Abscisic acid-mediated autoregulation of the MYB41-BRAHMA module enhances drought tolerance in Arabidopsis.

Drought stress poses a substantial challenge to plant growth and agricultural productivity worldwide. Upon water depletion, plants activate an abscisic acid (ABA) signaling pathway, leading to stomatal closure to reduce water loss. The MYB family of transcription factors plays diverse roles in growth, development, stress responses and biosynthesis, yet their involvement in stomatal regulation remains unclear. Here, we demonstrate that ABA significantly upregulates the expression of MYB41, MYB74, and MYB102, with MYB41 serving as a key regulator that induces the expression of both MYB74 and MYB102. Through luciferase assays, chromatin immunoprecipitation (ChIP) assays and electrophoretic mobility shift assays (EMSA), we reveal that MYB41 engages in positive feedback regulation by binding to its own promoter, thus amplifying its transcription in Arabidopsis (Arabidopsis thaliana). Furthermore, our investigation showed that MYB41 recruits BRAHMA (BRM), the core ATPase subunit of the SWI/SNF complex, to the MYB41 promoter, facilitating the binding of HISTONE DEACETYLASE 6 (HDA6). This recruitment triggers epigenetic modifications, resulting in reduced MYB41 expression characterized by elevated H3K27me3 levels and concurrent decreases in H3ac, H3K27ac, and H3K14ac levels in wild-type plants compared to brm knockout mutant plants. Our genetic and molecular analyses show that ABA mediates autoregulation of the MYB41-BRM module, which intricately modulates stomatal movement in A. thaliana. This discovery sheds light on a drought response mechanism with the potential to greatly enhance agricultural productivity.

Shoot hydraulic impairments induced by root waterlogging: parallels and contrasts with drought.

Soil waterlogging and drought correspond to contrasting water extremes resulting in plant dehydration. Dehydration in response to waterlogging occurs due to impairments to root water transport, but no previous study has addressed whether limitations to water transport occur beyond this organ or whether dehydration alone can explain shoot impairments. Using common bean (Phaseolus vulgaris) as a model species, we report that waterlogging also impairs water transport in leaves and stems. During the very first hours of waterlogging, leaves transiently dehydrated to water potentials close to the turgor loss point, possibly driving rapid stomatal closure and partially explaining the decline in leaf hydraulic conductance. The initial decline in leaf hydraulic conductance (occurring within 24 h), however, surpassed the levels predicted to occur based solely on dehydration. Constraints to leaf water transport resulted in a hydraulic disconnection between leaves and stems, furthering leaf dehydration during waterlogging and after soil drainage. As leaves dehydrated later during waterlogging, leaf embolism initiated and extensive embolism levels amplified leaf damage. The hydraulic disconnection between leaves and stems prevented stem water potentials from declining below the threshold for critical embolism levels in response to waterlogging. This allowed plants to survive waterlogging and soil drainage. In summary, leaf and stem dehydration are central in defining plant impairments in response to waterlogging, thus creating similarities between waterlogging and drought. Yet, our findings point to the existence of additional players (likely chemicals) partially controlling the early declines in leaf hydraulic conductance and contributing to leaf damage during waterlogging.

Jasmonic acid enhances osmotic stress responses by MYC2-mediated inhibition of protein phosphatase 2C1 and response regulators 26 transcription factor in tomato.

The jasmonic acid (JA) signaling pathway is involved in the plant response to drought stress. JA and other hormones synergistically regulate the drought response in plants. However, the molecular mechanism underlying this synergism remains poorly defined. In the present study, transcriptome analyses of guard cells and quantitative PCR experiments revealed that MYC2 negatively regulated the negative regulator of ABA signaling, SlPP2C1, and the type-B response regulator in the cytokinin pathway, SlRR26, and this negative regulation was direct. SlRR26 overexpression reduced drought tolerance in transgenic tomatoes, whereas slrr26cr lines were more tolerant to drought. SlRR26 negatively modulated reactive oxygen species levels in stomata and stomatal closure through RobhB. Moreover, SlRR26 overexpression counteracted JA-mediated stomatal closure, suggesting that SlRR26 played a negative role in the JA-mediated drought response. These findings suggest that MYC2 plays a key role in JA-regulated stomatal closure under drought stress by inhibiting SlPP2C1 and SlRR26.

Regulation of drought tolerance in Arabidopsis involves the PLATZ4-mediated transcriptional repression of plasma membrane aquaporin PIP2;8.

Plant A/T-rich protein and zinc-binding protein (PLATZ) transcription factors play important roles in plant growth, development and abiotic stress responses. However, how PLATZ influences plant drought tolerance remains poorly understood. The present study showed that PLATZ4 increased drought tolerance in Arabidopsis thaliana by causing stomatal closure. Transcriptional profiling analysis revealed that PLATZ4 affected the expression of a set of genes involved in water and ion transport, antioxidant metabolism, small peptides and abscisic acid (ABA) signaling. Among these genes, the direct binding of PLATZ4 to the A/T-rich sequences in the plasma membrane intrinsic protein 2;8 (PIP2;8) promoter was identified. PIP2;8 consistently reduced drought tolerance in Arabidopsis through inhibiting stomatal closure. PIP2;8 was localized in the plasma membrane, exhibited water channel activity in Xenopus laevis oocytes and acted epistatically to PLATZ4 in regulating the drought stress response in Arabidopsis. PLATZ4 increased ABA sensitivity through upregulating the expression of ABSCISIC ACID INSENSITIVE 3 (ABI3), ABI4 and ABI5. The transcripts of PLATZ4 were induced to high levels in vegetative seedlings under drought and ABA treatments within 6 and 3 h, respectively. Collectively, these findings reveal that PLATZ4 positively influences plant drought tolerance through regulating the expression of PIP2;8 and genes involved in ABA signaling.

1-Butanol treatment enhances drought stress tolerance in Arabidopsis thaliana.

Abiotic stress is a major factor affecting crop productivity. Chemical priming is a promising strategy to enhance tolerance to abiotic stress. In this study, we evaluated the use of 1-butanol as an effectual strategy to enhance drought stress tolerance in Arabidopsis thaliana. We first demonstrated that, among isopropanol, methanol, 1-butanol, and 2-butanol, pretreatment with 1-butanol was the most effective for enhancing drought tolerance. We tested the plants with a range of 1-butanol concentrations (0, 10, 20, 30, 40, and 50 mM) and further determined that 20 mM was the optimal concentration of 1-butanol that enhanced drought tolerance without compromising plant growth. Physiological tests showed that the enhancement of drought tolerance by 1-butanol pretreatment was associated with its stimulation of stomatal closure and improvement of leaf water retention. RNA-sequencing analysis revealed the differentially expressed genes (DEGs) between water- and 1-butanol-pretreated plants. The DEGs included genes involved in oxidative stress response processes. The DEGs identified here partially overlapped with those of ethanol-treated plants. Taken together, the results show that 1-butanol is a novel chemical priming agent that effectively enhances drought stress tolerance in Arabidopsis plants, and provide insights into the molecular mechanisms of alcohol-mediated abiotic stress tolerance.

Stomatal response to VPD is not triggered by changes in soil-leaf hydraulic conductance in Arabidopsis or Callitris.

Stomatal closure under high VPDL (leaf to air vapour pressure deficit) is a primary means by which plants prevent large excursions in transpiration rate and leaf water potential (Ψleaf) that could lead to tissue damage. Yet, the drivers of this response remain controversial. Changes in Ψleaf appear to drive stomatal VPDL response, but many argue that dynamic changes in soil-to-leaf hydraulic conductance (Ks-l) make an important contribution to this response pathway, even in well-hydrated soils. Here, we examined whether the regulation of whole plant stomatal conductance (gc) in response to typical changes in daytime VPDL is influenced by dynamic changes in Ks-l. We use well-watered plants of two species with contrasting ecological and physiological features: the herbaceous Arabidopsis thaliana (ecotype Columbia-0) and the dry forest conifer Callitris rhomboidea. The dynamics of Ks-l and gc were continuously monitored by combining concurrent in situ measurements of Ψleaf using an open optical dendrometer and whole plant transpiration using a balance. Large changes in VPDL were imposed to induce stomatal closure and observe the impact on Ks-l. In both species, gc was observed to decline substantially as VPDL increased, while Ks-l remained stable. Our finding suggests that stomatal regulation of transpiration is not contingent on a decrease in Ks-l. Static Ks-l provides a much simpler explanation for transpiration control in hydrated plants and enables simplified modelling and new methods for monitoring plant water use in the field.

Synergistic Interaction Between PbbZIP88 and PbSRK2E Enhances Drought Resistance in Pear Through Regulation of PbATL18 Expression and Stomatal Closure.

Drought poses significant challenges to agricultural production, ecological stability and global food security. While wild pear trees exhibit strong drought resistance, cultivated varieties show weaker drought tolerance. This study aims to elucidate the molecular mechanisms underlying pear trees' response to drought stress. We identified a drought resistance-related transcription factor, PbbZIP88, which binds to and activates the expression of the drought-responsive gene PbATL18. Overexpression of PbbZIP88 in Arabidopsis and pear seedlings resulted in enhanced drought resistance and significantly improved physiological parameters under drought stress. We discovered that PbbZIP88 interacts with the key protein PbSRK2E in the ABA signalling pathway. This interaction enhances PbbZIP88's ability to activate PbATL18 expression, leading to higher levels of PbATL18. Furthermore, the PbbZIP88 and PbSRK2E interaction accelerates the regulation of stomatal closure under ABA treatment conditions, reducing water loss more effectively. Experimental evidence showed that silencing PbbZIP88 and PbSRK2E genes significantly decreased drought resistance in pear seedlings. In conclusion, this study reveals the synergistic role of PbbZIP88 and PbSRK2E in enhancing drought resistance in pear trees, particularly in the upregulation of PbATL18 expression, and the accelerated promotion of stomatal closure. These findings provide new candidate genes for breeding drought-resistant varieties and offer a theoretical foundation and technical support for achieving sustainable agriculture.

The double-edged sword of potassium and sodium fertilization in xylem embolism resistance of two Eucalyptus species under drought stress.

Sodium (Na+) is a beneficial element for most plants that may replace potassium (K+) in osmoregulatory process to a certain extent, increasing plant water-use efficiency. Thus, understanding coordinated mechanisms underlying the combined use of K+ and Na+ in tree drought tolerance is a key challenge for the agricultural industry in dealing with forest productivity and water limitations. A pot experiment with three ratios of K/Na (K-supplied, partial K replacement by Na and K-deficient plants) and two water regimes, well-watered (W+) and water-stressed (W-), was conducted on saplings of two Eucalyptus species with contrasting drought sensitivities. We evaluated the point of stomatal closure (Pgs90), xylem embolism thresholds (P12, P50, P88), hydraulic safety margin (HSM), leaf gas exchange (A, E, gs and dark respiration), leaf water potential (ΨPD and ΨMD), long-term water use efficiency (WUEL) and total dry mass (TDM). Partial K replacement by Na increased the leaf gas exchange, WUEL and TDM, while Pgs90, P12, P50, P88 and ΨMD decreased (more negative), compared to plants exclusively supplied with K and K-deficient plants of both species. Fertilized plants had narrower HSMs than K-deficient plants, indicating that these Eucalyptus species adopt the functional adaptive strategy of operating close to their hydraulic limits to maximize carbon uptake while increasing the risk of hydraulic failure under drought-stress.

Negative regulation of chitosan-induced stomatal closure by glutathione in Arabidopsis thaliana.

Chitosan (CHT) is a deacylated derivative of chitin and improves growth and yield performance, activates defensive genes, and also induces stomatal closure in plants. Glutathione (GSH) has significant functions in the growth, development, defense systems, signaling, and gene expression. GSH negatively regulates abscisic acid-, methyl jasmonate-, and salicylic acid-induced stomatal closure. However, the negative regulation by GSH of CHT-induced stomatal closure is still unknown. Regulation of CHT-induced stomatal closure by GSH in guard cells was investigated using two GSH-deficient mutants, cad2-1 and chlorina 1-1 (ch1-1), and a GSH-decreasing chemical, 1-chloro-2,4-dinitrobenzene (CDNB). The cad2-1 and ch1-1 mutations and CDNB treatment enhanced CHT-induced stomatal closure. Treatment with glutathione monoethyl ester restored the GSH level in the guard cells of cad2-1 and ch1-1 and complemented the stomatal phenotype of the mutants. These results indicate that GSH negatively regulates CHT-induced stomatal closure in Arabidopsis thaliana.

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.

Sinapate Esters Mediate UV-B-Induced Stomatal Closure by Regulating Nitric Oxide, Hydrogen Peroxide, and Malate Accumulation in Arabidopsis thaliana.

Sinapate esters, which are induced in plants under ultraviolet-B (UV-B) irradiation, have important roles not only in the protection against UV-B irradiation but also in the regulation of stomatal closure. Here, we speculated that sinapate esters would function in the stomatal closure of Arabidopsis thaliana in response to UV-B. We measured the stomatal aperture size of the wild-type (WT) and bright trichomes 1 (brt1) and sinapoylglucose accumulator 1 (sng1) mutants under UV-B irradiation; the latter two mutants are deficient in the conversion of sinapic acid to sinapoylglucose (SG) and SG to sinapoylmalate (SM), respectively. Both the brt1 and sng1 plants showed smaller stomatal apertures than the WT under normal light and UV-B irradiation conditions. The accumulation of SM and malate were induced by UV-B irradiation in WT and brt1 plants but not in sng1 plants. Consistently, exogenous malate application reduced UV-B-induced stomatal closure in WT, brt1 and sng1 plants. Nonetheless, levels of reactive oxygen species (ROS), nitric oxide (NO) and cytosolic Ca2+ were higher in guard cells of the sng1 mutant than in those of the WT under normal white light and UV-B irradiation, suggesting that disturbance of sinapate metabolism induced the accumulation of these signaling molecules that promote stomatal closure. Unexpectedly, exogenous sinapic acid application prevented stomatal closure of WT, brt1 and sng1 plants. In summary, we hypothesize that SG or other sinapate esters may promote the UV-B-induced malate accumulation and stomatal closure, whereas sinapic acid inhibits the ROS-NO pathway that regulates UV-B-induced cytosolic Ca2+ accumulation and stomatal closure.

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.

GhPYL9-5D and GhPYR1-3 A positively regulate Arabidopsis and cotton responses to ABA, drought, high salinity and osmotic stress.

BACKGROUND: Abscisic acid (ABA) receptor pyrabactin resistance 1/PYR1-like/regulatory components of ABA receptor proteins (PYR/PYL/RCARs) have been demonstrated to play pivotal roles in ABA signaling and in response to diverse environmental stimuli including drought, salinity and osmotic stress in Arabidopsis. However, whether and how GhPYL9-5D and GhPYR1-3A, the homologues of Arabidopsis PYL9 and PYR1 in cotton, function in responding to ABA and abiotic stresses are still unclear. RESULTS: GhPYL9-5D and GhPYR1-3A were targeted to the cytoplasm and nucleus. Overexpression of GhPYL9-5D and GhPYR1-3A in Arabidopsis wild type and sextuple mutant pyr1pyl1pyl2pyl4pyl5pyl8 plants resulted in ABA hypersensitivity in terms of seed germination, root growth and stomatal closure, as well as seedling tolerance to water deficit, salt and osmotic stress. Moreover, the VIGS (Virus-induced gene silencing) cotton plants, in which GhPYL9-5D or GhPYR1-3A were knocked down, showed clearly reduced tolerance to polyethylene glycol 6000 (PEG)-induced drought, salinity and osmotic stresses compared with the controls. Additionally, transcriptomic data revealed that GhPYL9-5D was highly expressed in the root, and GhPYR1-3A was strongly expressed in the fiber and stem. GhPYL9-5D, GhPYR1-3A and their homologs in cotton were highly expressed after treatment with PEG or NaCl, and the two genes were co-expressed with redox signaling components, transcription factors and auxin signal components. These results suggest that GhPYL9-5D and GhPYR1-3A may serve important roles through interplaying with hormone and other signaling components in cotton adaptation to salt or osmotic stress. CONCLUSIONS: GhPYL9-5D and GhPYR1-3A positively regulate ABA-mediated seed germination, primary root growth and stomatal closure, as well as tolerance to drought, salt and osmotic stresses likely through affecting the expression of multiple downstream stress-associated genes in Arabidopsis and cotton.

The C2 H2 -type zinc finger transcription factor OSIC1 positively regulates stomatal closure under osmotic stress in poplar.

Salt and drought impair plant osmotic homeostasis and greatly limit plant growth and development. Plants decrease stomatal aperture to reduce water loss and maintain osmotic homeostasis, leading to improved stress tolerance. Herein, we identified the C2 H2 transcription factor gene OSMOTIC STRESS INDUCED C2 H2 1 (OSIC1) from Populus alba var. pyramidalis to be induced by salt, drought, polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA). Overexpression of OSIC1 conferred transgenic poplar more tolerance to high salinity, drought and PEG6000 treatment by reducing stomatal aperture, while its mutant generated by the CRISPR/Cas9 system showed the opposite phenotype. Furthermore, OSIC1 directly up-regulates PalCuAOζ in vitro and in vivo, encoding a copper-containing polyamine oxidase, to enhance H2 O2 accumulation in guard cells and thus modulates stomatal closure when stresses occur. Additionally, ABA-, drought- and salt-induced PalMPK3 phosphorylates OSIC1 to increase its transcriptional activity to PalCuAOζ. This regulation of OSIC1 at the transcriptional and protein levels guarantees rapid stomatal closure when poplar responds to osmotic stress. Our results revealed a novel transcriptional regulatory mechanism of H2 O2 production in guard cells mediated by the OSIC1-PalCuAOζ module. These findings deepen our understanding of how perennial woody plants, like poplar, respond to osmotic stress caused by salt and drought and provide potential targets for breeding.

In situ characterisation of whole-plant stomatal responses to VPD using leaf optical dendrometry.

Vapour pressure deficit (VPD) plays a crucial role in regulating plant carbon and water fluxes due to its influence on stomatal behaviour and transpiration. Yet, characterising stomatal responses of the whole plant to VPD remains challenging due to methodological limitations. Here, we develop a novel method for in situ assessment of whole-plant stomatal responses (gc ) to VPD in the herbaceous plant Tanacetum cinerariifolium. To do this, we examine the relationship between daytime VPD and the corresponding soil-stem water potential gradient (ΔΨ) monitored using the optical dendrometry in well-hydrated plants under nonlimiting light in both glasshouse and field conditions. In glasshouse plants, ΔΨ increased proportionally with the VPD up to a threshold of 1.53 kPa, beyond which the slope decreased, suggesting a two-phase response in gc . This pattern aligned with corresponding gravimetrically measured gc behaviour, which also showed a decline when VPD exceeded a similar threshold. This response was then compared with that of field plants monitored using the optical dendrometry technique over a growing season under naturally variable VPD conditions and nonlimiting light and water supply. Field plants exhibited a similar threshold-type response to VPD but were more sensitive than glasshouse individuals with a VPD threshold of 0.74 kPa. The results showed that whole-plant gc responses to VPD can be characterised optically in T. cinerariifolium, introducing a new tool for the monitoring and characterisation of stomatal behaviour in situ.

Drought survival in conifer species is related to the time required to cross the stomatal safety margin.

The regulation of water loss and the spread of xylem embolism have mostly been considered separately. The development of an integrated approach taking into account the temporal dynamics and relative contributions of these mechanisms to plant drought responses is urgently needed. Do conifer species native to mesic and xeric environments display different hydraulic strategies and temporal sequences under drought? A dry-down experiment was performed on seedlings of four conifer species differing in embolism resistance, from drought-sensitive to extremely drought-resistant species. A set of traits related to drought survival was measured, including turgor loss point, stomatal closure, minimum leaf conductance, and xylem embolism resistance. All species reached full stomatal closure before the onset of embolism, with all but the most drought-sensitive species presenting large stomatal safety margins, demonstrating that highly drought-resistant species do not keep their stomata open under drought conditions. Plant dry-down time to death was significantly influenced by the xylem embolism threshold, stomatal safety margin, and minimum leaf conductance, and was best explained by the newly introduced stomatal margin retention index (SMRIΨ50) which reflects the time required to cross the stomatal safety margin. The SMRIΨ50 may become a key tool for the characterization of interspecific drought survival variability in trees.

Aridity-dependent sequence of water potentials for stomatal closure and hydraulic dysfunctions in woody plants.

The sequence of physiological events during drought strongly impacts plants' overall performance. Here, we synthesized the global data of stomatal and hydraulic traits in leaves and stems of 202 woody species to evaluate variations in the water potentials for key physiological events and their sequence along the climatic gradient. We found that the seasonal minimum water potential, turgor loss point, stomatal closure point, and leaf and stem xylem vulnerability to embolism were intercorrelated and decreased with aridity, indicating that water stress drives trait co-selection. In xeric regions, the seasonal minimum water potential occurred at lower water potential than turgor loss point, and the subsequent stomatal closure delayed embolism formation. In mesic regions, however, the seasonal minimum water potential did not pose a threat to the physiological functions, and stomatal closure occurred even at slightly more negative water potential than embolism. Our study demonstrates that the sequence of water potentials for physiological dysfunctions of woody plants varies with aridity, that is, xeric species adopt a more conservative sequence to prevent severe tissue damage through tighter stomatal regulation (isohydric strategy) and higher embolism resistance, while mesic species adopt a riskier sequence via looser stomatal regulation (anisohydric strategy) to maximize carbon uptake at the cost of hydraulic safety. Integrating both aridity-dependent sequence of water potentials for physiological dysfunctions and gap between these key traits into the hydraulic framework of process-based vegetation models would improve the prediction of woody plants' responses to drought under global climate change.

Overexpression of the Wheat TaPsb28 Gene Enhances Drought Tolerance in Transgenic Arabidopsis.

Psb28 is a soluble protein in the photosystem II (PSII) complex, but its role in the drought stress response of wheat remains unclear. Here, we functionally characterized the TaPsb28 gene, which positively regulates drought tolerance in wheat. When the full-length 546-bp TaPsb28 cDNA was transferred into Arabidopsis thaliana, it was located in the guard cell chloroplast around the stroma. Overexpression of TaPsb28 conferred drought tolerance, as exhibited by the increases in the survival rate. Transgenic plants maintained lower MDA content and higher chlorophyll content by inducing chlorophyll synthase (ChlG) gene transcription. The content of abscisic acid (ABA) and zeatin increased significantly in wild-type (WT) plants under drought stress, and the transcriptional expression levels of RD22, dihydroflavonol 4-reductase (DFR) and anthocyanin reductase (ANR) genes were induced, thus enhancing the contents of endogenous cyanidin, delphinidin, and proanthocyanidins. However, in transgenic plants, although anthocyanins were further aggregated, the ABA increase was inhibited, zeatin was restored to the control level under drought stress, and stomatal closure was promoted. These findings indicate ABA and zeatin have opposite synergistic effects in the process of drought tolerance caused by TaPsb28 because only after the effect of zeatin is alleviated can ABA better play its role in promoting anthocyanin accumulation and stomatal closure, thus enhancing the drought tolerance of transgenic plants. The results suggest that overexpression of TaPsb28 exerts a positive role in the drought response by influencing the functional metabolism of endogenous hormones. The understanding acquired through the research laid a foundation for further in-depth investigation of the function of TaPsb28 in drought resistance in wheat, especially its relationship with anthocyanidin accumulation.

Transcription Factor ZmNAC20 Improves Drought Resistance by Promoting Stomatal Closure and Activating Expression of Stress-Responsive Genes in Maize.

Drought is a major environmental threat that limits crop growth, development, and productivity worldwide. Improving drought resistance with genetic engineering methods is necessary to tackle global climate change. It is well known that NAC (NAM, ATAF and CUC) transcription factors play a critical role in coping with drought stress in plants. In this study, we identified an NAC transcription factor ZmNAC20, which regulates drought stress response in maize. ZmNAC20 expression was rapidly upregulated by drought and abscisic acid (ABA). Under drought conditions, the ZmNAC20-overexpressing plants had higher relative water content and survival rate than the wild-type maize inbred B104, suggesting that overexpression of ZmNAC20 improved drought resistance in maize. The detached leaves of ZmNAC20-overexpressing plants lost less water than those of wild-type B104 after dehydration. Overexpression of ZmNAC20 promoted stomatal closure in response to ABA. ZmNAC20 was localized in the nucleus and regulated the expression of many genes involved in drought stress response using RNA-Seq analysis. The study indicated that ZmNAC20 improved drought resistance by promoting stomatal closure and activating the expression of stress-responsible genes in maize. Our findings provide a valuable gene and new clues on improving crop drought resistance.

The Over-Expression of Two R2R3-MYB Genes, PdMYB2R089 and PdMYB2R151, Increases the Drought-Resistant Capacity of Transgenic Arabidopsis.

The R2R3-MYB genes in plants play an essential role in the drought-responsive signaling pathway. Plenty of R2R3-MYB S21 and S22 subgroup genes in Arabidopsis have been implicated in dehydration conditions, yet few have been covered in terms of the role of the S21 and S22 subgroup genes in poplar under drought. PdMYB2R089 and PdMYB2R151 genes, respectively belonging to the S21 and S22 subgroups of NL895 (Populus deltoides × P. euramericana cv. 'Nanlin895'), were selected based on the previous expression analysis of poplar R2R3-MYB genes that are responsive to dehydration. The regulatory functions of two target genes in plant responses to drought stress were studied and speculated through the genetic transformation of Arabidopsis thaliana. PdMYB2R089 and PdMYB2R151 could promote the closure of stomata in leaves, lessen the production of malondialdehyde (MDA), enhance the activity of the peroxidase (POD) enzyme, and shorten the life cycle of transgenic plants, in part owing to their similar conserved domains. Moreover, PdMYB2R089 could strengthen root length and lateral root growth. These results suggest that PdMYB2R089 and PdMYB2R151 genes might have the potential to improve drought adaptability in plants. In addition, PdMYB2R151 could significantly improve the seed germination rate of transgenic Arabidopsis, but PdMYB2R089 could not. This finding provides a clue for the subsequent functional dissection of S21 and S22 subgroup genes in poplar that is responsive to drought.