence of environmental factors. Breeders use molecular markers to enhance the precision of the selection of genetic resources for the best trial combination.

The first study based on molecular markers was initiated in the 1990s when restriction fragment length polymorphism (RFLP) markers were used for identifying genetic diversity, homologous chromosome identification and wheat-rye identification [99]. The use of RFLP is to be sure very successful in the development of linkage groups in wheat. However, it was not so much intriguing due to time consuming, laborious, low frequency and high cost. With more improvement in the marker system, researchers, later on, focused on PCR-based markers including Randomly Amplified Polymorphic DNA (RAPD) and Simple Sequence Repeats (SSR) due to their mapping friendly and cost-effective features. Among PCR-based markers, RAPD was not used extensively due to the availability of scanty information about the location in the genome and lack of reproducibility [100]. Compared to RFLP, SSR markers are reproducible and have a specific location in the genome thereby, more applicable in genome-specific studies. In wheat, the first SSR markers system was reported in 1998 which opens up a new direction for identifying new genetic loci and better yield traits [101]. With time, researchers focused on single nucleotide polymorphism (SNP) and developed trait linked SNP markers. It has higher accuracy than SSR markers. A variety of trait linked DNA markers for wheat were identified for disease resistance and quality of grain. For example, Cre resistance genes (Cre3, Cre1) are used in marker assisted selection (MAS) program of wheat to identify cereal cyst resistant genotypes [102].

5.3.4 Genome-wide association studies (GWAS)

Identification of gene function is a long-standing goal of biology which provides important information for crop improvements. So far, forwards genetics has been the prime approach in which first we mutate the plant, followed by phenotypic screeing to identify the gene function. The identification of genes with major effect is easy as comparision to the gene with minor effect. To overcome this barrier, association mapping (AM) and bi-parental quantitative trait loci (QTL) mapping was introduced with ability to identify genes with subtle effects [103]. Subsequent aim of genetic is to identify a link between a phenotypic function and genotypic data, and AM is one of the approaches to link the phenotype with genotypes. Revolutionary AM orianted approaches were carried out in last decade [169]. Genome-wide association study (GWAS) varies from bi-parental QTL mapping because it is performed on a natural population with a wide genetic base and this wide track of natural variation provides finer resolution of QTL location [103]. The basic apprehension of AM is to identify superior associations (false positive) that can result from population stratification and enigmatic relatedness [104, 105]. To control this issue different statistical methods have been adopted, a mixed linear model (MLM) with population structure and kinship matrix incorporation efficiently eliminate false positive in association mapping [106, 107]. Sequenced-based GWAS has successfully been applied for mapping the agronomic traits and identified the candidate genes inside the significant agronomic regions of wheat [108]. GWAS is a powerful tool to identify the genomic region linked with different traits (linked with biotics and abiotic stress tolerance) in different crops including wheat. It generally highlights linkage among SNPs and traits and is based on GWAS design, genotyping tools, statistical models for examination, and results from interpretation [109]. Using GWAS, Sukumaran et al. [110] detected multiple significant QTL associated with yield and its linked traits of durum wheat grown under drought and heat stress. Similarly, some other studies identified QTL associated with heat and drought tolerance related traits at the seedling stage in wheat [109, 111]. However, limited studies on drought tolerance of wheat have been conducted at the seedling stage.

5.3.5 Genomic selection (GS) in wheat improvement

One of the important technologies utilized in the improvement of the plant is genomic selection along with doubled haploid production, sequencing, QTL mapping, association mapping, genome editing and formation of transgenic plants is genomic selection. In genomic selection, genome-wide markers are used to identify the genotype of a plant and subsequently phenotyped for a particular trait by selection. Contrary to the marker-assisted selection, which utilizes a small number of markers associated with major QTL, GS involves genome-wide markers along with phenotyping data to evaluate genomic estimated breeding values (GEBVs) in one population that will previse the performance of lines in another population only using markers. This technique avoids multiple testing and there is no need to identify marker-trait associations based on arbitrarily chosen significance threshold [112].

Due to the complex genetic makeup of wheat, it requires 10–15 years to transfer new genes into elite germplasm. Genomic selection makes it possible to select parents purely before enter in field trials and nurseries based on genomic estimated breeding values. Annual genetic gain through GS is predicted to be double or triple that of conventional selection due to alleviation in the selection cycle. However, there is still little information regarding GS application in wheat. Improved predictive ability to target traits is cardinal to successful implementation of GS [113]. It is considered that item-based collaborative filtering (IBCF) could be used alternative to conventional predictive model for important target traits in a wheat breeding program [114].

5.3.6 Transcriptome profiling of wheat

RNA sequencing technologies give abundant transcriptomic data which requires expertise in bioinformatics. The wheat hexaploid genome has one of the largest genomes in different crop species constituting 17 Gb in size. Until now, approximately 76% of the wheat genome has been sequenced (International Wheat Genome Sequencing Consortium [IWGSC], [115]. Functional annotation of the wheat genome by homology is becoming very useful but is far from complete as compared to model plants. Transcriptomics in wheat has been facing many challenges due to its complicated genome. Furthermore, RNA sequencing and proteomics study will help in the production of markers associated with particular traits to improve the breeding program. Okada et al., [116] reported that the transcriptional profile of wheat was very useful in the development of molecular markers and was used for the study of wild relative of wheat (Ae. Umbellulata) for population genetics studies. Moreover, many biotic and abiotic stresses can also be studied using expression profiles like drought tolerance mechanisms of two cultivars (Alpowa and Idaho) were studied by Alotaibi [117] using RNA sequencing profiling tool. They identified that differentially expressed genes were 2.32 and 3.9 times more up-regulated and down-regulated respectively in Alpowa as compared to Idaho.

5.3.7 Proteomics in wheat

Proteins play a cardinal role in stress responses, therefore, proteome alterations at different stressed conditions need to be deciphered for the comprehensive understanding of related mechanisms. Stress sensing is the initial pathway to respond to stress conditions followed by the signaling process. For a better understanding of stress coping mechanisms of plants, isolation and characterization of stress-responsive proteins is required. Further, comprehension of post-translational modifications is also needed in plants under stressed conditions. Proteomics plays a very important role in the fine-tuning of pathways that are involved in stress alleviation [42]. For the comprehensive understanding of functional proteomics, there is a dire need to focus on the subcellular proteomics of wheat. To this end, the isolation of proteins from a target organelle is challenging. The conventional approach for the fractionation of subcellular organelles is differential and density gradient centrifugation. Free-flow electrophoresis is also used for the subcellular fractionation based on the isoelectric point of proteins. Despite the diverse application of various proteomics techniques, various subcellular proteins including both stress-induced proteins and housekeeping proteins, remain unclassified. Thus, wheat proteomics data will address the physiological role of the plant under stressed conditions [118].

5.3.8 Metabolomics in wheat

Improvement in genetics is required for the development of new wheat varieties that can work efficiently under stressed conditions. Improvement in the genetics of wheat cultivars would lead to changes in physiological and biochemical responses. Likewise, their change in the metabolic profile that is related to a particular phenotype would result in the development of metabolic markers. Wheat is a crop of higher latitude, therefore, heat stress changes the metabolites in the wheat plant during early summer and terminal heat [119]. Physiological and morphological traits are also important, but they cannot provide the overall picture of the underlying mechanism with changes in metabolic profile under stress conditions. With the advancement in omics techniques, mass spectrometry provides the metabolic profiles of crop genotypes [120]. The metabolic profile of wheat revealed that highly branched amino acids are intolerant in water-deficit stress conditions [121]. It is also reported that different groups of peroxidase genes (TaPrx112-D, TaPrx113-F and TaPrx111-A) were induced by cereal cyst nematodes in some of the resistant wheat lines [122]. Taken together, an amalgamation of wheat “Omics” data including genomics, transcriptomics, proteomics and metabolomics with advanced bioinformatics tools is required to construct a mathematical model that will provide a deep insight into the underlying mechanism of plant undergoing stress condition.

5.3.9 Genetic modification

5.3.9.1 Transformation

Gene transformation is a technique through which the foreign DNA/gene is transferred into target species using molecular methods. Transformation efficiency depends on regeneration frequency of donor tissue (e.g. shoot), the procedure utilized and embryogenesis from somatic or pollen tissue [123]. In monocots, the main challenges for gene transformation are regeneration of explant and difficulties in DNA delivery using monotonous methods of gene transformation [124]. Improvement in DNA delivery methods and advancement in protocols for developing transgenes have led to the expansion of wheat genome sequence information, high-density molecular markers mapping and cloning of several wheat genes [125]. The gene transformation methods can be classified into direct and indirect gene transformation methods (Figure 2) [126].

Figure 2.

Gene transformation methods (direct and indirect).

5.3.9.2 Biolistic transformation

The first successful wheat transformation was reported using particle bombardment of embryogenic callus. Particle bombardment, also known as ‘Biolistic transformation”, is a physical means of forcing DNA molecules into the plant cells and is a most ideal method, only next to Agrobacterium-mediated transformation. Klein et al. [127] established the first particle bombardment system for plants, which was later used in various transformation models and for the transformation of crop species such as; maize, rice, onion and wheat [128]. Wheat crop is one of the most challenging crops to transform, with only limited options viable for gene transfer in wheat. Microinjection and PEG (polyethylene glycol)-mediated transformation are not feasible options because regeneration from wheat protoplast is not possible. As a consequence, the discovery of Agrobacterium tumefaciens ability to infect monocot species made wheat transformation possible by exploiting this mechanism, biolistic gene transfer was the primary transformation method for wheat [129].

Wheat offers only a few suitable explant tissues for regeneration through tissue culture. The most common explant of choice is the “scutellum” surface of immature embryos, which is responsive to DNA uptake through both AMT and biolistics and can readily form embryogenic callus through regeneration. An integrated method of gene transformation called Agrolistics, have also been reported, that combines biolistics and Agrobacterium-mediated transformation [130]. Biolistics gene transfer has become a robust platform for wheat transformation and per 300 immature embryos bombarded; 5–20 independent transgenic plants are produced. Unlike AMT, biolistic-mediated plant transformation does not depend on the receptivity or genotype of the host. Moreover, biolistics transformation is generally more efficient, often results in scrambled and multiple integrations [131] and is less challenging concerning vector requirements because the GOI is co-bombarded with a selectable and separate marker plasmid.

5.3.9.3 Agrobacterium-mediated transformation (AMT)

A. tumefaciens, originally Bacterium tumefaciens, is a gram-negative soil born bacteria that has the unique ability to induce tumors in plants [132]. This potential of Agrobacterium to genetically transform plants and totipotency of plant kingdom has been exploited and combined to develop a new method for genetic transformation in plants. First Agrobacterium-mediated transformed spring wheat was developed by Chen et al [129] using embryo-derived immature and regenerable callus. Wounding of the target tissue is an integral step in this method that allows entry of bacterium and stimulates the production of transfer DNA (T-DNA). For this purpose plant tissues are subjected to sonication in presence of Agrobacterium carrying the GOI or this can also be done with naked DNA. Once the target tissue is infected, bacterium initiates a unidirectional DNA transfer from their plasmid leading to stable integration of donor DNA into the host nuclear genome [133].

A successful AMT depends on the nature of the explant, Agrobacterium strain and plasmids. As mentioned earlier, monocots, i.e. wheat offer a limited choice of explants; shoot apical meristems [134], mature seed callus [135], immature embryos, embryogenic pollen cultures [136] and isolated ovules [137] proved useful for the production of transgenic plants in Triticeae cereals. Moreover, a careful selection of vectors is necessary for cereals’ transformation, because most of the plasmids developed for dicot plant species prove to be unsuitable for grasses, especially the marker genes and promoters. Selected plasmids should be highly stable throughout the co-cultivation period, e.g. pVS1-based vector backbones proved particularly valuable in this regard. In addition, hyper-virulent Agrobacterium strains such as AGL1 increase the efficiency of cereal transformation because they carry additional copies of virulent genes (Vir) [138].

5.3.9.4 In-planta transformation

In-planta transformation method was developed to avoid the problems associated with regeneration and tissue-culture based transformation. This method allows direct introduction of exogenous DNA into intact plant tissue and has been applied in various plant species such as; tomato (Solanum lycopersicum), barrel medic (Medicago truncatula) and some cereals [139]. In this method, whole plant, plant tissue or flower can be used as explant. The production of a large number of uniform plants in a short time, fewer labour efforts and minimal reagents requirements are some of the main advantages of in-planta transformation system [140]. The main techniques of in-planta gene transformation are as follows: Agrobacterium injection, pollen tube-mediated gene transfer (PTT), vacuum infiltration, floral dip and floral spray methods.

5.3.9.5 Agrobacterium injection

Razzaq et al. [141] developed a rapid and improved in-planta based transformation protocol for wheat variety GA-2002. A. tumefaciens strain LBA 4404 harboring pBI121 plasmid carrying GOI was used for direct in-planta transformation. Agraobacterium suspension was injected into florets and apical meristem followed by co-cultivation on filter paper. GUS assay and kanamycin was used to screen the transgenic plants which showed that 26 and 27% transgenics gave a positive response to GUS and PCR, respectively.

5.3.9.6 Pollen tube-mediated gene transfer (PTT)

Pollen tube-mediated gene transfer (PTT) was first reported by Zhou et al. [142] in cotton (Gossypium hirsutum L.). PTT method is simpler than tissue-culture based transformation techniques and can be performed in three major steps; 1) foreign gene injection into pollen tube, 2) gene integration into the host plant genome, 3) and marker-based selection of transgenic plants. Introduction of a foreign gene into target plant can be done by; direct microinjection, direct application of exogenous DNA on stigma or by co-culturing of foreign gene and pollens and pollination utilizing these pollens [143].

5.3.9.7 Vacuum infiltration-assisted agrobacterium-mediated genetic transformation (VIAAT)

In VIAAT, plant tissues are submerged in a liquid suspension of A. tumefaciens and subjected to decreased pressure followed by rapid re-pressurization [144]. Vacuum treatment exposes plant cells, more susceptible to transformation, to GOI carrying Agrobacterium and this phenomenon occurs when vacuum is broken and rapid increase in pressure produces a suction effect which leads to force entry of cell suspension into explant to replace the discharged genes with GOI [145]. Transgenic plants selection is done on screening media containing markers such as antibiotics and herbicides [146]. Stable transgenic plants with lower transformation frequency were produced through this method.

Zale et al. [147] devised an efficient in-planta method specifically for wheat to address the regeneration problems. Uninucleated young, mid and late-stage microspores from spikes were immersed in a suspension containing Agrobacterium via infiltration method and paromomycin spray was used to select the resulting plantlets. Transformed plantlets stayed green while the non-transgenic plants died in response to the screening marker.

5.3.9.8 Floral dip and floral spray

In this method, the inflorescence of plants is submerged at the early stages of flowering in an Agrobacterium suspension with strong optical density to produce transgenic plants. This method is commonly referred to as the ‘floral-dip method’. This method is reliable, quick and free from microbial attacks. A slight modification of floral-dip is floral-spray method, where Agrobacterium suspension is sprayed on inflorescence shoots instead of immersion [148]. Transformation through floral-dip method can result in more than 100 seeds per reproduction cycle in plants and its efficiency ranges between 0.1 and 5 percent [149]. Supertana et al. [150] developed transgenic wheat variety “Shiranekomugi” by using this method and 33% maximum transformation efficiency was achieved. The one major disadvantages of floral dip method is the random integration of foreign genes into the host genome and their low transformation efficiency [151]. While transformation protocols have improved dramatically, lack of public acceptance and patents have prevented the use of transgenic wheat varieties, but, the hope to get better yielding crops with wide range of adaptability is still there.

5.3.10 Genome editing in wheat

Genome editing is one of the most advanced technologies for crop improvement. The basic mechanism is almost the same in all types of these editing technologies. These technologies involve the generation of double-strand breaks (DSBs) at a target site in a genome using programmable sequence-specific nucleases (SSN) followed by the exploitation of endogenous DSB repair mechanisms to generate a mutation at a particular site. There are two endogenous mechanisms to repair DSBs i.e., non-homologous end joining (NHEJ) and homologous recombination (HR) [152]. In NHEJ, the two broken strands are re-ligated with the generation of insertion and/or deletion. It is error-prone and does not require a homologous template. HR requires a homologous template and is more reliable [153]. However, SSNs use NHEJ frequently as a repair mechanism [153]. Three types of SSNs introduce DSB at a specific site [154]. These include Zinc-Finger Nucleases (ZFN), Transcription Activator-Like Effector Nucleases (TALENs) and CRISPR/Cas9.

5.3.10.1 Zinc-finger nucleases (ZFNs)

ZFNs are artificial endonucleases and consist of designed (according to the target site) zinc finger DNA binding protein (ZFP) fused to the cleavage domain of FokI restriction enzyme. ZFP is generally composed of 3–4 zinc finger arrays. Each array can recognize 3 bp long sequence. The two ZFN monomers are designed in such a way that can recognize 6 bp sequence of a target site and allow the FokI monomer to form an active dimer that can generate DSB at a specific site. Using this genome editing technique, mutation at desirable sites can be created which would lead to the improvement of the plan. However, the presence of very few target sites, difficulty in the engineering of specific zinc finger domains and frequent off-target effects are the main constraint in the application of ZFNs [155].

5.3.10.2 Transcription activator -like effector nucleases (TALENs)

Another DNA binding protein exclusive to plant pathogens is Transcription Activator -Like Effector Nucleases (TALENs). It consists of 33–35 long tandem repeats of amino acids followed by 20 amino acids known as “half repeat” and FokI cleavage domain. IN the TALEN monomer, 12th and 13th position impart specificity to nucleotide recognition. Due to the specificity of these two residues (at 12th and 13th position), these are termed as repeat variable di-residues (RVDs). TALENs works similarly as ZFNs do. They can generate DSBs and introduce mutation at a specific site. Engineering of TALENs is much easier than ZFNs. However, their large size of repetitive sequences, high cost and labor for the construction of novel TALENs are the major drawbacks of this technology.

5.3.10.3 Clustered regularly interspaced short palindromic repeats (CRISPR/Cas9)

CRISPR/Cas9 is simple, cheap and more efficient in contrast to ZFNs and TALENs that require specifically tailored DNA binding protein (Figure 3). There are two important components of CRISPR system: guide RNA (gRNA) and CRISPR associated (Cas9) protein. gRNA consists of two components: CRISPR RNA (crRNA) and Trans-activating CRISPR RNA (tracrRNA). crRNA is 18–20 bp in length confers specificity to target DNA. However, trcrRNA is a stretch of loop and acts as a binding scaffold for Cas9. Cas9 protein is an endonuclease consisting of two subparts: 1) Recognition part 2) Nuclease part. The recognition part of Cas protein has two domains i.e., REC1 and REC2 which are responsible for binding with gRNA. Whereas the Nuclease part consists of RuvC, HNH and Protospacer Adjacent Motif (PAM) interacting domain. Former two domains (RuvC and HNH) play role in the cutting of single-stranded DNA. Later domain (PAM interacting domain) confers PAM specificity and initiate the process of binding to target DNA. PAM sequence is 2-5 bp sequence [156]. The mechanism of CRISPR/Cas9 is divided into three steps: recognition, digestion, and repair. gRNA recognizes the specific site on template DNA followed by the generation of DSB at a site 3 bp upstream of the PAM by Cas9. Cas9 can recognize the PAM sequence at 5′-NGG-3′ (where N can be any nucleotide). Finally, DSB is repaired by either NHEJ or HR [157].

Figure 3.

CRISPR consists of sgRNA and Cas9 protein. Cas 9 protein guided by sgRNA produces double strand break. It would lead to DNA repair either by non-homologous end joining method (NHEJ) or by homology recombination (HR) which require template DNA strand.

5.3.10.4 Base editing and prime editing- a new era of CRISPR/Cas9

Base editing and prime editing are the modified versions of CRISPR/Cas9. In base editing approach, point mutation is created without DSB, foreign donor template or involvement of any repair mechanism. This technique comprises gRNA and catalytically inactive Cas9 (Cas9 nickase) fused with single-stranded DNA deaminase. gRNA directs modified Cas9 deaminase to bind to the locus which produces ssDNA R-loop that exposes the DNA to deaminase. Deaminases are of different types. Based on the type of deaminase, base editing is categorized into two types: Cytidine Base Editor (CBE) and adenine base editor (ABE) [158].

CBE edit cytidine into uridine. This system is comprised of gRNA, Cas9 nickase (D10A) that is fused with two more proteins viz. cytosine deaminase (CD) and uracil DNA glycosylase inhibitor (UGI) (Figure 4). Guided by gRNA, CD converts C into U which is then repaired by the base excision repair pathway and generates C to T substitution. ABE edit adenine into inosine which is treated as guanosine by the polymerase (Figure 5). This system is comprised of gRNA, Cas9 nickase fused with adenosine deaminase and also works in the same way as CBE. However, it converts A (Adenosine) into I (Inosine) which is treated as G (Guanine) by DNA polymerase thus generating A to G substitution. Both CBE and ABE can change the base from one purine to another purine or one pyrimidine to another pyrimidine. This is the main shortcoming of this system that purine cannot be replaced by pyrimidine and vice versa [158].

Figure 4.

Cytidine Base editor (CBE) consists of sgRNA, nCas9, cytosine deaminase (CD) and uracil glycosylase inhibitor (UGI). CD causes the deamination of cytosine (C) to uracil (U) which is followed by DNA repair with a result of changing from C:G > T:A.

Figure 5.

Adenine base editor (ABE) consists of sgRNA, nCas9 and adenosine deaminase (AD). AD causes the deamination of adenosine (a) to inosine (I) which is treated as guanosine (G) by DNA polymerase. Deamination is followed by DNA repair with a result of changing from a:T > G:C.

To address this issue, prime editing method was introduced (Figure 6). This method consists of Cas9 nickase (H840A) which is fused with reverse transcriptase and prime edited guide RNA (pegRNA). Guided by pegRNA, reverse transcriptase prime new DNA containing the desired editing at the target site. After attaining flat equilibrium, excision, ligation and repairing, DNA is stably edited with desirable incorporation [158]. The main application of CRISPR/Cas9 in wheat was demonstrated in suspension cultures and protoplast. Variety of genes were targeted in wheat protoplast and suspension culture after the publication of the original principle of CRISPR/Cas9 [159]. Generally, Agrobacterium or particle bombardment are used as a delivery system of plasmids carrying cassettes for the co-expression of gRNA and Cas9. In the case of wheat genome editing, Cas9 has expressed from a codon-optimized gene under the control of RNA polymerase II promoter (ZmUbi or CaMV35S), whereas gRNA is expressed under the control of polymerase III promoter (mostly U6 and U3) [160].

Figure 6.

Prime editing is comprised of Cas9 nickase (H840A) which is fused with reverse transcriptase and prime edited guide RNA (pegRNA). Guided by pegRNA, reverse transcriptase primes new DNA containing the desired editing at the targeted site. After flap equilibration, cleavage, ligation, and DNA repair, the desired editing is incorporated.

5.3.10.5 RNA interference (RNAi) technique in wheat improvement

In eukaryotes, the regulatory mechanism of gene expression is commonly depends upon RNAi. To study functional gene analysis or the development of novel phenotypes, RNAi is a robust tool. This technique involves the expression of antisense or hairpin RNAi constructs to direct gene silencing in a sequence-specific manner [160]. The first wheat gene that was targeted by RNAi was the vernalization gene (TaVRN2). The suppression of this gene provided insight for comprehending the molecular mechanism of flowering time and requirement of vernalization in wheat which is ultimately helpful in varying environments in which wheat can be grown [161].

6. Conclusion

Climate change is a complex of many factors and alarming the world by its destructive effects on crops. Climate change has devastating effects on wheat plant growth and yield. Plants mainly suffer from abiotic stresses. To cope with changing environmental conditions, an integrated management programme is required in addition to crop improvement through conventional and non-conventional methods. To develop better plants under changing climate conditions some bottleneck molecular and physiological encounters present in plants need to be resolved. The rise in temperature and fluctuations in rain fall patterns are very important indicators of climate change. To tackle, this problem different advanced approaches need to be adopted to secure the agriculture future. Climate-resilient crops should be developed using basic breeding approaches. Marker-assisted breeding, omics and proteomics approaches, Genome-wide association studies (GWAS), genomic selection (GS) genetic modification genome editing, CRISPR/Cas9 and RNA interference techniques all are noteworthy in identifying the different genes linked to tolerance against different stresses. Genetic engineering is a good tool to develop a transgenic plant with improved resistance against stress. CRISPR/Cas9 is the best suitable approach to develop eco-friendly genome-edited wheat plants In future to fight a battle against climate change.