Activation of dimeric ABA receptors elicits guard cell closure, ABA-regulated gene expression, and drought tolerance

Crystal structure and mechanistic studies of the PPM1D serine/threonine phosphatase catalytic domain

Protein phosphatase 1D (PPM1D, Wip1) is induced by the tumor suppressor p53 during DNA damage response signaling and acts as an oncoprotein in several human cancers. Although PPM1D is a potential therapeutic target, insights into its atomic structure were challenging due to flexible regions unique to this family member. Here we report the first crystal structure of the PPM1D catalytic domain to 1.8 Å resolution. The structure reveals the active site with two Mg2+ ions bound, similar to other structures. The flap subdomain and B-loop, which are crucial for substrate recognition and catalysis, were also resolved, with the flap forming two short helices and three short β-strands that are followed by an irregular loop. Unexpectedly, a nitrogen-oxygen-sulfur bridge was identified in the catalytic domain. Molecular dynamics simulations and kinetic studies provided further mechanistic insights into the regulation of PPM1D catalytic activity. In particular, the kinetic experiments demonstrated a magnesium concentration-dependent lag in PPM1D attaining steady-state velocity, a feature of hysteretic enzymes that show slow transitions compared with catalytic turnover. All combined, these results advance the understanding of PPM1D function and will support the development of PPM1D-targeted therapeutics.

Abscisic acid-mediated guard cell metabolism regulation

Abscisic acid (ABA) is crucial for plant water deficit (WD) acclimation, but how the interplay between ABA and guard cell (GC) metabolism aids plant WD acclimation remains unclear. Here, we investigated how ABA regulates GC metabolism and how this contributes to plant WD acclimation using tomato wild type (WT) and the ABA-deficient sitiens mutant. These genotypes were characterized at physiological, metabolic, and transcriptional levels under recurring WD periods and were used to perform a13C-glucose labelling experiment using isolated guard cells following exogenously applied ABA. ABA deficiency altered the level of sugars and organic acids in GCs in both irrigated and WD plants and the dynamic of accumulation/degradation of these compounds in GCs during the dark-to-light transition. WD-induced metabolic changes were more pronounced in sitiens than WT GCs. Results from the 13C-labelling experiment indicate that ABA is required for the glycolytic fluxes toward malate and acts as a negative regulator of a putative sucrose substrate cycle. The expression of key ABA-biosynthetic genes was higher in WT than in sitiens GCs after two cycles of WD. Additionally, the intrinsic leaf water use efficiency increased only in WT after the second WD cycle, compared to sitiens. Our results highlight that ABA deficiency disrupts the homeostasis of GC primary metabolism and the WD memory, negatively affecting plant WD acclimation. Our study demonstrates which metabolic pathways are activated by WD and/or regulated by ABA in GCs, which improves our understanding of plant WD acclimation, with clear consequences for plant metabolic engineering in the future.

Rapeseed PP2C37 Interacts with PYR/PYL Abscisic Acid Receptors and Negatively Regulates Drought Tolerance

Global water deficit is a severe abiotic stress threatening the yielding and quality of crops. Abscisic acid (ABA) is a phytohormone that mediates drought tolerance. Protein kinases and phosphatases function as molecular switches in eukaryotes. Protein phosphatases type 2C (PP2Cs) are a major family that play essential roles in ABA signaling and stress responses. However, the role and underlying mechanism of PP2C in rapeseed (Brassica napus L.) mediating drought response has not been reported yet. Here, we characterized a PP2C family member, BnaPP2C37, and its expression level was highly induced by ABA and dehydration treatments. It negatively regulates drought tolerance in rapeseed. We further identified that BnaPP2C37 interacted with multiple PYR/PYL receptors and a drought regulator BnaCPK5 (calcium-dependent protein kinase 5) through yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. Specifically, BnaPYL1 and BnaPYL9 repress BnaPP2C37 phosphatase activity. Moreover, the pull-down assay and phosphatase assays show BnaPP2C37 interacts with BnaCPK5 to dephosphorylate BnaCPK5 and its downstream BnaABF3. Furthermore, a dual-luciferase assay revealed BnaPP2C37 transcript level was enhanced by BnaABF3 and BnaABF4, forming a negative feedback regulation to ABA response. In summary, we identified that BnaPP2C37 functions negatively in drought tolerance of rapeseed, and its phosphatase activity is repressed by BnaPYL1/9 whereas its transcriptional level is upregulated by BnaABF3/4.

Highlights in gibberellin research: A tale of the dwarf and the slender

It has been almost a century since biologically active gibberellin (GA) was isolated. Here, we give a historical overview of the early efforts in establishing the GA biosynthesis and catabolism pathway, characterizing the enzymes for GA metabolism, and elucidating their corresponding genes. We then highlight more recent studies that have identified the GA receptors and early GA signaling components (DELLA repressors and F-box activators), determined the molecular mechanism of DELLA-mediated transcription reprograming, and revealed how DELLAs integrate multiple signaling pathways to regulate plant vegetative and reproductive development in response to internal and external cues. Finally, we discuss the GA transporters and their roles in GA-mediated plant development.

Regulatory networks in plant responses to drought and cold stress

Drought and cold represent distinct types of abiotic stress, each initiating unique primary signaling pathways in response to dehydration and temperature changes, respectively. However, a convergence at the gene regulatory level is observed where a common set of stress-responsive genes is activated to mitigate the impacts of both stresses. In this review, we explore these intricate regulatory networks, illustrating how plants coordinate distinct stress signals into a collective transcriptional strategy. We delve into the molecular mechanisms of stress perception, stress signaling, and the activation of gene regulatory pathways, with a focus on insights gained from model species. By elucidating both the shared and distinct aspects of plant responses to drought and cold, we provide insight into the adaptive strategies of plants, paving the way for the engineering of stress-resilient crop varieties that can withstand a changing climate.

Role of Microbes in Alleviating Crop Drought Stress: A Review

Drought stress is an annual global phenomenon that has devastating effects on crop production, so numerous studies have been conducted to improve crop drought resistance. Plant-associated microbiota play a crucial role in crop health and growth; however, we have a limited understanding of the key processes involved in microbiome-induced crop adaptation to drought stress. In this review, we summarize the adverse effects of drought stress on crop growth in terms of germination, photosynthesis, nutrient uptake, biomass, and yield, with a focus on the response of soil microbial communities to drought stress and plant-microbe interactions under drought stress. Moreover, we review the morpho-physiological, biochemical, and molecular mechanisms underlying the mitigation effect of microbes on crop drought stress. Finally, we highlight future research directions, including the characterization of specific rhizosphere microbiome species with corresponding root exudates and the efficiency of rhizobacteria inoculants under drought conditions. Such research will advance our understanding of the complex interactions between crops and microbes and improve crop resistance to drought stress through the application of beneficial drought-adaptive microbes.

Constitutive activation of ABA receptors in Arabidopsis reveals unique regulatory circuitries

Abscisic acid (ABA) is best known for regulating the responses to abiotic stressors. Thus, applications of ABA signaling pathways are considered promising targets for securing yield under stress. ABA levels rise in response to abiotic stress, mounting physiological and metabolic responses that promote plant survival under unfavorable conditions. ABA elicits its effects by binding to a family of soluble receptors found in monomeric and dimeric states, differing in their affinity to ABA and co-receptors. However, the in vivo significance of the biochemical differences between these receptors remains unclear. We took a gain-of-function approach to study receptor-specific functionality. First, we introduced activating mutations that enforce active ABA-bound receptor conformation. We then transformed Arabidopsis ABA-deficient mutants with the constitutive receptors and monitored suppression of the ABA deficiency phenotype. Our findings suggest that PYL4 and PYL5, monomeric ABA receptors, have differential activity in regulating transpiration and transcription of ABA biosynthesis and stress response genes. Through genetic and metabolic data, we demonstrate that PYR1, but not PYL5, is sufficient to activate the ABA positive feedback mechanism. We propose that ABA signaling - from perception to response - flows differently when triggered by different PYLs, due to tissue and transcription barriers, thus resulting in distinct circuitries.

Root transcriptomic provides insights on molecular mechanisms involved in the tolerance to water deficit in Pisum sativum inoculated with Pseudomonas sp

MAIN CONCLUSION

Root transcriptomics and biochemical analyses in water-stressed Pisum sativum plants inoculated with Pseudomonas spp. suggested preservation of ABA-related pathway and ROS detoxification, resulting in an improved tolerance to stress. Drought already affects agriculture in large areas of the globe and, due to climate change, these areas are predicted to become increasingly unsuitable for agriculture. For several years, plant growth-promoting bacteria (PGPB) have been used to improve legume yields, but many aspects of this interaction are still unclear. To elucidate the mechanisms through which root-associated PGPB can promote plant growth in dry environments, we investigated the response of pea plants inoculated with a potentially beneficial Pseudomonas strain (PK6) and subjected to two different water regimes. Combined biometric, biochemical, and root RNA-seq analyses revealed that PK6 improved pea growth specifically under water deficit, as inoculated plants showed an increased biomass, larger leaves, and longer roots. Abscisic acid (ABA) and proline quantification, together with the transcriptome analysis, suggested that PK6-inoculated plant response to water deficit was more diversified compared to non-inoculated plants, involving alternative metabolic pathways for the detoxification of reactive oxygen species (ROS) and the preservation of the ABA stress signaling pathway. We suggest that the metabolic response of PK6-inoculated plants was more effective in their adaptation to water deprivation, leading to their improved biometric traits. Besides confirming the positive role that PGPB can have in the growth of a legume crop under adverse conditions, this study offers novel information on the mechanisms regulating plant-bacteria interaction under varying water availability. These mechanisms and the involved genes could be exploited in the future for the development of legume varieties, which can profitably grow in dry climates.

Resolving binding pathways and solvation thermodynamics of plant hormone receptors

Plant hormones are small molecules that regulate plant growth, development, and responses to biotic and abiotic stresses. They are specifically recognized by the binding site of their receptors. In this work, we resolved the binding pathways for eight classes of phytohormones (auxin, jasmonate, gibberellin, strigolactone, brassinosteroid, cytokinin, salicylic acid, and abscisic acid) to their canonical receptors using extensive molecular dynamics simulations. Furthermore, we investigated the role of water displacement and reorganization at the binding site of the plant receptors through inhomogeneous solvation theory. Our findings predict that displacement of water molecules by phytohormones contributes to free energy of binding via entropy gain and is associated with significant free energy barriers for most systems analyzed. Also, our results indicate that displacement of unfavorable water molecules in the binding site can be exploited in rational agrochemical design. Overall, this study uncovers the mechanism of ligand binding and the role of water molecules in plant hormone perception, which creates new avenues for agrochemical design to target plant growth and development.

Inspired by Nature: Isostere Concepts in Plant Hormone Chemistry

Chemical concepts such as isosteres and scaffold hopping have proven to be powerful tools in agrochemical innovation processes. They offer opportunities to modify known molecular lead structures with the aim to improve a range of parameters, including biological efficacy and spectrum, physicochemical properties, stability, and toxicity. While recent biochemical insights into plant-specific receptors and signaling pathways trigger the discovery of the first lead structures, the disclosure of such a new chemical structure sparks a broad range of synthesis activities giving rise to diverse chemical innovation and often a considerable boost in biological activity. Herein, recent examples of isostere concepts in plant-hormone chemistry will be discussed, outlining how synthetic creativity can broaden the scope of natural product chemistry and giving rise to new opportunities in research fields such as abiotic stress tolerance and growth promotion.

An ecological transcriptome approach to capture the molecular and physiological mechanisms of mass flowering in Shorea curtisii

Climatic factors have commonly been attributed as the trigger of general flowering, a unique community-level mass flowering phenomenon involving most dipterocarp species that forms the foundation of Southeast Asian tropical rainforests. This intriguing flowering event is often succeeded by mast fruiting, which provides a temporary yet substantial burst of food resources for animals, particularly frugivores. However, the physiological mechanism that triggers general flowering, particularly in dipterocarp species, is not well understood largely due to its irregular and unpredictable occurrences in the tall and dense forests. To shed light on this mechanism, we employed ecological transcriptomic analyses on an RNA-seq dataset of a general flowering species, Shorea curtisii (Dipterocarpaceae), sequenced from leaves and buds collected at multiple vegetative and flowering phenological stages. We assembled 64,219 unigenes from the transcriptome of which 1,730 and 3,559 were differentially expressed in the leaf and the bud, respectively. Differentially expressed unigene clusters were found to be enriched with homologs of Arabidopsis thaliana genes associated with response to biotic and abiotic stresses, nutrient level, and hormonal treatments. When combined with rainfall data, our transcriptome data reveals that the trees were responding to a brief period of drought prior to the elevated expression of key floral promoters and followed by differential expression of unigenes that indicates physiological changes associated with the transition from vegetative to reproductive stages. Our study is timely for a representative general flowering dipterocarp species that occurs in forests that are under the constant threat of deforestation and climate change as it pinpoints important climate sensitive and flowering-related homologs and offers a glimpse into the cascade of gene expression before and after the onset of floral initiation.

PoWRKY71 is involved in Paeonia ostii resistance to drought stress by directly regulating light-harvesting chlorophyll a/b-binding 151 gene

Although the functions of WRKY transcription factors in drought resistance are well known, their regulatory mechanisms in response to drought by stabilising photosynthesis remain unclear. Here, a differentially expressed PoWRKY71 gene that was highly expressed in drought-treated Paeonia ostii leaves was identified through transcriptome analysis. PoWRKY71 positively responded to drought stress with significantly enhanced expression patterns and overexpressing PoWRKY71 in tobacco greatly improved plant tolerance to drought stress, whereas silencing PoWRKY71 in P. ostii resulted in a drought-intolerant phenotype. Furthermore, lower chlorophyll contents, photosynthesis, and inhibited expression of photosynthesis-related light-harvesting chlorophyll a/b-binding 151 (CAB151) gene were found in PoWRKY71-silenced P. ostii. Meanwhile, a homologous system indicated that drought treatment increased PoCAB151 promoter activity. Interactive assays revealed that PoWRKY71 directly bound on the W-box element of PoCAB151 promoter and activated its transcription. In addition, PoCAB151 overexpressing plants demonstrated increased drought tolerance, together with significantly higher chlorophyll contents and photosynthesis, whereas these indices were dramatically lower in PoCAB151-silenced P. ostii. The above results indicated that PoWRKY71 activated the expression of PoCAB151, thus stabilising photosynthesis via regulating chloroplast homeostasis and chlorophyll content in P. ostii under drought stress. This study reveals a novel drought-resistance mechanism in plants and provides a feasible strategy for improving plant drought resistance via stabilising photosynthesis.

A fungal sesquiterpene biosynthesis gene cluster critical for mutualist-pathogen transition in Colletotrichum tofieldiae

Plant-associated fungi show diverse lifestyles from pathogenic to mutualistic to the host; however, the principles and mechanisms through which they shift the lifestyles require elucidation. The root fungus Colletotrichum tofieldiae (Ct) promotes Arabidopsis thaliana growth under phosphate limiting conditions. Here we describe a Ct strain, designated Ct3, that severely inhibits plant growth. Ct3 pathogenesis occurs through activation of host abscisic acid pathways via a fungal secondary metabolism gene cluster related to the biosynthesis of sesquiterpene metabolites, including botrydial. Cluster activation during root infection suppresses host nutrient uptake-related genes and changes mineral contents, suggesting a role in manipulating host nutrition state. Conversely, disruption or environmental suppression of the cluster renders Ct3 beneficial for plant growth, in a manner dependent on host phosphate starvation response regulators. Our findings indicate that a fungal metabolism cluster provides a means by which infectious fungi modulate lifestyles along the parasitic-mutualistic continuum in fluctuating environments.

Plant Regulation Functions of Novel Phthalimide Compounds Based on AtPYL2

Novel agents contain the structure of phthalimide, which has antibacterial, insecticidal, and herbicidal activities. Recently, studies reported that these compounds can bind to plant hormone receptors and play important regulatory roles. In this study, the functions of agents were studied with in vitro and in vivo assays. The abscisic acid (ABA) receptor pyrabactin resistant-like 2 (PYL2) protein in Arabidopsis thaliana was expressed, purified, and crystallized; the analysis results of the crystal structure showed three AtPYL2 subunits in each asymmetric unit. The affinity of compounds Z1-Z11 to the AtPYL2 protein was tested by microscale thermophoresis (MST) and then verified by isothermal titration calorimetry (ITC). Furthermore, the binding pockets were found using molecular docking to verify the target relationships. Relevant in vivo assays for seed germination and a root growth assay were conducted, with the plant samples being treated with target compounds. The results show that the compounds Z3, Z5, and Z10 target AtPYL2 and that the dissociation constants for binding by MST were 3.59, 3.54, and 3.97 μmol/L, respectively, among them, and the molecular docking results showed that compounds Z3, Z5, and Z10 formed hydrophobic interactions with amino acid residues through hydrogen or halogen bonding. This highlights their potential as an ABA receptor protein agonist. On the other hand, in vivo, compounds Z3, Z5, and Z10 had different inhibitory effects on seed germination, with compound Z5 inhibiting the root growth of A. thaliana and compound Z10 affecting root growth. In conclusion, these compounds could regulate plant growth and could be further developed as new plant-regulating agents.

PKL is stabilized by MMS21 to negatively regulate Arabidopsis drought tolerance through directly repressing AFL1 transcription

Drought stress causes substantial losses in crop production per year worldwide, threatening global food security. Identification of the genetic components underlying drought tolerance in plants is of great importance. In this study, we report that loss-of-function of the chromatin-remodeling factor PICKLE (PKL), which is involved in repression of transcription, enhances drought tolerance of Arabidopsis. At first, we find that PKL interacts with ABI5 to regulate seed germination, but PKL regulates drought tolerance independently of ABI5. Then, we find that PKL is necessary for repressing the drought-tolerant gene AFL1, which is responsible for the drought-tolerant phenotype of pkl mutant. Genetic complementation tests demonstrate that the Chromo domain and ATPase domain but not the PHD domain are required for the function of PKL in regulating drought tolerance. Interestingly, we find that the DNA-binding domain (DBD) is essential for the protein stability of PKL. Furthermore, we demonstrate that the SUMO E3 ligase MMS21 interacts with and enhances the protein stability of PKL. Genetic interaction analysis shows that MMS21 and PKL additively regulate plant drought tolerance. Collectively, our findings uncover a MMS21-PKL-AFL1 module in regulating plant drought tolerance and offer insights into a novel strategy to improve crop drought tolerance.

A Potential ABA Analog to Increase Drought Tolerance in Arabidopsis thaliana

Abscisic acid (ABA) plays an important role in the response of plants to drought stress. However, the chemical structure of ABA is unstable, which severely limits its application in agricultural production. Here, we report the identification of a small molecule compound of tetrazolium as an ABA analog (named SLG1) through virtual screening. SLG1 inhibits the seedling growth and promotes drought resistance of Arabidopsis thaliana with higher stability. Yeast two-hybrid and PP2C inhibition assays show that SLG1 acts as a potent activator of multiple ABA receptors in A. thaliana. Results of molecular docking and molecular dynamics show that SLG1 mainly binds to PYL2 and PYL3 through its tetrazolium group and the combination is stable. Together, these results demonstrate that SLG1, as an ABA analogue, protects A. thaliana from drought stress. Moreover, the newly identified tetrazolium group of SLG1 that binds to ABA receptors can be used as a new option for structural modification of ABA analogs.

Persistence of Abscisic Acid Analogs in Plants: Chemical Control of Plant Growth and Physiology

Abscisic acid (ABA) is a plant hormone that regulates numerous plant processes, including plant growth, development, and stress physiology. ABA plays an important role in enhancing plant stress tolerance. This involves the ABA-mediated control of gene expression to increase antioxidant activities for scavenging reactive oxygen species (ROS). ABA is a fragile molecule that is rapidly isomerized by ultraviolet (UV) light and catabolized in plants. This makes it challenging to apply as a plant growth substance. ABA analogs are synthetic derivatives of ABA that alter ABA's functions to modulate plant growth and stress physiology. Modifying functional group(s) in ABA analogs alters the potency, selectivity to receptors, and mode of action (i.e., either agonists or antagonists). Despite current advances in developing ABA analogs with high affinity to ABA receptors, it remains under investigation for its persistence in plants. The persistence of ABA analogs depends on their tolerance to catabolic and xenobiotic enzymes and light. Accumulated studies have demonstrated that the persistence of ABA analogs impacts the potency of its effect in plants. Thus, evaluating the persistence of these chemicals is a possible scheme for a better prediction of their functionality and potency in plants. Moreover, optimizing chemical administration protocols and biochemical characterization is also critical in validating the function of chemicals. Lastly, the development of chemical and genetic controls is required to acquire the stress tolerance of plants for multiple different uses.

Transcriptome and metabolome analysis reveals key genes and secondary metabolites of Casuarina equisetifolia ssp. incana in response to drought stress

Casuarina equisetifolia is drought tolerant, salt tolerant, and able to grow in barren environments. It is often used to reduce wind damage, to prevent sand erosion, and to help establish plant communities in tropical and subtropical coastal zones. To determine the basis for its drought tolerance, we conducted transcriptomic and metabolic analyses of young branchlets under a non-drought treatment (D_0h) and 2-, 12-, and 24-h-long drought treatments (D_2h, D_12h, and D_24h). A total of 5033 and 8159 differentially expressed genes (DEGs) were identified in D_2h/D_0h and D_24h/D_0h. These DEGs were involved in plant hormone signal transduction, jasmonic acid (JA) biosynthesis, flavonoid biosynthesis, and phenylpropanoid biosynthesis. A total of 148 and 168 differentially accumulated metabolites (DAMs) were identified in D_12h/D_0h and D_24h/D_0h, which were mainly amino acids, phenolic acids, and flavonoids. In conclusion, C. equisetifolia responds to drought by regulating plant hormone signal transduction and the biosynthesis of JA, flavonoid, and phenylpropanoid. These results increase the understanding of drought tolerance in C. equisetifolia at both transcriptional and metabolic levels and provide new insights into coastal vegetation reconstruction and management.

Subtype-selective agonists of plant hormone co-receptor COI1-JAZs identified from the stereoisomers of coronatine

Severe genetic redundancy is particularly clear in gene families encoding plant hormone receptors, each subtype sharing redundant and specific functions. Genetic redundancy of receptor family members represents a major challenge for the functional dissection of each receptor subtype. A paradigmatic example is the perception of the hormone (+)-7-iso-jasmonoyl-L-isoleucine, perceived by several COI1-JAZ complexes; the specific role of each receptor subtype still remains elusive. Subtype-selective agonists of the receptor are valuable tools for analyzing the responses regulated by individual receptor subtypes. We constructed a stereoisomer library consisting of all stereochemical isomers of coronatine (COR), a mimic of the plant hormone (+)-7-iso-jasmonoyl-L-isoleucine, to identify subtype-selective agonists for COI1-JAZ co-receptors in Arabidopsis thaliana and Solanum lycopersicum. An agonist selective for the Arabidopsis COI1-JAZ9 co-receptor efficiently revealed that JAZ9 is not involved in most of the gene downregulation caused by COR, and the degradation of JAZ9-induced defense without inhibiting growth.

Structure-guided engineering of a receptor-agonist pair for inducible activation of the ABA adaptive response to drought

Strategies to activate abscisic acid (ABA) receptors and boost ABA signaling by small molecules that act as ABA receptor agonists are promising biotechnological tools to enhance plant drought tolerance. Protein structures of crop ABA receptors might require modifications to improve recognition of chemical ligands, which in turn can be optimized by structural information. Through structure-based targeted design, we have combined chemical and genetic approaches to generate an ABA receptor agonist molecule (iSB09) and engineer a CsPYL1 ABA receptor, named CsPYL1^5m, which efficiently binds iSB09. This optimized receptor-agonist pair leads to activation of ABA signaling and marked drought tolerance. No constitutive activation of ABA signaling and hence growth penalty was observed in transformed Arabidopsis thaliana plants. Therefore, conditional and efficient activation of ABA signaling was achieved through a chemical-genetic orthogonal approach based on iterative cycles of ligand and receptor optimization driven by the structure of ternary receptor-ligand-phosphatase complexes.

Effects of drought, subsequent waterlogging and redrying on growth, physiology and metabolism of wheat

With climate change, longer periods without precipitation but also heavy rains will become more frequent. Thus, understanding and predicting the implications of drought-waterlogging-redrying cycles for plants is essential. We examined the effects of such events on wheat (Triticum aestivum). We measured the impacts of subsequent water treatments (drought-waterlogging-redrying) on plant shoot and root biomass, photosynthesis and transpiration, as well as on primary metabolites and transcripts of leaves. Drought and drought followed by waterlogging severely reduced shoot and root biomass. Chlorophyll fluorescence parameters and the CO2 assimilation rate per unit leaf area were not affected by the treatments but, after the redrying phase, plants grown under the stress treatments showed a higher transpiration rate per unit leaf area and a lower instantaneous water use efficiency. Many organic acids of the citrate cycle were less concentrated in leaves of stressed plants, while most amino acids were more concentrated. Transcript analysis of genes involved in signalling and metabolism revealed different expression patterns. While some genes responded only to drought or drought followed by waterlogging, several genes were induced upon both treatments and some were still upregulated at the end of the redrying phase. We provide insights into how wheat responds to changes in water regimes, with some of the changes probably allowing the plants to cope with these stressors, at least to a certain degree.

Discovery of 2,6-Dihalopurines as Stomata Opening Inhibitors: Implication of an LRX-Mediated H+-ATPase Phosphorylation Pathway

Stomata are pores in the leaf epidermis of plants and their opening and closing regulate gas exchange and water transpiration. Stomatal movements play key roles in both plant growth and stress responses. In recent years, small molecules regulating stomatal movements have been used as a powerful tool in mechanistic studies, as well as key players for agricultural applications. Therefore, the development of new molecules regulating stomatal movement and the elucidation of their mechanisms have attracted much attention. We herein describe the discovery of 2,6-dihalopurines, AUs, as a new stomatal opening inhibitor, and their mechanistic study. Based on biological assays, AUs may involve in the pathway related with plasma membrane H⁺-ATPase phosphorylation. In addition, we identified leucine-rich repeat extensin proteins (LRXs), LRX3, LRX4 and LRX5 as well as RALF, as target protein candidates of AUs by affinity based pull down assay and molecular dynamics simulation. The mechanism of stomatal movement related with the LRXs-RALF is an unexplored pathway, and therefore further studies may lead to the discovery of new signaling pathways and regulatory factors in the stomatal movement.

Tomato ABA-IMPORTING TRANSPORTER 1.1 inhibits seed germination under high salinity conditions

The plant hormone abscisic acid (ABA) plays a central role in the regulation of seed maturation and dormancy. ABA also restrains germination under abiotic-stress conditions. Here, we show in tomato (Solanum lycopersicum) that the ABA importer ABA-IMPORTING TRANSPORTER 1.1 (AIT1.1/NPF4.6) has a role in radicle emergence under salinity conditions. AIT1.1 expression was upregulated following seed imbibition, and CRISPR/Cas9-derived ait1.1 mutants exhibited faster radicle emergence, increased germination and partial resistance to ABA. AIT1.1 was highly expressed in the endosperm, but not in the embryo, and ait1.1 isolated embryos did not show resistance to ABA. On the other hand, loss of AIT1.1 activity promoted the expression of endosperm-weakening-related genes, and seed-coat scarification eliminated the promoting effect of ait1.1 on radicle emergence. Therefore, we propose that imbibition-induced AIT1.1 expression in the micropylar endosperm mediates ABA-uptake into micropylar cells to restrain endosperm weakening. While salinity conditions strongly inhibited wild-type M82 seed germination, high salinity had a much weaker effect on ait1.1 germination. We suggest that AIT1.1 evolved to inhibit germination under unfavorable conditions, such as salinity. Unlike other ABA mutants, ait1.1 exhibited normal seed longevity, and therefore, the ait1.1 allele may be exploited to improve seed germination in crops.

Abscisic acid agonists suitable for optimizing plant water use

Climate change and overexploitation of groundwater resources cause constraints on water demand for agriculture, thus threatening crop productivity. For future food security, there is an urgent need for crops of high water use efficiency combined with high crop productivity, i.e. having high water productivity. High water productivity means efficient biomass accumulation at reduced transpiration. Recent studies show that plants are able to optimize carbon uptake per water transpired with little or no trade-off in yield. The phytohormone abscisic acid (ABA) plays a pivotal role in minimizing leaf transpiration and mediating enhanced water productivity. Hence, ABA and more chemically stable ABA agonists have the potential to improve crop water productivity. Synthesis, screening, and identification of suitable ABA agonists are major efforts currently undertaken. In this study, we used yeast expressing the plant ABA signal pathway to prescreen ABA-related cyano cyclopropyl compounds (CCPs). The yeast analysis allowed testing the ABA agonists for general toxicity, efficient uptake, and specificity in regulating different ABA receptor complexes. Subsequently, promising ABA-mimics were analyzed in vitro for ligand-receptor interaction complemented by physiological analyses. Several CCPs activated ABA signaling in yeast and plant cells. CCP1, CCP2, and CCP5 were by an order of magnitude more efficient than ABA in minimizing transpiration of Arabidopsis plants. In a progressive drought experiment, CCP2 mediated an increase in water use efficiency superior to ABA without trade-offs in biomass accumulation.

Abscisic acid modulates neighbor proximity-induced leaf hyponasty in Arabidopsis

Leaves of shade-avoiding plants such as Arabidopsis (Arabidopsis thaliana) change their growth pattern and position in response to low red to far-red ratios (LRFRs) encountered in dense plant communities. Under LRFR, transcription factors of the phytochrome-interacting factor (PIF) family are derepressed. PIFs induce auxin production, which is required for promoting leaf hyponasty, thereby favoring access to unfiltered sunlight. Abscisic acid (ABA) has also been implicated in the control of leaf hyponasty, with gene expression patterns suggesting that LRFR regulates the ABA response. Here, we show that LRFR leads to a rapid increase in ABA levels in leaves. Changes in ABA levels depend on PIFs, which regulate the expression of genes encoding isoforms of the enzyme catalyzing a rate-limiting step in ABA biosynthesis. Interestingly, ABA biosynthesis and signaling mutants have more erect leaves than wild-type Arabidopsis under white light but respond less to LRFR. Consistent with this, ABA application decreases leaf angle under white light; however, this response is inhibited under LRFR. Tissue-specific interference with ABA signaling indicates that an ABA response is required in different cell types for LRFR-induced hyponasty. Collectively, our data indicate that LRFR triggers rapid PIF-mediated ABA production. ABA plays a different role in controlling hyponasty under white light than under LRFR. Moreover, ABA exerts its activity in multiple cell types to control leaf position.

Potential abiotic stress targets for modern genetic manipulation

Research into crop yield and resilience has underpinned global food security, evident in yields tripling in the past 5 decades. The challenges that global agriculture now faces are not just to feed 10+ billion people within a generation, but to do so under a harsher, more variable, and less predictable climate, and in many cases with less water, more expensive inputs, and declining soil quality. The challenges of climate change are not simply to breed for a "hotter drier climate," but to enable resilience to floods and droughts and frosts and heat waves, possibly even within a single growing season. How well we prepare for the coming decades of climate variability will depend on our ability to modify current practices, innovate with novel breeding methods, and communicate and work with farming communities to ensure viability and profitability. Here we define how future climates will impact farming systems and growing seasons, thereby identifying the traits and practices needed and including exemplars being implemented and developed. Critically, this review will also consider societal perspectives and public engagement about emerging technologies for climate resilience, with participatory approaches presented as the best approach.

Co-Expression of ZmVPP1 with ZmNAC111 Confers Robust Drought Resistance in Maize

Drought is a primary environmental factor limiting maize production globally. Although transferring a single gene to maize can enhance drought resistance, maize response to water deficit requires further improvement to accommodate the steadily intensifying drought events worldwide. Here, we generated dual transgene lines simultaneously overexpressing two drought-resistant genes, ZmVPP1 (encoding a vacuolar-type H+ pyrophosphatase) and ZmNAC111 (encoding a NAM, ATAF, and CUC (NAC)-type transcription factor). Following drought stress, survival rates of the pyramided transgenic seedlings reached 62-66%, while wild-type and single transgene seedling survival rates were 23% and 37-42%, respectively. Maize seedlings co-expressing ZmVPP1 and ZmNAC111 exhibited higher photosynthesis rates, antioxidant enzyme activities, and root-shoot ratios than the wild type, and anthesis-silking intervals were shorter while grain yields were higher under water deficit conditions in field trials. Additionally, RNA-sequencing analysis confirmed that photosynthesis and stress-related metabolic processes were stimulated in the dual transgene plants under drought conditions. The findings in this work illustrate how high co-expression of different drought-related genes can reinforce drought resistance over that of individual transgene lines, providing a path for developing arid climate-adapted elite maize varieties.

Direct Reaction of Nitroarenes and Thiols via Photodriven Oxygen Atom Transfer for Access to Sulfonamides

Sulfonamide is a common motif in medicines and agrochemicals. Typically, this class of functional groups is prepared by reacting amines with sulfonyl chlorides that are presynthesized from nitro compounds and thiols, respectively. Here, we report a novel strategy that directly couples nitro compounds and thiols to form sulfonamides atom- and redox-economically. Mechanistic studies suggest our reaction proceeds via direct photoexcitation of nitroarenes that eventually transfers the oxygen atoms from the nitro group to the thiol unit.

Rapid biosensor development using plant hormone receptors as reprogrammable scaffolds

A general method to generate biosensors for user-defined molecules could provide detection tools for a wide range of biological applications. Here, we describe an approach for the rapid engineering of biosensors using PYR1 (Pyrabactin Resistance 1), a plant abscisic acid (ABA) receptor with a malleable ligand-binding pocket and a requirement for ligand-induced heterodimerization, which facilitates the construction of sense-response functions. We applied this platform to evolve 21 sensors with nanomolar to micromolar sensitivities for a range of small molecules, including structurally diverse natural and synthetic cannabinoids and several organophosphates. X-ray crystallography analysis revealed the mechanistic basis for new ligand recognition by an evolved cannabinoid receptor. We demonstrate that PYR1-derived receptors are readily ported to various ligand-responsive outputs, including enzyme-linked immunosorbent assay (ELISA)-like assays, luminescence by protein-fragment complementation and transcriptional circuits, all with picomolar to nanomolar sensitivity. PYR1 provides a scaffold for rapidly evolving new biosensors for diverse sense-response applications.

A Modified Yeast Two-Hybrid Platform Enables Dynamic Control of Expression Intensities to Unmask Properties of Protein-Protein Interactions

The yeast two-hybrid (Y2H) assay is widely used for protein-protein interaction characterization due to its simplicity and accessibility. However, it may mask changes in affinity caused by mutations or ligand activation due to signal saturation. To overcome this drawback, we modified the Y2H system to have tunable protein expression by introducing a fluorescent reporter and a pair of synthetic inducible transcription factors to regulate the expression of interacting components. We found that the application of inducers allowed us to adjust the concentrations of interacting proteins to avoid saturation and observe interactions otherwise masked in the canonical Y2H assay, such as the abscisic acid-mediated increase in affinity of monomeric abscisic acid receptors to the coreceptor. When applied in future studies, our modified system may provide a more accurate characterization of protein-protein interactions.

A briefly overview of the research progress for the abscisic acid analogues

Abscisic acid (ABA) is an important plant endogenous hormone that participates in the regulation of various physiological processes in plants, including the occurrence and development of somatic embryos, seeddevelopment and dormancy. ABA is called “plant stress resistance factor”, while with the limitation of the rapid metabolic inactivation and photoisomerization inactivation of ABA for its large-scale use. Understanding the function and role of ABA in plants is of great significance to promote its application. For decades, scientists have conducted in-depth research on its mechanism of action and signaling pathways, a series of progress were achieved, and hundreds of ABA analogues (similar in structure or function) have been synthesized to develop highly active plant growth regulators and tools to elucidate ABA perception. In this review, we summarize a variety of ABA analogues, especially the ABA receptor analogues, and explore the mechanisms of ABA action and catabolism, which will facilitate the development of novel ABA analogues with high biological activities.

Monomerization of abscisic acid receptors through CARKs-mediated phosphorylation

Cytosolic ABA Receptor Kinases (CARKs) play a pivotal role in abscisic acid (ABA)-dependent pathway in response to dehydration, but their regulatory mechanism in ABA signaling remains unexplored. In this study, we showed that CARK4/5 of CARK family physically interacted with ABA receptors (RCARs/PYR1/PYLs), including RCAR3, RCAR11-RCAR14, while CARK2/7/11 only interacted with RCAR11-RCAR14, but not RCAR3. It indicates that the members in CARK family function redundantly and differentially in ABA signaling. RCAR12 can form heterodimer with RCAR3 in vitro and in vivo. Moreover, the members of CARK family can form homodimer or heterodimer in a kinase activity dependent manner. ITC (isothermal titration calorimetry) analysis demonstrated that the phosphorylation of RCAR12 by CARK1 enhanced the ABA binding affinity. The phosphor-mimic RCAR12^T105D significantly displayed ABA-induced inhibition of the phosphatase ABI1 (ABA insensitive 1) activity, leading to upregulation of ABA-responsive genes RD29A and RD29B in cark157:RCAR12^T105D transgenic plants, which exhibited ABA hypersensitive phenotype. The transcription factor ABI5 (ABA insensitive 5) activates the transcriptions of CARK1 and CARK3 by binding to ABA-response elements (ABREs) of their promoters. Collectively, our data imply that the dimeric CARKs phosphorylate homodimer or heterodimer ABA receptors, leading to monomerization for triggering ABA responses in Arabidopsis.

Real-Time Fluorescence Imaging of the Abscisic Acid Receptor Allows Nondestructive Visualization of Plant Stress

Environmental stress greatly decreases crop yield. The application of noninvasive techniques is one of the most practical and feasible ways of monitoring the health condition of plants under stress. However, it remains largely unsolved. A chemical fluorescent probe can be applied as a typical nondestructive method, but it has not been applied in living plants for stress detection to date. The abscisic acid (ABA) receptor plays a central role in conferring tolerance to environmental stresses and is an excellent target for developing fluorescent probes. Herein, we developed a fluorescence molecular imaging technology to monitor live plant stress by visualizing the protein expression level of the ABA receptor PYR1. A computer-aided designed indicator dye, flubactin, exhibited an 8-fold enhancement in fluorescence intensity upon interaction with PYR1. In vitro and in vivo experiments showed that flubactin is suitable to be used to detect salt stress in plants in real time. Moreover, the low toxicity of flubactin promotes its application in the future. Our work opens a new era for the nondestructive visualization of plant stress in vivo.

Structure-Based Modulation of the Ligand Sensitivity of a Tomato Dimeric Abscisic Acid Receptor Through a Glu to Asp Mutation in the Latch Loop

The binding of the plant phytohormone Abscisic acid (ABA) to the family of ABA receptors (PYR/PYL/RCAR) triggers plant responses to abiotic stress. Thus, the implementation of genetic or chemical strategies to modulate PYR/PYL activity might be biotechnologically relevant. We have employed the available structural information on the PYR/PYL receptors to design SlPYL1, a tomato receptor, harboring a single point mutation that displays enhanced ABA dependent and independent activity. Interestingly, crystallographic studies show that this mutation is not directly involved in ABA recognition or in the downstream phosphatase (PP2C) inhibitory interaction, rather, molecular dynamic based ensemble refinement restrained by crystallographic data indicates that it enhances the conformational variability required for receptor activation and it is involved in the stabilization of an active form of the receptor. Moreover, structural studies on this receptor have led to the identification of niacin as an ABA antagonist molecule in vivo. We have found that niacin blocks the ABA binding site by mimicking ABA receptor interactions, and the niacin interaction inhibits the biochemical activity of the receptor.

The wheat ABA receptor gene TaPYL1-1B contributes to drought tolerance and grain yield by increasing water-use efficiency

The role of abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs), is well established in ABA signalling and plant drought response, but limited research has explored the regulation of wheat PYLs in this process, especially the effects of their allelic variations on drought tolerance or grain yield. Here, we found that the overexpression of a TaABFs-regulated PYL gene, TaPYL1-1B, exhibited higher ABA sensitivity, photosynthetic capacity and water-use efficiency (WUE), all contributed to higher drought tolerance than that of wild-type plants. This heightened water-saving mechanism further increased grain yield and protected productivity during water deficit. Candidate gene association analysis revealed that a favourable allele TaPYL1-1B^In-442 , carrying an MYB recognition site insertion in the promoter, is targeted by TaMYB70 and confers enhanced expression of TaPYL1-1B in drought-tolerant genotypes. More importantly, an increase in frequency of the TaPYL1-1B^In-442 allele over decades among modern Chinese cultivars and its association with high thousand-kernel weight together demonstrated that it was artificially selected during wheat improvement efforts. Taken together, our findings illuminate the role of TaPYL1-1B plays in coordinating drought tolerance and grain yield. In particular, the allelic variant TaPYL1-1B^In-442 substantially contributes to enhanced drought tolerance while maintaining high yield, and thus represents a valuable genetic target for engineering drought-tolerant wheat germplasm.

Brassinosteroid-Insensitive 1-Associated Receptor Kinase 1 Modulates Abscisic Acid Signaling by Inducing PYR1 Monomerization and Association With ABI1 in Arabidopsis

Brassinosteroid-Insensitive 1-Associated Receptor Kinase 1 (BAK1) is a versatile kinase involved in many different plant developmental responses. Previously, we showed that BAK1 interacts with open stomata 1 (OST1), a cytoplasmic kinase, to promote abscisic acid (ABA)-induced stomatal closure. ABA is a plant hormone that primarily regulates stress responses and is recognized by the PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL)/REGULATORY COMPONENT OF ABA RECEPTORS (RCAR), which activates ABA signaling. Here, we demonstrated that BAK1 interacts with PYR1 and phosphorylates PYR1 in response to ABA in plants. We identified T137 and S142 of PYR1 as the phosphosites targeted by BAK1. Using phosphomimetic (PYR1DD) and phospho-dead (PYR1AA) PYR1 compared with wild-type PYR1, we showed that transgenic plants overexpressing a phosphomimetic PYR1 exhibited hypersensitivity to the inhibition of ABA-induced root growth and seed germination and increased ABA-induced stomatal closure and ABA-inducible gene expression. As underlying reasons for these phenomena, we further demonstrated that phosphorylated PYR1 existed in a monomeric form, in which ABA binding was increased, and the degree of complex formation with ABI1 was also increased. These results suggest that BAK1 positively modulates ABA signaling through interaction with PYR1, in addition to OST1.

Novel small molecules targeting bZIP23 TF improve stomatal conductance and photosynthesis under mild drought stress by regulating ABA

Drought-induced abscisic acid (ABA) accumulation plays a key role in plant water relations by regulating stomatal movements. Although ABA helps in the survival of the plants, reduced carbon gain affects plant productivity. To improve crop productivity under mild drought stress conditions, it is necessary to manipulate ABA responses. Other research groups have used forward chemical genomics for the identification of ABA agonists and antagonists aiming to manipulate ABA biosynthesis and signalling. In the present study, we identified indolyl-ethyl amine and serotonin small molecules using a reverse chemical genomics approach, with these acting as potent inhibitors of ABA biosynthesis through transient regulation of bZIP23 transcription factor activity. In rice, wheat and soybean, each of the small molecules enhanced the germination of seeds, even in the presence of ABA. These molecules nullified the effect of ABA on intact and detached leaves, resulting in higher photosynthesis. Furthermore, these small molecules effectively reduced the transcription levels of bZIP23 targeting NCED4, PP2C49 and CO3 genes. Rice plants treated with the small molecules were found to have improved stomatal conductance, spikelet fertility and yield compared to untreated plants under mild drought stress conditions. Our results suggest that indolyl-ethyl amine and serotonin small molecules could be utilized to improve yield under mild drought conditions.

Chemical Approaches for Improving Plant Water Use

Agricultural productivity in rain-fed crops has been threatened in recent decades due to increased instances of drought and diminishing freshwater resources. This has led to the development of novel chemical and genetic approaches for improving plant water use efficiency. Agrochemical water-banking with the aid of synthetic mimics of phytohormone abscisic acid (ABA) is one such approach, whereby plant transpiration can be chemically tuned to ensure water availability during critical stages of growth. Here, we describe the use of infrared thermography, a noninvasive quantitative technique to evaluate antitranspirant efficacy of existing ABA receptor agonists in crops such as wheat and tomato.

Mechanisms of Abscisic Acid-Mediated Drought Stress Responses in Plants

Drought is one of the major constraints to rain-fed agricultural production, especially under climate change conditions. Plants evolved an array of adaptive strategies that perceive stress stimuli and respond to these stress signals through specific mechanisms. Abscisic acid (ABA) is a premier signal for plants to respond to drought and plays a critical role in plant growth and development. ABA triggers a variety of physiological processes such as stomatal closure, root system modulation, organizing soil microbial communities, activation of transcriptional and post-transcriptional gene expression, and metabolic alterations. Thus, understanding the mechanisms of ABA-mediated drought responses in plants is critical for ensuring crop yield and global food security. In this review, we highlighted how plants adjust ABA perception, transcriptional levels of ABA- and drought-related genes, and regulation of metabolic pathways to alter drought stress responses at both cellular and the whole plant level. Understanding the synergetic role of drought and ABA will strengthen our knowledge to develop stress-resilient crops through integrated advanced biotechnology approaches. This review will elaborate on ABA-mediated drought responses at genetic, biochemical, and molecular levels in plants, which is critical for advancement in stress biology research.

Improving crop drought resistance with plant growth regulators and rhizobacteria: Mechanisms, applications, and perspectives

Drought is one of the main abiotic stresses that cause crop yield loss. Improving crop yield under drought stress is a major goal of crop breeding, as it is critical to food security. The mechanism of plant drought resistance has been well studied, and diverse drought resistance genes have been identified in recent years, but transferring this knowledge from the laboratory to field production remains a significant challenge. Recently, some new strategies have become research frontiers owing to their advantages of low cost, convenience, strong field operability, and/or environmental friendliness. Exogenous plant growth regulator (PGR) treatment and microbe-based plant biotechnology have been used to effectively improve crop drought tolerance and preserve yield under drought stress. However, our understanding of the mechanisms by which PGRs regulate plant drought resistance and of plant-microbiome interactions under drought is still incomplete. In this review, we summarize these two strategies reported in recent studies, focusing on the mechanisms by which these exogenous treatments regulate crop drought resistance. Finally, future challenges and directions in crop drought resistance breeding are discussed.

Molecular basis of the activation and dissociation of dimeric PYL2 receptor in abscisic acid signaling

Phytohormone abscisic acid (ABA) is essential for plant responses to biotic and abiotic stresses. Dimeric receptors are a class of PYR1/PYL/RCAR (pyrabactin resistance 1/PYR1-like/regulatory component of ABA receptors) ABA receptors that are important for various ABA responses. While extensive experimental and computational studies have investigated these receptors, it remains not fully understood how ABA leads to their activation and dissociation for interaction with downstream protein phosphatase 2C (PP2C). Here, we study the activation and the homodimeric association processes of the PYL2 receptor as well as its heterodimeric association with protein phosphatase 2C 16 (HAB1) using molecular dynamics simulations. Free energy landscapes from ∼223 μs simulations show that dimerization substantially constrains PYL2 conformational plasticity and stabilizes the inactive state, resulting in lower ABA affinity. Also, we establish the thermodynamic model for competitive binding between homodimeric PYL2 association and heterodimeric PYL2-HAB1 association in the absence and presence of ABA. Our results suggest that the binding of ABA destabilizes the PYL2 complex and further stabilizes PYL2-HAB1 association, thereby promoting PYL2 dissociation. Overall, this study explains several key aspects on the activation of dimeric ABA receptors, which provide new avenues for selective regulation of these receptors.

R, Choudhary AK, Salam MD, Sahoo MR, Bhutia TL, Devi SH, Thounaojam AS, Behera C, M. N. H, Kumar A, Dasgupta M, Devi YP, Singh D, Bhagowati S, Devi CP, Singh HR, Khaba CI. Role of biostimulants in mitigating the effects of climate change on crop performance

Climate change is a critical yield-limiting factor that has threatened the entire global crop production system in the present scenario. The use of biostimulants in agriculture has shown tremendous potential in combating climate change-induced stresses such as drought, salinity, temperature stress, etc. Biostimulants are organic compounds, microbes, or amalgamation of both that could regulate plant growth behavior through molecular alteration and physiological, biochemical, and anatomical modulations. Their nature is diverse due to the varying composition of bioactive compounds, and they function through various modes of action. To generate a successful biostimulatory action on crops under different parameters, a multi-omics approach would be beneficial to identify or predict its outcome comprehensively. The 'omics' approach has greatly helped us to understand the mode of action of biostimulants on plants at cellular levels. Biostimulants acting as a messenger in signal transduction resembling phytohormones and other chemical compounds and their cross-talk in various abiotic stresses help us design future crop management under changing climate, thus, sustaining food security with finite natural resources. This review article elucidates the strategic potential and prospects of biostimulants in mitigating the adverse impacts of harsh environmental conditions on plants.

Evaluation of the Anti-transpirant Activity of ABA Receptor Agonists in Monocot and Eudicot Plants

ABA receptor agonists capable of improving plant performance under drought conditions have been described during the last years. However, monocot and eudicot plant species respond differently to various agonists. Here, we provide a detailed methodology to evaluate the anti-transpirant activity of ABA receptor agonists in both monocot and eudicot plant species using infrared imaging and image data analysis. Plant growth conditions, chemical application, and infrared image analysis are explained in detail to evaluate the anti-transpirant activity of ABA receptor agonists in the eudicot model Arabidopsis thaliana and in the C4-monocot model Setaria viridis.

Rice functional genomics: decades' efforts and roads ahead

Rice (Oryza sativa L.) is one of the most important crops in the world. Since the completion of rice reference genome sequences, tremendous progress has been achieved in understanding the molecular mechanisms on various rice traits and dissecting the underlying regulatory networks. In this review, we summarize the research progress of rice biology over past decades, including omics, genome-wide association study, phytohormone action, nutrient use, biotic and abiotic responses, photoperiodic flowering, and reproductive development (fertility and sterility). For the roads ahead, cutting-edge technologies such as new genomics methods, high-throughput phenotyping platforms, precise genome-editing tools, environmental microbiome optimization, and synthetic methods will further extend our understanding of unsolved molecular biology questions in rice, and facilitate integrations of the knowledge for agricultural applications.

Transcriptome Reveals the Dynamic Response Mechanism of Pearl Millet Roots under Drought Stress

Drought is a major threat to global agricultural production that limits the growth, development and survival rate of plants, leading to tremendous losses in yield. Pearl millet (Cenchrus americanus (L.) Morrone) has an excellent drought tolerance, and is an ideal plant material for studying the drought resistance of cereal crops. The roots are crucial organs of plants that experience drought stress, and the roots can sense and respond to such conditions. In this study, we explored the mechanism of drought tolerance of pearl millet by comparing transcriptomic data under normal conditions and drought treatment at four time points (24 h, 48 h, 96 h, and 144 h) in the roots during the seedling stage. A total of 1297, 2814, 7401, and 14,480 differentially expressed genes (DEGs) were found at 24 h, 48 h, 96 h, and 144 h, respectively. Based on Kyoto Encyclopedia of Genes and Genomes and Gene Ontology enrichment analyses, we found that many DEGs participated in plant hormone-related signaling pathways and the "oxidoreductase activity" pathway. These results should provide a theoretical basis to enhance drought resistance in other plant species.

Rice functional genomics: decades' efforts and roads ahead

Rice (Oryza sativa L.) is one of the most important crops in the world. Since the completion of rice reference genome sequences, tremendous progress has been achieved in understanding the molecular mechanisms on various rice traits and dissecting the underlying regulatory networks. In this review, we summarize the research progress of rice biology over past decades, including omics, genome-wide association study, phytohormone action, nutrient use, biotic and abiotic responses, photoperiodic flowering, and reproductive development (fertility and sterility). For the roads ahead, cutting-edge technologies such as new genomics methods, high-throughput phenotyping platforms, precise genome-editing tools, environmental microbiome optimization, and synthetic methods will further extend our understanding of unsolved molecular biology questions in rice, and facilitate integrations of the knowledge for agricultural applications.