The Cotton Mitogen-Activated Protein Kinase Kinase 3 Functions in Drought Tolerance by Regulating Stomatal Responses and Root Growth

StMAPKK5 responds to heat stress by regulating potato growth, photosynthesis, and antioxidant defenses

Backgrounds

As a conserved signaling pathway, mitogen-activated protein kinase (MAPK) cascade regulates cellular signaling in response to abiotic stress. High temperature may contribute to a significant decrease in economic yield. However, research into the expression patterns of StMAPKK family genes under high temperature is limited and lacks experimental validation regarding their role in supporting potato plant growth.

Methods

To trigger heat stress responses, potato plants were grown at 35°C. qRT-PCR was conducted to analyze the expression pattern of StMAPKK family genes in potato plants. Plant with StMAPKK5 loss-of-function and gain-of-function were developed. Potato growth and morphological features were assessed through measures of plant height, dry weight, and fresh weight. The antioxidant ability of StMAPKK5 was indicated by antioxidant enzyme activity and H2O2 content. Cell membrane integrity and permeability were suggested by relative electrical conductivity (REC), and contents of MDA and proline. Photosynthetic capacity was next determined. Further, mRNA expression of heat stress-responsive genes and antioxidant enzyme genes was examined.

Results

In reaction to heat stress, the expression profiles of StMAPKK family genes were changed. The StMAPKK5 protein is located to the nucleus, cytoplasm and cytomembrane, playing a role in controlling the height and weight of potato plants under heat stress conditions. StMAPKK5 over-expression promoted photosynthesis and maintained cell membrane integrity, while inhibited transpiration and stomatal conductance under heat stress. Overexpression of StMAPKK5 triggered biochemical defenses in potato plant against heat stress, modulating the levels of H2O2, MDA and proline, as well as the antioxidant activities of CAT, SOD and POD. Overexpression of StMAPKK5 elicited genetic responses in potato plants to heat stress, affecting heat stress-responsive genes and genes encoding antioxidant enzymes.

Conclusion

StMAPKK5 can improve the resilience of potato plants to heat stress-induced damage, offering a promising approach for engineering potatoes with enhanced adaptability to challenging heat stress conditions.

Identification and analysis of MAPK cascade gene families of Camellia oleifera and their roles in response to cold stress

BACKGROUND

Low-temperature severely limits the growth and development of Camellia oleifera (C. oleifera). The mitogen-activated protein kinase (MAPK) cascade plays a key role in the response to cold stress.

METHODS AND RESULTS

Our study aims to identify MAPK cascade genes in C. oleifera and reveal their roles in response to cold stress. In our study, we systematically identified and analyzed the MAPK cascade gene families of C. oleifera, including their physical and chemical properties, conserved motifs, and multiple sequence alignments. In addition, we characterized the interacting networks of MAPKK kinase (MAPKKK)-MAPK kinase (MAPKK)-MAPK in C. oleifera. The molecular mechanism of cold stress resistance of MAPK cascade genes in wild C. oleifera was analyzed by differential gene expression and real-time quantitative reverse transcription-PCR (qRT-PCR).

CONCLUSION

In this study, 21 MAPKs, 4 MAPKKs and 55 MAPKKKs genes were identified in the leaf transcriptome of C. oleifera. According to the phylogenetic results, MAPKs were divided into 4 groups (A, B, C and D), MAPKKs were divided into 3 groups (A, B and D), and MAPKKKs were divided into 2 groups (MEKK and Raf). Motif analysis showed that the motifs in each subfamily were conserved, and most of the motifs in the same subfamily were basically the same. The protein interaction network based on Arabidopsis thaliana (A. thaliana) homologs revealed that MAPK, MAPKK, and MAPKKK genes were widely involved in C. oleifera growth and development and in responses to biotic and abiotic stresses. Gene expression analysis revealed that the CoMAPKKK5/CoMAPKKK43/CoMAPKKK49-CoMAPKK4-CoMAPK8 module may play a key role in the cold stress resistance of wild C. oleifera at a high-elevation site in Lu Mountain (LSG). This study can facilitate the mining and utilization of genetic resources of C. oleifera with low-temperature tolerance.

The WRKY17-WRKY50 complex modulates anthocyanin biosynthesis to improve drought tolerance in apple

Drought stress is increasing worldwide due to global warming, which severely reduces apple (Malus domestica) yield. Clarifying the basis of drought tolerance in apple could accelerate the molecular breeding of drought-tolerant cultivars to maintain apple production. We identified a transcription factor MdWRKY50 by yeast two-hybrid (Y2H) assays as an interactor of the drought-tolerant protein MdWRKY17, and confirmed their interaction by bimolecular fluorescence complementation (BiFC) and pull-down assays. MdWRKY50 was induced by drought and when overexpressed in apple, conferred transgenic apple plants enhanced drought tolerance by directly binding to the promoter of anthocyanin synthetic gene Chalcone synthase (MdCHS) to upregulate its expression for higher anthocyanin. Increased anthocyanin relieves apple plants from oxidative damage under drought stress. MdWRKY50 RNA-interference transgenic apple plants showed opposite phenotypes. The dimerization of MdWRKY50 with mutated MdWRKY17DP mimicking drought-induced phosphorylation by the mitogen-activated protein kinase kinase 2 (MEK2)-MPK6 cascade, compared with MdWRKY17AP and MdWRKY17, further promoted anthocyanin biosynthesis, suggesting dimerization with MdWRKY17 makes MdWRKY50 more powerful in promoting anthocyanin biosynthesis under drought stress. Taken together, we isolated an entire MEK2-MAPK6-MdWRKY17-MdWRKY50-MdCHS pathway for drought tolerance and generated transgenic apple germplasm with enhanced drought tolerance and higher anthocyanin levels.

Uncovering molecular mechanisms involved in microbial volatile compounds-induced stomatal closure in Arabidopsis thaliana

Microbial volatile compounds (mVCs) may cause stomatal closure to limit pathogen invasion as part of plant innate immune response. However, the mechanisms of mVC-induced stomatal closure remain unclear. In this study, we co-cultured Enterobacter aerogenes with Arabidopsis (Arabidopsis thaliana) seedlings without direct contact to initiate stomatal closure. Experiments using the reactive oxygen species (ROS)-sensitive fluorescent dye, H2DCF-DA, showed that mVCs from E. aerogenes enhanced ROS production in guard cells of wild-type plants. The involvement of ROS in stomatal closure was then demonstrated in an ROS production mutant (rbohD). In addition, we identified two stages of signal transduction during E. aerogenes VC-induced stomatal closure by comparing the response of wild-type Arabidopsis with a panel of mutants. In the early stage (3 h exposure), E. aerogenes VCs induced stomatal closure in wild-type and receptor-like kinase THESEUS1 mutant (the1-1) but not in rbohD, plant hormone-related mutants (nced3, erf4, jar1-1), or MAPK kinase mutants (mkk1 and mkk3). However, in the late stage (24 h exposure), E. aerogenes VCs induced stomatal closure in wild-type and rbohD but not in nced3, erf4, jar1-1, the1-1, mkk1 or mkk3. Taken together, our results suggest that E. aerogenes mVC-induced plant immune responses modulate stomatal closure in Arabidopsis by a multi-phase mechanism.

The GhMAP3K62-GhMKK16-GhMPK32 kinase cascade regulates drought tolerance by activating GhEDT1-mediated ABA accumulation in cotton

INTRODUCTION

Drought is the principal abiotic stress that severely impacts cotton (Gossypium hirsutum) growth and productivity. Upon sensing drought, plants activate stress-related signal transduction pathways, including ABA signal and mitogen-activated protein kinase (MAPK) cascade. However, as the key components with the fewest members in the MAPK cascade, the function and regulation of GhMKKs need to be elucidated. In addition, the relationship between MAPK module and the ABA core signaling pathway remains incompletely understood.

OBJECTIVE

Here we aim to elucidate the molecular mechanism of cotton response to drought, with a focus on mitogen-activated protein kinase (MAPK) cascades activating ABA signaling.

METHODS

Biochemical, molecular and genetic analysis were used to study the GhMAP3K62-GhMKK16-GhMPK32-GhEDT1 pathway genes.

RESULTS

A nucleus- and membrane-localized MAPK cascade pathway GhMAP3K62-GhMKK16-GhMPK32, which targets and phosphorylates the nuclear-localized transcription factor GhEDT1, to activate downstream GhNCED3 to mediate ABA-induced stomatal closure and drought response was characterized in cotton. Overexpression of GhMKK16 promotes ABA accumulation, and enhances drought tolerance via regulating stomatal closure under drought stress. Conversely, RNAi-mediated knockdown of GhMKK16 expression inhibits ABA accumulation, and reduces drought tolerance. Virus-induced gene silencing (VIGS)-mediated knockdown of either GhMAP3K62, GhMPK32 or GhEDT1 expression represses ABA accumulation and reduces drought tolerance through inhibiting stomatal closure. Expression knockdown of GhMPK32 or GhEDT1 in GhMKK16-overexpressing cotton reinstates ABA content and stomatal opening-dependent drought sensitivity to wild type levels. GhEDT1 could bind to the HD boxes in the promoter of GhNCED3 to activate its expression, resulting in ABA accumulation. We propose that the MAPK cascade GhMAP3K62-GhMKK16-GhMPK32 pathway functions on drought response through ABA-dependent stomatal movement in cotton.

Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Recent progression and future perspectives in cotton genomic breeding

Upland cotton is an important global cash crop for its long seed fibers and high edible oil and protein content. Progress in cotton genomics promotes the advancement of cotton genetics, evolutionary studies, functional genetics, and breeding, and has ushered cotton research and breeding into a new era. Here, we summarize high-impact genomics studies for cotton from the last 10 years. The diploid Gossypium arboreum and allotetraploid Gossypium hirsutum are the main focus of most genetic and genomic studies. We next review recent progress in cotton molecular biology and genetics, which builds on cotton genome sequencing efforts, population studies, and functional genomics, to provide insights into the mechanisms shaping abiotic and biotic stress tolerance, plant architecture, seed oil content, and fiber development. We also suggest the application of novel technologies and strategies to facilitate genome-based crop breeding. Explosive growth in the amount of novel genomic data, identified genes, gene modules, and pathways is now enabling researchers to utilize multidisciplinary genomics-enabled breeding strategies to cultivate "super cotton", synergistically improving multiple traits. These strategies must rise to meet urgent demands for a sustainable cotton industry.

NUCLEAR TRANSPORT FACTOR 2-LIKE improves drought tolerance by modulating leaf water loss in alfalfa (Medicago sativa L.)

Drought is a major environmental factor that limits the production of alfalfa (Medicago sativa). In the present study, M. sativa NUCLEAR TRANSPORT FACTOR 2-LIKE (MsNTF2L) was identified as a nucleus-, cytoplasm-, and plasma membrane-localized protein. Its transcriptional expression was highly induced by ABA and drought stress. Overexpression of MsNTF2L in Arabidopsis resulted in hypersensitivity to ABA during both the seed germination and seedling growth stages. However, transgenic Arabidopsis plants exhibited enhanced tolerance to drought stress by reducing the levels of reactive oxygen species (ROS) and increasing the expression of stress/ABA-inducible genes. Consistently, analysis of MsNTF2L overexpression (OE) and RNA interference (RNAi) alfalfa plants revealed that MsNTF2L confers drought tolerance through promoting ROS scavenging, a decrease in stomatal density, ABA-induced stomatal closure, and epicuticular wax crystal accumulation. MsNTF2L highly affected epicuticular wax deposition, as a large group of wax biosynthesis and transport genes were influenced in the alfalfa OE and RNAi lines. Furthermore, transcript profiling of drought-treated alfalfa WT, OE, and RNAi plants showed a differential drought response for genes related to stress/ABA signaling, antioxidant defense, and photosynthesis. Taken together, these results reveal that MsNTF2L confers drought tolerance in alfalfa via modulation of leaf water loss (by regulating both stomata and wax deposition), antioxidant defense, and photosynthesis.

De novo assembly provides new insights into the evolution of Elaeagnus angustifolia L

BACKGROUND

Elaeagnus angustifolia L. is a deciduous tree in the family Elaeagnaceae. It is widely used to study abiotic stress tolerance in plants and to improve desertification-affected land because of its ability to withstand diverse types of environmental stress, such as drought, salt, cold, and wind. However, no studies have examined the mechanisms underlying the resistance of E. angustifolia to environmental stress and its adaptive evolution.

METHODS

Here, we used PacBio, Hi-C, resequencing, and RNA-seq to construct the genome and transcriptome of E. angustifolia and explore its adaptive evolution.

RESULTS

The reconstructed genome of E. angustifolia was 526.80 Mb, with a contig N50 of 12.60 Mb and estimated divergence time of 84.24 Mya. Gene family expansion and resequencing analyses showed that the evolution of E. angustifolia was closely related to environmental conditions. After exposure to salt stress, GO pathway analysis showed that new genes identified from the transcriptome were related to ATP-binding, metal ion binding, and nucleic acid binding.

CONCLUSION

The genome sequence of E. angustifolia could be used for comparative genomic analyses of Elaeagnaceae family members and could help elucidate the mechanisms underlying the response of E. angustifolia to drought, salt, cold, and wind stress. Generally, these results provide new insights that could be used to improve desertification-affected land.

Late embryogenesis abundant gene LEA3 (Gh_A08G0694) enhances drought and salt stress tolerance in cotton

Plants have evolved a complex and organized response to abiotic stress that involves physiological and metabolic reprogramming, transcription control, epigenetic regulation, and expressions of thousand interacting genes for instance the late embryogenesis abundant (LEA) proteins are expressed in multiple environmental variables during the plant developmental period, and thus play critical role in enhancing drought and salt stress tolerance. A comprehensive molecular and functional characterization of the LEA3 gene was carried out in cotton under abiotic stress conditions in order to elucidate their functions. Seventy eight genes were identified in cotton, and were clustered into six clades moreover; the LEA genes were more upregulated in the tissues of the tetraploid cotton compared to the diploid type. A key gene, Gh_A08G0694 was the most upregulated, and was knocked in tetraploid cotton, the knocked out significantly increased the susceptibility of cotton plants to salinity and drought stresses, moreover, several ABA/stress-associated genes were down regulated. Similarly, overexpression of the key gene, significantly increased tolerance of the overexpressed plants to drought and salinity stress. The key gene is homologous to GhLEA3 protein, found to have strong interaction to key abiotic stress tolerance genes, voltage-dependent anion channel 1 (VDAC1) and glyceraldehyde-3-phosphate dehydrogenase A (gapA).

Melatonin Mediated Differential Regulation of Drought Tolerance in Sensitive and Tolerant Varieties of Upland Cotton (Gossypium hirsutum L.)

Melatonin (N-acetyl-5-methoxytryptamine), a biomolecule with multifunctional phyto-protectant activities, enhances the tolerance to broad-spectrum biotic and abiotic stresses in plants. However, little information is available on the effect of melatonin on different morpho-physiological, biochemical, and molecular parameters during drought stress incidence in varieties contrastingly differing in their tolerance levels. The present study is aimed at investigating the drought stress responses of drought-sensitive (var. L-799) and drought-tolerant (var. Suraj) varieties after exogenous melatonin priming and gaining mechanistic insights into drought tolerance in upland cotton (Gossypium hirsutum). Melatonin-priming enhanced the tolerance of L-799 to drought stress by modulating the antioxidant system, with increased photosynthetic activity, water-use efficiency, and nitrogen metabolism. Higher endogenous melatonin content and upregulated expression of candidate stress-responsive genes in primed L-799 suggested their involvement in drought tolerance. The higher expression of autophagosome marker [lipidated (ATG8-PE)] in melatonin-primed drought-stressed plants of L-799 also indicated the role of autophagy in alleviating drought stress. Interestingly, melatonin-priming did not show pronounced differences in the different parameters studied during the presence or absence of drought stress in Suraj. In conclusion, this study showed that melatonin plays an important role in mitigating drought stress effects by modulating several physiological, biochemical, and molecular processes, with the key regulatory factor being the plant tolerance level that serves as the switch that turns the priming effects on/off.

Transcriptome analysis of Auricularia fibrillifera fruit-body responses to drought stress and rehydration

BACKGROUND

Drought stress severely restricts edible fungus production. The genus Auricularia has a rare drought tolerance, a rehydration capability, and is nutrient rich.

RESULTS

The key genes and metabolic pathways involved in drought-stress and rehydration were investigated using a transcriptome analysis to clarify the relevant molecular mechanisms. In total, 173.93 Mb clean reads, 26.09 Gb of data bulk, and 52,954 unigenes were obtained. Under drought-stress and rehydration conditions, 14,235 and 8539 differentially expressed genes, respectively, were detected. 'Tyrosine metabolic', 'caffeine metabolism', 'ribosome', 'phagosome', and 'proline and arginine metabolism', as well as 'peroxisome' and 'mitogen-activated protein kinase signaling' pathways, had major roles in A. fibrillifera responses to drought stress. 'Tyrosine' and 'caffeine metabolism' might reveal unknown mechanisms for the antioxidation of A. fibrillifera under drought-stress conditions. During the rehydration process, 'diterpenoid biosynthesis', 'butanoate metabolism', 'C5-branched dibasic acid', and 'aflatoxin biosynthesis' pathways were significantly enriched. Gibberellins and γ-aminobutyric acid were important in the recovery of A. fibrillifera growth after rehydration. Many genes related to antibiotics, vitamins, and other health-related ingredients were found in A. fibrillifera.

CONCLUSION

These findings suggested that the candidate genes and metabolites involved in crucial biological pathways might regulate the drought tolerance or rehydration of Auricularia, shedding light on the corresponding mechanisms and providing new potential targets for the breeding and cultivation of drought-tolerant fungi.

Morphological, physiological and molecular assessment of cotton for drought tolerance under field conditions

Climate change could be an existential threat to many crops. Drought and heat stress are becoming harder for cultivated crops. Cotton in Pakistan is grown under natural high temperature and low moisture, could be used as a source of heat and drought tolerance. Therefore, the study was conducted to morphological, physiological and molecular characterization of cotton genotypes under field conditions. A total of 25 cotton genotypes were selected from the gene pool of Pakistan based on tolerance to heat and drought stress. In field trail, the stress related traits like boll retention percentage, plant height, number of nodes and inter-nodal distance were recorded. In physiological assessment, traits such as photosynthesis rate, stomatal conductance, transpiration rate, leaf temperature, relative water content and excised leaf water loss were observed. At molecular level, a set of 19 important transcription factors, controlling drought/heat stress tolerance (HSPCB, GHSP26, HSFA2, HSP101, HSP3, DREB1A, DREB2A, TPS, GhNAC2, GbMYB5, GhWRKY41, GhMKK3, GhMPK17, GhMKK1, GhMPK2, APX1, HSC70, ANNAT8, and GhPP2A1) were analyzed from all genotypes. Data analyses depicted that boll retention percentage, photosynthesis, stomatal conductance, relative water content under the stress conditions were associated with the presence of important drought & heat TF/genes which depicts high genetic potential of Pakistani cotton varieties against abiotic stress. The variety MNH-886 appeared in medium plant height, high boll retention percentage, high relative water content, photosynthesis rate, stomatal conductance, transpiration rate and with maximum number transcription factors under study. The variety may be used as source material for heat and drought tolerant cotton breeding. The results of this study may be useful for the cotton breeders to develop genotype adoptable to environmental stresses under climate change scenario.

Overexpression of GhMPK3 from Cotton Enhances Cold, Drought, and Salt Stress in Arabidopsis

Cotton production is hampered by a variety of abiotic stresses that wreak havoc on the growth and development of plants, resulting in significant financial losses. According to reports, cotton production areas have declined around the world as a result of the ongoing stress. Therefore, plant breeding programs are concentrating on abiotic stress-tolerant cotton varieties. Mitogen-activated protein kinase (MAPK) cascades are involved in plant growth, stress responses, and the hormonal signaling pathway. In this research, three abiotic stresses (cold, drought, and salt) were analyzed on GhMPK3 transformed Arabidopsis plants. The transgenic plant’s gene expression and morphologic analysis were studied under cold, drought, and salt stress. Physiological parameters such as relative leaf water content, excised leaf water loss, chlorophyll content, and ion leakage showed that overexpressed plants possess more stable content under stress conditions compared with the WT plants. Furthermore, GhMPK3 overexpressed plants had greater antioxidant activities and weaker oxidant activities. Silencing GhMPK3 in cotton inhibited its tolerance to drought stress. Our research findings strongly suggest that GhMPK3 can be regarded as an essential gene for abiotic stress tolerance in cotton plants.

RING finger protein RGLG1 and RGLG2 negatively modulate MAPKKK18 mediated drought stress tolerance in Arabidopsis

Mitogen activated protein kinase kinase kinase 18 (MAPKKK18) mediated signaling cascade plays important roles in Arabidopsis drought stress tolerance. However, the post-translational modulation patterns of MAPKKK18 are not characterized. In this study, we found that the protein level of MAPKKK18 was tightly controlled by the 26S proteasome. Ubiquitin ligases RGLG1 and RGLG2 ubiquitinated MAPKKK18 at lysine residue K32 and K154, and promoted its degradation. Deletion of RGLG1 and RGLG2 stabilized MAPKKK18 and further enhanced the drought stress tolerance of MAPKKK18-overexpression plants. Our data demonstrate that RGLG1 and RGLG2 negatively regulate MAPKKK18-mediated drought stress tolerance in Arabidopsis.

Plant Mitogen-Activated Protein Kinase Cascades in Environmental Stresses

Due to global warming and population growth, plants need to rescue themselves, especially in unfavorable environments, to fulfill food requirements because they are sessile organisms. Stress signal sensing is a crucial step that determines the appropriate response which, ultimately, determines the survival of plants. As important signaling modules in eukaryotes, plant mitogen-activated protein kinase (MAPK) cascades play a key role in regulating responses to the following four major environmental stresses: high salinity, drought, extreme temperature and insect and pathogen infections. MAPK cascades are involved in responses to these environmental stresses by regulating the expression of related genes, plant hormone production and crosstalk with other environmental stresses. In this review, we describe recent major studies investigating MAPK-mediated environmental stress responses. We also highlight the diverse function of MAPK cascades in environmental stress. These findings help us understand the regulatory network of MAPKs under environmental stress and provide another strategy to improve stress resistance in crops to ensure food security.

Cytokinins as central regulators during plant growth and stress response

Cytokinins are a class of phytohormone that participate in the regulation of the plant growth, development, and stress response. In this review, the potential regulating mechanism during plant growth and stress response are discussed. Cytokinins are a class of phytohormone that participate in the regulation of plant growth, physiological activities, and yield. Cytokinins also play a key role in response to abiotic stresses, such as drought, salt and high or low temperature. Through the signal transduction pathway, cytokinins interact with various transcription factors via a series of phosphorylation cascades to regulate cytokinin-target gene expression. In this review, we systematically summarize the biosynthesis and metabolism of cytokinins, cytokinin signaling, and associated gene regulation, and highlight the function of cytokinins during plant development and resistance to abiotic stress. We also focus on the importance of crosstalk between cytokinins and other classes of phytohormones, including auxin, ethylene, strigolactone, and gibberellin. Our aim is to provide a comprehensive overview of recent findings on the mechanisms by which cytokinins act as central regulators of plant development and stress reactions, and highlight topics for future research.

Regulatory Network of Cotton Genes in Response to Salt, Drought and Wilt Diseases (Verticillium and Fusarium): Progress and Perspective

In environmental conditions, crop plants are extremely affected by multiple abiotic stresses including salinity, drought, heat, and cold, as well as several biotic stresses such as pests and pathogens. However, salinity, drought, and wilt diseases (e.g., Fusarium and Verticillium) are considered the most destructive environmental stresses to cotton plants. These cause severe growth interruption and yield loss of cotton. Since cotton crops are central contributors to total worldwide fiber production, and also important for oilseed crops, it is essential to improve stress tolerant cultivars to secure future sustainable crop production under adverse environments. Plants have evolved complex mechanisms to respond and acclimate to adverse stress conditions at both physiological and molecular levels. Recent progresses in molecular genetics have delivered new insights into the regulatory network system of plant genes, which generally includes defense of cell membranes and proteins, signaling cascades and transcriptional control, and ion uptake and transport and their relevant biochemical pathways and signal factors. In this review, we mainly summarize recent progress concerning several resistance-related genes of cotton plants in response to abiotic (salt and drought) and biotic (Fusarium and Verticillium wilt) stresses and classify them according to their molecular functions to better understand the genetic network. Moreover, this review proposes that studies of stress related genes will advance the security of cotton yield and production under a changing climate and that these genes should be incorporated in the development of cotton tolerant to salt, drought, and fungal wilt diseases (Verticillium and Fusarium).

Molecular characterization, expression and interaction of MAPK, MAPKK and MAPKKK genes in upland cotton

Mitogen-activated protein kinase (MAPK) signaling cascades, consisting of three types of sequentially phosphorylated kinases (MAPKKK, MAPKK, and MAPK), play vital roles in various processes including plant development and stress response. In this study, 52 GhMAPKs, 23 GhMAPKKs, and 166 GhMAPKKKs were identified in upland cotton. Chromosomal locations, gene duplication and structure, motifs, cis-regulatory elements, and protein subcellular localization were further analyzed. With the identified MAPK cascade genes in G. arboretum and G. raimondii, a syntenic diagram of three cotton species was constructed. The interactions of seven GhMAPK cascade genes were investigated. Two complete signaling modules were defined: The GhMEKK24/GhMEKK31-GhMAPKK9-GhMAPK10 and GhMEKK3/GhMEKK24/GhMEKK31-GhMAPKK16-GhMAPK10/GhMAPK11 cascades. Moreover, interaction networks and the interaction pairs were combined with their expression patterns and demonstrated that the network mediated by the MAPK signaling cascade participates in abiotic stress signaling. Our research provides a foundation for studying the molecular mechanism of the MAPK signaling pathway under abiotic stress.

ROS Homeostasis in Abiotic Stress Tolerance in Plants

Climate change-induced abiotic stress results in crop yield and production losses. These stresses result in changes at the physiological and molecular level that affect the development and growth of the plant. Reactive oxygen species (ROS) is formed at high levels due to abiotic stress within different organelles, leading to cellular damage. Plants have evolved mechanisms to control the production and scavenging of ROS through enzymatic and non-enzymatic antioxidative processes. However, ROS has a dual function in abiotic stresses where, at high levels, they are toxic to cells while the same molecule can function as a signal transducer that activates a local and systemic plant defense response against stress. The effects, perception, signaling, and activation of ROS and their antioxidative responses are elaborated in this review. This review aims to provide a purview of processes involved in ROS homeostasis in plants and to identify genes that are triggered in response to abiotic-induced oxidative stress. This review articulates the importance of these genes and pathways in understanding the mechanism of resistance in plants and the importance of this information in breeding and genetically developing crops for resistance against abiotic stress in plants.

Characterization of Genetic and Allelic Diversity Amongst Cultivated and Wild Lentil Accessions for Germplasm Enhancement

Intensive breeding of cultivated lentil has resulted in a relatively narrow genetic base, which limits the options to increase crop productivity through selection. Assessment of genetic diversity in the wild gene pool of lentil, as well as characterization of useful and novel alleles/genes that can be introgressed into elite germplasm, presents new opportunities and pathways for germplasm enhancement, followed by successful crop improvement. In the current study, a lentil collection consisting of 467 wild and cultivated accessions that originated from 10 diverse geographical regions was assessed, to understand genetic relationships among different lentil species/subspecies. A total of 422,101 high-confidence SNP markers were identified against the reference lentil genome (cv. CDC Redberry). Phylogenetic analysis clustered the germplasm collection into four groups, namely, Lens culinaris/Lens orientalis, Lens lamottei/Lens odemensis, Lens ervoides, and Lens nigricans. A weak correlation was observed between geographical origin and genetic relationship, except for some accessions of L. culinaris and L. ervoides. Genetic distance matrices revealed a comparable level of variation within the gene pools of L. culinaris (Nei’s coefficient 0.01468–0.71163), L. ervoides (Nei’s coefficient 0.01807–0.71877), and L. nigricans (Nei’s coefficient 0.02188–1.2219). In order to understand any genic differences at species/subspecies level, allele frequencies were calculated from a subset of 263 lentil accessions. Among all cultivated and wild lentil species, L. nigricans exhibited the greatest allelic differentiation across the genome compared to all other species/subspecies. Major differences were observed on six genomic regions with the largest being on Chromosome 1 (c. 1 Mbp). These results indicate that L. nigricans is the most distantly related to L. culinaris and additional structural variations are likely to be identified from genome sequencing studies. This would provide further insights into evolutionary relationships between cultivated and wild lentil germplasm, for germplasm improvement and introgression.

Genome-wide identification of MAPK cascade genes reveals the GhMAP3K14-GhMKK11-GhMPK31 pathway is involved in the drought response in cotton

The mitogen-activated protein kinase (MAPK) cascade pathway, which has three components, MAP3Ks, MKKs and MPKs, is involved in diverse biological processes in plants. In the current study, MAPK cascade genes were identified in three cotton species, based on gene homology with Arabidopsis. Selection pressure analysis of MAPK cascade genes revealed that purifying selection occurred among the cotton species. Expression pattern analysis showed that some MAPK cascade genes differentially expressed under abiotic stresses and phytohormones treatments, and especially under drought stress. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) experiments showed extensive interactions between different MAPK cascade proteins. Virus-induced gene silencing (VIGS) assays showed that some MAPK cascade modules play important roles in the drought stress response, and the GhMAP3K14-GhMKK11-GhMPK31 signal pathway was demonstrated to regulate drought stress tolerance in cotton. This study provides new information on the function of MAPK cascade genes in the drought response, and will help direct molecular breeding for improved drought stress tolerance in cotton.

Transcriptome analysis uncovers the gene expression profile of salt-stressed potato (Solanum tuberosum L.)

Potato (Solanum tuberosum L.) is an important staple food worldwide. However, its growth has been heavily suppressed by salt stress. The molecular mechanisms of salt tolerance in potato remain unclear. It has been shown that the tetraploid potato Longshu No. 5 is a salt-tolerant genotype. Therefore, in this study we conducted research to identify salt stress response genes in Longshu No. 5 using a NaCl treatment and time-course RNA sequencing. The total number of differentially expressed genes (DEGs) in response to salt stress was 5508. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, it was found that DEGs were significantly enriched in the categories of nucleic acid binding, transporter activity, ion or molecule transport, ion binding, kinase activity and oxidative phosphorylation. Particularly, the significant differential expression of encoding ion transport signaling genes suggests that this signaling pathway plays a vital role in salt stress response in potato. Finally, the DEGs in the salt response pathway were verified by Quantitative real-time PCR (qRT-PCR). These results provide valuable information on the salt tolerance of molecular mechanisms in potatoes, and establish a basis for breeding salt-tolerant cultivars.

Genetic components of root architecture and anatomy adjustments to water-deficit stress in spring barley

Roots perform vital roles for adaptation and productivity under water-deficit stress, even though their specific functions are poorly understood. In this study, the genetic control of the nodal-root architectural and anatomical response to water deficit were investigated among diverse spring barley accessions. Water deficit induced substantial variations in the nodal root traits. The cortical, stele, and total root cross-sectional areas of the main-shoot nodal roots decreased under water deficit, but increased in the tiller nodal roots. Root xylem density and arrested nodal roots increased under water deficit, with the formation of root suberization/lignification and large cortical aerenchyma. Genome-wide association study implicated 11 QTL intervals in the architectural and anatomical nodal root response to water deficit. Among them, three and four QTL intervals had strong effects across seasons and on both root architectural and anatomical traits, respectively. Genome-wide epistasis analysis revealed 44 epistatically interacting SNP loci. Further analyses showed that these QTL intervals contain important candidate genes, including ZIFL2, MATE, and PPIB, whose functions are shown to be related to the root adaptive response to water deprivation in plants. These results give novel insight into the genetic architectures of barley nodal root response to soil water deficit stress in the fields, and thus offer useful resources for root-targeted marker-assisted selection.

Insights into Drought Stress Signaling in Plants and the Molecular Genetic Basis of Cotton Drought Tolerance

Drought stress restricts plant growth and development by altering metabolic activity and biological functions. However, plants have evolved several cellular and molecular mechanisms to overcome drought stress. Drought tolerance is a multiplex trait involving the activation of signaling mechanisms and differentially expressed molecular responses. Broadly, drought tolerance comprises two steps: stress sensing/signaling and activation of various parallel stress responses (including physiological, molecular, and biochemical mechanisms) in plants. At the cellular level, drought induces oxidative stress by overproduction of reactive oxygen species (ROS), ultimately causing the cell membrane to rupture and stimulating various stress signaling pathways (ROS, mitogen-activated-protein-kinase, Ca2+, and hormone-mediated signaling). Drought-induced transcription factors activation and abscisic acid concentration co-ordinate the stress signaling and responses in cotton. The key responses against drought stress, are root development, stomatal closure, photosynthesis, hormone production, and ROS scavenging. The genetic basis, quantitative trait loci and genes of cotton drought tolerance are presented as examples of genetic resources in plants. Sustainable genetic improvements could be achieved through functional genomic approaches and genome modification techniques such as the CRISPR/Cas9 system aid the characterization of genes, sorted out from stress-related candidate single nucleotide polymorphisms, quantitative trait loci, and genes. Exploration of the genetic basis for superior candidate genes linked to stress physiology can be facilitated by integrated functional genomic approaches. We propose a third-generation sequencing approach coupled with genome-wide studies and functional genomic tools, including a comparative sequenced data (transcriptomics, proteomics, and epigenomic) analysis, which offer a platform to identify and characterize novel genes. This will provide information for better understanding the complex stress cellular biology of plants.

The cotton endocycle-involved protein SPO11-3 functions in salt stress via integrating leaf stomatal response, ROS scavenging and root growth

The SPORULATION 11 (SPO11) proteins are among eukaryotic the topoisomerase VIA (Topo VIA) homologs involved in modulating various important biological processes, such as growth, development and stress response via endoreduplication in plants, but the underlying mechanism response to stress remains largely unknown under salt treatment. Here, we attempted to characterize a homolog of TOP VIA in upland cotton (Gossypium hirsutum L.), designated as GhSPO11-3. The silencing of GhSPO11-3 in cotton plants resulted in a dwarf phenotype with a failure of cell endoreduplication and a phase shift in the ploidy levels. The GhSPO11-3-silenced plants also showed substantial changes including accumulated malondialdehyde, significantly reduced chlorophyll and proline contents and decreased antioxidative enzyme activity after salt treatment. In addition, transgenic Arabidopsis lines overexpressing GhSPO11-3 accelerated both leaf and root growth with cell expansion and endopolyploidy. Both leaf stomatal density and aperture were markedly decreased, and the transgenic Arabidopsis lines were more tolerant with expression of stress-responsive genes under salinity stress. Furthermore, consistent with the reduced reactive oxygen species (ROS), the expression of ROS scavenging-related genes was largely reinforced, and antioxidant enzyme activities were accordingly significantly enhanced in transgenic Arabidopsis lines under salt stress. In general, these results indicated that GhSPO11-3 likely respond to salt stress by positively regulating root growth, stomatal response, ROS production and the expression of stress-related genes to cope with adverse conditions in plants.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

Pod-wall proteomics provide novel insights into soybean seed-filling process under chemical-induced terminal drought stress

BACKGROUND

Drought is very detrimental when it occurs during the reproductive phase of soybeans, leading to considerable yield loss due to the disproportionate allocation of photo-assimilates to competing sinks. As pod walls are known to play a crucial role in regulating carbon partitioning during seed filling under stress conditions, the present study aims to analyze the stage-specific carbon allocation pattern during potassium iodide (KI)-simulated terminal drought, and to provide an insight into the pod-wall proteome responses during drought onset.

RESULTS

A comparative proteomics approach was adopted to visualize the differential protein expression in soybean pod-wall at stage R5 (seed initiation). Sugar status was analyzed using high-performance liquid chromatography (HPLC) and biochemical methods. Potassium iodide-simulated terminal drought during reproductive stages 4, 5 and 6 (R4, R5, and R6) caused a significant decline in starch, total carbohydrate, and reducing sugar in the leaves; however, the pod-wall and seeds showed a reduction only in the total carbohydrate content, whereas starch and reducing sugar levels remained unchanged. A pod-wall proteome at stage R5 showed immediate induction of proteins belonging to stress signaling / regulation, protein folding / stabilization, redox-homeostasis, cellular energy, and carbon utilization and down-regulation of negative regulators of drought stress and protein degradation-related proteins.

CONCLUSIONS

A KI spray effectively simulated terminal drought stress and caused around 50% yield loss when compared to controls. Our results indicate that, at the very onset of desiccation stress, the pod wall (stage R5) activates strong protective responses to maintain the carbon allocation to the surviving seeds. © 2018 Society of Chemical Industry.

Milestones achieved in response to drought stress through reverse genetic approaches

Drought stress is the most important abiotic stress that constrains crop production and reduces yield drastically. The germplasm of most of the cultivated crops possesses numerous unknown drought stress tolerant genes. Moreover, there are many reports suggesting that the wild species of most of the modern cultivars have abiotic stress tolerant genes. Due to climate change and population booms, food security has become a global issue. To develop drought tolerant crop varieties knowledge of various genes involved in drought stress is required. Different reverse genetic approaches such as virus-induced gene silencing (VIGS), clustered regularly interspace short palindromic repeat (CRISPR), targeting induced local lesions in genomes (TILLING) and expressed sequence tags (ESTs) have been used extensively to study the functionality of different genes involved in response to drought stress. In this review, we described the contributions of different techniques of functional genomics in the study of drought tolerant genes.

The cotton MAPK kinase GhMPK20 negatively regulates resistance to Fusarium oxysporum by mediating the MKK4-MPK20-WRKY40 cascade

Fusarium wilt is one of the most serious diseases affecting cotton. However, the pathogenesis and mechanism by which Fusarium oxysporum overcomes plant defence responses are unclear. Here, a new group D mitogen-activated protein kinase (MAPK) gene, GhMPK20, was identified and functionally analysed in cotton. GhMPK20 expression was significantly induced by F. oxysporum. Virus-induced gene silencing (VIGS) of GhMPK20 in cotton increased the tolerance to F. oxysporum, whereas ectopic GhMPK20 overexpression in Nicotiana benthamiana reduced F. oxysporum resistance via disruption of the salicylic acid (SA)-mediated defence pathway. More importantly, an F. oxysporum-induced MAPK cascade pathway composed of GhMKK4, GhMPK20 and GhWRKY40 was identified. VIGS of GhMKK4 and GhWRKY40 also enhanced F. oxysporum resistance in cotton, and the function of GhMKK4-GhMPK20 was shown to be essential for F. oxysporum-induced GhWRKY40 expression. Together, our results indicate that the GhMKK4-GhMPK20-GhWRKY40 cascade in cotton plays an important role in the pathogenesis of F. oxysporum. This research broadens our knowledge of the negative role of the MAPK cascade in disease resistance in cotton and provides an important scientific basis for the formulation of Fusarium wilt prevention strategies.

Control of plant growth and development by overexpressing MAP3K17, an ABA-inducible MAP3K, in Arabidopsis

Abscisic acid (ABA) plays an important role in plant growth, development, and stress responses. ABA regulates many aspects of plant growth and development, including seed maturation, dormancy, germination, the transition from vegetative to reproductive growth, leaf senescence and responses to environmental stresses, such as drought, high salinity and cold. It is also known that mitogen-activated protein kinase (MAPK) cascades function in ABA signaling. Recently, we and another group have identified the ABA-inducible MAP3Ks MAP3K17 and MAP3K18 as the upstream MAP3Ks of MKK3, implicating the MAP3K17/18-MKK3-MPK1/2/7/14 cascade in ABA signaling. It has also been reported that overexpression of MAP3K18 in Arabidopsis causes an early leaf senescence phenotype, ABA hypersensitive stomata closing, and drought tolerance. In this study, we generated transgenic plants overexpressing MAP3K17 (35S:MAP3K17) and its kinase-inactive form (35S:MAP3K17KN). The bolting of 35S:MAP3K17 was earlier than WT, and the fresh weights of the seedlings were smaller, whereas 35S:MAP3K17KN showed the opposite phenotype. These results indicate that the transition from vegetative to reproductive growth can be regulated by overexpression of MAP3K17 and its kinase-inactive form. Moreover, 35S:MAP3K17 showed lower sensitivity to ABA during post-germinated growth, whereas 35S:MAP3K17 KN showed the opposite phenotype, suggesting the negative roles of MAP3K17 in the response to ABA. Our work provides the possibility to regulate plant growth and development by the genetic manipulation of ABA-induced MAPK cascades, leading to improved crop growth and productivity.

Identification on mitogen-activated protein kinase signaling cascades by integrating protein interaction with transcriptional profiling analysis in cotton

Plant mitogen-activated protein kinase (MAPK) cascades play important roles in development and stress responses. In previous studies, we have systematically investigated the mitogen-activated protein kinase kinase (MKK) and MAPK gene families in cotton. However, the complete interactions between MAPK gene family members in MAPK signaling cascade is poorly characterized. Herein, we investigated the mitogen-activated protein kinase kinase kinase (MAPKKK) family members and identified a total of 89 MAPKKK genes in the Gossypium raimondii genome. We cloned 51 MAPKKKs in G. hirsutum and investigated the interactions between MKK and MAPKKK proteins through yeast-two hybrid assays. A total of 18 interactive protein pairs involved in 14 MAPKKKs and six MKKs were found. Among these, 13 interactive pairs had not been reported previously. Gene expression patterns revealed that 12 MAPKKKs were involved in diverse signaling pathways triggered by hormone treatments or abiotic stresses. By combining the MKK-MAPK and MKK-MAPKKK protein interactions with gene expression patterns, 38 potential MAPK signaling modules involved in the complicated cross-talks were identified, which provide a basis on elucidating biological function of the MAPK cascade in response to hormonal and/or stress responses. The systematic investigation in MAPK signaling cascades will lay a foundation for understanding the functional roles of different MAPK cascades in signal transduction pathways, and for the improvement of various defense responses in cotton.

Genome-wide classification, evolutionary analysis and gene expression patterns of the kinome in Gossypium

The protein kinase (PK, kinome) family is one of the largest families in plants and regulates almost all aspects of plant processes, including plant development and stress responses. Despite their important functions, comprehensive functional classification, evolutionary analysis and expression patterns of the cotton PK gene family has yet to be performed on PK genes. In this study, we identified the cotton kinomes in the Gossypium raimondii, Gossypium arboretum, Gossypium hirsutum and Gossypium barbadense genomes and classified them into 7 groups and 122-24 subfamilies using software HMMER v3.0 scanning and neighbor-joining (NJ) phylogenetic analysis. Some conserved exon-intron structures were identified not only in cotton species but also in primitive plants, ferns and moss, suggesting the significant function and ancient origination of these PK genes. Collinearity analysis revealed that 16.6 million years ago (Mya) cotton-specific whole genome duplication (WGD) events may have played a partial role in the expansion of the cotton kinomes, whereas tandem duplication (TD) events mainly contributed to the expansion of the cotton RLK group. Synteny analysis revealed that tetraploidization of G. hirsutum and G. barbadense contributed to the expansion of G. hirsutum and G. barbadense PKs. Global expression analysis of cotton PKs revealed stress-specific and fiber development-related expression patterns, suggesting that many cotton PKs might be involved in the regulation of the stress response and fiber development processes. This study provides foundational information for further studies on the evolution and molecular function of cotton PKs.

Compound Synthesis or Growth and Development of Roots/Stomata Regulate Plant Drought Tolerance or Water Use Efficiency/Water Uptake Efficiency

Water is crucial to plant growth and development because it serves as a medium for all cellular functions. Thus, the improvement of plant drought tolerance or water use efficiency/water uptake efficiency is important in modern agriculture. In this review, we mainly focus on new genetic factors for ameliorating drought tolerance or water use efficiency/water uptake efficiency of plants and explore the involvement of these genetic factors in the regulation of improving plant drought tolerance or water use efficiency/water uptake efficiency, which is a result of altered stomata density and improving root systems (primary root length, hair root growth, and lateral root number) and enhanced production of osmotic protectants, which is caused by transcription factors, proteinases, and phosphatases and protein kinases. These results will help guide the synthesis of a model for predicting how the signals of genetic and environmental stress are integrated at a few genetic determinants to control the establishment of either water use efficiency or water uptake efficiency. Collectively, these insights into the molecular mechanism underpinning the control of plant drought tolerance or water use efficiency/water uptake efficiency may aid future breeding or design strategies to increase crop yield.

Mitogen-Activated Protein Kinase Cascades in Plant Hormone Signaling

Mitogen-activated protein kinase (MAPK) modules play key roles in the transduction of environmental and developmental signals through phosphorylation of downstream signaling targets, including other kinases, enzymes, cytoskeletal proteins or transcription factors, in all eukaryotic cells. A typical MAPK cascade consists of at least three sequentially acting serine/threonine kinases, a MAP kinase kinase kinase (MAPKKK), a MAP kinase kinase (MAPKK) and finally, the MAP kinase (MAPK) itself, with each phosphorylating, and hence activating, the next kinase in the cascade. Recent advances in our understanding of hormone signaling pathways have led to the discovery of new regulatory systems. In particular, this research has revealed the emerging role of crosstalk between the protein components of various signaling pathways and the involvement of this crosstalk in multiple cellular processes. Here we provide an overview of current models and mechanisms of hormone signaling with a special emphasis on the role of MAPKs in cell signaling networks. One-sentence summary: In this review we highlight the mechanisms of crosstalk between MAPK cascades and plant hormone signaling pathways and summarize recent findings on MAPK regulation and function in various cellular processes.

Regulation of cotton (Gossypium hirsutum) drought responses by mitogen-activated protein (MAP) kinase cascade-mediated phosphorylation of GhWRKY59

Drought is a key limiting factor for cotton (Gossypium spp.) production, as more than half of the global cotton supply is grown in regions with high water shortage. However, the underlying mechanism of the response of cotton to drought stress remains elusive. By combining genome-wide transcriptome profiling and a loss-of-function screen using virus-induced gene silencing, we identified Gossypium hirsutum GhWRKY59 as an important transcription factor that regulates the drought stress response in cotton. Biochemical and genetic analyses revealed a drought stress-activated mitogen-activated protein (MAP) kinase cascade consisting of GhMAP3K15-Mitogen-activated Protein Kinase Kinase 4 (GhMKK4)-Mitogen-activated Protein Kinase 6 (GhMPK6) that directly phosphorylates GhWRKY59 at residue serine 221. Interestingly, GhWRKY59 is required for dehydration-induced expression of GhMAPK3K15, constituting a positive feedback loop of GhWRKY59-regulated MAP kinase activation in response to drought stress. Moreover, GhWRKY59 directly binds to the W-boxes of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 2 (GhDREB2), which encodes a dehydration-inducible transcription factor regulating the plant hormone abscisic acid (ABA)-independent drought response. Our study identified a complete MAP kinase cascade that phosphorylates and activates a key WRKY transcription factor, and elucidated a regulatory module, consisting of GhMAP3K15-GhMKK4-GhMPK6-GhWRKY59-GhDREB2, that is involved in controlling the cotton drought response.

Drought coping strategies in cotton: increased crop per drop

The growth and yield of many crops, including cotton, are affected by water deficit. Cotton has evolved drought specific as well as general morpho-physiological, biochemical and molecular responses to drought stress, which are discussed in this review. The key physiological responses against drought stress in cotton, including stomata closing, root development, cellular adaptations, photosynthesis, abscisic acid (ABA) and jasmonic acid (JA) production and reactive oxygen species (ROS) scavenging, have been identified by researchers. Drought stress induces the expression of stress-related transcription factors and genes, such as ROS scavenging, ABA or mitogen-activated protein kinases (MAPK) signalling genes, which activate various drought-related pathways to induce tolerance in the plant. It is crucial to elucidate and induce drought-tolerant traits via quantitative trait loci (QTL) analysis, transgenic approaches and exogenous application of substances. The current review article highlights the natural as well as engineered drought tolerance strategies in cotton.

Activation of ABA Receptors Gene GhPYL9-11A Is Positively Correlated with Cotton Drought Tolerance in Transgenic Arabidopsis

The sensitivity to abscisic acid (ABA) by its receptors, pyrabactin resistance-like proteins (PYLs), is considered a most important factor in activating the ABA signal pathway in response to abiotic stress. However, it is still unknown which PYL is the crucial ABA receptor mediating response to drought stress in cotton (Gossypium hirsutum L.). Here, we reported the identification and characterization of highly induced ABA receptor GhPYL9-11A in response to drought in cotton. It is observed that GhPYL9-11A was highly induced by ABA treatment. GhPYL9-11A binds to protein phosphatase 2Cs (PP2Cs) in an ABA-independent manner. Moreover, the GhPYL-11A-PP2C interactions are partially disrupted by mutations, proline (P84) and histidine (H111), in the gate-latch region. Transgenic Arabidopsis overexpressing GhPYL9-11A plants were hypersensitive to ABA during seed germination and early seedling stage. Further, the increased in root growth and up regulation of drought stress-related genes in transgenic Arabidopsis as compared to wild type confirmed the potential role of GhPYL9-11A in abiotic stress tolerance. Consistently, the expression level of GhPYL9-11A is on average higher in drought-tolerant cotton cultivars than in drought-sensitive cottons under drought treatment. In conclusion, the manipulation of GhPYL9-11A expression could be a useful strategy for developing drought-tolerant cotton cultivars.

Convergence of Multiple MAP3Ks on MKK3 Identifies a Set of Novel Stress MAPK Modules

Since its first description in 1995 and functional characterization 12 years later, plant MKK3-type MAP2Ks have emerged as important integrators in plant signaling. Although they have received less attention than the canonical stress-activated mitogen-activated protein kinases (MAPKs), several recent publications shed light on their important roles in plant adaptation to environmental conditions. Nevertheless, the MKK3-related literature is complicated. This review summarizes the current knowledge and discrepancies on MKK3 MAPK modules in plants and highlights the singular role of MKK3 in green plants. In the light of the latest data, we hypothesize a general model that all clade-III MAP3Ks converge on MKK3 and C-group MAPKs, thereby defining a set of novel MAPK modules which are activated by stresses and internal signals through the transcriptional regulation of MAP3K genes.