Water deficit as a regulatory switch for legume root responses

Targeted metabolomics reveals fatty acid abundance adjustments as playing a crucial role in drought-stress response and post-drought recovery in wheat

Drought stress is one of the abiotic stresses restricting plant development, reproductive growth, and survival. In the present study, the effect of drought stress and post-drought recovery for the selected local wheat cultivar, Atta Habib, was studied. Wheat was grown for 16 days followed by drought stress for 7 days and allowed to recover for 7 days after the removal of the drought stress. Same-aged untreated plants were also grown as a control. The effect of drought stress and post-drought recovery on morphology (root length, shoot length, root weight, and shoot weight), enzymatic activity, and fatty acid profile were analyzed. The results showed that shoot weight (93.1 mg), root weight (85.2 mg), and shoot length (11.1 cm) decreased in the stressed plants but increased steadily in the recovered plants compared to the same-aged control plants, while root length showed a higher increase (14.0 cm) during drought stress and tended to normalize during the recovery phase (13.4 cm). The ascorbate peroxidase activity increased in the stressed plants (5.44 unit/mg protein) compared to the control, while gradually normalizing in the recovery phase (5.41 unit/mg protein). Gas chromatography coupled mass spectrometric analysis revealed abundance changes in important fatty acids, such as palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. Palmitic acid (39.1%) and oleic acid (2.11%) increased in the drought-stressed plants, while a reduction in linoleic acid (6.85%) and linolenic acid (51.18%) was observed compared to the same-aged control plants, i.e., palmitic (33.71%), oleic (0.95%), linoleic (7.52%), and linolenic acid (55.23%). The results suggest that wheat tries to recover in the post-drought stage by repairing oxidative damage through ascorbate peroxidase, and by adjusting fatty acid abundances under drought stress and during the post-drought phase in an effort to maintain membranes' integrity and a suitable fat metabolism route, thus helping recovery. Targeted metabolomics may be further used to explore the role of other metabolites in the drought-stress response mechanism in wheat. Furthermore, this relatively little explored avenue of post-drought recovery needs more detailed studies involving multiple stress durations.

Reducing Drought Stress in Plants by Encapsulating Plant Growth-Promoting Bacteria with Polysaccharides

Drought is a major abiotic stress imposed by climate change that affects crop production and soil microbial functions. Plants respond to water deficits at the morphological, biochemical, and physiological levels, and invoke different adaptation mechanisms to tolerate drought stress. Plant growth-promoting bacteria (PGPB) can help to alleviate drought stress in plants through various strategies, including phytohormone production, the solubilization of mineral nutrients, and the production of 1-aminocyclopropane-1-carboxylate deaminase and osmolytes. However, PGPB populations and functions are influenced by adverse soil factors, such as drought. Therefore, maintaining the viability and stability of PGPB applied to arid soils requires that the PGPB have to be protected by suitable coatings. The encapsulation of PGPB is one of the newest and most efficient techniques for protecting beneficial bacteria against unfavorable soil conditions. Coatings made from polysaccharides, such as sodium alginate, chitosan, starch, cellulose, and their derivatives, can absorb and retain substantial amounts of water in the interstitial sites of their structures, thereby promoting bacterial survival and better plant growth.

MeRAV5 promotes drought stress resistance in cassava by modulating hydrogen peroxide and lignin accumulation

Cassava, an important food and energy crop, is relatively more resistant to drought stress than other crops. However, the molecular mechanism underlying this resistance remains elusive. Herein, we report that silencing a drought stress-responsive transcription factor MeRAV5 significantly reduced drought stress resistance, with higher levels of hydrogen peroxide (H₂ O₂ ) and less lignin during drought stress. Yeast two-hybrid, pull down and bimolecular fluorescence complementation (BiFC) showed that MeRAV5 physically interacted with peroxidase (MePOD) and lignin-related cinnamyl alcohol dehydrogenase 15 (MeCAD15) in vitro and in vivo. MeRAV5 promoted the activities of both MePOD and MeCAD15 to affect H₂ O₂ and endogenous lignin accumulation respectively, which are important in drought stress resistance in cassava. When either MeCAD15 or MeRAV5 was silenced, or both were co-silenced, cassava showed lower lignin content and drought-sensitive phenotype, whereas exogenous lignin alkali treatment increased drought stress resistance and alleviated the drought-sensitive phenotype of these silenced cassava plants. This study documents that the modulation of H₂ O₂ and lignin by MeRAV5 is essential for drought stress resistance in cassava.

Comparative proteomic analysis reveals molecular differences between incompatible and compatible interaction of Erysiphe pisi in garden pea

Comparative proteome analysis of Erysiphe pisi-infected pea genotypes; JI-2480 carrying er2 resistant gene and Arkel, the susceptible genotype by liquid chromatography- mass spectrometry (LCMS/MS QTOF) at 72 h post inoculation (hpi) revealed several differentially abundant proteins (DAPs) of both the host and the pathogen. The functional annotation of proteins through gene enrichment and KEGG pathway analyses revealed strong up-regulation of pathogenesis related protein NPR1, proteins related to defense, transportation and signal transduction, hypersensitive response, cell wall modifications, phenylpropanoid and metabolic pathways in J-72. Significant abundance of membrane-related polypeptides, kinase domains and small GTPase signal transduction-related proteins suggested their major role in plant defense. The abundance of cellular antioxidant protein, catalase and its isozyme along with calreticulin-1 and 2 in J-72 confirmed their intervention in maintaining a redox balance in powdery mildew defense. High abundance levels of Glycolysis-related proteins indicated it as a major pathway for energy source during fungal growth. The majority of pathogenicity and virulence genes were downregulated in J-72 compared to A-72, while four EKA (Effectors homologues to Avk1 and Avra10) like avirulence proteins were significantly upregulated in incompatible interaction suggesting their role in eliciting hypersensitive response in pea against E. pisi.

Mitigation of drought-induced oxidative damage by enhanced carbon assimilation and an efficient antioxidative metabolism under high CO2 environment in pigeonpea (Cajanus cajan L.)

In the current study, pigeonpea (Cajanus cajan L.), a promising legume food crop was assessed for its photosynthetic physiology, antioxidative system as well as C and N metabolism under elevated CO₂ and combined drought stress (DS). Pigeonpea was grown in open top chambers under elevated CO₂ (600 µmol mol^-1) and ambient CO₂ (390 ± 20 µmol mol^-1) concentrations, later subjected to DS by complete water withholding. The DS plants were re-watered and recovered (R) to gain normal physiological growth and assessed the recoverable capacity in both elevated and ambient CO₂ concentrations. The elevated CO₂ grown pigeonpea showed greater gas exchange physiology, nodule mass and total dry biomass over ambient CO₂ grown plants under well-watered (WW) and DS conditions albeit a decrease in leaf relative water content (LRWC). Glucose, fructose and sucrose levels were measured to understand the role of hexose to sucrose ratios (H:S) in mediating the drought responses. Free amino acid levels as indicative of N assimilation provided insights into C and N balance under DS and CO₂ interactions. The enzymatic and non-enzymatic antioxidants showed significant upregulation in elevated CO₂ grown plants under DS thereby protecting the plant from oxidative damage caused by the reactive oxygen species. Our results clearly demonstrated the protective role of elevated CO₂ under DS at lower LRWC and gained comparative advantage of mitigating the DS-induced damage over ambient CO₂ grown pigeonpea.

Plant adaptation to drought stress

Plants in their natural habitats adapt to drought stress in the environment through a variety of mechanisms, ranging from transient responses to low soil moisture to major survival mechanisms of escape by early flowering in absence of seasonal rainfall. However, crop plants selected by humans to yield products such as grain, vegetable, or fruit in favorable environments with high inputs of water and fertilizer are expected to yield an economic product in response to inputs. Crop plants selected for their economic yield need to survive drought stress through mechanisms that maintain crop yield. Studies on model plants for their survival under stress do not, therefore, always translate to yield of crop plants under stress, and different aspects of drought stress response need to be emphasized. The crop plant model rice ( Oryza sativa) is used here as an example to highlight mechanisms and genes for adaptation of crop plants to drought stress.

Physiological and Molecular Aspects of Tolerance to Environmental Constraints in Grain and Forage Legumes

Despite the agronomical and environmental advantages of the cultivation of legumes, their production is limited by various environmental constraints such as water or nutrient limitation, frost or heat stress and soil salinity, which may be the result of pedoclimatic conditions, intensive use of agricultural lands, decline in soil fertility and environmental degradation. The development of more sustainable agroecosystems that are resilient to environmental constraints will therefore require better understanding of the key mechanisms underlying plant tolerance to abiotic constraints. This review provides highlights of legume tolerance to abiotic constraints with a focus on soil nutrient deficiencies, drought, and salinity. More specifically, recent advances in the physiological and molecular levels of the adaptation of grain and forage legumes to abiotic constraints are discussed. Such adaptation involves complex multigene controlled-traits which also involve multiple sub-traits that are likely regulated under the control of a number of candidate genes. This multi-genetic control of tolerance traits might also be multifunctional, with extended action in response to a number of abiotic constraints. Thus, concrete efforts are required to breed for multifunctional candidate genes in order to boost plant stability under various abiotic constraints.

Genome-wide transcriptomic comparison of cotton (Gossypium herbaceum) leaf and root under drought stress

In this study, the 454 pyrosequencing platform was used for analyzing the comparative transcriptomic profiles of leaf and root tissues of 1-month-old cotton (Gossypium herbaceum) plants under drought stress. A total of 56,354 and 49,308 reads were generated from leaf and root tissues, respectively, and clustered into 6,313 and 5,858 unigenes. The differentially expressed unigenes that showed up-regulation (≥2-fold) or down-regulation (2≤-fold) were considered for further analysis. A total of 3,517 unigenes were differentially expressed in both tissues. The 1,528 genes specific to leaves and 1,128 specific to roots were obtained. The 28 biological pathways in two tissues were found to respond significantly to drought stress. A total of 289 in leaf and 277 in root unknown (novel) unigenes were found to be remarkably regulated by drought stress. Some key regulatory genes involved in abiotic stress such as WRKY, ERF, AP2 EREBP, MYB, and LEA were highly expressed in leaves. The genes RHD3, LBD, and transcription factor WRKY75, known for root development under various stress conditions, were expressed specifically in root. The genes related to chlorophyll a/b binding protein and photosystem-related proteins showed significant higher expression in roots and as compared to leaves. It can be concluded that cotton leaves are distinct from roots in terms of molecular mechanisms for responses to drought stress.

Detoxification potential and expression analysis of eutypine reducing aldehyde reductase (VrALR) during progressive drought and recovery in Vigna radiata (L.) Wilczek roots

Generation of reactive oxygen species (ROS) in plants is an inevitable consequence of adverse environmental cues and the ability to detoxify deleterious by-products of ROS-mediated oxidation reactions reflect an important defence strategy to combat abiotic stress. Here, we have cloned the eutypine reducing aldehyde reductase gene (VrALR) from Vigna radiata (L.) Wilczek roots. We have expressed and purified the VrALR protein and analyzed its enzyme kinetic parameters and catalytic efficiency with three different substrates to confirm its identity. The functional characterization of this enzyme was unravelled through heterologous expression of the gene in Escherichia coli BL21 and an oxidative stress-sensitive Saccharomyces cerevisiae mutant strain, W3O3-1-A. Finally, the endogenous VrALR enzyme activity and the mRNA expression patterns of the VrALR gene in the roots of V. radiata in response to progressive drought stress in vivo was studied to correlate the ROS-detoxifying role of this important enzyme under the influence of progressive drought stress. Our results, for the first time, demonstrate that eutypine reducing VrALR provides varying degree of stress tolerance in bacteria, yeast systems and also plays a promising protective role against oxidative stress in V. radiata roots during gradual water deprivation. The present study provides an unequivocal evidence to understand the crucial role of aldehyde reductase ROS-detoxifying system which is highly essential for developing stress tolerance in economically important crop plants.