Gibberellin Deficiency Confers Both Lodging and Drought Tolerance in Small Cereals

The role of omics in improving the orphan crop tef

Tef or teff [Eragrostis tef (Zucc.) Trotter] is a cereal crop indigenous to the Horn of Africa, where it is a staple food for a large population. The popularity of tef arises from its resilience to environmental stresses and its nutritional value. For many years, tef has been considered an orphan crop, but recent research initiatives from across the globe are helping to unravel its undisclosed potential. Advanced omics tools and techniques have been directed toward the exploration of tef's diversity with the aim of increasing its productivity. In this review, we report on the most recent advances in tef omics that brought the crop into the spotlight of international research.

Genetic study for seed germination and shattering in Euphorbia lagascae in response to different seed treatments

Euphorbia lagascae Spreng is a promising emerging oilseed crop, with its seed oil accounting for approximately 50% of the seed weight. Euphorbia oil contains a significant amount of vernolic acid, comprising two-thirds of its composition, which boasts various industrial applications, including acting as a stabilizer-plasticizer and natural dye. However, this species was known to have a high degree of seed-shattering and a low germination rate, which act as two important barriers to large-scale production and exploitation. Therefore, the objective of this study is to determine the genetic control of seed germination and seed-shattering traits in order to develop a reliable pipeline that would be applicable for industries and breeders to select superior E. lagascae lines and design a robust breeding scheme in a short time at reduced labor costs. For this objective, five different wild-type genotypes of E. lagascae that demonstrated high germination potential were crossed with an ethyl methanesulfonate (EMS) mutant genotype that produces non-shattering capsules. The F2 populations from two successful crosses (A and B) were separated into three different treated groups for seed germination evaluation and to study the segregation of 200 individuals per F2 population. The three treatments were: light, gibberellic acid (GA3), and control treatment. Consequently, plants treated with approximately 250 μmol/m2/s of light showed significant improvement in germination up to 75% in cross A and 82.4 % in cross B compared with the control plants and the group treated with 0.05% GA3. According to the chi-square test results, the inheritance pattern of seed germination in response to light treatment follows a 3:1 segregation ratio between germinated and non-germinated seeds, indicating a dominant gene action in the F2 generation. The same conclusion was followed for the shattering trait in the group treated with light, which was also simply inherited as a 3:1 ratio for shattering vs. non-shattering capsules. Our results emphasize the importance and significance of light treatment in producing uniform populations through acceptable germination and shattering resistance of the mutant genotypes of E. lagascae. This is the first report of light treatment that significantly improved seed germination of E. lagascae, which may enhance efforts in the development of this new industrial crop as a feedstock for vernolic acid production.

Synergistic effect of biochar-based compounds from vegetable wastes and gibberellic acid on wheat growth under salinity stress

Soil salinization is a prevalent form of land degradation particularly in water-deficient regions threatening agricultural sustainability. Present desalinization methods demand excessive water use. Biochar has been recognized as a potential remedy for saline soils and Gibberellic acids (GA3) are known to mediate various biochemical processes aiding in stress mitigation. This study was undertaken at The Islamia University of Bahawalpur during winter 2022-23 to explore the combined effect of biochar and GA3 on wheat (Triticum aestivum L.) in saline conditions. Employing a fully randomized design wheat seeds in 24 pots were subjected to two salinity levels with three replications across eight treatments: T1 to T8 ranging from controls with different soil electrical conductivities (ECs) to treatments involving combinations of GA3, biochar and varying soil ECs. These treatments included T1 (control with soil EC of 2.43dS/m), T2 (salinity stress with soil EC of 5.11dS/m), T3 (10 ppm GA3 with soil EC of 2.43dS/m), T4 (10 ppm GA3 with soil EC of 5.11dS/m), T5 (0.75% Biochar with soil EC of 2.43dS/m), T6 (0.75% Biochar with soil EC of 5.11dS/m), T7 (10 ppm GA3 combined with 0.75% biochar at soil EC of 2.43dS/m) and T8 (10 ppm GA3 plus 0.75% biochar at soil EC of 5.11dS/m). The results indicated that the combined applications of GA3 and biochar significantly enhanced plant growth in saline conditions viz. germination rate by 73%, shoot length of 15.54 cm, root length of 4.96 cm, plant height of 16.89 cm, shoot fresh weight 43.18 g, shoot dry weight 11.57 g, root fresh weight 24.26 g, root dry weight 9.31 g, plant water content 60.77%, photosynthetic rate 18.58(CO2 m-2 s-1) carotenoid 3.03 g, chlorophyll a 1.01 g, chlorophyll b 0.69 g, total chlorophyll contents by 1.9 g as compared to the control. The findings suggest that the combined application of these agents offers a sustainable and effective strategy for cultivating wheat in saline soils. The synergy between biochar and GA3 presents a promising avenue for sustainable wheat cultivation in saline conditions. This combined approach not only improves plant growth but also offers an innovative, water-efficient solution for enhancing agricultural productivity in saline-affected regions.

Genome-wide transcriptomic and functional analyses provide new insights into the response of spring barley to drought stress

Drought is a major abiotic stress that impairs the physiology and development of plants, ultimately leading to crop yield losses. Drought tolerance is a complex quantitative trait influenced by multiple genes and metabolic pathways. However, molecular intricacies and subsequent morphological and physiological changes in response to drought stress remain elusive. Herein, we combined morpho-physiological and comparative RNA-sequencing analyses to identify core drought-induced marker genes and regulatory networks in the barley cultivar 'Giza134'. Based on field trials, drought-induced declines occurred in crop growth rate, relative water content, leaf area duration, flag leaf area, concentration of chlorophyll (Chl) a, b and a + b, net photosynthesis, and yield components. In contrast, the Chl a/b ratio, stoma resistance, and proline concentration increased significantly. RNA-sequence analysis identified a total of 2462 differentially expressed genes (DEGs), of which 1555 were up-regulated and 907 were down-regulated in response to water-deficit stress (WD). Comparative transcriptomics analysis highlighted three unique metabolic pathways (carbohydrate metabolism, iron ion binding, and oxidoreductase activity) as containing genes differentially expressed that could mitigate water stress. Our results identified several drought-induced marker genes belonging to diverse physiochemical functions like chlorophyll concentration, photosynthesis, light harvesting, gibberellin biosynthetic, iron homeostasis as well as Cis-regulatory elements. These candidate genes can be utilized to identify gene-associated markers to develop drought-resilient barley cultivars over a short period of time. Our results provide new insights into the understanding of water stress response mechanisms in barley.

Improving Yield and Yield Stability in Winter Rye by Hybrid Breeding

Rye is the only cross-pollinating small-grain cereal. The unique reproduction biology results in an exceptional complexity concerning genetic improvement of rye by breeding. Rye is a close relative of wheat and has a strong adaptation potential that refers to its mating system, making this overlooked cereal readily adjustable to a changing environment. Rye breeding addresses the emerging challenges of food security associated with climate change. The systematic identification, management, and use of its valuable natural diversity became a feasible option in outbreeding rye only following the establishment of hybrid breeding late in the 20th century. In this article, we review the most recent technological advances to improve yield and yield stability in winter rye. Based on recently released reference genome sequences, SMART breeding approaches are described to counterbalance undesired linkage drag effects of major restorer genes on grain yield. We present the development of gibberellin-sensitive semidwarf hybrids as a novel plant breeding innovation based on an approach that is different from current methods of increasing productivity in rye and wheat. Breeding of new rye cultivars with improved performance and resilience is indispensable for a renaissance of this healthy minor cereal as a homogeneous commodity with cultural relevance in Europe that allows for comparatively smooth but substantial complementation of wheat with rye-based diets, supporting the necessary restoration of the balance between human action and nature.

The chrysanthemum DEAD-box RNA helicase CmRH56 regulates rhizome outgrowth in response to drought stress

Plants have evolved complex mechanisms to reprogram growth in response to drought stress. In herbaceous perennial plant species, the rhizome, which is normally an organ for propagation and food storage, can also support plant growth in stressful environments, and allows the plant to perennate and survive stress damage. However, the mechanisms that regulate rhizome growth in perennial herbs during abiotic stresses are unknown. Here, we identified a chrysanthemum (Chrysanthemum morifolium) DEAD-box RNA helicase gene, CmRH56, that is specifically expressed in the rhizome shoot apex. Knock down of CmRH56 transcript levels decreased the number of rhizomes and enhanced drought stress tolerance. We determined that CmRH56 represses the expression of a putative gibberellin (GA) catabolic gene, GA2 oxidase6 (CmGA2ox6). Exogenous GA treatment and silencing of CmGA2ox6 resulted in more rhizomes. These results demonstrate that CmRH56 suppresses rhizome outgrowth under drought stress conditions by blocking GA biosynthesis.

CRISPR/Cas9-mediated tetra-allelic mutation of the 'Green Revolution' SEMIDWARF-1 (SD-1) gene confers lodging resistance in tef (Eragrostis tef)

Tef is a staple food and a valuable cash crop for millions of people in Ethiopia. Lodging is a major limitation to tef production, and for decades, the development of lodging resistant varieties proved difficult with conventional breeding approaches. We used CRISPR/Cas9 to introduce knockout mutations in the tef orthologue of the rice SEMIDWARF-1 (SD-1) gene to confer semidwarfism and ultimately lodging resistance. High frequency recovery of transgenic and SD-1 edited tef lines was achieved in two tef cultivars by Agrobacterium-mediated delivery into young leaf explants of gene editing reagents along with transformation and regeneration enhancing morphogenic genes, BABY BOOM (BBM) and WUSCHEL2 (WUS2). All of the 23 lines analyzed by next-generation sequencing had at least two or more alleles of SD-1 mutated. Of these, 83% had tetra-allelic frameshift mutations in the SD-1 gene in primary tef regenerants, which were inherited in subsequent generations. Phenotypic data generated on T₁ and T₂ generations revealed that the sd-1 lines have reduced culm and internode lengths with no reduction in either panicle or peduncle lengths. These characteristics are comparable with rice sd-1 plants. Measurements of lodging, in greenhouse-grown plants, showed that sd-1 lines have significantly higher resistance to lodging at the heading stage compared with the controls. This is the first demonstration of the feasibility of high frequency genetic transformation and CRISPR/Cas9-mediated genome editing in this highly valuable but neglected crop. The findings reported here highlight the potential of genome editing for the improvement of lodging resistance and other important traits in tef.

E3 ligase AtAIRP5/GARU regulates drought stress response by stimulating SERINE CARBOXYPEPTIDASE-LIKE1 turnover

Ubiquitination is a major mechanism of eukaryotic posttranslational protein turnover that has been implicated in abscisic acid (ABA)-mediated drought stress response. Here, we isolated T-DNA insertion mutant lines in which ABA-insensitive RING protein 5 (AtAIRP5) was suppressed, resulting in hyposensitive ABA-mediated germination compared to wild-type Arabidopsis (Arabidopsis thaliana) plants. A homology search revealed that AtAIRP5 is identical to gibberellin (GA) receptor RING E3 ubiquitin (Ub) ligase (GARU), which downregulates GA signaling by degrading the GA receptor GID1, and thus AtAIRP5 was renamed AtAIRP5/GARU. The atairp5/garu knockout progeny were impaired in ABA-dependent stomatal closure and were markedly more susceptible to drought stress than wild-type plants, indicating a positive role for AtAIRP5/GARU in the ABA-mediated drought stress response. Yeast two-hybrid, pull-down, target ubiquitination, and in vitro and in planta degradation assays identified serine carboxypeptidase-like1 (AtSCPL1), which belongs to the clade 1A AtSCPL family, as a ubiquitinated target protein of AtAIRP5/GARU. atscpl1 single and atairp5/garu-1 atscpl1-2 double mutant plants were more tolerant to drought stress than wild-type plants in an ABA-dependent manner, suggesting that AtSCPL1 is genetically downstream of AtAIRP5/GARU. After drought treatment, the endogenous ABA levels in atscpl1 and atairp5/garu-1 atscpl1-2 mutant leaves were higher than those in wild-type and atairp5/garu leaves. Overall, our results suggest that AtAIRP5/GARU RING E3 Ub ligase functions as a positive regulator of the ABA-mediated drought response by promoting the degradation of AtSCPL1.

Comparative hormonal and metabolic profile analysis based on mass spectrometry provides information on the regulation of water-deficit stress response of sunflower (Helianthus annuus L.) inbred lines with different water-deficit stress sensitivity

Water-deficit stress is the most important abiotic stress restricting plant growth, development and yield. The effects of this stress, however, depend on genotypes, among other factors. This study assembles morpho-physiological and metabolic approaches to assess hormonal and metabolic profile changes, upon water-deficit stress, in the shoot and roots of two contrasting sunflower inbred lines, B59 (water-deficit stress sensitive) and B71 (water-deficit stress tolerant). The analyses were carried out using mass spectrometry and performing a multivariate statistical analysis to identify relationships between the analyzed variables. Water-deficit stress reduced all morpho-physiological parameters, except for root length in the tolerant inbred line. The hormonal pathways were active in mediating the seedling performance to imposed water-deficit stress in both lines, although with some differences between lines at the organ level. B59 displayed a diverse metabolite battery, including organic acids, organic compounds as well as sugars, mainly in the shoot, whereas B71 showed primary amino acids, organic acids and organic compounds predominantly in its roots. The discrimination between control and water-deficit stress conditions was possible thanks to potential biomarkers of stress treatment, e.g., proline, maleic acid and malonic acid. This study indicated that the studied organs of sunflower seedlings have different mechanisms of regulation under water-deficit stress. These findings could help to better understand the physio-biochemical pathways underlying stress tolerance in sunflower at early-growth stage.

Phytohormone signaling and crosstalk in regulating drought stress response in plants

Phytohormones are ubiquitously involved in plant biological processes and regulate cellular signaling pertaining to unheralded environmental cues, such as salinity, drought, extreme temperature and nutrient deprivation. The association of phytohormones to nearly all the fundamental biological processes epitomizes the phytohormone syndicate as a candidate target for consideration during engineering stress endurance in agronomically important crops. The drought stress response is essentially driven by phytohormones and their intricate network of crosstalk, which leads to transcriptional reprogramming. This review is focused on the pivotal role of phytohormones in water deficit responses, including their manipulation for mitigating the effect of the stressor. We have also discussed the inherent complexity of existing crosstalk accrued among them during the progression of drought stress, which instigates the tolerance response. Therefore, in this review, we have highlighted the role and regulatory aspects of various phytohormones, namely abscisic acid, auxin, gibberellic acid, cytokinin, brassinosteroid, jasmonic acid, salicylic acid, ethylene and strigolactone, with emphasis on drought stress tolerance.

The transcription factor KNAT2/6b mediates changes in plant architecture in response to drought via down-regulating GA20ox1 in Populus alba × P. glandulosa

Plant architecture is genetically controlled, but is influenced by environmental factors. Plants have evolved adaptive mechanisms that allow changes in their architecture under stress, in which phytohormones play a central role. However, the gene regulators that connect growth and stress signals are rarely reported. Here, we report that a class I KNOX gene, PagKNAT2/6b, can directly inhibit the synthesis of gibberellin (GA), altering plant architecture and improving drought resistance in Populus. Expression of PagKNAT2/6b was significantly induced under drought conditions, and transgenic poplars overexpressing PagKNAT2/6b exhibited shorter internode length and smaller leaf size with short or even absent petioles. Interestingly, these transgenic plants showed improved drought resistance under both short- and long-term drought stress. Histological observations indicated that decreased internode length and leaf size were mainly caused by the inhibition of cell elongation and expansion. GA content was reduced, and the GA20-oxidase gene PagGA20ox1 was down-regulated in overexpressing plants. Expression of PagGA20ox1 was negatively related to that of PagKNAT2/6b under drought stress. ChIP and transient transcription activity assays revealed that PagGA20ox1 was directly targeted by PagKNAT2/6b. Therefore, this study provides evidence that PagKNAT2/6b mediates stress signals and changes in plant architecture via GA signaling by down-regulating PagGA20ox1.

Improving drought tolerance in rice: Ensuring food security through multi-dimensional approaches

Drought has been highly prevalent around the world especially in Sub-Saharan Africa and South-East Asian countries. Consistent climatic instabilities and unpredictable rainfall patterns are further worsening the situation. Rice is a C₃ staple cereal and an important food crop for the majority of the world's population and drought stress is one of the major growth retarding threats for rice that slashes down grain quality and yield. Drought deteriorates rice productivity and induces various acclimation responses that aids in stress mitigation. However, the complexity of traits associated with drought tolerance has made the understanding of drought stress-induced responses in rice a challenging process. An integrative understanding based on physiological adaptations, omics, transgenic and molecular breeding approaches successively backed up to developing drought stress-tolerant rice. The review represents a step forward to develop drought-resilient rice plants by exploiting the knowledge that collaborates with omics-based developments with integrative efforts to ensure the compilation of all the possible strategies undertaken to develop drought stress-tolerant rice.

Alternative Strategies for Multi-Stress Tolerance and Yield Improvement in Millets

Millets are important cereal crops cultivated in arid and semiarid regions of the world, particularly Africa and southeast Asia. Climate change has triggered multiple abiotic stresses in plants that are the main causes of crop loss worldwide, reducing average yield for most crops by more than 50%. Although millets are tolerant to most abiotic stresses including drought and high temperatures, further improvement is needed to make them more resilient to unprecedented effects of climate change and associated environmental stresses. Incorporation of stress tolerance traits in millets will improve their productivity in marginal environments and will help in overcoming future food shortage due to climate change. Recently, approaches such as application of plant growth-promoting rhizobacteria (PGPRs) have been used to improve growth and development, as well as stress tolerance of crops. Moreover, with the advance of next-generation sequencing technology, genome editing, using the clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) system are increasingly used to develop stress tolerant varieties in different crops. In this paper, the innate ability of millets to tolerate abiotic stresses and alternative approaches to boost stress resistance were thoroughly reviewed. Moreover, several stress-resistant genes were identified in related monocots such as rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays), and other related species for which orthologs in millets could be manipulated by CRISPR/Cas9 and related genome-editing techniques to improve stress resilience and productivity. These cutting-edge alternative strategies are expected to bring this group of orphan crops at the forefront of scientific research for their potential contribution to global food security.

From Traditional Breeding to Genome Editing for Boosting Productivity of the Ancient Grain Tef [Eragrostis tef (Zucc.) Trotter]

Tef (Eragrostis tef (Zucc.) Trotter) is a staple food crop for 70% of the Ethiopian population and is currently cultivated in several countries for grain and forage production. It is one of the most nutritious grains, and is also more resilient to marginal soil and climate conditions than major cereals such as maize, wheat and rice. However, tef is an extremely low-yielding crop, mainly due to lodging, which is when stalks fall on the ground irreversibly, and prolonged drought during the growing season. Climate change is triggering several biotic and abiotic stresses which are expected to cause severe food shortages in the foreseeable future. This has necessitated an alternative and robust approach in order to improve resilience to diverse types of stresses and increase crop yields. Traditional breeding has been extensively implemented to develop crop varieties with traits of interest, although the technique has several limitations. Currently, genome editing technologies are receiving increased interest among plant biologists as a means of improving key agronomic traits. In this review, the potential application of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (CRISPR-Cas) technology in improving stress resilience in tef is discussed. Several putative abiotic stress-resilient genes of the related monocot plant species have been discussed and proposed as target genes for editing in tef through the CRISPR-Cas system. This is expected to improve stress resilience and boost productivity, thereby ensuring food and nutrition security in the region where it is needed the most.

GIBBERELLINS IN REGULATION OF PLANT GROWTH AND DEVELOPMENT UNDER ABIOTIC STRESSES

Background. Gibberellins (GAs), a class of diterpenoid phytohormones, play an important role in regulation of plant growth and development. Among more than 130 different gibberellin molecules, only a few are bioactive. GA1, GA3, GA4, and GA7 regulate plant growth through promotion the degradation of the DELLA proteins, a family of nuclear growth repressors – negative regulator of GAs signaling. Recent studies on GAs biosynthesis, metabolism, transport, and signaling, as well as crosstalk with other phytohormones and environment have achieved great progress thanks to molecular genetics and functional genomics. Aim. In this review, we focused on the role of GAs in regulation of plant gtowth in abiotic stress conditions. Results. We represented a key information on GAs biosynthesis, signaling and functional activity; summarized current understanding of the crosstalk between GAs and auxin, cytokinin, abscisic acid and other hormones and what is the role of GAs in regulation of adaptation to drought, salinization, high and low temperature conditions, and heavy metal pollution. We emphasize that the effects of GAs depend primarily on the strength and duration of stress and the phase of ontogenesis and tolerance of the plant. By changing the intensity of biosynthesis, the pattern of the distribution and signaling of GAs, plants are able to regulate resistance to abiotic stress, increase viability and even avoid stress. The issues of using retardants – inhibitors of GAs biosynthesis to study the functional activity of hormones under abiotic stresses were discussed. Special attention was focused on the use of exogenous GAs for pre-sowing priming of seeds and foliar treatment of plants. Conclusion. Further study of the role of gibberellins in the acquisition of stress resistance would contribute to the development of biotechnology of exogenous use of the hormone to improve growth and increase plant yields under adverse environmental conditions.

Silicon Enhances Biomass and Grain Yield in an Ancient Crop Tef [Eragrostis tef (Zucc.) Trotter]

Silicon (Si) is one of the beneficial plant mineral nutrients which is known to improve biotic and abiotic stress resilience and productivity in several crops. However, its beneficial role in underutilized or "orphan" crop such as tef [Eragrostis tef (Zucc.) Trotter] has never been studied before. In this study, we investigated the effect of Si application on tef plant performance. Plants were grown in soil with or without exogenous application of Na₂SiO₃ (0, 1.0, 2.0, 3.0, 4.0, and 5.0 mM), and biomass and grain yield, mineral content, chlorophyll content, plant height, and expression patterns of putative Si transporter genes were studied. Silicon application significantly increased grain yield (100%) at 3.0 mM Si, and aboveground biomass yield by 45% at 5.0 mM Si, while it had no effect on plant height. The observed increase in grain yield appears to be due to enhanced stress resilience and increased total chlorophyll content. Increasing the level of Si increased shoot Si and Na content while it significantly decreased the content of other minerals including K, Ca, Mg, P, S, Fe, and Mn in the shoot, which is likely due to the use of Na containing Si amendment. A slight decrease in grain Ca, P, S, and Mn was also observed with increasing Si treatment. The increase in Si content with increasing Si levels prompted us to analyze the expression of Si transporter genes. The tef genome contains seven putative Si transporters which showed high homology with influx and efflux Lsi transporters reported in various plant species including rice. The tef Lsi homologs were deferentially expressed between tissues (roots, leaves, nodes, and inflorescences) and in response to Si, suggesting that they may play a role in Si uptake and/or translocation. Taken together, these results show that Si application improves stress resilience and yield and regulates the expression of putative Si transporter genes. However, further study is needed to determine the physiological function of the putative Si transporters, and to study the effect of field application of Si on tef productivity.

Mutations in the tomato gibberellin receptors suppress xylem proliferation and reduce water loss under water-deficit conditions

Low gibberellin (GA) activity in tomato (Solanum lycopersicum) inhibits leaf expansion and reduces stomatal conductance. This leads to lower transpiration and improved water status under transient drought conditions. Tomato has three GIBBERELLIN-INSENSITIVE DWARF1 (GID1) GA receptors with overlapping activities and high redundancy. We tested whether mutation in a single GID1 reduces transpiration without affecting growth and productivity. CRISPR-Cas9 gid1 mutants were able to maintain higher leaf water content under water-deficit conditions. Moreover, while gid1a exhibited normal growth, it showed reduced whole-plant transpiration and better recovery from dehydration. Mutation in GID1a inhibited xylem vessel proliferation, which led to lower hydraulic conductance. In stronger GA mutants, we also found reduced xylem vessel expansion. These results suggest that low GA activity affects transpiration by multiple mechanisms: it reduces leaf area, promotes stomatal closure, and reduces xylem proliferation and expansion, and as a result, xylem hydraulic conductance. We further examined if gid1a performs better than the control M82 in the field. Under these conditions, the high redundancy of GID1s was lost and gid1a plants were semi-dwarf, but their productivity was not affected. Although gid1a did not perform better under drought conditions in the field, it exhibited a higher harvest index.

Panicle Angle is an Important Factor in Tef Lodging Tolerance

Tef [Eragrostis tef (Zucc.) Trotter] is an important crop in the Horn of Africa, particularly in Ethiopia, where it is a staple food for over 60 million people. However, the productivity of tef remains extremely low in part due to its susceptibility to lodging. Lodging is the displacement of the plant from the upright position, and it is exacerbated by rain, wind and the application of fertilizer. In order to address the issue of global food security, especially in the Horn of Africa, greater insight into the causes of tef lodging is needed. In this study, we combine modeling and biomechanical measurements to compare the properties relating to lodging tolerance in high yielding, improved tef genotypes, and lower yielding natural landraces. Our results indicate that the angle of the panicle contributes to the likelihood of lodging in tef. Varieties with compact panicles and reduced height had increased lodging resistance compared to the other varieties. By comparing different varieties, we found that overall, the landraces of tef lodged less than improved varieties. We constructed a model of stem bending and found that panicle angle was an important determinant of the amount of lodging. The findings from this study provide key information to those involved in tef improvement, especially those interested in lodging tolerance.

The Effect of Drought on Transcriptome and Hormonal Profiles in Barley Genotypes With Contrasting Drought Tolerance

Like many cereal crops, barley is also negatively affected by drought stress. However, due to its simple genome as well as enhanced stress resilient nature compared to rice and wheat, barley has been considered as a model to decipher drought tolerance in cereals. In the present study, transcriptomic and hormonal profiles along with several biochemical features were compared between drought-tolerant (Otis) and drought-sensitive (Baronesse) barley genotypes subjected to drought to identify molecular and biochemical differences between the genotypes. The drought-induced decrease in the leaf relative water content, net photosynthesis, and biomass accumulation was relatively low in Otis compared to Baronesse. The hormonal profiles did not reveal significant differences for majority of the compounds other than the GA20 and the cis-zeatin-o-glucoside (c-ZOG), whose levels were greatly increased in Otis compared to Baronesse under drought. The major differences that emerged from the transcriptome analysis are; (1), the overall number of differentially expressed genes was relatively low in drought-tolerant Otis compared to drought-sensitive Baronesse; (2), a wax biosynthesis gene (CER1), and NAC transcription factors were specifically induced in Otis but not in Baronesse; (3), the degree of upregulation of betaine aldehyde dehydrogenase and a homeobox transcription factor (genes with proven roles in imparting drought tolerance), was greater in Otis compared to Baronesse; (4) the extent of downregulation of gene expression profiles for proteins of the reaction center photosystem II (PSII) (D1 and D2) was low in Otis compared to Baronesse; and, (5), alternative splicing (AS) was also found to differ between the genotypes under drought. Taken together, the overall transcriptional responses were low in drought-tolerant Otis but the genes that could confer drought tolerance were either specifically induced or greatly upregulated in the tolerant genotype and these differences could be important for drought tolerance in barley.

Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants

Abiotic stresses, including drought, salinity, extreme temperature, and pollutants, are the main cause of crop losses worldwide. Novel climate-adapted crops and stress tolerance-enhancing compounds are increasingly needed to counteract the negative effects of unfavorable stressful environments. A number of natural products and synthetic chemicals can protect model and crop plants against abiotic stresses through induction of molecular and physiological defense mechanisms, a process known as molecular priming. In addition to their stress-protective effect, some of these compounds can also stimulate plant growth. Here, we provide an overview of the known physiological and molecular mechanisms that induce molecular priming, together with a survey of the approaches aimed to discover and functionally study new stress-alleviating chemicals.

Metabolite signatures of grasspea suspension-cultured cells illustrate the complexity of dehydration response

This represents the first report deciphering the dehydration response of suspension-cultured cells of a crop species, highlighting unique and shared pathways, and adaptive mechanisms via profiling of 330 metabolites. Grasspea, being a hardy legume, is an ideal model system to study stress tolerance mechanisms in plants. In this study, we investigated the dehydration-responsive metabolome in grasspea suspension-cultured cells (SCCs) to identify the unique and shared metabolites crucial in imparting dehydration tolerance. To reveal the dehydration-induced metabolite signatures, SCCs of grasspea were exposed to 10% PEG, followed by metabolomic profiling. Chromatographic separation by HPLC coupled with MRM-MS led to the identification of 330 metabolites, designated dehydration-responsive metabolites (DRMs), which belonged to 28 varied functional classes. The metabolome was found to be constituted by carboxylic acids (17%), amino acids (13.5%), flavonoids (10.9%) and plant growth regulators (10%), among others. Pathway enrichment analysis revealed predominance of metabolites involved in phytohormone biosynthesis, secondary metabolism and osmotic adjustment. Exogenous application of DRMs, arbutin and acetylcholine, displayed improved physiological status in stress-resilient grasspea as well as hypersensitive pea, while administration of lauric acid imparted detrimental effects. This represents the first report on stress-induced metabolomic landscape of a crop species via a suspension culture system, which would provide new insights into the molecular mechanism of stress responses and adaptation in crop species.

Improving Lodging Resistance: Using Wheat and Rice as Classical Examples

One of the most chronic constraints to crop production is the grain yield reduction near the crop harvest stage by lodging worldwide. This is more prevalent in cereal crops, particularly in wheat and rice. Major factors associated with lodging involve morphological and anatomical traits along with the chemical composition of the stem. These traits have built up the remarkable relationship in wheat and rice genotypes either prone to lodging or displaying lodging resistance. In this review, we have made a comparison of our conceptual perceptions with foregoing published reports and proposed the fundamental controlling techniques that could be practiced to control the devastating effects of lodging stress. The management of lodging stress is, however, reliant on chemical, agronomical, and genetic factors that are reducing the risk of lodging threat in wheat and rice. But, still, there are many questions remain to be answered to elucidate the complex lodging phenomenon, so agronomists, breeders, physiologists, and molecular biologists require further investigation to address this challenging problem.

Gene Expression Profiling and Fine Mapping Identifies a Gibberellin 2-Oxidase Gene Co-segregating With the Dominant Dwarfing Gene Ddw1 in Rye (Secale cereale L.)

The gibberellin (GA)-sensitive dwarfing gene Ddw1 provides an opportunity to genetically reduce plant height in rye. Genetic analysis in a population of recombinant inbred lines confirmed a monogenetic dominant inheritance of Ddw1. Significant phenotypic differences in PH between homo- and heterozygotic genotypes indicate an incomplete dominance of Ddw1. De novo transcriptome sequencing of Ddw1 mutant as well as tall genotypes resulted in 113,547 contigs with an average length of 318 bp covering 36.18 Mbp rye DNA. A hierarchical cluster analysis based on individual groups of rye homologs of functionally characterized rice genes controlling morphological or physiological traits including plant height, flowering time, and source activity identified the gene expression profile of stems at the begin of heading to most comprehensively mirror effects of Ddw1. Genome-wide expression profiling identified 186 transcripts differentially expressed between semi-dwarf and tall genotypes in stems. In total, 29 novel markers have been established and mapped to a 27.2 cM segment in the distal part of the long arm of chromosome 5R. Ddw1 could be mapped within a 0.4 cM interval co-segregating with a marker representing the C20-GA2-oxidase gene ScGA2ox12, that is up-regulated in stems of Ddw1 genotypes. The increased expression of ScGA2ox12 observed in semi-dwarf rye as well as structural alterations in transcript sequences associated with the ScGA2ox12 gene implicate, that Ddw1 is a dominant gain-of-function mutant. Integration of the target interval in the wheat reference genome sequence indicated perfect micro-colinearity between the Ddw1 locus and a 831 kb segment on chromosome 5A, which resides inside of a 11.21 Mb interval carrying the GA-sensitive dwarfing gene Rht12 in wheat. The potential of Ddw1 as a breeder's option to improve lodging tolerance in rye is discussed.

Soil drenching of paclobutrazol: An efficient way to improve quinoa performance under salinity

Salinity extent and severity is rising because of poor management practices on agricultural lands, possibility lies to grow salt-tolerant crops with better management techniques. Therefore, a highly nutritive salt-tolerant crop quinoa with immense potential to contribute for future food security was selected for this investigation. Soil drenching of paclobutrazol (PBZ; 20 mg l^-1 ) was used to understand the ionic relations, gaseous exchange characteristics, oxidative defense system and yield under saline conditions (400 mM NaCl) including normal (0 mM NaCl) and no PBZ (0 mg l^-1 ) as controls. The results revealed that salinity stress reduced the growth and yield of quinoa through perturbing ionic homeostasis with the consequences of overproduction of reactive oxygen species (ROS), oxidative damages and reduced photosynthesis. PBZ improved the quinoa performance through regulation of ionic homeostasis by decreasing Na⁺ , Cl^- , while improving K⁺ , Mg²⁺ and Ca²⁺ concentration. It also enhanced the antioxidative system including ascorbic acid, phenylalanine ammonia-lyase, polyphenol oxidase and glutathione peroxidase, which scavenged the ROS (H₂ O₂ and O₂ ^•- ) and lowered the oxidative damages (malondialdehyde level) under salinity in roots and more specifically in leaf tissues. The photosynthetic rate and stomatal conductance consequently improved (16 and 21%, respectively) in salt-stressed quinoa PBZ-treated compared to the non-treated ones and contributed to the improvement of panicle length (33%), 100-grain weight (8%) and grain yield (38%). Therefore, PBZ can be opted as a shotgun approach to improve quinoa performance and other crops under high saline conditions.

Application of paclobutrazol: a strategy for inducing lodging resistance of wheat through mediation of plant height, stem physical strength, and lignin biosynthesis

Lodging is a major constraint contributing to poor grain yield and quality of wheat (Triticum aestivum L.) worldwide. The use of plant growth regulators is becoming a foremost agro-chemical approach for minimizing the risk of lodging in cereal crops. The present study was conducted to examine the effects of the paclobutrazol application on culm physical strength, lignin content, and lodging resistance of wheat. Wheat seeds were soaked in paclobutrazol at the concentrations of 0 (CK, as control), 200 (PB1), 300 (PB2), and 400 (PB3) mg L^-1. Our results showed that paclobutrazol resulted in a dose-dependent decrease of plant height, internode length, and center of gravity height. Paclobutrazol treatments evidently increased the culm diameter, culm filling degree, and wall thickness of basal internodes, resulting in greater stalk-breaking strength and lodging resistance index (CLRI), where their maximum values were obtained with PB1 treatment. In addition, the activities of lignin-related enzymes were improved by paclobutrazol, particularly at low concentration, which increased the lignin accumulation of the basal internodes of wheat, subsequently improving the capability of stalk lodging resistance. Moreover, the correlation analysis revealed significant correlations between stem diameter, culm filling degree, and lignin with stalk bending strength and CLRI. The paclobutrazol concentration ≥ 300 mg L^-1 (PB2 and PB3 treatments) showed inhibitive effects on various culm morphological traits. These results suggest that not only the plant height, but also the lignin contents and physical strength of internodes are closely related with the lodging resistance of wheat, and reduction in plant height along with improved culm morphological characteristics and higher lignin accumulation in basal internodes could effectively relieve the risk of lodging.

Abiotic Stress Signaling in Wheat - An Inclusive Overview of Hormonal Interactions During Abiotic Stress Responses in Wheat

Rapid global warming directly impacts agricultural productivity and poses a major challenge to the present-day agriculture. Recent climate change models predict severe losses in crop production worldwide due to the changing environment, and in wheat, this can be as large as 42 Mt/°C rise in temperature. Although wheat occupies the largest total harvested area (38.8%) among the cereals including rice and maize, its total productivity remains the lowest. The major production losses in wheat are caused more by abiotic stresses such as drought, salinity, and high temperature than by biotic insults. Thus, understanding the effects of these stresses becomes indispensable for wheat improvement programs which have depended mainly on the genetic variations present in the wheat genome through conventional breeding. Notably, recent biotechnological breakthroughs in the understanding of gene functions and access to whole genome sequences have opened new avenues for crop improvement. Despite the availability of such resources in wheat, progress is still limited to the understanding of the stress signaling mechanisms using model plants such as Arabidopsis, rice and Brachypodium and not directly using wheat as the model organism. This review presents an inclusive overview of the phenotypic and physiological changes in wheat due to various abiotic stresses followed by the current state of knowledge on the identified mechanisms of perception and signal transduction in wheat. Specifically, this review provides an in-depth analysis of different hormonal interactions and signaling observed during abiotic stress signaling in wheat.

Constitutive gibberellin response in grafted tomato modulates root-to-shoot signaling under drought stress

Plants are sessile organisms that must perceive and respond to various environmental constraints throughout their life cycle. Among these constraints, drought stress has become the main limiting factor to crop production around the world. Water deprivation is perceived primarily by the roots, which efficiently signal the shoot to trigger drought responses in order to maximize a plant's ability to survive. In this study, the tomato (Solanum lycopersicum L.) mutant procera (pro), with a constitutive response to gibberellin (GA), and its near isogenic line cv. Micro-Tom (MT), were used in reciprocal grafting under well-watered and water stress conditions to evaluate the role of GA signaling in root-to-shoot communication during drought stress. Growth, oxidative stress, gene expression, water relations and hormonal content were measured in order to provide insights into GA-mediated adjustments to water stress. All graft combinations with pro (i.e. pro/pro, MT/pro and pro/MT) prevented the reduction of growth under stress conditions without a reduction in oxidative stress. The increase of oxidative stress was followed by upregulation of SlDREB2, a drought-tolerance related gene, in all drought-stressed plants. Scions harboring the pro mutation tended to increase the abscisic acid (ABA) content, independent of the rootstock. Moreover, the GA sensitivity of the rootstock modulated stomatal conductance and water use efficiency under drought stress, indicating GA and ABA crosstalk in the adjustment of growth and water economy.

African Orphan Crops under Abiotic Stresses: Challenges and Opportunities

A changing climate, a growing world population, and a reduction in arable land devoted to food production are all problems facing the world food security. The development of crops that can yield under uncertain and extreme climatic and soil growing conditions can play a key role in mitigating these problems. Major crops such as maize, rice, and wheat are responsible for a large proportion of global food production but many understudied crops (commonly known as "orphan crops") including millets, cassava, and cowpea feed millions of people in Asia, Africa, and South America and are already adapted to the local environments in which they are grown. The application of modern genetic and genomic tools to the breeding of these crops can provide enormous opportunities for ensuring world food security but is only in its infancy. In this review, the diversity and types of understudied crops will be introduced, and the beneficial traits of these crops as well as their role in the socioeconomics of Africa will be discussed. In addition, the response of orphan crops to diverse types of abiotic stresses is investigated. A review of the current tools and their application to the breeding of enhanced orphan crops will also be described. Finally, few examples of global efforts on tackling major abiotic constraints in Africa are presented.

Abscisic Acid and Gibberellins Antagonistically Mediate Plant Development and Abiotic Stress Responses

Phytohormones regulate numerous important biological processes in plant development and biotic/abiotic stress response cascades. More than 50 and 100 years have passed since the initial discoveries of the phytohormones abscisic acid (ABA) and gibberellins (GA), respectively. Over the past several decades, numerous elegant studies have demonstrated that ABA and GA antagonistically regulate many plant developmental processes, including seed maturation, seed dormancy and germination, root initiation, hypocotyl and stem elongation, and floral transition. Furthermore, as a well-established stress hormone, ABA plays a key role in plant responses to abiotic stresses, such as drought, flooding, salinity and low temperature. Interestingly, recent evidence revealed that GA are also involved in plant response to adverse environmental conditions. Consequently, the complex crosstalk networks between ABA and GA, mediated by diverse key regulators, have been extensively investigated and documented. In this updated mini-review, we summarize the most recent advances in our understanding of the antagonistically regulatory roles of ABA and GA in different stages of plant development and in various plant-environment interactions, focusing on the crosstalk between ABA and GA at the levels of phytohormone metabolism and signal transduction.

A Functional Genomic Perspective on Drought Signalling and its Crosstalk with Phytohormone-mediated Signalling Pathways in Plants

INTRODUCTION

Drought stress is one of the most important abiotic stresses that negatively influence crop performance and productivity. Plants acclimatize to drought stress conditions through altered molecular, biochemical and physiological responses. Gene and/or protein expression and regulation are thought to be modulated upon stress perception and signal transduction for providing requisite endurance to plants.Plant growth regulators or phytohormones are important molecules required for various biological processes in plants and are also central to stress signalling pathways. Among various phytohormones, Abscisic Acid (ABA) and Ethylene (ET) are considered to be the most vital growth regulators implicated in drought stress signalling and tolerance. Besides the above two known classical phytohormones, Salicylic Acid (SA) and Jasmonic Acid (JA) have also been found to potentially enhance abiotic stress tolerance particularly that of drought, salinity, and heat stress tolerance in plants. Apart from these several other growth regulators such as Cytokinins (CKs), Auxin (AUX), Gibberellic Acid (GA), Brassinosteroids (BRs) and Strigolactones (SLs) have also been reported to actively participate in abiotic stress responses and tolerance in plants. The abiotic stress signalling in plants regulated by these hormones further depends upon the nature, intensity, and duration of exposure to various environmental stresses. It has been reported that all these phytohormones are also involved in extensive crosstalk and signal transduction among themselves and/or with other factors.

CONCLUSION

This review thus summarizes the molecular mechanism of drought signalling and its crosstalk with various phytohormone signalling pathways implicated in abiotic stress response and tolerance.