Journal of Experimental Botany

Drought adaptation for water-limited environments relies on traits that optimize plant water budgets. Limited transpiration (LT) reduces water demand under high vapor pressure deficit (VPD) (i.e., dry air condition), conserving water for efficient use during the reproductive stage. Although studies in controlled environments report genetic variation for LT, confirming its replicability in field conditions is critical for developing water-resilient crops. Here we test the existence of genetic variation for LT in sorghum in field trials and whether canopy temperature (TC) is a surrogate method to discriminate this trait. We phenotyped transpiration response to VPD (TR-VPD) via stomatal conductance (gs), canopy temperature (TC) from fixed IRT sensors (TCirt), and unoccupied aerial system thermal imagery (TCimg) in 11 genotypes. Replicability among phenomic approaches for three genotypes revealed genetic variability for TR-VPD. Genotypes BTx2752 and SC979 carry the LT trait, while genotype DKS54-00 has the non-LT trait. TC can determine differences in TR-VPD. However, the broad sense heritability (H2) and correlations suggest that canopy architecture and stand count hampers TCirt and TCimg measurement. Unexpectedly, observations of gs and VPD showed non-linear patterns for genotypes with LT and non-LT traits. Our findings provide further insights into the genetics of plant water dynamics.

Stomatal traits balance carbon gain with water loss, yet their breeding potential in wheat remains underexploited. This study investigated physiological and anatomical stomatal responses alongside yield across two years of large-scale field trials under water-limitation and delayed sowing-induced heat exposure. Across both seasons, stomatal conductance (gs) declined under stress, reflecting strong environmental constraint on gas-exchange (water-limitation: -26.9%; heat: -13.8%). Partitioning responses by leaf surface and genotype identified the adaxial surface as the dominant contributor to gs variation and the most stress responsive. Despite increases in theoretical anatomical gas-exchange capacity (gsmax), gs-efficiency declined, indicating partial decoupling between structural potential and realised conductance. Drought reduced stomatal size while increasing density whereas heat increased size, suggesting stress-specific anatomical plasticity. Moderate-to-high heritability was observed for anatomical traits (Water-limitation: 0.13-0.57; Heat: 0.42-0.71), contrasting with lower and less stable heritability for gs (water-limitation: 0.13-0.41; heat: 0.13-0.50). Genome-wide-association-mapping identified 169 putative QTLs, predominantly for anatomical traits, including stable and co-localised pleiotropic loci. Fourteen sets of closely positioned markers were detected across seasons or studies, with stable regions on chromosomes 2B, 3B and 7B emerging as key loci. Focusing on stable loci controlling adaxial stomatal anatomy offers a realistic strategy to enhance wheat photosynthetic efficiency and climate resilience. HighlightAdaxial stomatal traits dominate gas exchange responses to heat and drought in wheat, with stable anatomical QTL identified on chromosomes 2B, 3B and 7B. Their stability across environments supports their relevance for crop improvement in water-limited and high temperature systems.

Daily minimum temperature (Tmin) is increasing faster than maximum temperature (Tmax). However, the impact of Tmin on crop productivity is barely studied. Effects of environmental covariates on yield were examined using 42 years of trials at 255 sites representing spring wheat regions globally. Grain-filling was the most sensitive growth stage: Average Tmin explained 40% of yield variation, and 52% when also considering radiation, while average Tmax explained just 20% of variation. Yield declined linearly between the observed range from 8 to 22{o}C average Tmin. Generally, a 1{o}C increased Tmin reduced yield by [~]0.5 t/ha, with high radiation partially offsetting negative effects. Average increase of 1.2{o}C at test sites over 42 years reduced yield by more than 10%. Shorter grain-filling duration likely reduced yield, as well as increased nocturnal rate of dark respiration. A better understanding of drivers of variation in respiration and adaptation to warmer nights could generate a step change in wheat yield.

The leaf pavement cells of many plant species develop fascinating jigsaw puzzle-like shapes in which neighboring cells interdigitate with each other, providing an ideal model for the study of cell shape acquisition. We analyzed pavement cell shape complexity in a natural population of European aspen (Populus tremula) genotypes and then used a genome-wide association study (GWAS) approach to identify a new candidate gene in cell shape regulation, Potra2n8c18226, encoding the transcription factor MYB305a. We subsequently validated a role for MYB305a in regulating aspen leaf pavement cell shape. We then demonstrated that drought conditions strongly induced MYB305a promoter expression in these cells and provided evidence implying that MYB305a plays a role in simplification of the cell shape in response to drought stress. Finally, we demonstrated negative correlations of pavement cell shape complexity with water-use efficiency, as well as with average precipitation, latitude and longitude of the genotypes original sampling sites in the natural European aspen population. Taken together, our results suggest that climatic variables affect the shape complexity of pavement cells in aspen leaf and provide a first step towards unravelling the molecular mechanisms controlling pavement cell shape acquisition in this species in response to environmental conditions, by implicating the involvement of the transcription factor MY305a.

The domestication of crops, with the development of the agroecosystems, is associated with major environmental changes and represent a model to test the role of phenotypic plasticity. Here we investigated 32 genotypes representing key stages of tetraploid wheat domestication. We developed a dedicated pipeline combining RNA-Seq data, estimates of evolvability and QST to characterize the plasticity of gene expression and identify signatures of selection under different nitrogen conditions. The analysis of gene expression diversity showed contrasting results between primary and secondary domestication in relation to nitrogen availability. Indeed, nitrogen triggered the expression of twice the number of genes in durum wheat compared to emmer and wild emmer. QST distributions and QST-FST comparisons revealed distinct selection signatures at each domestication stage. While primary domestication affected the expression of genes involved in biotic interactions, secondary domestication was associated with changes in expression of genes involved in metabolism of amino acids, particularly lysine. Selection signatures were found also in differentially expressed genes, specifically involved in nitrogen metabolism, such as glutamate dehydrogenase. Overall, our findings show that nitrogen availability had a pivotal role during the domestication and adaptive responses of a major food crop, with varying effects across different traits and growth conditions.

O_LIPearl millet is a key cereal for food security in drylands but its yield is strongly impacted by drought. We investigated how root anatomical traits contribute to mitigating the effects of vegetative drought stress in pearl millet. C_LIO_LIWe examined associations between root anatomical traits and agronomical performance in a pearl millet diversity panel under irrigated and vegetative drought stress treatments in field trials. The impact of associated anatomical traits on transpiration was assessed using subpanels grown in different soil within a greenhouse. C_LIO_LIIn the field, total metaxylem area was positively correlated with grain weight and its maintenance under drought. In the greenhouse, genotypes with larger metaxylem area grown in sandy soil exhibited a consumerist water use strategy under irrigation, which shifted to a conservative strategy under drought. Water savings was mediated by transpiration restriction under high evaporative demand. This mechanism was dependent on soil hydraulics as it was not observed in peat soil with higher hydraulic conductivity upon soil drying. C_LIO_LIWe propose that water savings under drought, mediated by large metaxylem area and its interaction with soil hydraulics, help mitigate vegetative drought stress. Our findings highlight the role of soil hydraulic properties in shaping plant hydraulics and drought tolerance. C_LI

The plant cuticle is a hydrophobic layer that serves as the primary barrier between plant surfaces and the external environment, limiting water loss and protecting against various stresses. This study investigates the genetic interaction between the maize ZmFDL1 and ZmGL15 genes and their role in modulating juvenile cuticle deposition and leaf permeability. The research was undertaken to understand how these genes influence cuticle composition and structure, which are crucial for plant protection against environmental stresses such as drought. We analysed the chemical composition of cutin and waxes, as well as cuticle-dependent leaf permeability. Our findings reveal that ZmFDL1 and ZmGL15 individually and synergically regulate the deposition of cuticular components, with significant impacts on leaf permeability. The gl15-S mutant exhibited an adult-like cuticle with higher cutin and lower wax contents, leading to reduced leaf permeability and improved water retention under drought conditions. These results highlight the importance of cutin in forming an effective water barrier and suggest that modulating cuticle composition with enhanced cutin content could be a strategy for improving drought tolerance in crops. This study provides new insights into the genetic regulation of cuticle biosynthesis and its relevance for plant adaptation to water scarcity. HighlightO_LIZmFDL1 and ZmGL15 interact to modulate cuticle composition and reduce leaf water loss. C_LIO_LIZmFDL1 and ZmGL15 genes regulate juvenile cuticle deposition in maize. C_LIO_LIThe gl15-S mutant shows an adult-like cuticle with higher cutin and lower wax contents. C_LIO_LIThe gl15-S mutation is epistatic to fdl1-1, partially rescuing the defective fdl1 cuticle phenotype. C_LIO_LIThe cuticle composition in gl15-S mutants leads to reduced leaf permeability and improved water retention under drought conditions. C_LIO_LICuticular layer with enhanced cutin content could improve drought tolerance in crops. C_LI

Macroautophagy is known for long as essential for the degradation and the recycling of different macromolecules in eukaryotes. However how important is autophagy for nitrogen management at the whole plant level and for plant biomass and yield productivity in unstressed and well feed plants needed further investigation. In this study, we used both autophagy knock-out mutants and autophagy over-expressors that constitutively produce numerous autophagosomes. These mutants and over-expressors were cultivated using hydroponic system to observe and compare their phenotypes under sufficient nitrate supply, and when submitted after a while to strict nitrate starvation. The shift from nitrate sufficient condition to nitrate starvation allowed us to determine how autophagy defective or stimulated lines can use their own nitrogen resources to complete their cycle. Unexpectedly we observed that irrespective of the nitrate conditions, both mutants and over-expressors exhibited early leaf senescence phenotypes relative to wild type. While autophagy mutants exhibited strong defect for N remobilisation and seed production irrespective of nitrate condition, the better performance of autophagy-over expressors for N remobilisation and seeds production was only significant under sufficient nitrate supply, i.e. when autophagy was not naturally stimulated by nitrate limitation. Interestingly, comparisons of genotypes showed that the nitrogen pool used for seed filling originated from rosette leaves, as if rosette and seeds were used as communicating vessels independently of the stem and pod connecting organs. Altogether, results show that autophagy is a master player in nitrogen management at the whole plant level that controls yield production and leaf senescence.

Arthropod herbivory possess a significant threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest, Tetranychus urticae, inflicts rapid damage and remains a challenge due to its broad target range. In this study, we explored Arabidopsis thalianas response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, including stomatal closure during water stress. Leveraging a FRET-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types post-mite feeding. While ABAs role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation, alongside intact canonical biotic stress signalling, indicating an independent function of ABA in mite defense. Through genetic and pharmacological interventions targeting ABA levels, ABA signalling, stomatal aperture, and density, we established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, underscores the intricate relationship between these two stress types.

Plant apoplast is the first hub of plant-pathogen communication where pathogen effectors are recognized by plant defensive proteins and cell receptors and several signal transduction pathways are activated. As a result of this first contact, the host triggers a defence response that involves the modulation of several extra and intracellular proteins. In grapevine-pathogen interactions, little is known about the communication between cells and apoplast. Also, the role of apoplastic proteins in response to pathogens still remains a blackbox. In this study we focused on the first 6 hours after Plasmopara viticola inoculation to evaluate grapevine proteome modulation in the apoplastic fluid (APF) and whole leaf tissue. Plasmopara viticola proteome was also assessed enabling a deeper understanding of plant and pathogen communication. Our results showed that oomycete recognition, plant cell wall modifications, ROS signalling and disruption of oomycete structures are triggered in Regent after P. viticola inoculation. Our results highlight a strict relation between the apoplastic pathways modulated and the proteins identified in the whole leaf proteome. On the other hand, P. viticola proteins related to growth/morphogenesis and virulence mechanisms were the most predominant. This pioneer study highlights the early dynamics of extra and intracellular communication in grapevine defence activation that leads to the successful establishment of an incompatible interaction.

New durum wheat (Triticum turgidum L. ssp. Durum) cultivars with improved adaptation to variable rainfall environments are required to sustain productivity in the face of climate change. Physiological traits related to canopy development underpin the production of biomass and yield, as they interact with solar radiation and affect the timing of water use throughout the growing season. This study explored the temporal canopy dynamics of durum wheat using a nested-association mapping population evaluated for longitudinal normalized difference vegetation index (NDVI) measurements. Association mapping was performed to identify quantitative trait loci (QTL) for time-point NDVI and spline-smoothed NDVI trajectory traits. Yield effects associated with QTL for canopy development were investigated using data from four rainfed field trials. Four QTL associated with slower canopy closure, improved yield in specific environments, and notably, were not associated with a yield penalty in any environment. This was likely due to optimised timing of water-use and pleiotropic effects on yield component traits, including spike number and spike length. Overall, this study suggests that slower canopy closure is beneficial for durum wheat production in rainfed environments. Selection for traits or loci associated with canopy development may improve yield stability of durum wheat in water limited environments.

A sudden cold exposure (4{degrees}C, 24 h) primes resistance of Arabidopsis thaliana against the virulent biotrophic pathogen Pseudomonas syringae pv. tomato DC3000 (Pst) for several days. This effect is mediated by chloroplast cold sensing and the activity of stromal and thylakoid-bound ascorbate peroxidases (sAPX/tAPX). In this study, we investigated the impact of such cold exposure on plant defence against the necrotrophic fungus Botrytis cinerea. Plant resistance was transiently enhanced if the B. cinerea infection occurred immediately after the cold exposure, but this cold-enhanced B. cinerea resistance was absent when the cold treatment and the infection were separated by 5 days at normal growth conditions. Plastid ascorbate peroxidases partially contributed to the transient cold-enhanced resistance against the necrotrophic fungus. In response to B. cinerea, the levels of reactive oxygen species (ROS) were significantly higher in cold-pretreated Arabidopsis leaves. Pathogen-triggered ROS levels varied in the absence of sAPX, highlighting the strong capacity for sAPX-dependent ROS regulation in the chloroplast stroma. The cold-enhanced resistance against B. cinerea was associated with cold-induced plant cell wall modifications, including sAPX-dependent callose formation and significant lignification in cold-treated Arabidopsis leaves. FundingThis work was supported by the German Research Foundation (CRC973/C4) and the FU Berlin.

In Arabidopsis, a dry stigma surface enables a gradual hydration of pollen grains by a controlled release of water. Occasionally the grains may be exposed to extreme precipitations that cause rapid water influx, swelling and eventually lead to pollen membrane (PM) rupture. In metazoans, calcium- and phospholipids-binding proteins, referred to as annexins participate in repair of the plasma membrane damages. It remains unclear, however, how this process is conducted in plants. Here, we examined whether the plant annexin 5 (ANN5), the most abundant member of the annexin family in pollen, is involved in the restoration of PM integrity. We analyzed a cellular dynamics of ANN5 in the pollen grains undergoing in vitro and in vivo hydration. We observed a transient ANN5 association to PM during the in vitro hydration that did not occur in the pollen grains being hydrated on the stigma. To simulate a rainfall, we performed spraying of the pollinated stigma with deionized water that induced ANN5 accumulation at PM. Similarly, calcium or magnesium application affected PM properties and induced ANN5 recruitment to PM. Our data suggest a model, in which ANN5 is involved in the maintenance of membrane integrity in pollen grains exposed to osmotic or ionic imbalances.

O_LIPhytophthora spp. incite serious plant damages by exploiting a large number of effector proteins and small RNAs (sRNAs). Several reports are describing modulation of host RNA biogenesis and defence gene expression. Here, we analysed P. infestans Argonaute (Ago) 1 associated small RNAs during potato leaf infection. C_LIO_LIsRNAs were co-immunoprecipitated, deep sequenced and analysed against the P. infestans and potato genomes, followed by transgenic and biochemical analyses on a predicted host target. C_LIO_LIExtensive targeting of potato and pathogen-derived sRNAs to a large number of mRNAs was observed, including 206 sequences coding for resistance (R) proteins in the host genome. The single miRNA encoded by P. infestans (miR8788) was found to target a potato lipase-like membrane protein-encoding gene (StLL1) localized to the tonoplast. Analyses of stable transgenic potato lines harbouring overexpressed StLL1 or artificial miRNA gene constructs demonstrated the importance of StLL1 during infection by P. infestans. Similarly, a miR8788 knock-down strain showed reduced growth on potato compared to the wild-type strain 88069. C_LIO_LIThe data suggest that sRNA encoded by P. infestans can affect potato mRNA and thereby promote disease. Knowledge of the impact of pathogen small RNAs in plant defence mechanisms is of major significance to succeed in improved disease control management. C_LI

To investigate the interactive effects of elevated CO2 and heat stress (HS), we grew two contrasting wheat cultivars, early-maturing Scout and high-tillering Yitpi, under non-limiting water and nutrients at ambient (aCO2, 450 ppm) or elevated (eCO2, 650 ppm) CO2 and 22{degrees}C in the glasshouse. Plants were exposed to two 3-day HS cycles at the vegetative (38.1{degrees}C) and/or flowering (33.5{degrees}C) stage. At aCO2, both wheat cultivars showed similar responses of photosynthesis and mesophyll conductance to temperature and produced similar grain yield. Relative to aCO2, eCO2 enhanced photosynthesis rate and reduced stomatal conductance and maximal carboxylation rate (Vcmax). During HS, high temperature stimulated photosynthesis at eCO2 in both cultivars, while eCO2 stimulated photosynthesis in Scout. Electron transport rate (Jmax) was unaffected by any treatment. eCO2 equally enhanced biomass and grain yield of both cultivars in control, but not HS, plants. HS reduced biomass and yield of Scout at eCO2. Yitpi, the cultivar with higher grain nitrogen, underwent a trade-off between grain yield and nitrogen. In conclusion, eCO2 improved photosynthesis of control and HS wheat, and improved biomass and grain yield of control plants only. Under well-watered conditions, HS was not detrimental to photosynthesis or growth but precluded a yield response to eCO2. Key messageHigh temperatures increased photosynthetic rates only at eCO2 and photosynthesis was upregulated after recovery from heat stress at eCO2 in Scout suggesting that eCO2 increased optimum temperature of photosynthesis.

Current climate change scenarios predict an increased incidence of drought episodes likely to affect potato crops worldwide. Potato exhibits a low-density, shallow root system that makes it particularly vulnerable to water shortage and any successful attempt to implement drought tolerance in cultivated potato varieties is potentially relevant from an agronomic standpoint. In this study, we assessed the potential of tomato cystatin SlCYS8 to promote drought tolerance in SlCYS8-expressing potato lines by induction of stress-related pleiotropy. Up to now, protease inhibitors of the cystatin protein superfamily have been mostly considered as biotechnological tools to engineer pest or pathogen resistance in crops, but several recent studies have also revealed a possible link between abiotic stress tolerance and these regulatory proteins in leaf tissue. SlCYS8-expressing plantlets grown on culture medium containing the drought mimic polyethylene glycol (PEG) exhibited an elevated root-to-shoot ratio, an indicator of drought tolerance in potato. A similar conclusion could be drawn with greenhouse-grown acclimated plants, confirming a relative root growth-promoting effect for the recombinant inhibitor upon water deficit. SlCYS8-potato lines also showed a high tuber yield compared to the control line under both limiting and non-limiting water regimes, suggesting an improved efficiency of the primary metabolism and the avoidance of a growth- stress response tradeoff in the modified lines. Accordingly, SlCYS8 expression was associated with a stress response-oriented proteome in leaves likely explained by pleiotropic effects of the recombinant cystatin driving the constitutive expression of stress-related proteins and the upregulation of primary metabolism-associated proteins. Overall, these data suggest the potential of cystatins as molecular triggers of tuber biomass production and drought resilience in potato. Complementary studies will be warranted to assess tuber yield of the SlCYS8-lines under different water regimes in field conditions.

Sensing and responding to photoperiod changes is essential for plants to adapt to seasonal progression. Most of our understanding of how plants sense photoperiodic changes is through studies on flowering time. However, other aspects of plant development are regulated by the photoperiod, including hypocotyl elongation. Unlike flowering, hypocotyl elongation displays a greater plasticity to changes in the photoperiod with increases in daylength causing greater inhibition of growth until a threshold is met. Previous studies have only looked at hypocotyl development in the context of a stationary photoperiod. It is unknown if changes in the photoperiod during development influence hypocotyl elongation. Here, we developed a physiological assay to investigate this question. We have discovered that hypocotyl elongation is influenced by a memory of past photoperiod exposure in Arabidopsis and Brassicaceae cultivars used for microgreen agriculture. Photoperiodic memory persisted for multiple days, although it weakened over time, and the strength of the memory was dependent on the genetic background. We identified that phyB and ELF3, key regulators of hypocotyl development, were required for photoperiodic memory. Finally, we identified that the circadian clock is unlikely to function as a repository for photoperiodic memory as circadian rhythms quickly re-aligned with the new photoperiod. In summary, our work highlights for the first-time evidence of a photoperiodic memory that can control plant development.

O_LIInteractions between plant and soil microbes are widespread and modulate plant-insect herbivore interactions. Still, it remains unclear how these shapes the overall plant defence responses and the mechanisms involved. C_LIO_LIHere, we performed bioassays with barley (Hordeum vulgare) plants to study the underlying molecular pathways induced by two rhizobacteria, Acidovorax radicis or Bacillus subtilis, against the phloem feeding aphid Sitobion avenae over three timepoints. C_LIO_LIRoot colonization by A. radicis or B. subtilis suppressed aphid populations on barley. Analysis of differentially expressed genes and co-expressed gene modules revealed a combination of rhizobacteria and aphid induced plant responses. Aphid feeding triggered distinct plant responses in rhizobacteria-inoculated barley compared to controls, in phytohormone, glutathione, and phenylpropanoid pathways within 24 hours. By day 7, stronger responses were observed in phenylpropanoid and nutrient pathways. By day 21, changes occurred in flavonoid pathways and genes related to tissue damage and repair. C_LIO_LIOur study suggests that rhizobacteria inoculation of barley against aphids is dynamic and acts through several molecular pathways to induce plant resistance (defences) and tolerance (nutrition and growth) to aphids. Future research holds promise for exploiting these interactions for sustainable crop protection and pest management in agriculture. C_LI

Seed dormancy and timing of its release is important developmental transition determining the survival of individual as well as population and species. We used Medicago truncatula as model to study legume seed dormancy in ecological and genomics context. The effect of oscillating temperatures as one of the dormancy release factor was tested over the period of 88 days on the set of 178 accessions originating from variable environmental conditions of Mediterranean basin. Phenotypic plasticity of final dormancy was significantly correlated with increased aridity, suggesting that plastic responses to external stimuli provide seeds with strong bet-hedging capacity and the potential to cope with high levels of environmental heterogeneity. Genome-wide association analysis identified candidate genes associated with dormancy release related to secondary metabolites synthesis, hormone regulation and modification of the cell wall likely mediating seed coat permeability and ultimately imbibition and germination. HighlightMedicago seed dormancy was correlated with increased aridity of the environment, suggesting that plastic responses provide seeds with a bet-hedging capacity. Genome-wide association analysis identified candidate genes associated with release from dormancy.

Dehydration proteins (dehydrins, DHNs) confer tolerance to water-stress deficit to plants, thus playing a fundamental role in plant response and adaptation to water-deprivation stressful environments. We have performed a comparative genomics and evolutionary study of DHN genes in four model Brachypodium grass species, and a drought-induced functional analysis in 32 ecotypes of the flagship species B. distachyon, to gain insight into the origins and dynamics of these proteins and the correlated drought-mediated phenotypic responses in ecotypes showing different hydric requirements. Genomic sequence analysis detected 10 types of dehydrin genes (Bdhn) across the Brachypodium species, totalling 47 genes. Domain and conserved motif contents of peptides encoded by Bdhn genes revealed eight protein architectures, YS{phi}K2 being the most common architecture. Bdhn genes were spread across several chromosomes and more frequent in syntenic chromosomes 3 and 4 of B. distachyon, 4 and 5 of B. stacei and 4 of B. sylvaticum. Tandem and segmental duplication events were detected for four Bdhn genes. Selection analysis indicated that all the Bdhn genes were constrained by purifying selection. Three upstream cis-regulatory motifs (BES1, MYB124, ZAT) were consistently detected in several Bdhn genes. Functional analysis in 32 natural accessions of B. distachyon demonstrated that only four Bdhn genes (Bdhn1, Bdhn2, Bdhn3, Bdhn7) were expressed in mature leaves and that all of them were significantly more highly expressed in plants under drought conditions. These genes corresponded to wheat orthologs that were also significantly more expressed under drought stress. Brachypodium dehydrin expression was significantly correlated with drought-response phenotypic traits (plant biomass, leaf carbon and proline contents and WUE increases, leaf water and nitrogen content changes) being more pronounced in drought-tolerant ecotypes. Bdhn expression, associated phenotypic trait changes and climate niche variation did not show significant phylogenetic signal when tested in the B. distachyon genealogical-species tree. By contrast, some of them showed low or marginal significant phylogenetic signal when tested in the B. distachyon Bdhn tree, suggesting that Bdhn gene evolution is partially related to adaptation to drought in this species. Our results demonstrate that dehydrin composition and regulation is a key factor determining the acquisition of water-stress tolerance in grasses.