Limited intraspecific variation in drought resistance along a pronounced tropical rainfall gradient.

Assessing within-species variation in response to drought is crucial for predicting species' responses to climate change and informing restoration and conservation efforts, yet experimental data are lacking for the vast majority of tropical tree species. We assessed intraspecific variation in response to water availability across a strong rainfall gradient for 16 tropical tree species using reciprocal transplant and common garden field experiments, along with measurements of gene flow and key functional traits linked to drought resistance. Although drought resistance varies widely among species in these forests, we found little evidence for within-species variation in drought resistance. For the majority of functional traits measured, we detected no significant intraspecific variation. The few traits that did vary significantly between drier and wetter origins of the same species all showed relationships opposite to expectations based on drought stress. Furthermore, seedlings of the same species originating from drier and wetter sites performed equally well under drought conditions in the common garden experiment and at the driest transplant site. However, contrary to expectation, wetter-origin seedlings survived better than drier-origin seedlings under wetter conditions in both the reciprocal transplant and common garden experiment, potentially due to lower insect herbivory. Our study provides the most comprehensive picture to date of intraspecific variation in tropical tree species' responses to water availability. Our findings suggest that while drought plays an important role in shaping species composition across moist tropical forests, its influence on within-species variation is limited.

Comprehensive assessment of drought resistance and recovery in kiwifruit genotypes using multivariate analysis.

As global climate change persists, ongoing warming exposes plants, including kiwifruit, to repeated cycles of drought stress and rewatering, necessitating the identification of drought-resistant genotypes for breeding purposes. To better understand the physiological mechanisms underlying drought resistance and recovery in kiwifruit, moderate (40-45% field capacity) and severe (25-30% field capacity) drought stresses were applied, followed by rewatering (80-85% field capacity) to eight kiwifruit rootstocks in this study. We then conducted a multivariate analysis of 20 indices for the assessment of drought resistance and recovery capabilities. Additionally, we identified four principal components, each playing a vital role in coping with diverse water conditions. Three optimal indicator groups were pinpointed, enhancing precision in kiwifruit drought resistance and recovery assessment and simplifying the evaluation system. Finally, MX-1 and HW were identified as representative rootstocks for future research on kiwifruit's responses to moderate and severe drought stresses. This study not only enhances our understanding of the response mechanisms of kiwifruit rootstocks to progressive drought stress and recovery but also provides theoretical guidance for reliable screening of drought-adaptive kiwifruit genotypes.

Isohydricity and hydraulic isolation explain reduced hydraulic failure risk in an experimental tree species mixture.

Species mixture is promoted as a crucial management option to adapt forests to climate change. However, there is little consensus on how tree diversity affects tree water stress, and the underlying mechanisms remain elusive. By using a greenhouse experiment and a soil-plant-atmosphere hydraulic model, we explored whether and why mixing the isohydric Aleppo pine (Pinus halepensis, drought avoidant) and the anisohydric holm oak (Quercus ilex, drought tolerant) affects tree water stress during extreme drought. Our experiment showed that the intimate mixture strongly alleviated Q. ilex water stress while it marginally impacted P. halepensis water stress. Three mechanistic explanations for this pattern are supported by our modelling analysis. First, the difference in stomatal regulation between species allowed Q. ilex trees to benefit from additional soil water in mixture, thereby maintaining higher water potentials and sustaining gas exchange. By contrast, P. halepensis exhibited earlier water stress and stomatal regulation. Second, P. halepensis trees showed stable water potential during drought, although soil water potential strongly decreased, even when grown in a mixture. Model simulations suggested that hydraulic isolation of the root from the soil associated with decreased leaf cuticular conductance was a plausible explanation for this pattern. Third, the higher predawn water potentials for a given soil water potential observed for Q. ilex in mixture can - according to model simulations - be explained by increased soil-to-root conductance, resulting from higher fine root length. This study brings insights into the mechanisms involved in improved drought resistance of mixed species forests.

Heat-shock protein 40 is the key farnesylation target in meristem size control, abscisic acid signaling, and drought resistance.

Protein farnesylation is central to molecular cell biology. In plants, protein farnesyl transferase mutants are pleiotropic and exhibit defective meristem organization, hypersensitivity to the hormone abscisic acid, and increased drought resistance. The precise functions of protein farnesylation in plants remain incompletely understood because few relevant farnesylated targets have been identified. Here, we show that defective farnesylation of a single factor-heat-shock protein 40 (HSP40), encoded by the J2 and J3 genes-is sufficient to confer ABA hypersensitivity, drought resistance, late flowering, and enlarged meristems, indicating that altered function of chaperone client proteins underlies most farnesyl transferase mutant phenotypes. We also show that expression of an abiotic stress-related microRNA (miRNA) regulon controlled by the transcription factor SPL7 requires HSP40 farnesylation. Expression of a truncated SPL7 form mimicking its activated proteolysis fragment of the membrane-bound SPL7 precursor partially restores accumulation of SPL7-dependent miRNAs in farnesyl transferase mutants. These results implicate the pathway directing SPL7 activation from its membrane-bound precursor as an important target of farnesylated HSP40, consistent with our demonstration that HSP40 farnesylation facilitates its membrane association. The results also suggest that altered gene regulation via select miRNAs contributes to abiotic stress-related phenotypes of farnesyl transferase mutants.

A chromosome level genome assembly of Pseudoroegneria Libanotica reveals a key Kcs gene involves in the cuticular wax elongation for drought resistance.

BACKGROUND: The genus Pseudoroegneria (Nevski) Löve (Triticeae, Poaceae), whose genome symbol was designed as "St", accounts for more than 60% of perennial Triticeae species. The diploid species Psudoroegneria libanotica (2n = 14) contains the most ancient St genome, exhibited strong drought resistance, and was morphologically covered by cuticular wax on the aerial part. Therefore, the St-genome sequencing data could provide fundamental information for studies of genome evolution and reveal its mechanisms of cuticular wax and drought resistance. RESULTS: In this study, we reported the chromosome-level genome assembly for the St genome of Pse. libanotica, with a total size of 2.99 Gb. 46,369 protein-coding genes annotated and 71.62% was repeat sequences. Comparative analyses revealed that the genus Pseudoroegneria diverged during the middle and late Miocene. During this period, unique genes, gene family expansion, and contraction in Pse. libanotica were enriched in biotic and abiotic stresses, such as fatty acid biosynthesis which may greatly contribute to its drought adaption. Furthermore, we investigated genes associated with the cuticular wax formation and water deficit and found a new Kcs gene evm.TU.CTG175.54. It plays a critical role in the very long chain fatty acid (VLCFA) elongation from C18 to C26 in Pse. libanotica. The function needs more evidence to be verified. CONCLUSIONS: We sequenced and assembled the St genome in Triticeae and discovered a new KCS gene that plays a role in wax extension to cope with drought. Our study lays a foundation for the genome diversification of Triticeae species and deciphers cuticular wax formation genes involved in drought resistance.

Rapidly mining candidate cotton drought resistance genes based on key indicators of drought resistance.

BACKGROUND: Focusing on key indicators of drought resistance is highly important for quickly mining candidate genes related to drought resistance in cotton. RESULTS: In the present study, drought resistance was identified in drought resistance-related RIL populations during the flowering and boll stages, and multiple traits were evaluated; these traits included three key indicators: plant height (PH), single boll weight (SBW) and transpiration rate (Tr). Based on these three key indicators, three groups of extreme mixing pools were constructed for BSA-seq. Based on the mapping interval of each trait, a total of 6.27 Mb QTL intervals were selected on chromosomes A13 (3.2 Mb), A10 (2.45 Mb) and A07 (0.62 Mb) as the focus of this study. Based on the annotation information and qRT‒PCR analysis, three key genes that may be involved in the drought stress response of cotton were screened: GhF6'H1, Gh3AT1 and GhPER55. qRT‒PCR analysis of parental and extreme germplasm materials revealed that the expression of these genes changed significantly under drought stress. Cotton VIGS experiments verified the important impact of key genes on cotton drought resistance. CONCLUSIONS: This study focused on the key indicators of drought resistance, laying the foundation for the rapid mining of drought-resistant candidate genes in cotton and providing genetic resources for directed molecular breeding of drought resistance in cotton.

Upland rice genomic signatures of adaptation to drought resistance and navigation to molecular design breeding.

Upland rice is a distinctive drought-aerobic ecotype of cultivated rice highly resistant to drought stress. However, the genetic and genomic basis for the drought-aerobic adaptation of upland rice remains largely unclear due to the lack of genomic resources. In this study, we identified 25 typical upland rice accessions and assembled a high-quality genome of one of the typical upland rice varieties, IRAT109, comprising 384 Mb with a contig N50 of 19.6 Mb. Phylogenetic analysis revealed upland and lowland rice have distinct ecotype differentiation within the japonica subgroup. Comparative genomic analyses revealed that adaptive differentiation of lowland and upland rice is likely attributable to the natural variation of many genes in promoter regions, formation of specific genes in upland rice, and expansion of gene families. We revealed differentiated gene expression patterns in the leaves and roots of the two ecotypes and found that lignin synthesis mediated by the phenylpropane pathway plays an important role in the adaptive differentiation of upland and lowland rice. We identified 28 selective sweeps that occurred during domestication and validated that the qRT9 gene in selective regions can positively regulate drought resistance in rice. Eighty key genes closely associated with drought resistance were appraised for their appreciable potential in drought resistance breeding. Our study enhances the understanding of the adaptation of upland rice and provides a genome navigation map of drought resistance breeding, which will facilitate the breeding of drought-resistant rice and the "blue revolution" in agriculture.

E3 ubiquitin ligase TaSDIR1-4A activates membrane-bound transcription factor TaWRKY29 to positively regulate drought resistance.

Drought is a deleterious abiotic stress factor that constrains crop growth and development. Post-translational modification of proteins mediated by the ubiquitin-proteasome system is an effective strategy for directing plant responses to stress, but the regulatory mechanisms in wheat remain unclear. In this study, we showed that TaSDIR1-4A is a positive modulator of the drought response. Overexpression of TaSDIR1-4A increased the hypersensitivity of stomata, root length and endogenous abscisic acid (ABA) content under drought conditions. TaSDIR1-4A encodes a C3H2C3-type RING finger protein with E3 ligase activity. Amino acid mutation in its conserved domain led to loss of activity and altered the subcellular localization. The membrane-bound transcription factor TaWRKY29 was identified by yeast two-hybrid screening, and it was confirmed as interacting with TaSDIR1-4A both in vivo and in vitro. TaSDIR1-4A mediated the polyubiquitination and proteolysis of the C-terminal amino acid of TaWRKY29, and its translocation from the plasma membrane to the nucleus. Activated TaWRKY29 bound to the TaABI5 promoter to stimulate its expression, thereby positively regulating the ABA signalling pathway and drought response. Our findings demonstrate the positive role of TaSDIR1-4A in drought tolerance and provide new insights into the involvement of UPS in the wheat stress response.

Integrating high-throughput phenotyping and genome-wide association studies for enhanced drought resistance and yield prediction in wheat.

Drought, especially terminal drought, severely limits wheat growth and yield. Understanding the complex mechanisms behind the drought response in wheat is essential for developing drought-resistant varieties. This study aimed to dissect the genetic architecture and high-yielding wheat ideotypes under terminal drought. An automated high-throughput phenotyping platform was used to examine 28 392 image-based digital traits (i-traits) under different drought conditions during the flowering stage of a natural wheat population. Of the i-traits examined, 17 073 were identified as drought-related. A genome-wide association study (GWAS) identified 5320 drought-related significant single-nucleotide polymorphisms (SNPs) and 27 SNP clusters. A notable hotspot region controlling wheat drought tolerance was discovered, in which TaPP2C6 was shown to be an important negative regulator of the drought response. The tapp2c6 knockout lines exhibited enhanced drought resistance without a yield penalty. A haplotype analysis revealed a favored allele of TaPP2C6 that was significantly correlated with drought resistance, affirming its potential value in wheat breeding programs. We developed an advanced prediction model for wheat yield and drought resistance using 24 i-traits analyzed by machine learning. In summary, this study provides comprehensive insights into the high-yielding ideotype and an approach for the rapid breeding of drought-resistant wheat.

Leaf isotopes reveal tree diversity effects on the functional responses to the pan-European 2018 summer drought.

Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N, as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan-European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness.

Patterns, timing, and environmental drivers of growth in two coexisting green-stemmed Mediterranean alpine shrubs species.

The Mediterranean alpine is one of the most vulnerable ecosystems under future environmental change. Yet, patterns, timing and environmental controls of plant growth are poorly investigated. We aimed at an improved understanding of growth processes, as well as stem swelling and shrinking patterns, by examining two common coexisting green-stemmed shrub species. Using dendrometers to measure daily stem diameter changes, we separated these changes into water-related shrinking and swelling and irreversible growth. Implementing correlation analysis, linear mixed effects models, and partial least squares regression on time series of stem diameter changes, with corresponding soil temperature and moisture data as environmental predictors, we found species-specific growth patterns related to different drought-adaptive strategies. We show that the winter-cold-adapted species Cytisus galianoi uses a drought tolerance strategy combined with a high ecological plasticity, and is, thus, able to gain competitive advantages under future climate warming. In contrast, Genista versicolor is restricted to a narrower ecological niche using a winter-cold escape and drought avoidance strategy, which might be of disadvantage in a changing climate. Pregrowth environmental conditions were more relevant than conditions during growth, controlling the species' resource availability. Thus, studies focusing on current driver constellations of growth may fail to predict a species' ecological niche and its potential future performance.

Exploring interspecific hybridization dynamics in artificial forests of Pinus brutia and P. halepensis: Implications for sustainable afforestation.

Interspecific hybridization increases genetic diversity, which is essential for coping with changing environments. Hybrid zones, occurring naturally in overlapping habitats of closely related species, can be artificially established during afforestation. The resulting interspecific hybridization may promote sustainability in artificial forests, particularly in regions facing degradation due to climate change. Currently, there is limited evidence of hybridization during regeneration of artificial forests. Here, we studied the frequency of Pinus brutia Ten. × P. halepensis Mill. hybridization in five planted forests in Israel in three stages of forest regeneration: seeds before dispersal, emerged seedlings and recruited seedlings at the end of the dry season. We found hybrids on P. brutia, but not on P. halepensis trees due to asynchronous cone production phenology. Using 94 single-nucleotide polymorphism (SNP) markers, we found hybrids at all stages, most of which were hybrids of advanced generations. The hybrid proportions increased from 4.7 ± 2.1 to 8.2 ± 1.4 and 21.6 ± 6.4 per cent, from seeds to emerged seedlings and to recruited seedlings stages, respectively. The increased hybrid ratio implies an advantage of hybrids over P. brutia during forest regeneration. To test this hypothesis, we measured seedling growth rate and morphological traits under controlled conditions and found that the hybrid seedlings exhibited selected traits of the two parental species, which likely contributed to the fitness and survival of the hybrids during the dry season. This study highlights the potential contribution of hybrids to sustainable-planted forests and contributes to the understanding of genetic changes that occur during the regeneration of artificial forests.

Gradients in embolism resistance within stems driven by secondary growth in herbs.

The stems of some herbaceous species can undergo basal secondary growth, leading to a continuum in the degree of woodiness along the stem. Whether the formation of secondary growth in the stem base results in differences in embolism resistance between the base and the upper portions of stems is unknown. We assessed the embolism resistance of leaves and the basal and upper portions of stems simultaneously within the same individuals of two divergent herbaceous species that undergo secondary growth in the mature stem bases. The species were Solanum lycopersicum (tomato) and Senecio minimus (fireweed). Basal stem in mature plants of both species displayed advanced secondary growth and greater resistance to embolism than the upper stem. This also resulted in significant vulnerability segmentation between the basal stem and the leaves in both species. Greater embolism resistance in the woodier stem base was found alongside decreases in the pith-to-xylem ratio, increases in the proportion of secondary xylem, and increases in lignin content. We show that there can be considerable variation in embolism resistance across the stem in herbs and that this variation is linked to the degree of secondary growth present. A gradient in embolism resistance across the stem in herbaceous plants could be an adaptation to ensure reproduction or basal resprouting during episodes of drought late in the lifecycle.

Rootstocks affect the vulnerability to embolism and pit membrane thickness in Citrus scions.

Embolism resistance of xylem tissue varies among species and is an important trait related to drought resistance, with anatomical attributes like pit membrane thickness playing an important role in avoiding embolism spread. Grafted Citrus trees are commonly grown in orchards, with the rootstock being able to affect the drought resistance of the whole plant. Here, we evaluated how rootstocks affect the vulnerability to embolism resistance of the scion using several rootstock/scion combinations. Scions of 'Tahiti' acid lime, 'Hamlin', 'Pera' and 'Valencia' oranges grafted on a 'Rangpur' lime rootstock exhibit similar vulnerability to embolism. In field-grown trees, measurements of leaf water potential did not suggest significant embolism formation during the dry season, while stomata of Citrus trees presented an isohydric response to declining water availability. When 'Valencia' orange scions were grafted on 'Rangpur' lime, 'IAC 1710' citrandarin, 'Sunki Tropical' mandarin or 'Swingle' citrumelo rootstocks, variation in intervessel pit membrane thickness of the scion was found. The 'Rangpur' lime rootstock, which is known for its drought resistance, induced thicker pit membranes in the scion, resulting in higher embolism resistance than the other rootstocks. Similarly, the rootstock 'IAC 1710' citrandarin generated increased embolism resistance of the scion, which is highly relevant for citriculture.

Three-dimensional image analysis specifies the root distribution for drought avoidance in the early growth stage of rice.

BACKGROUND AND AIMS: Root system architecture (RSA) plays a key role in plant adaptation to drought because deep rooting enables better water uptake than shallow rooting under terminal drought. Understanding RSA during early plant development is essential for improving crop yields, as early drought can affect subsequent shoot growth. Herein, we demonstrate that root distribution in the topsoil significantly impacts shoot growth during the early stages of rice (Oryza sativa) development under drought, as assessed through three-dimensional (3D) image analysis. METHODS: We used 109 F12 recombinant inbred lines (RILs) obtained from a cross between shallow-rooting lowland rice and deep-rooting upland rice, representing a population with diverse RSA. We applied a moderate drought during the early development of rice grown in a plant pot (25 cm height) by stopping irrigation 14 days after sowing (DAS). Time-series RSA at 14, 21, and 28 DAS was visualized by X-ray computed tomography, and subsequently compared between drought and well-watered conditions. Following this analysis, we further investigated drought-avoidant RSA by testing 20 randomly selected RILs under drought conditions. KEY RESULTS: We inferred the root location that most influences shoot growth using a hierarchical Bayes approach: the root segment depth, which positively impacted shoot growth, ranged between 1.7-3.4 cm under drought conditions and between 0.0-1.7 cm under well-watered conditions. Drought-avoidant RILs had a higher root density in the lower layers of the topsoil compared to the others. CONCLUSIONS: Fine classification of soil layers using 3D image analysis revealed that increasing root density in the lower layers of the topsoil, rather than in the subsoil, is advantageous for drought avoidance during the early growth stage of rice.

Effects of leaf silicon on drought performance of tropical tree seedlings.

Elevated leaf silicon (Si) concentrations improve drought resistance in cultivated plants, suggesting Si might also improve drought performance of wild species. Tropical tree species, for instance, take up substantial amounts of Si, and leaf Si varies markedly at local and regional scales, suggesting consequences for seedling drought resistance. Yet, whether elevated leaf Si improves seedling drought performance in tropical forests is unknown. To manipulate leaf Si concentrations, seedlings of seven tropical tree species were grown in Si-rich and -poor soil, before exposing them to drought in the forest understorey. Survival, growth and wilting were monitored. Elevated leaf Si did not improve drought survival and growth in any of the species. In one species, drought survival was reduced in seedlings previously grown in Si-rich soil, contrary to our expectation. Our results suggest that elevated leaf Si does not improve drought resistance of wild tropical tree species. Elevated leaf Si may even reduce drought performance, suggesting differences in soil conditions influencing leaf Si may contribute to soil-related variation of tropical seedling performance. Furthermore, our results are at odds with most studies on cultivated species and show that alleviative effects of Si in crops cannot be generalized to wild plants in natural systems.

The White Clover TrMYB33-TrSAMS1 Module Contributes to Drought Tolerance by Modulation of Spermidine Biosynthesis via an ABA-Dependent Pathway.

Spermidine is well known to accumulate in plants exposed to drought, but the regulatory network associated with its biosynthesis and accumulation and the underlying molecular mechanisms remain unclear. Here, we demonstrated that the Trifolium repens TrMYB33 relayed the ABA signal to modulate drought-induced spermidine production by directly regulating the expression of TrSAMS1, which encodes an S-adenosylmethionine synthase. This gene was identified by transcriptome and expression analysis in T. repens. TrSAMS1 overexpression and its pTRV-VIGS-mediated silencing demonstrated that TrSAMS1 is a positive regulator of spermidine synthesis and drought tolerance. TrMYB33 was identified as an interacting candidate through yeast one-hybrid library screening with the TrSAMS1 promoter region as the bait. TrMYB33 was confirmed to bind directly to the predicted TAACCACTAACCA (the TAACCA MYB binding site is repeated twice in tandem) within the TrSAMS1 promoter and to act as a transcriptional activator. Additionally, TrMYB33 contributed to drought tolerance by regulating TrSAMS1 expression and modulating spermidine synthesis. Additionally, we found that spermidine accumulation under drought stress depended on ABA and that TrMYB33 coordinated ABA-mediated upregulation of TrSAMS1 and spermidine accumulation. This study elucidated the role of a T. repens MYB33 homolog in modulating spermidine biosynthesis. The further exploitation and functional characterization of the TrMYB33-TrSAMS1 regulatory module can enhance our understanding of the molecular mechanisms responsible for spermidine accumulation during drought stress.

An alfalfa MYB-like transcriptional factor MsMYBH positively regulates alfalfa seedling drought resistance and undergoes MsWAV3-mediated degradation.

Drought is a major threat to alfalfa (Medicago sativa L.) production. The discovery of important alfalfa genes regulating drought response will facilitate breeding for drought-resistant alfalfa cultivars. Here, we report a genome-wide association study of drought resistance in alfalfa. We identified and functionally characterized an MYB-like transcription factor gene (MsMYBH), which increases the drought resistance in alfalfa. Compared with the wild-types, the biomass and forage quality were enhanced in MsMYBH overexpressed plants. Combined RNA-seq, proteomics and chromatin immunoprecipitation analysis showed that MsMYBH can directly bind to the promoters of MsMCP1, MsMCP2, MsPRX1A and MsCARCAB to improve their expression. The outcomes of such interactions include better water balance, high photosynthetic efficiency and scavenge excess H2O2 in response to drought. Furthermore, an E3 ubiquitin ligase (MsWAV3) was found to induce MsMYBH degradation under long-term drought, via the 26S proteasome pathway. Furthermore, variable-number tandem repeats in MsMYBH promoter were characterized among a collection of germplasms, and the variation is associated with promoter activity. Collectively, our findings shed light on the functions of MsMYBH and provide a pivotal gene that could be leveraged for breeding drought-resistant alfalfa. This discovery also offers new insights into the mechanisms of drought resistance in alfalfa.

SUPPRESSOR of MAX2 1 (SMAX1) and SMAX1-LIKE2 (SMXL2) Negatively Regulate Drought Resistance in Arabidopsis thaliana.

Recent investigations in Arabidopsis thaliana suggest that SUPPRESSOR of MORE AXILLARY GROWTH 2 1 (SMAX1) and SMAX1-LIKE2 (SMXL2) are negative regulators of karrikin (KAR) and strigolactone (SL) signaling during plant growth and development, but their functions in drought resistance and related mechanisms of action remain unclear. To understand the roles and mechanisms of SMAX1 and SMXL2 in drought resistance, we investigated the drought-resistance phenotypes and transcriptome profiles of smax1 smxl2 (s1,2) double-mutant plants in response to drought stress. The s1,2 mutant plants showed enhanced drought-resistance and lower leaf water loss when compared with wild-type (WT) plants. Transcriptome comparison of rosette leaves from the s1,2 mutant and the WT under normal and dehydration conditions suggested that the mechanism related to cuticle formation was involved in drought resistance. This possibility was supported by enhanced cuticle formation in the rosette leaves of the s1,2 mutant. We also found that the s1,2 mutant plants were more sensitive to abscisic acid in assays of stomatal closure, cotyledon opening, chlorophyll degradation and growth inhibition, and they showed a higher reactive oxygen species detoxification capacity than WT plants. In addition, the s1,2 mutant plants had longer root hairs and a higher root-to-shoot ratio than the WT plants, suggesting that the mutant had a greater capacity for water absorption than the WT. Taken together, our results indicate that SMAX1 and SMXL2 negatively regulate drought resistance, and disruption of these KAR- and SL-signaling-related genes may therefore provide a novel means for improving crop drought resistance.

Genome wide identification of GDSL gene family explores a novel GhirGDSL26 gene enhancing drought stress tolerance in cotton.

BACKGROUND: Current climate change scenarios are posing greater threats to the growth and development of plants. Thus, significant efforts are required that can mitigate the negative effects of drought on the cotton plant. GDSL esterase/lipases can offer an imperative role in plant development and stress tolerance. However, thesystematic and functional roles of the GDSL gene family, particularly in cotton under water deficit conditions have not yet been explored. RESULTS: In this study, 103, 103, 99, 198, 203, 239, 249, and 215 GDSL proteins were identified in eight cotton genomes i.e., Gossypium herbaceum (A1), Gossypium arboretum (A2), Gossypium raimondii (D5), Gossypium hirsutum (AD1), Gossypium barbadense (AD2), Gossypium tomentosum (AD3), Gossypium mustelinum (AD4), Gossypium darwinii (AD5), respectively. A total of 198 GDSL genes of Gossypium hirsutum were divided into eleven clades using phylogenetic analysis, and the number of GhirGDSL varied among different clades. The cis-elements analysis showed that GhirGDSL gene expression was mainly related to light, plant hormones, and variable tense environments. Combining the results of transcriptome and RT-qPCR, GhirGDSL26 (Gh_A01G1774), a highly up-regulated gene, was selected for further elucidating its tole in drought stress tolerance via estimating physiological and biochemical parameters. Heterologous expression of the GhirGDSL26 gene in Arabidopsis thaliana resulted in a higher germination and survival rates, longer root lengths, lower ion leakage and induced stress-responsive genes expression under drought stress. This further highlighted that overexpressed plants had a better drought tolerance as compared to the wildtype plants. Moreover, 3, 3'-diaminobenzidine (DAB) and Trypan staining results indicated reduced oxidative damage, less cell membrane damage, and lower ion leakage in overexpressed plants as compared to wild type. Silencing of GhirGDSL26 in cotton via VIGS resulting in a susceptible phenotype, higher MDA and H2O2 contents, lower SOD activity, and proline content. CONCLUSION: Our results demonstrated that GhirGDSL26 plays a critical role in cotton drought stress tolerance. Current findings enrich our knowledge of GDSL genes in cotton and provide theoretical guidance and excellent gene resources for improving drought tolerance in cotton.