Elevated Abscisic Acid Levels Research Articles

Spider mite herbivory induces an abscisic acid-driven stomatal defense.

Arthropod herbivory poses a serious threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest two-spotted spider mite (Tetranychus urticae) inflicts rapid damage and remains challenging due to its broad target range. In this study, we explored the Arabidopsis (Arabidopsis thaliana) response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, and stomatal closure during water stress. Leveraging a FRET-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types post-mite feeding. While ABA's role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation alongside intact canonical biotic stress signaling, indicating an independent function of ABA in mite defense. We established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage through genetic and pharmacological interventions targeting ABA levels, ABA signaling, stomatal aperture, and density. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, reinforces the intricate relationship between these stress types.

Heat‐stress‐induced fertility loss in summer maize (Zea mays L.): Quantitative analysis of contributions from developmental and physiological damage to pollen

AbstractIn recent years, the frequency and intensity of exposure to heat stress have increased gradually, seriously hampering the production of maize. This paper presents a study designed to analyze how the development, physiology and dispersal of pollen from the heat‐resistant maize variety Zhengdan958 and the heat‐sensitive maize variety Xianyu335 are affected by exposure to heat stress during the tasselling stage. Our results showed That exposure to heat stress significantly increased the antioxidant enzyme activity in pollen. Upon visual inspection of the pollen, we found that the lower water content had given rise to wrinkles in the pollen surface, sunken germination pores, and morphological deformations. In addition, the anther dehiscence process was hindered, resulting in a reduced amount of pollen being dispersed. We also found elevated levels of abscisic acid (ABA), jasmonic acid (JA) and its derivatives, indole acetic acid (IAA) and gibberellin‐3 (GA3) in heat‐pollens, as well as elevated ratios of IAA to ABA and ABA to GA3. Ultimately impaired pollen fertility. Summarizing, our experiment revealed that reduced pollen quantity and quality are significant contributors to fertility losses in summer maize exposed to heat stress at anthesis, and we hope that our analysis of the physiological mechanisms involved can contribute to the development of crop management measures aimed at countering the increasingly detrimental effects of heat stress on the production of summer maize.

Abscisic acid inhibits germination of Striga seeds and is released by them likely as a rhizospheric signal supporting host infestation.

Seeds of the root parasitic plant Striga hermonthica undergo a conditioning process under humid and warm environments before germinating in response to host-released stimulants, particularly strigolactones (SLs). The plant hormone abscisic acid (ABA) regulates different growth and developmental processes, and stress response; however, its role during Striga seed germination and early interactions with host plants is under-investigated. Here, we show that ABA inhibited Striga seed germination and that hindering its biosynthesis induced conditioning and germination in unconditioned seeds, which was significantly enhanced by treatment with the SL analog rac-GR24. However, the inhibitory effect of ABA remarkably decreased during conditioning, confirming the loss of sensitivity towards ABA in later developmental stages. ABA measurement showed a substantial reduction of its content during the early conditioning stage and a significant increase upon rac-GR24-triggered germination. We observed this increase also in released seed exudates, which was further confirmed by using the Arabidopsis ABA-reporter GUS marker line. Seed exudates of germinated seeds, containing elevated levels of ABA, impaired the germination of surrounding Striga seeds in vitro and promoted root growth of a rice host towards germinated Striga seeds. Application of ABA as a positive control caused similar effects, indicating its function in Striga/Striga and Striga/host communications. In summary, we show that ABA is an essential player during seed dormancy and germination processes in Striga and acts as a rhizospheric signal likely to support host infestation.

Involvement of brassinosteroids and abscisic acid in spikelet degeneration in rice under soil drying during meiosis.

Spikelet degeneration in rice (Oryza sativa L.) is a serious physiological defect, and can be regulated by soil moisture status and phytohormones. This study investigated the possibility that brassinosteroids (BRs) in collaboration with abscisic acid (ABA) are involved in mediating the effect of soil drying during meiosis on spikelet degeneration in rice. Three rice cultivars were field grown and three irrigation regimes including well watered (WW), moderate soil drying (MD), and severe soil drying (SD) were imposed during meiosis. MD significantly decreased spikelet degeneration in comparison with WW, due mainly to the alleviation in oxidative damage via enhancing ascorbate-glutathione (AsA-GSH) cycle activity in young panicles, and SD exhibited the opposite effects. Enhanced AsA-GSH cycle strength, decreased oxidative stress, and spikelet degeneration rate were closely associated with the synergistically elevated BR and ABA levels in young panicles in MD. In contrast, low BR and excessive ABA levels led to an increase in spikelet degeneration in SD. The three cultivars exhibited the same tendencies. The intrinsic link among AsA-GSH cycle, oxidative stress, spikelet degeneration rate, and BR and ABA levels was further verified by using transgenic rice lines and chemical regulators. BRs or ABA play a unique role in regulating spikelet degeneration. Synergistically increased BR and ABA levels in MD could work together to strengthen AsA-GSH cycle activity, leading to a reduction in oxidative damage and spikelet degeneration. On the other hand, a severe imbalance between low BR and excessive ABA levels may have contributed to the opposite effects in SD.

Temporal and spatial transcriptional regulation of phytohormone metabolism during seed development in barley (Hordeum vulgare L.).

Plant hormones play important roles in seed development; however, transcriptional regulation of their metabolism and levels of the respective bioactive forms during barley seed development is poorly understood. To this end, this study performed a comprehensive analysis of changes in the expression patterns phytohormone metabolism genes and levels of the respective bioactive forms in the embryo and endosperm tissues. Our study showed the presence of elevated levels of abscisic acid (ABA), bioactive forms of gibberellins (GAs), jasmonate (JA) and cytokinins (CKs), auxin and salicylic acid (SA) in the endosperm and embryo tissues at early stage of seed filling (SF). The levels of all hormones in both tissues, except that of ABA, decreased to low levels during SF. In contrast, embryonic ABA level increased during SF and peaked at physiological maturity (PM) while the endospermic ABA was maintained at a similar level observed during SF. Although its level decreased high amount of ABA was still present in the embryo during post-PM. We detected low levels of ABA in the endosperm and all the other hormones in both tissues during post-PM phase except the relatively higher levels of jasmonoyl-isoleucine and SA detected at late stage of post-PM. Our data also showed that spatiotemporal changes in the levels of plant hormones during barley seed development are mediated by the expression of specific genes involved in their respective metabolic pathways. These results indicate that seed development in barley is mediated by spatiotemporal modulation in the metabolism and levels of plant hormones.

Divergent Metabolic Changes in Rhizomes of Lowland and Upland Switchgrass (Panicum virgatum) from Early Season through Dormancy Onset.

High-biomass-yielding southerly adapted switchgrasses (Panicum virgatum L.) frequently suffer from unpredictable winter hardiness at more northerly sites arising from damage to rhizomes that prevent effective spring regrowth. Previously, changes occurring over the growing season in rhizomes sampled from a cold-adapted tetraploid upland cultivar, Summer, demonstrated a role for abscisic acid (ABA), starch accumulation, and transcriptional reprogramming as drivers of dormancy onset and potential keys to rhizome health during winter dormancy. Here, rhizome metabolism of a high-yielding southerly adapted tetraploid switchgrass cultivar, Kanlow-which is a significant source of genetics for yield improvement-was studied over a growing season at a northern site. Metabolite levels and transcript abundances were combined to develop physiological profiles accompanying greening through the onset of dormancy in Kanlow rhizomes. Next, comparisons of the data to rhizome metabolism occurring in the adapted upland cultivar Summer were performed. These data revealed both similarities as well as numerous differences in rhizome metabolism that were indicative of physiological adaptations unique to each cultivar. Similarities included elevated ABA levels and accumulation of starch in rhizomes during dormancy onset. Notable differences were observed in the accumulation of specific metabolites, the expression of genes encoding transcription factors, and several enzymes linked to primary metabolism.

Increasingly amplified stimulation mediated by TaNAC69-B is crucial for the leaf senescence in wheat.

Leaf senescence involves massive multidimensional alterations, such as nutrient redistribution, and is closely related to crop yield and quality. No apical meristem, Arabidopsis transcription activation factor, and Cup-shaped cotyledon (NAC)-type transcription factors integrate various signals and modulate an enormous number of target genes to ensure the appropriate progression of leaf senescence. However, few leaf senescence-related NACs have been functionally characterized in wheat. Based on our previous RNA-sequencing (RNA-seq) data, we focused on a NAC family member, TaNAC69-B, which is increasingly expressed during leaf senescence in wheat. Overexpression of TaNAC69-B led to precocious leaf senescence in wheat and Arabidopsis, and affected several agricultural traits in transgenic wheat. Moreover, impaired expression of TaNAC69-B by virus-induced gene silencing retarded the leaf senescence in wheat. By RNA-seq and quantitative real-time polymerase chain reaction analysis, we confirmed that some abscisic acid (ABA) biosynthesis genes, including AAO3 and its ortholog in wheat, TraesCS2B02G270600 (TaAO3-B), were elevated by the overexpression of TaNAC69-B. Consistently, we observed more severe ABA-induced leaf senescence in TaNAC69-B-OE wheat and Arabidopsis plants. Furthermore, we determined that TaNAC69-B bound to the NAC binding site core (CGT) on the promoter regions of AAO3 and TaAO3-B. Moreover, we confirmed elevated ABA levels in TaNAC69-B-OE wheat lines. Although TaNAC69-B shares 39.83% identity (amino acid) with AtNAP, TaNAC69-B did not completely restore the delayed leaf senescence in the atnap mutant. Collectively, our results revealed a positive feedback loop, consisting of TaNAC69-B, ABA biosynthesis and leaf senescence, that is essential for the regulation of leaf senescence in wheat.

Elevated CO2 and high endogenous ABA level alleviate PEG-induced short-term osmotic stress in tomato plants

Elevated CO 2 concentration ( e [CO 2 ]) alleviates the impact of drought stress on plants where abscisic acid (ABA) is involved. To explore the mechanisms by which tomato plants respond to short-term osmotic stress, Solanum lycopersicum cv. Ailsa Craig (AC), a transgenic line overproducing ABA (sp5), and an ABA-deficient mutant ( flacca ) were hydroponically grown under ambient CO 2 (400 ppm) and e [CO 2 ] (800 ppm) and then exposed to 10% or 15% (w/v) polyethylene glycol (PEG) 6000 for 24 h before transferring to PEG-free nutrient solution for 24 h. Under non-stress condition, e [CO 2 ] decreased root hydraulic conductance ( K root ), which was overridden by high endogenous ABA in sp5 through increasing specific leaf area and root branching intensity. Basically, e [CO 2 ] improved stress resistance through enhanced water status. PEG stress decreased stomatal conductance and osmotic potential in AC but these effects were less pronounced in sp5, which exhibited a stronger osmotic adjustment (OA) and improved plant fitness. A greater flexibility of hydraulic system and a reduced sensitivity of K root to ABA might confer sp5 a great ability to recover from PEG stress. On the contrary, high stomatal density, size and pore aperture of flacca rendered plants suffering severe stress. Moreover, the premise that PEG stress could mimic soil water deficit was the sufficient achievement of OA. Our results indicate that e [CO 2 ] and high endogenous ABA level could improve osmotic stress resistance in tomato plants via osmotic and hydraulic adjustments. • High endogenous ABA increased specific leaf area and root branching intensity. • High endogenous ABA overrode the effects of e [CO 2 ] on root hydraulic conductance. • Sufficient osmotic adjustment improved drought resistance. • PEG stress could not mimic soil drought unless it triggered fast osmotic adjustment.

Tomato root senses horizontal/vertical mechanical impedance and correspondingly modulates root/shoot metabolome

Plant root encounters coarse environs right after emergence from the seed. Little is known about the metabolic changes enabling the root to overcome the soil impedance. It is also not known whether roots respond differently to soil hardness when grown in the horizontal and vertical orientation.We grew tomato (Solanum lycopersicum) seedlings vertically or horizontally on agarose with increasing hardness (0.2 % → 1.2 %). We examined the morphology of roots and shoots of the seedling and also profiled phytohormones, primary metabolite levels, and transcript levels of related genes from the respective organs.Tomato seedlings grown vertically or horizontally, on agarose with increasing hardness, exhibited lateral roots proliferation, shorter hypocotyl, and primary root. In primary root tip, hardness increase elicited loss of amyloplast staining; induced reactive oxygen species, and nitric oxide accumulation. The level of indole butyric acid, zeatin, jasmonates, and salicylic acid markedly differed in root and shoot exposed to increasing hardness. Increasing hardness lowered indole acetic acid and elevated abscisic acid level, while increased ethylene emission was confined to the horizontally-impeded seedling. The trajectories of metabolomic shift distinctly differed between vertically/horizontally-impeded root/shoot. In the horizontal root, amino acids were the major affected group, while in the vertical root, sugars were the major group. Commonly affected metabolites in root and shoot, trehalose, dopamine, caffeoylquinic acid, and suberic acid, hallmarked the signature for hardness. Increasing hardness lowered Snf1-related protein kinase1a (SnRK1a) expression in root/shoot implying regulation of metabolic homeostasis by the SnRK1 signalling module. The lower E2Fa expression may lead to growth inhibition by reduced meristematic activity.Our study highlights the importance of metabolic homeostasis in facilitating root ramification in the soil. Though hardness is a common denominator, root distinguishes the horizontal/vertical orientation and correspondingly modulates metabolites level. Altogether, the data uncovers ABA, E2Fa, and SnRK1 as key regulators of hardness-induced growth inhibition of tomato seedlings.

Both high and low water nitrogen and phosphorus concentrations differentially affect turion formation in Potamogeton crispus

Plants of Potamogeton crispus, a submersed macrophyte, were cultivated in the water free of algae and containing different concentrations of inorganic nitrogen (0.2 and 20 mg N L−1) and phosphorus (0.02 and 2.0 mg P L−1). The changes in plant growth and turion formation and the carbohydrate contents in plants and turions were investigated, and the endogenous abscisic acid (ABA) levels and the expressions of ABA biosynthetic genes in the stem apices analysed. The purpose of this study was to clarify the effects of water N and P levels on the plant growth and propagation capacity of P. crispus and to reveal whether ABA metabolism is involved in the turion formation of the plant under different ambient nutritional conditions. Finding the biomass of plants was not affected by the water N and P concentrations, except for those grown in water with low N and high P that had higher biomass accumulation and carbohydrate contents. Higher P promoted plant N uptake from the water, but higher N inhibited plant P uptake from the water with high P. High water N significantly delayed the turion initiation of P. crispus. Plants formed more apical turions with a greater size and more carbohydrate reserves when grown in water containing low N and low P, which leads to higher propagation of the plant population. The combination of high N and high P in water inhibited the formation and growth of turions, resulting in significant attenuation of the propagation capacity. High N combinated with low P or high P combinated with low N promoted the formation of more axillary turions and total turions but inhibited the turion growth. ABA levels and the expressions of ABA biosynthetic genes in stem apices at the turion initiation were changed by water N and P levels. The elevated ABA levels were consistent with the increased total turion number per plant when grown in the water with low N and/ or low P. The up-regulation of ZEP (zeaxanthin epoxidase) or NCED6 (9-cis-epoxycarotenoid dioxygenase6) may account for the ABA accumulation in the stem apices. The involvement of ABA metabolism in the turion formation relies on varying gene expression patterns when the plant grows in water containing different N and P concentrations.

Xanthomonas translucens commandeers the host rate-limiting step in ABA biosynthesis for disease susceptibility

Plants are vulnerable to disease through pathogen manipulation of phytohormone levels, which otherwise regulate development, abiotic, and biotic responses. Here, we show that the wheat pathogen Xanthomonas translucens pv. undulosa elevates expression of the host gene encoding 9-cis-epoxycarotenoid dioxygenase (TaNCED-5BS), which catalyzes the rate-limiting step in the biosynthesis of the phytohormone abscisic acid and a component of a major abiotic stress-response pathway, to promote disease susceptibility. Gene induction is mediated by a type III transcription activator-like effector. The induction of TaNCED-5BS results in elevated abscisic acid levels, reduced host transpiration and water loss, enhanced spread of bacteria in infected leaves, and decreased expression of the central defense gene TaNPR1 The results represent an appropriation of host physiology by a bacterial virulence effector.

A Nck‐associated protein 1‐like protein affects drought sensitivity by its involvement in leaf epidermal development and stomatal closure in rice

SummaryWater deficit is a major environmental threat affecting crop yields worldwide. In this study, a drought stress‐sensitive mutant drought sensitive 8 (ds8) was identified in rice (Oryza sativa L.). The DS8 gene was cloned using a map‐based approach. Further analysis revealed that DS8 encoded a Nck‐associated protein 1 (NAP1)‐like protein, a component of the SCAR/WAVE complex, which played a vital role in actin filament nucleation activity. The mutant exhibited changes in leaf cuticle development. Functional analysis revealed that the mutation of DS8 increased stomatal density and impaired stomatal closure activity. The distorted actin filaments in the mutant led to a defect in abscisic acid (ABA)‐mediated stomatal closure and increased ABA accumulation. All these resulted in excessive water loss in ds8 leaves. Notably, antisense transgenic lines also exhibited increased drought sensitivity, along with impaired stomatal closure and elevated ABA levels. These findings suggest that DS8 affects drought sensitivity by influencing actin filament activity.

Approach and mechanism in enhancing the remobilization of assimilates and grain-filling in rice and wheat

Monocarpic plants such as rice and wheat need to initiate the whole plant senescence before their pre-stored assimilates can be remobilized for the grain filling. However, plant senescence and photosynthesis are a pair of trade-off processes. How to coordinate plant senescence, photosynthesis, and remobilization of assimilates is a long-term unsolved problem in cereals. Solving this problem would have great significance in not only understanding the mechanism of the remobilization of assimilates to grain and grain-filling but also effectively coping with the poor remobilization of assimilates from vegetative tissues to grain and slow grain-filling for some cultivars or under the condition of heavy use of nitrogen in the current rice and wheat production systems. This paper reviewed crop management and physiological mechanism in enhancing the remobilization of assimilates to grain and grain-filling in rice and wheat. There are three important findings. (i) Moderate soil-drying (MSD) during post-anthesis can regulate the relationship of plant senescence, photosynthesis, and remobilization of assimilates, and accelerate grain-filing. With post-anthesis MSD, plant can rehydrate overnight but not severely inhibit leaf photosynthesis at day time. More importantly, it can timely and appropriately initiate the process of plant senescence, trigger assimilate remobilization from vegetative tissues to grain, accelerate grain-filling, especially for the late-flowering inferior caryopses, and lead to increases in grain yield, harvest index, and water use efficiency. The MSD therefore provides a new way to coordinate the relationship among plant senescence, photosynthesis, and remobilization of assimilates during grain-filling and to achieve the dual goal of increasing grain yield and saving water in cereals. (ii) Abscisic acid (ABA) and its interaction with ethylene and gibberellins (GAs) regulate assimilate remobilization and grain-filling. During the active grain-filling period, the filling of grain requires a higher level of endogenous ABA and higher ratios of ABA to ethylene and to GAs. Post-anthesis MDS enhances the remobilization of assimilates to grain and grain-filling through increases in ABA levels and the ratios of ABA to ethylene and/or to GAs, which reveals the mechanism in which plant hormones regulate assimilate remobilization and grain-filling, and provides a physiological regulation to improve grain-filling in cereals. (iii) A modest increase in ABA level in plants can enhance activities of the key enzymes involved in carbon metabolism, and thereby increase assimilate loading and unloading capacity. An elevated ABA level through MSD or applying ABA with a low concentration can increase activities of the key enzymes in starch or fructan degradation and sucrose synthesis in vegetative tissues, leading to the enhancement in assimilate loading capacity, and enhance activities of the key enzymes in sucrose-to-starch conversion in the sink organ, and consequently, increase assimilate unloading capacity and starch synthesis in grain, which reveals the mechanism in which ABA regulates assimilate remobilization and grain-filling. Further research is needed to understand the molecular mechanism, such as from the aspect of signal transduction, in which assimilate remobilization and grain filling are regulated in cereals, to investigate the regulatory mechanism underlying nitrogen remobilization from vegetative tissues to grain, and to elucidate the mechanism in which the MSD reduces spikelet degeneration and improves grain quality of cereals.

Increasing the abscisic acid level in maize grains induces precocious maturation by accelerating grain filling and dehydration

Elevated levels of abscisic acid (ABA) are closely associated with cereal grain filling under water deficit. However, grain dehydration during grain filling has received little attention. In this paper, three experiments with drought stress and exogenous ABA treatments were conducted to investigate the relationship between ABA and grain dehydration in maize (Zea mays L.) during the grain-filling period. The results indicated that exogenous ABA application and drought stress led to the same tendency of the grain ABA concentration, carbohydrate concentration and dehydration rate to increase but the moisture content to decrease. Moreover, the time to reach the maximum grain-filling rate was advanced, and the grain-filling period was shortened. In in vitro culture experiments, the sucrose-to-starch conversion was promoted, mainly influenced by sucrose synthase, ADP-glucose pyrophosphorylase (AGPase), and soluble starch synthase during the middle grain-filling stage, and the improvement in starch synthesis was possibly induced by AGPase. Correlation analysis showed that the ABA level was significantly negatively correlated with the moisture content and positively correlated with the starch level. A close and notably negative correlation was observed between the grain moisture content and starch level. In summary, adequate grain ABA promoted sucrose-to-starch conversion, shortened the duration of grain filling and accelerated grain dehydration, resulting in precocious grain maturation.

Spatiotemporal modulation of abscisic acid and gibberellin metabolism and signalling mediates the effects of suboptimal and supraoptimal temperatures on seed germination in wheat (Triticum aestivum L.).

Seed germination is a complex process regulated by intrinsic hormonal cues such as abscisic acid (ABA) and gibberellin (GA), and environmental signals including temperature. Using pharmacological, molecular and metabolomics approaches, we show that supraoptimal temperature delays wheat seed germination through maintaining elevated embryonic ABA level via increased expression of ABA biosynthetic genes (TaNCED1 and TaNCED2), increasing embryo ABA sensitivity through upregulation of genes regulating ABA signalling positively (TaPYL5, TaSnRK2, ABI3 and ABI5) and decreasing embryo GA sensitivity via induction of TaRHT1 that regulates GA signalling negatively. Endospermic ABA and GA appeared to have minimal roles in regulating germination at supraoptimal temperature. Germination inhibition by suboptimal temperature is associated with elevated ABA level in the embryo and endosperm tissues, mediated by induction of TaNCEDs and decreased expression of endospermic ABA catabolic genes (TaCYP707As), and increased ABA sensitivity in both tissues via upregulation of TaPYL5, TaSnRK2, ABI3 and ABI5 in the embryo and TaSnRK2 and ABI5 in the endosperm. Furthermore, suboptimal temperature suppresses GA synthesis in both tissues and GA sensitivity in the embryo via repressing GA biosynthetic genes (TaGA20ox and TaGA3ox2) and inducing TaRHT1, respectively. These results highlight that spatiotemporal modulation of ABA and GA metabolism and signalling in wheat seeds underlies germination response to temperature.

Rice NAC transcription factor ONAC095 plays opposite roles in drought and cold stress tolerance.

BackgroundThe NAC (NAM, ATAF and CUC) transcriptional factors constitute a large family with more than 150 members in rice and some of them have been demonstrated to play crucial roles in plant abiotic stress response. Here, we report the characterization of a rice stress-responsive NAC gene, ONAC095, and the exploration of its function in drought and cold stress tolerance.ResultsExpression of ONAC095 was up-regulated by drought stress and abscisic acid (ABA) but down-regulated by cold stress. ONAC095 protein had transactivation activity and the C2 domain in C-terminal was found to be critical for transactivation activity. Transgenic rice lines with overexpression of ONAC095 (ONAC095-OE) and dominant chimeric repressor-mediated suppression of ONAC095 (ONAC095-SRDX) were generated. The ONAC095-OE plants showed comparable phenotype to wild type under drought and cold stress conditions. However, the ONAC095-SRDX plants displayed an improved drought tolerance but exhibited an attenuated cold tolerance. The ONAC095-SRDX plants had decreased water loss rate, increased proline and soluble sugar contents, and up-regulated expression of drought-responsive genes under drought condition, whereas the ONAC095-SRDX plants accumulated excess reactive oxygen species, increased malondialdehyde content and down-regulated expression of cold-responsive genes under cold condition. Furthermore, ONAC095-SRDX plants showed an increased ABA sensitivity, contained an elevated ABA level, and displayed altered expression of ABA biosynthetic and metabolic genes as well as some ABA signaling-related genes.ConclusionFunctional analyses through dominant chimeric repressor-mediated suppression of ONAC095 demonstrate that ONAC095 plays opposite roles in drought and cold stress tolerance, acting as a negative regulator of drought response but as a positive regulator of cold response in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0897-y) contains supplementary material, which is available to authorized users.

The Chloroplast Protease AMOS1/EGY1 Affects Phosphate Homeostasis under Phosphate Stress.

Plastid intramembrane proteases in Arabidopsis (Arabidopsis thaliana) are involved in jasmonic acid biosynthesis, chloroplast development, and flower morphology. Here, we show that Ammonium-Overly-Sensitive1 (AMOS1), a member of the family of plastid intramembrane proteases, plays an important role in the maintenance of phosphate (P) homeostasis under P stress. Loss of function of AMOS1 revealed a striking resistance to P starvation. amos1 plants displayed retarded root growth and reduced P accumulation in the root compared to wild type (Col-0) under P-replete control conditions, but remained largely unaffected by P starvation, displaying comparable P accumulation and root and shoot growth under P-deficient conditions. Further analysis revealed that, under P-deficient conditions, the cell wall, especially the pectin fraction of amos1, released more P than that of wild type, accompanied by a reduction of the abscisic acid (ABA) level and an increase in ethylene production. By using an ABA-insensitive mutant, abi4, and applying ABA and ACC exogenously, we found that ABA inhibits cell wall P remobilization while ethylene facilitates P remobilization from the cell wall by increasing the pectin concentration, suggesting ABA can counteract the effect of ethylene. Furthermore, the elevated ABA level and the lower ethylene production also correlated well with the mimicked P deficiency in amos1 Thus, our study uncovers the role of AMOS1 in the maintenance of P homeostasis through ABA-antagonized ethylene signaling.

Core clock, SUB1, and ABAR genes mediate flooding and drought responses via alternative splicing in soybean.

Circadian clocks are a great evolutionary innovation and provide competitive advantage during the day/night cycle and under changing environmental conditions. The circadian clock mediates expression of a large proportion of genes in plants, achieving a harmonious relationship between energy metabolism, photosynthesis, and biotic and abiotic stress responses. Here it is shown that multiple paralogues of clock genes are present in soybean (Glycine max) and mediate flooding and drought responses. Differential expression of many clock and SUB1 genes was found under flooding and drought conditions. Furthermore, natural variation in the amplitude and phase shifts in PRR7 and TOC1 genes was also discovered under drought and flooding conditions, respectively. PRR3 exhibited flooding- and drought-specific splicing patterns and may work in concert with PRR7 and TOC1 to achieve energy homeostasis under flooding and drought conditions. Higher expression of TOC1 also coincides with elevated levels of abscisic acid (ABA) and variation in glucose levels in the morning and afternoon, indicating that this response to abiotic stress is mediated by ABA, endogenous sugar levels, and the circadian clock to fine-tune photosynthesis and energy utilization under stress conditions. It is proposed that the presence of multiple clock gene paralogues with variation in DNA sequence, phase, and period could be used to screen exotic germplasm to find sources for drought and flooding tolerance. Furthermore, fine tuning of multiple clock gene paralogues (via a genetic engineering approach) should also facilitate the development of flooding- and drought-tolerant soybean varieties.

Negative regulation of ABA signaling by WRKY33 is critical for Arabidopsis immunity towards Botrytis cinerea 2100.

The Arabidopsis mutant wrky33 is highly susceptible to Botrytis cinerea. We identified >1680 Botrytis-induced WRKY33 binding sites associated with 1576 Arabidopsis genes. Transcriptional profiling defined 318 functional direct target genes at 14 hr post inoculation. Comparative analyses revealed that WRKY33 possesses dual functionality acting either as a repressor or as an activator in a promoter-context dependent manner. We confirmed known WRKY33 targets involved in hormone signaling and phytoalexin biosynthesis, but also uncovered a novel negative role of abscisic acid (ABA) in resistance towards B. cinerea 2100. The ABA biosynthesis genes NCED3 and NCED5 were identified as direct targets required for WRKY33-mediated resistance. Loss-of-WRKY33 function resulted in elevated ABA levels and genetic studies confirmed that WRKY33 acts upstream of NCED3/NCED5 to negatively regulate ABA biosynthesis. This study provides the first detailed view of the genome-wide contribution of a specific plant transcription factor in modulating the transcriptional network associated with plant immunity.

Agrochemical control of plant water use using engineered abscisic acid receptors.

Rising temperatures and lessening fresh water supplies are threatening agricultural productivity and have motivated efforts to improve plant water use and drought tolerance. During water deficit, plants produce elevated levels of abscisic acid (ABA), which improves water consumption and stress tolerance by controlling guard cell aperture and other protective responses. One attractive strategy for controlling water use is to develop compounds that activate ABA receptors, but agonists approved for use have yet to be developed. In principle, an engineered ABA receptor that can be activated by an existing agrochemical could achieve this goal. Here we describe a variant of the ABA receptor PYRABACTIN RESISTANCE 1 (PYR1) that possesses nanomolar sensitivity to the agrochemical mandipropamid and demonstrate its efficacy for controlling ABA responses and drought tolerance in transgenic plants. Furthermore, crystallographic studies provide a mechanistic basis for its activity and demonstrate the relative ease with which the PYR1 ligand-binding pocket can be altered to accommodate new ligands. Thus, we have successfully repurposed an agrochemical for a new application using receptor engineering. We anticipate that this strategy will be applied to other plant receptors and represents a new avenue for crop improvement.