Sounds emitted by plants under stress are airborne and informative.

Stressed plants show altered phenotypes, including changes in color, smell, and shape. Yet, airborne sounds emitted by stressed plants have not been investigated before. Here we show that stressed plants emit airborne sounds that can be recorded from a distance and classified. We recorded ultrasonic sounds emitted by tomato and tobacco plants inside an acoustic chamber, and in a greenhouse, while monitoring the plant's physiological parameters. We developed machine learning models that succeeded in identifying the condition of the plants, including dehydration level and injury, based solely on the emitted sounds. These informative sounds may also be detectable by other organisms. This work opens avenues for understanding plants and their interactions with the environment and may have significant impact on agriculture.

Developmental Responses to Water and Salinity in Root Systems.

Roots provide the primary mechanism that plants use to absorb water and nutrients from their environment. These functions are dependent on developmental mechanisms that direct root growth and branching into regions of soil where these resources are relatively abundant. Water is the most limiting factor for plant growth, and its availability is determined by the weather, soil structure, and salinity. In this review, we define the developmental pathways that regulate the direction of growth and branching pattern of the root system, which together determine the expanse of soil from which a plant can access water. The ability of plants to regulate development in response to the spatial distribution of water is a focus of many recent studies and provides a model for understanding how biological systems utilize positional cues to affect signaling and morphogenesis. A better understanding of these processes will inform approaches to improve crop water use efficiency to more sustainably feed a growing population.

Evolution and functional divergence of glycosyltransferase genes shaped the quality and cold tolerance of tea plants.

Plant glycosyltransferases (UGTs) play a key role in plant growth and metabolism. Here, we examined the evolutionary landscape among UGTs in 28 fully sequenced species from early algae to angiosperms. Our findings revealed a distinctive expansion and contraction of UGTs in the G and H groups in tea (Camellia sinensis), respectively. Whole-genome duplication and tandem duplication events jointly drove the massive expansion of UGTs, and the interplay of natural and artificial selection has resulted in marked functional divergence within the G group of the sinensis-type tea population. In Cluster II of group G, differences in substrate selection (e.g., Abscisic Acid) of the enzymes encoded by UGT genes led to their functional diversification, and these genes influence tolerance to abiotic stresses such as low temperature and drought via different modes of positive and negative regulation, respectively. UGTs in Cluster III of the G group have diverse aroma substrate preferences, which contributes a diverse aroma spectrum of the sinensis-type tea population. All Cluster III genes respond to low-temperature stress, whereas UGTs within Cluster III-1, shaped by artificial selection, are unresponsive to drought. This suggests that artificial selection of tea plants focused on improving quality and cold tolerance as primary targets.

Constitutively active B2 Raf-like kinases are required for drought-responsive gene expression upstream of ABA-activated SnRK2 kinases.

Osmotic stresses, such as drought and high salinity, adversely affect plant growth and productivity. The phytohormone abscisic acid (ABA) accumulates in response to osmotic stress and enhances stress tolerance in plants by triggering multiple physiological responses through ABA signaling. Subclass III SNF1-related protein kinases 2 (SnRK2s) are key regulators of ABA signaling. Although SnRK2s have long been considered to be self-activated by autophosphorylation after release from PP2C-mediated inhibition, they were recently revealed to be activated by two independent subfamilies of group B Raf-like kinases, B2-RAFs and B3-RAFs, under osmotic stress conditions. However, the relationship between SnRK2 phosphorylation by these RAFs and SnRK2 autophosphorylation and the individual physiological roles of each RAF subfamily remain unknown. In this study, we indicated that B2-RAFs are constantly active and activate SnRK2s when released from PP2C-mediated inhibition by ABA-binding ABA receptors, whereas B3-RAFs are activated only under stress conditions in an ABA-independent manner and enhance SnRK2 activity. Autophosphorylation of subclass III SnRK2s is not sufficient for ABA responses, and B2-RAFs are needed to activate SnRK2s in an ABA-dependent manner. Using plants grown in soil, we found that B2-RAFs regulate subclass III SnRK2s at the early stage of drought stress, whereas B3-RAFs regulate SnRK2s at the later stage. Thus, B2-RAFs are essential kinases for the activation of subclass III SnRK2s in response to ABA under mild osmotic stress conditions, and B3-RAFs function as enhancers of SnRK2 activity under severe stress conditions.

Genome-wide mapping of DNase I hypersensitive sites revealed differential chromatin accessibility and regulatory DNA elements under drought stress in rice cultivars.

Drought stress (DS) is one of the major constraints limiting yield in crop plants including rice. Gene regulation under DS is largely governed by accessibility of the transcription factors (TFs) to their cognate cis-regulatory elements (CREs). In this study, we used DNase I hypersensitive assays followed by sequencing to identify the accessible chromatin regions under DS in a drought-sensitive (IR64) and a drought-tolerant (N22) rice cultivar. Our results indicated that DNase I hypersensitive sites (DHSs) were highly enriched at transcription start sites (TSSs) and numerous DHSs were detected in the promoter regions. DHSs were concurrent with epigenetic marks and the genes harboring DHSs in their TSS and promoter regions were highly expressed. In addition, DS induced changes in DHSs (∆DHSs) in TSS and promoter regions were positively correlated with upregulation of several genes involved in drought/abiotic stress response, those encoding TFs and located within drought-associated quantitative trait loci, much preferentially in the drought-tolerant cultivar. The CREs representing the binding sites of TFs involved in DS response were detected within the ∆DHSs, suggesting differential accessibility of TFs to their cognate sites under DS in different rice cultivars, which may be further deployed for enhancing drought tolerance in rice.

Arabidopsis DREB26/ERF12 and its close relatives regulate cuticular wax biosynthesis under drought stress condition.

Land plants have evolved a hydrophobic cuticle on the surface of aerial organs as an adaptation to ensure survival in terrestrial environments. Cuticle is mainly composed of lipids, namely cutin and intracuticular wax, with epicuticular wax deposited on plant surface. The composition and permeability of cuticle have a large influence on its ability to protect plants against drought stress. However, the regulatory mechanisms underlying cuticular wax biosynthesis in response to drought stress have not been fully elucidated. Here, we identified three AP2/ERF transcription factors (DREB26/ERF12, ERF13 and ERF14) involved in the regulation of water permeability of the plant surface. Transmission electron microscopy revealed thicker cuticle on the leaves of DREB26-overexpressing (DREB26OX) plants, and thinner cuticle on the leaves of transgenic plants expressing SRDX repression domain-fused DREB26 (DREB26SR). Genes involved in cuticular wax formation were upregulated in DREB26OX and downregulated in DREB26SR. The levels of very-long chain (VLC) alkanes, which are a major wax component, increased in DREB26OX leaves and decreased in DREB26SR leaves. Under dehydration stress, water loss was reduced in DREB26OX and increased in DREB26SR. The erf12/13/14 triple mutant showed delayed growth, decreased leaf water content, and reduced drought-inducible VLC alkane accumulation. Taken together, our results indicate that the DREB26/ERF12 and its closed family members, ERF13 and ERF14, play an important role in cuticular wax biosynthesis in response to drought stress. The complex transcriptional cascade involved in the regulation of cuticular wax biosynthesis under drought stress conditions is discussed.

Smart selection of soil microbes for resilient and sustainable viticulture.

The grapevine industry is of high economic importance in several countries worldwide. Its growing market demand led to an acceleration of the entire production processes, implying increasing use of water resources at the expense of environmental water balance and the hydrological cycle. Furthermore, in recent decades climate change and the consequent expansion of drought have further compromised water availability, making current agricultural systems even more fragile from ecological and economical perspectives. Consequently, farmers' income and welfare are increasingly unpredictable and unstable. Therefore, it is urgent to improve the resilience of vineyards, and of agro-ecosystems in general, by developing sustainable and environmentally friendly farming practices by more rational biological and natural resources use. The PRIMA project PROSIT addresses these challenges by characterizing and harnessing grapevine-associated microbiota to propose innovative and sustainable agronomic practices. PROSIT aims to determine the efficacy of natural microbiomes transferred from grapevines adapted to arid climate to commonly cultivated grapevine cultivars. In doing so it will test those natural microbiome effects on drought tolerance. This multidisciplinary project will utilize in vitro culture techniques, bioimaging, microbiological tests, metabolomics, metabarcoding and epigenetic analyses. These will be combined to shed light on molecular mechanisms triggered in plants by microbial associations upon water stress. To this end it is hoped that the project will serve as a blueprint not only for studies uncovering the microbiome role in drought stress in a wide range of species, but also for analyzing its effect on a wide range of stresses commonly encountered in modern agricultural systems.

PoWRKY69-PoVQ11 module positively regulates drought tolerance by accumulating fructose in Paeonia ostii.

Drought is a detrimental environmental factor that restricts plant growth and threatens food security throughout the world. WRKY transcription factors play vital roles in abiotic stress response. However, the roles of IIe subgroup members from WRKY transcription factor family in soluble sugar mediated drought response are largely elusive. In this study, we identified a drought-responsive IIe subgroup WRKY transcription factor, PoWRKY69, from Paeonia ostii. PoWRKY69 functioned as a positive regulator in response to drought stress with nucleus expression and transcriptional activation activity. Silencing of PoWRKY69 increased plants sensitivity to drought stress, whereas conversely, overexpression of PoWRKY69 enhanced drought tolerance in plants. As revealed by yeast one-hybrid, electrophoretic mobility shift assay, and luciferase reporter assays, PoWRKY69 could directly bind to the W-box element of fructose-1,6-bisphosphate aldolase 5 (PoFBA5) promoter, contributing to a cascade regulatory network to activate PoFBA5 expression. Furthermore, virus-induced gene silencing and overexpression assays demonstrated that PoFBA5 functioned positively in response to drought stress by accumulating fructose to alleviate membrane lipid peroxidation and activate antioxidant defense system, these changes resulted in reactive oxygen species scavenging. According to yeast two-hybrid, bimolecular fluorescence complementation, and firefly luciferase complementation imaging assays, valine-glutamine 11 (PoVQ11) physically interacted with PoWRKY69 and led to an enhanced activation of PoWRKY69 on PoFBA5 promoter activity. This study broadens our understanding of WRKY69-VQ11 module regulated fructose accumulation in response to drought stress and provides feasible molecular measures to create novel drought-tolerant germplasm of P. ostii.

The BTB-BACK-TAZ domain protein MdBT2 reduces drought resistance by weakening the positive regulatory effect of MdHDZ27 on apple drought tolerance via ubiquitination.

Drought stress is one of the dominating challenges to the growth and productivity in crop plants. Elucidating the molecular mechanisms of plants responses to drought stress is fundamental to improve fruit quality. However, such molecular mechanisms are poorly understood in apple (Malus domestica Borkh.). In this study, we explored that the BTB-BACK-TAZ protein, MdBT2, negatively modulates the drought tolerance of apple plantlets. Moreover, we identified a novel Homeodomain-leucine zipper (HD-Zip) transcription factor, MdHDZ27, using a yeast two-hybrid (Y2H) screen with MdBT2 as the bait. Overexpression of MdHDZ27 in apple plantlets, calli, and tomato plantlets enhanced their drought tolerance by promoting the expression of drought tolerance-related genes [responsive to dehydration 29A (MdRD29A) and MdRD29B]. Biochemical analyses demonstrated that MdHDZ27 directly binds to and activates the promoters of MdRD29A and MdRD29B. Furthermore, in vitro and in vivo assays indicate that MdBT2 interacts with and ubiquitinates MdHDZ27, via the ubiquitin/26S proteasome pathway. This ubiquitination results in the degradation of MdHDZ27 and weakens the transcriptional activation of MdHDZ27 on MdRD29A and MdRD29B. Finally, a series of transgenic analyses in apple plantlets further clarified the role of the relationship between MdBT2 and MdHDZ27, as well as the effect of their interaction on drought resistance in apple plantlets. Collectively, our findings reveal a novel mechanism by which the MdBT2-MdHDZ27 regulatory module controls drought tolerance, which is of great significance for enhancing the drought resistance of apple and other plants.

The transcription factor PtoMYB142 enhances drought tolerance in Populus tomentosa by regulating gibberellin catabolism.

Drought stress caused by global warming has resulted in significant tree mortality, driving the evolution of water conservation strategies in trees. Although phytohormones have been implicated in morphological adaptations to water deficits, the molecular mechanisms underlying these processes in woody plants remain unclear. Here, we report that overexpression of PtoMYB142 in Populus tomentosa results in a dwarfism phenotype with reduced leaf cell size, vessel lumen area, and vessel density in the stem xylem, leading to significantly enhanced drought resistance. We found that PtoMYB142 modulates gibberellin catabolism in response to drought stress by binding directly to the promoter of PtoGA2ox4, a GA2-oxidase gene induced under drought stress. Conversely, knockout of PtoMYB142 by the CRISPR/Cas9 system reduced drought resistance. Our results show that the reduced leaf size and vessel area, as well as the increased vessel density, improve leaf relative water content and stem water potential under drought stress. Furthermore, exogenous GA3 application rescued GA-deficient phenotypes in PtoMYB142-overexpressing plants and reversed their drought resistance. By suppressing the expression of PtoGA2ox4, the manifestation of GA-deficient characteristics, as well as the conferred resistance to drought in PtoMYB142-overexpressing poplars, was impeded. Our study provides insights into the molecular mechanisms underlying tree drought resistance, potentially offering novel transgenic strategies to enhance tree resistance to drought.

Climate-resilient crops: Lessons from xerophytes.

Developing climate-resilient crops is critical for future food security and sustainable agriculture under current climate scenarios. Of specific importance are drought and soil salinity. Tolerance traits to these stresses are highly complex, and the progress in improving crop tolerance is too slow to cope with the growing demand in food production unless a major paradigm shift in crop breeding occurs. In this work, we combined bioinformatics and physiological approaches to compare some of the key traits that may differentiate between xerophytes (naturally drought-tolerant plants) and mesophytes (to which the majority of the crops belong). We show that both xerophytes and salt-tolerant mesophytes have a much larger number of copies in key gene families conferring some of the key traits related to plant osmotic adjustment, abscisic acid (ABA) sensing and signalling, and stomata development. We show that drought and salt-tolerant species have (i) higher reliance on Na for osmotic adjustment via more diversified and efficient operation of Na+ /H+ tonoplast exchangers (NHXs) and vacuolar H+ - pyrophosphatase (VPPases); (ii) fewer and faster stomata; (iii) intrinsically lower ABA content; (iv) altered structure of pyrabactin resistance/pyrabactin resistance-like (PYR/PYL) ABA receptors; and (v) higher number of gene copies for protein phosphatase 2C (PP2C) and sucrose non-fermenting 1 (SNF1)-related protein kinase 2/open stomata 1 (SnRK2/OST1) ABA signalling components. We also show that the past trends in crop breeding for Na+ exclusion to improve salinity stress tolerance are counterproductive and compromise their drought tolerance. Incorporating these genetic insights into breeding practices could pave the way for more drought-tolerant and salt-resistant crops, securing agricultural yields in an era of climate unpredictability.

Complex plant responses to drought and heat stress under climate change.

Global climate change is predicted to result in increased yield losses of agricultural crops caused by environmental conditions. In particular, heat and drought stress are major factors that negatively affect plant development and reproduction, and previous studies have revealed how these stresses induce plant responses at physiological and molecular levels. Here, we provide a comprehensive overview of current knowledge concerning how drought, heat, and combinations of these stress conditions affect the status of plants, including crops, by affecting factors such as stomatal conductance, photosynthetic activity, cellular oxidative conditions, metabolomic profiles, and molecular signaling mechanisms. We further discuss stress-responsive regulatory factors such as transcription factors and signaling factors, which play critical roles in adaptation to both drought and heat stress conditions and potentially function as 'hubs' in drought and/or heat stress responses. Additionally, we present recent findings based on forward genetic approaches that reveal natural variations in agricultural crops that play critical roles in agricultural traits under drought and/or heat conditions. Finally, we provide an overview of the application of decades of study results to actual agricultural fields as a strategy to increase drought and/or heat stress tolerance. This review summarizes our current understanding of plant responses to drought, heat, and combinations of these stress conditions.

'Against all floods': plant adaptation to flooding stress and combined abiotic stresses.

Current climate change brings with it a higher frequency of environmental stresses, which occur in combination rather than individually leading to massive crop losses worldwide. In addition to, for example, drought stress (low water availability), also flooding (excessive water) can threaten the plant, causing, among others, an energy crisis due to hypoxia, which is responded to by extensive transcriptional, metabolic and growth-related adaptations. While signalling during flooding is relatively well understood, at least in model plants, the molecular mechanisms of combinatorial flooding stress responses, for example, flooding simultaneously with salinity, temperature stress and heavy metal stress or sequentially with drought stress, remain elusive. This represents a significant gap in knowledge due to the fact that dually stressed plants often show unique responses at multiple levels not observed under single stress. In this review, we (i) consider possible effects of stress combinations from a theoretical point of view, (ii) summarize the current state of knowledge on signal transduction under single flooding stress, (iii) describe plant adaptation responses to flooding stress combined with four other abiotic stresses and (iv) propose molecular components of combinatorial flooding (hypoxia) stress adaptation based on their reported dual roles in multiple stresses. This way, more future emphasis may be placed on deciphering molecular mechanisms of combinatorial flooding stress adaptation, thereby potentially stimulating development of molecular tools to improve plant resilience towards multi-stress scenarios.

A Solanum lycopersicum polyamine oxidase contributes to the control of plant growth, xylem differentiation, and drought stress tolerance.

Polyamines are involved in several plant physiological processes. In Arabidopsis thaliana, five FAD-dependent polyamine oxidases (AtPAO1 to AtPAO5) contribute to polyamine homeostasis. AtPAO5 catalyzes the back-conversion of thermospermine (T-Spm) to spermidine and plays a role in plant development, xylem differentiation, and abiotic stress tolerance. In the present study, to verify whether T-Spm metabolism can be exploited as a new route to improve stress tolerance in crops and to investigate the underlying mechanisms, tomato (Solanum lycopersicum) AtPAO5 homologs were identified (SlPAO2, SlPAO3, and SlPAO4) and CRISPR/Cas9-mediated loss-of-function slpao3 mutants were obtained. Morphological, molecular, and physiological analyses showed that slpao3 mutants display increased T-Spm levels and exhibit changes in growth parameters, number and size of xylem elements, and expression levels of auxin- and gibberellin-related genes compared to wild-type plants. The slpao3 mutants are also characterized by improved tolerance to drought stress, which can be attributed to a diminished xylem hydraulic conductivity that limits water loss, as well as to a reduced vulnerability to embolism. Altogether, this study evidences conservation, though with some significant variations, of the T-Spm-mediated regulatory mechanisms controlling plant growth and differentiation across different plant species and highlights the T-Spm role in improving stress tolerance while not constraining growth.

OsPUB75-OsHDA716 mediates deactivation and degradation of OsbZIP46 to negatively regulate drought tolerance in rice.

Histone deacetylases (HDACs) play crucial roles in plant stress responses via modification of histone as well as non-histone proteins; however, how HDAC-mediated deacetylation of non-histone substrates affects protein functions remains elusive. Here, we report that the Reduced Potassium Dependency3/Histone Deacetylase1 (RPD3/HDA1)-type histone deacetylase OsHDA716 and plant U-box (PUB) E3 ubiquitin ligase OsPUB75 form a complex to regulate rice drought response via deactivation and degradation of basic leucine zipper (bZIP) transcription factor OsbZIP46 in rice (Oryza sativa). OsHDA716 decreases ABA-induced drought tolerance, and mechanistic investigations showed that OsHDA716 interacts with and deacetylates OsbZIP46, a key regulator in ABA signaling and drought response, thus inhibiting its transcriptional activity. Furthermore, OsHDA716 recruits OsPUB75 to facilitate ubiquitination and degradation of deacetylated OsbZIP46. Therefore, the OsPUB75-OsHDA716 complex exerts double restrictions on the transcriptional activity and protein stability of OsbZIP46, leading to repression of downstream drought-responsive gene expression and consequently resulting in reduced drought tolerance. Conversely, OsbZIP46 acts as an upstream repressor to repress OsHDA716 expression, and therefore OsHDA716 and OsbZIP46 form an antagonistic pair to reciprocally inhibit each other. Genetic evidence showed that OsHDA716 works with OsbZIP46 in a common pathway to antagonistically regulate rice drought response, revealing that plants can fine-tune stress responses by the complex interplay between chromatin regulators and transcription factors. Our findings unveil an acetylation-dependent regulatory mechanism governing protein functions and shed light on the precise coordination of activity and stability of key transcription factors through a combination of different post-translational modifications.

MYB30-INTERACTING E3 LIGASE 1 regulates LONELY GUY 5-mediated cytokinin metabolism to promote drought tolerance in cotton.

Ubiquitination plays important roles in modulating the abiotic stress tolerance of plants. Drought seriously restricts agricultural production, but how ubiquitination participates in regulating drought tolerance remains largely unknown. Here, we identified a drought-inducible gene, MYB30-INTERACTING E3 LIGASE 1 (GhMIEL1), which encodes a RING E3 ubiquitin ligase in cotton (Gossypium hirsutum). GhMIEL1 was strongly induced by polyethylene glycol (PEG-6000) and the phytohormone abscisic acid (ABA). Overexpression and knockdown of GhMIEL1 in cotton substantially enhanced and reduced drought tolerance, respectively. GhMIEL1 interacted with the MYB transcription factor GhMYB66 and could ubiquitinate and degrade it in vitro. GhMYB66 directly bound to the LONELY GUY 5 (GhLOG5) promoter, a gene encoding cytokinin riboside 5'-monophosphate phosphoribohydrolase, to repress its transcription. Overexpression of GhMIEL1 and silencing of GhMYB66 altered the homeostasis of cytokinin of plant roots, increased total root length and number of root tips, and enhanced plant drought tolerance. Conversely, silencing GhLOG5 decreased total root length and number of root tips and reduced plant drought tolerance. Our studies reveal that the GhMIEL1-GhMYB66-GhLOG5 module positively regulates drought tolerance in cotton, which deepens our understanding of plant ubiquitination-mediated drought tolerance and provides insights for improving drought tolerance.

Microbe-induced drought tolerance by ABA-mediated root architecture and epigenetic reprogramming.

The use of beneficial microbes to mitigate drought stress tolerance of plants is of great potential albeit little understood. We show here that a root endophytic desert bacterium, Pseudomonas argentinensis strain SA190, enhances drought stress tolerance in Arabidopsis. Transcriptome and genetic analysis demonstrate that SA190-induced root morphogenesis and gene expression is mediated via the plant abscisic acid (ABA) pathway. Moreover, we demonstrate that SA190 primes the promoters of target genes in an epigenetic ABA-dependent manner. Application of SA190 priming on crops is demonstrated for alfalfa, showing enhanced performance under drought conditions. In summary, a single beneficial root bacterial strain can help plants to resist drought conditions.

Drought response revealed by chromatin organization variation and transcriptional regulation in cotton.

BACKGROUND: Cotton is a major world cash crop and an important source of natural fiber, oil, and protein. Drought stress is becoming a restrictive factor affecting cotton production. To facilitate the development of drought-tolerant cotton varieties, it is necessary to study the molecular mechanism of drought stress response by exploring key drought-resistant genes and related regulatory factors. RESULTS: In this study, two cotton varieties, ZY007 (drought-sensitive) and ZY168 (drought-tolerant), showing obvious phenotypic differences under drought stress, were selected. A total of 25,898 drought-induced genes were identified, exhibiting significant enrichment in pathways related to plant stress responses. Under drought induction, At subgenome expression bias was observed at the whole-genome level, which may be due to stronger inhibition of Dt subgenome expression. A gene co-expression module that was significantly associated with drought resistance was identified. About 90% of topologically associating domain (TAD) boundaries were stable, and 6613 TAD variation events were identified between the two varieties under drought. We identified 92 genes in ZY007 and 98 in ZY168 related to chromatin 3D structural variation and induced by drought stress. These genes are closely linked to the cotton response to drought stress through canonical hormone-responsive pathways, modulation of kinase and phosphatase activities, facilitation of calcium ion transport, and other related molecular mechanisms. CONCLUSIONS: These results lay a foundation for elucidating the molecular mechanism of the cotton drought response and provide important regulatory locus and gene resources for the future molecular breeding of drought-resistant cotton varieties.

Raffinose positively regulates maize drought tolerance by reducing leaf transpiration.

Drought stress is one of the major constraints of global crop production. Raffinose, a non-reducing trisaccharide, has been considered to regulate positively the plant drought stress tolerance; however, evidence that augmenting raffinose production in leaves results in enhanced plant drought stress tolerance is lacking. The biochemical mechanism through which raffinose might act to mitigate plant drought stress remains unidentified. ZmRAFS encodes Zea mays RAFFINOSE SYNTHASE, a key enzyme that transfers galactose from the galactoside galactinol to sucrose for raffinose production. Overexpression of ZmRAFS in maize increased the RAFS protein and the raffinose content and decreased the water loss of leaves and enhanced plant drought stress tolerance. The biomass of the ZmRAFS overexpressing plants was similar to that of non-transgenic control plants when grown under optimal conditions, but was significantly greater than that of non-transgenic plants when grown under drought stress conditions. In contrast, the percentage of water loss of the detached leaves from two independent zmrafs mutant lines, incapable of synthesizing raffinose, was greater than that from null segregant controls and this phenomenon was partially rescued by supplementation of raffinose to detached zmrafs leaves. In addition, while there were differences in water loss among different maize lines, there was no difference in stomata density or aperture. Taken together, our work demonstrated that overexpression of the ZmRAFS gene in maize, in contrast to Arabidopsis, increased the raffinose content in leaves, assisted the leaf to retain water, and enhanced the plant drought stress tolerance without causing a detectable growth penalty.

Abscisic acid collaborates with lignin and flavonoid to improve pre-silking drought tolerance by tuning stem elongation and ear development in maize (Zea mays L.).

Drought is a major abiotic stress reducing maize (Zea mays) yield worldwide especially before and during silking. The mechanism underlying drought tolerance in maize and the roles of different organs have not been elucidated. Hence, we conducted field trials under pre-silking drought conditions using two maize genotypes: FM985 (drought-tolerant) and ZD958 (drought-sensitive). The two genotypes did not differ in plant height, grain number, and yield under control conditions. However, the grain number per ear and the yield of FM985 were 38.1 and 35.1% higher and plants were 17.6% shorter than ZD958 under drought conditions. More 13 C photosynthates were transported to the ear in FM985 than in ZD958, which increased floret fertility and grain number. The number of differentially expressed genes was much higher in stem than in other organs. Stem-ear interactions are key determinants of drought tolerance, in which expression of genes related to abscisic acid, lignin, and flavonoid biosynthesis and carbon metabolism in the stem was induced by drought, which inhibited stem elongation and promoted assimilate allocation to the ear in FM985. In comparison with ZD958, the activities of trehalose 6-phosphate phosphatase and sucrose non-fermentation-associated kinase 1 were higher in the stem and lower in the kernel of FM985, which facilitated kernel formation. These results reveal that, beyond the ear response, stem elongation is involved in the whole process of drought tolerance before silking. Abscisic acid together with trehalose 6-phosphate, lignin, and flavonoid suppresses stem elongation and allocates assimilates into the ear, providing a novel and systematic regulatory pathway for drought tolerance in maize.