ABSCISIC ACID SIGNAL TRANSDUCTION

Effect of Abscisic Acid on Accumulation of Five Active Components in Root of Glycyrrhiza uralensis

Licorice is one of the most generally used herbal medicines in the world; however, wild licorice resources have decreased drastically. Cultivated Glycyrrhiza uralensis Fischer are the main source of licorice at present, but the content of main active components in cultivated G. uralensis are lower than in wild G. uralensis. Therefore, the production of high-quality cultivated G. uralensis is an urgent issue for the research and production fields. In this study, the content of five active components and seven endogenous phytohormones in cultivated G. uralensis (two-year-old) were determined by high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), respectively. Furthermore, different concentrations (25-200 mg/L) of exogenous abscisic acid (ABA) were sprayed on the leaves of G. uralensis in the fast growing period. Results showed that ABA, zeatin riboside (ZR), and dihydrozeatin riboside (DHZR) had strong correlation with active components. In addition, the content of five active components increased remarkably after ABA treatment. Our results indicate that ABA is significantly related to the accumulation of active components in G. uralensis, and the application of exogenous ABA at the proper concentration is able to promote the accumulation of main components in G. uralensis.

Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments

Crop productivity is affected by environmental and genetic factors. Microbes that are beneficial to plants are used to enhance the crop yield and are alternatives to chemical fertilizers and pesticides. Pseudomonas and Bacillus species are the predominant plant growth-promoting bacteria. The spore-forming ability of Bacillus is distinguished from that of Pseudomonas. Members of this genus also survive for a long time under unfavorable environmental conditions. Bacillus spp. secrete several metabolites that trigger plant growth and prevent pathogen infection. Limited studies have been conducted to understand the physiological changes that occur in crops in response to Bacillus spp. to provide protection against adverse environmental conditions. This review describes the current understanding of Bacillus-induced physiological changes in plants as an adaptation to abiotic and biotic stresses. During water scarcity, salinity and heavy metal accumulate in soil, Bacillus spp. produce exopolysaccharides and siderophores, which prevent the movement of toxic ions and adjust the ionic balance and water transport in plant tissues while controlling the pathogenic microbial population. In addition, the synthesis of indole-3-acetic acid, gibberellic acid and1-aminocyclopropane-1-carboxylate (ACC) deaminase by Bacillus regulates the intracellular phytohormone metabolism and increases plant stress tolerance. Cell-wall-degrading substances, such as chitosanase, protease, cellulase, glucanase, lipopeptides and hydrogen cyanide from Bacillus spp. damage the pathogenic bacteria, fungi, nematodes, viruses and pests to control their populations in plants and agricultural lands. The normal plant metabolism is affected by unfavorable environmental stimuli, which suppress crop growth and yield. Abiotic and biotic stress factors that have detrimental effects on crops are mitigated by Bacillus-induced physiological changes, including the regulation of water transport, nutrient up-take and the activation of the antioxidant and defense systems. Bacillus association stimulates plant immunity against stresses by altering stress-responsive genes, proteins, phytohormones and related metabolites. This review describes the beneficial effect of Bacillus spp. on crop plants, which improves plant productivity under unfavorable climatic conditions, and the current understanding of the mitigation mechanism of Bacillus spp. in stress-tolerant and/or stress-resistant plants.

Identification and Functional Divergence Analysis of WOX Gene Family in Paper Mulberry

The WOX (WUSCHEL-related homeobox) is a plant-specific transcription factor involved in plant development and stress response. However, few studies have been reported on the WOX gene in woody plants. In this study, 10 BpWOX genes were isolated from paper mulberry by RACE-PCR and categorized into three clades through phylogenetic analysis, ancient, intermediate and WUS clade. Among them, five members had the transcriptional activity detected by yeast one-hybrid and seven were uniquely localized to the nucleus through green fluorescent protein (GFP) observation. The expression patterns of BpWOX genes in different tissues and under diverse treatments were quantified by the qRT-PCR method. Results showed that BpWUS was expressed in the apical bud, stem and root, BpWOX5 and BpWOX7 functioned only in the root tip, and three BpWOXs regulated leaf development redundantly. BpWOX9 and BpWOX10 were induced by indole-3-acetic acid (IAA) or jasmonic acid (JA), while BpWOX2 was repressed by five phytohormones. Interestingly, most BpWOX genes were responsive to the abiotic stress stimuli of drought, salt, cold, and cadmium (CdCl₂). Together, our study revealed that BpWOXs were functionally divergent during paper mulberry development and environmental adaptation, which might be related to their evolutionary relationships. Our work will benefit the systematic understanding of the precise function of WOX in plant development and environmental stress responses.

BdCIPK31, a Calcineurin B-Like Protein-Interacting Protein Kinase, Regulates Plant Response to Drought and Salt Stress

Calcineurin B-like protein interacting protein kinases (CIPKs) are vital elements in plant abiotic stress signaling pathways. However, the functional mechanism of CIPKs has not been understood clearly, especially in Brachypodium distachyon, a new monocot model plant. In this study, BdCIPK31, a CIPK gene from B. distachyon was characterized. BdCIPK31 was downregulated by polyethylene glycol, NaCl, H2O2, and abscisic acid (ABA) treatments. Transgenic tobacco plants overexpressing BdCIPK31 presented improved drought and salt tolerance, and displayed hypersensitive response to exogenous ABA. Further investigations revealed that BdCIPK31 functioned positively in ABA-mediated stomatal closure, and transgenic tobacco exhibited reduced water loss under dehydration conditions compared with the controls. BdCIPK31 also affected Na+/K+ homeostasis and root K+ loss, which contributed to maintain intracellular ion homeostasis under salt conditions. Moreover, the reactive oxygen species scavenging system and osmolyte accumulation were enhanced by BdCIPK31 overexpression, which were conducive for alleviating oxidative and osmotic damages. Additionally, overexpression of BdCIPK31 could elevate several stress-associated gene expressions under stress conditions. In conclusion, BdCIPK31 functions positively to drought and salt stress through ABA signaling pathway. Overexpressing BdCIPK31 functions in stomatal closure, ion homeostasis, ROS scavenging, osmolyte biosynthesis, and transcriptional regulation of stress-related genes.

Identification and expression profiling of Oryza sativa nucleotidyl transferase protein (NTP) genes under various stress conditions

Nucleotidyl transferase proteins (NTPs) modify the 3' ends of mature small RNAs, leading to their stabilization or degradation. The first two plant NTPs, HESO1 and URT1, were identified in Arabidopsis. These two NTPs act cooperatively to uridylate the 3' terminal nucleotide of specific miRNAs, leading to their degradation and thereby affecting the expression of genes regulated by these miRNAs. Little is known about NTPs in other plants. Here, we performed a comprehensive analysis of 13 putative NTP genes in Oryza sativa, a major crop in global food production. Phylogenetic analysis showed homology among the NTPs from diverse plant species. Analysis of cis-acting promoter elements at OsNTP loci identified several stress response elements, indicating the potential involvement of NTPs in plant stress responses. The promoter analysis results were validated by expression of the OsNTP genes under abiotic stress treatments, with some OsNTPs clearly induced by salt, drought or cold stress. Moreover, the RT-PCR data showed that the OsNTP genes were differentially expressed in different developmental stages and tissues. These findings suggest that NTPs, which are involved in small RNA metabolic pathways, might play roles in plant stress resistance.

The function of OsbHLH068 is partially redundant with its homolog, AtbHLH112, in the regulation of the salt stress response but has opposite functions to control flowering in Arabidopsis

KEY MESSAGE

The homologous genes OsbHLH068 and AtbHLH112 have partially redundant functions in the regulation of the salt stress response but opposite functions to control flowering in Arabidopsis. The transcription factor (TF) basic/Helix-Loop-Helix (bHLH) is important for plant growth, development, and stress responses. OsbHLH068, which is a homologous gene of AtbHLH112 that is up-regulated under drought and salt stresses, as indicated by previous microarray data analysis. However, the intrinsic function of OsbHLH068 remains unknown. In the present study, we characterized the function and compared the role of OsbHLH068 with that of its homolog, AtbHLH112. Histochemical GUS staining indicated that OsbHLH068 and AtbHLH112 share a similar expression pattern in transgenic Arabidopsis during the juvenile-to-adult phase transition. Heterologous overexpression of OsbHLH068 in Arabidopsis delays seed germination, decreases salt-induced H2O2 accumulation, and promotes root elongation, whereas AtbHLH112 knock-out mutant displays an opposite phenotype. Both OsbHLH068-overexpressing transgenic Arabidopsis seedlings and the Atbhlh112 mutant display a late-flowering phenotype. Moreover, the expression of OsbHLH068-GFP driven by an AtbHLH112 promoter can compensate for the germination deficiency in the Atbhlh112 mutant, but the delayed-flowering phenotype tends to be more severe. Further analysis by microarray and qPCR indicated that the expression of FT is down-regulated in both OsbHLH068-overexpressing Arabidopsis plants and Atbhlh112 mutant plants, whereas SOC1 but not FT is highly expressed in AtbHLH112-overexpressing Arabidopsis plants. A comparative transcriptomic analysis also showed that several stress-responsive genes, such as AtERF15 and AtPUB23, were affected in both OsbHLH068- and AtbHLH112-overexpressing transgenic Arabidopsis plants. Thus, we propose that OsbHLH068 and AtbHLH112 share partially redundant functions in the regulation of abiotic stress responses but have opposite functions to control flowering in Arabidopsis, presumably due to the evolutionary functional divergence of homolog-encoded proteins.

Plant growth promoting effect of Bacillus amyloliquefaciens H-2-5 on crop plants and influence on physiological changes in soybean under soil salinity

This study was aimed to identify plant growth-promoting bacterial isolates from soil samples and to investigate their ability to improve plant growth and salt tolerance by analysing phytohormones production and phosphate solubilisation. Among the four tested bacterial isolates (I-2-1, H-1-4, H-2-3, and H-2-5), H-2-5 was able to enhance the growth of Chinese cabbage, radish, tomato, and mustard plants. The isolated bacterium H-2-5 was identified as Bacillus amyloliquefaciens H-2-5 based on 16S rDNA sequence and phylogenetic analysis. The secretion of gibberellins (GA₄, GA₈, GA₉, GA₁₉, and GA₂₀) from B. amyloliquefaciens H-2-5 and their phosphate solubilisation ability may contribute to enhance plant growth. In addition, the H-2-5-mediated mitigation of short term salt stress was tested on soybean plants that were affected by sodium chloride. Abscisic acid (ABA) produced by the H-2-5 bacterium suppressed the NaCl-induced stress effects in soybean by enhancing plant growth and GA₄ content, and by lowering the concentration of ABA, salicylic acid, jasmonic acid, and proline. These results suggest that GAs, ABA production, and the phosphate solubilisation capacity of B. amyloliquefaciens H-2-5 are important stimulators that promote plant growth through their interaction and also to improve plant growth by physiological changes in soybean at saline soil.

Physiological and biochemical perspectives of non-salt tolerant plants during bacterial interaction against soil salinity

Climatic changes on earth affect the soil quality of agricultural lands, especially by increasing salt deposition in soil, which results in soil salinity. Soil salinity is a major challenge to growth and reproduction among glycophytes (including all crop plants). Soil bacteria present in the rhizosphere and/or roots naturally protect plants from the adverse effects of soil salinity by reprogramming the stress-induced physiological changes in plants. Bacteria can enrich the soil with major nutrients (nitrogen, phosphorus, and potassium) in a form easily available to plants and prevent the transport of excess sodium to roots (exopolysaccharides secreted by bacteria bind with sodium ions) for maintaining ionic balance and water potential in cells. Salinity also affects plant growth regulators and suppresses seed germination and root and shoot growth. Bacterial secretion of indole-3-acetic acid and gibberellins compensates for the salt-induced hormonal decrease in plants, and bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase synthesis decreases ethylene production to stimulate plant growth. Furthermore, bacteria modulate the redox state of salinity-affected plants by enhancing antioxidants and polyamines, which leads to increased photosynthetic efficiency. Bacteria-induced accumulation of compatible solutes in stressed plants regulates plant cellular activities and prevents salt stress damage. Plant-bacterial interaction reprograms the expression of salt stress-responsive genes and proteins in salinity-affected plants, resulting in a precise stress mitigation metabolism as a defense mechanism. Soil bacteria increase the fertility of soil and regulate the plant functions to prevent the salinity effects in glycophytes. This review explains the current understanding about the physiological changes induced in glycophytes during bacterial interaction to alleviate the adverse effects of soil salinity stress.

Abscisic acid signaling is involved in regulating the mitogen-activated protein kinase cascade module, AIK1-MKK5-MPK6

Abscisic acid (ABA) plays roles in plant growth and development and in stress responses. Recently, we found that ABA regulates ABA-insensitive protein kinase 1 (AIK1), a mitogen-activated protein kinase kinase kinase. Compared with wild-type, aik1-1 showed downregulation of ABA-responsive genes (RD29A, MYC2, ABI3 and ABI4). Under ABA treatment, the transcript level of KRP1 (Kip-related protein, a cyclin-dependent kinase inhibitor) was lower in aik1-1 than in wild-type. The activity of ABA-activated MPK6 was decreased in abi1 abi2, and abi1 abi2 hab1, and increased in snrk2.2 snrk2.3 and pyr1 pyl1 pyl2 pyl4 mutants. These results indicated that AIK1-MKK5-MPK6 functions in ABA responses and requires ABA-responsive gene expression to regulate ABA-inhibited root growth and cell division. The ABA signaling pathway regulates this MAPK cascade.

Molecular and Functional Characterization of Wheat ARGOS Genes Influencing Plant Growth and Stress Tolerance

Auxin Regulated Gene involved in Organ Size (ARGOS) is significantly and positively associated with organ size and is involved in abiotic stress responses in plants. However, no studies on wheat ARGOS genes have been reported to date. In the present study, three TaARGOS homoeologous genes were isolated and located on chromosomes 4A, 4B, and 4D of bread wheat, all of which are highly conserved in wheat and its wild relatives. Comparisons of gene expression in different tissues demonstrated that the TaARGOSs were mainly expressed in the stem. Furthermore, the TaARGOS transcripts were significantly induced by drought, salinity, and various phytohormones. Transient expression of the TaARGOS-D protein in wheat protoplasts showed that TaARGOS-D localized to the endoplasmic reticulum. Moreover, overexpression of TaARGOS-D in Arabidopsis resulted in an enhanced germination rate, larger rosette diameter, increased rosette leaf area, and higher silique number than in wild-type (WT) plants. The roles of TaARGOS-D in the control of plant growth were further studied via RNA-seq, and it was found that 105 genes were differentially expressed; most of these genes were involved in 'developmental processes.' Interestingly, we also found that overexpression of TaARGOS-D in Arabidopsis improved drought and salinity tolerance and insensitivity to ABA relative to that in WT plants. Taken together, these results demonstrate that the TaARGOSs are involved in seed germination, seedling growth, and abiotic stress tolerance.

Improved cold tolerance in Elymus nutans by exogenous application of melatonin may involve ABA-dependent and ABA-independent pathways

Melatonin is an important secondary messenger that plays a central role in plant growth, as well as abiotic and biotic stress tolerance. However, the underlying physiological and molecular mechanisms of melatonin-mediated cold tolerance, especially interactions between melatonin and other key molecules in the plant stress response, remain unknown. Here, the interrelation between melatonin and abscisic acid (ABA) was investigated in two genotypes of Elymus nutans Griseb., the cold-tolerant Damxung (DX) and the cold-sensitive Gannan (GN) under cold stress. Pre-treatment with exogenous melatonin or ABA alleviated oxidative injury via scavenging ROS, while enhancing both antioxidant enzyme activities and non-enzymatic antioxidant contents. Treatment of fluridone, an ABA biosynthesis inhibitor caused membrane lipid peroxidation and lowered melatonin-induced antioxidant defense responses. It is worth noting that cold stress significantly induced both endogenous melatonin and ABA levels in both genotypes. Application of melatonin increased ABA production, while fluridone significantly suppressed melatonin-induced ABA accumulation. ABA and fluridone pre-treatments failed to affect the endogenous melatonin concentration. Moreover, exogenous melatonin up-regulated the expression of cold-responsive genes in an ABA-independent manner. These results indicate that both ABA-dependent and ABA-independent pathways may contribute to melatonin-induced cold tolerance in E. nutans.

Three zinc-finger RNA-binding proteins in cabbage (Brassica rapa) play diverse roles in seed germination and plant growth under normal and abiotic stress conditions

Despite the increasing understanding of the stress-responsive roles of zinc-finger RNA-binding proteins (RZs) in several plant species, such as Arabidopsis thaliana, wheat (Triticum aestivum) and rice (Oryza sativa), the functions of RZs in cabbage (Brassica rapa) have not yet been elucidated. In this study, the functional roles of the three RZ family members present in the cabbage genome, designated as BrRZ1, BrRZ2 and BrRZ3, were investigated in transgenic Arabidopsis under normal and environmental stress conditions. Subcellular localization analysis revealed that all BrRZ proteins were exclusively localized in the nucleus. The expression levels of each BrRZ were markedly increased by cold, drought or salt stress and by abscisic acid (ABA) treatment. Expression of BrRZ3 in Arabidopsis retarded seed germination and stem growth and reduced seed yield of Arabidopsis plants under normal growth conditions. Germination of BrRZ2- or BrRZ3-expressing Arabidopsis seeds was delayed compared with that of wild-type seeds under dehydration or salt stress conditions and cold stress conditions, respectively. Seedling growth of BrRZ3-expressing transgenic Arabidopsis plants was significantly inhibited under salt, dehydration or cold stress conditions. Notably, seedling growth of all three BrRZ-expressing transgenic Arabidopsis plants was inhibited upon ABA treatment. Importantly, all BrRZs possessed RNA chaperone activity. Taken together, these results indicate that the three cabbage BrRZs harboring RNA chaperone activity play diverse roles in seed germination and seedling growth of plants under abiotic stress conditions as well as in the presence of ABA.

Overexpression of Pyrabactin Resistance-Like Abscisic Acid Receptors Enhances Drought, Osmotic, and Cold Tolerance in Transgenic Poplars

Abscisic acid (ABA) has been known participate in a wider range of adaptive responses to diverse environmental abiotic stresses such as drought, osmosis, and low temperatures. ABA signaling is initiated by its receptors PYR/PYL/RCARs, a type of soluble proteins with a conserved START domain which can bind ABA and trigger the downstream pathway. Previously, we discovered that poplar (Populus trichocarpa) genome encodes 14 PYR/PYL/RCAR orthologs (PtPYRLs), and two of them, PtPYRL1 and PtPYRL5 have been functionally characterized to positively regulate drought tolerance. However, the physiological function of these ABA receptors in poplar remains uncharacterized. Here, we generated transgenic poplar plants overexpressing PtPYRL1 and PtPYRL5 and found that they exhibited more vigorous growth and produced greater biomass when exposed to drought stress. The improved drought tolerance was positively correlated with the key physiological responses dictated by the ABA signaling pathway, including increase in stomatal closure and decrease in leaf water loss. Further analyses revealed that overexpression lines showed improved capacity in scavenging reactive oxygen species and enhanced the activation of antioxidant enzymes under drought stress. Moreover, overexpression of PtPYRL1 or PtPYRL5 significantly increased the poplar resistance to osmotic and cold stresses. In summary, our results suggest that constitutive expression of PtPYRL1 and PtPYRL5 significantly enhances the resistance to drought, osmotic and cold stresses by positively regulating ABA signaling in poplar.

Overexpression of Muscadinia rotundifolia CBF2 gene enhances biotic and abiotic stress tolerance in Arabidopsis

C-repeat-binding factor dehydration-responsive element-binding factor 1C (CBF2/DREB1C) gene encodes a small family of transcriptional activator that has been described as playing an important role in freezing tolerance and cold acclimation of plants. We here report that CBF2 gene also plays an important role in the early response to the pathogen infection of grapevine downy mildew disease. The expression level of CBF2 increased dramatically and reached a peak at 7 h after infection in immune grapevine Muscadinia rotundifolia 'Noble', which was much faster than moderate resistant Vitis amurensis 'PI1288' and susceptible Vitis vinifera 'Cabernet Sauvignon'. Muscadinia rotundifolia MrCBF2 exhibited amino acid domains characteristic of Vitis CBF2 proteins with unique features including rich serine repeats and slight differences in NLS, DSAWRL, and AP2 domains. The MrCBF2 gene was introduced to Arabidopsis 'COL0' which are susceptible to downy mildew pathogen. The transgenic lines showed an increased resistance to downy mildew disease and more accumulation of SA as well as higher expression of pathogenesis-related (PR) genes (AtPR1, AtPR4, and AtPR5) as a consequence of MrCBF2 overexpression. Besides, constitutive expression of MrCBF2 enhanced phytohormone abscisic acid (ABA)-independent drought tolerance of transgenic plants. Freezing tolerance of transgenic lines was also enhanced accompanied with an increase in the expression of the cold-regulated genes AtCOR, AtCOR15A, AtKIN1, AtRD29A, and AtSuSy. In addition, the development of MrCBF2-overexpressing plants was seen to be altered and resulted in growth retardation, dwarfism, late flowering, and prone rosette leaves, which may be because of an increase in the gene expression of partial DELLA proteins and DDF1.

Chickpea transcription factor CaTLP1 interacts with protein kinases, modulates ROS accumulation and promotes ABA-mediated stomatal closure

Tubby and Tubby-like proteins (TLPs), in mammals, play critical roles in neural development, while its function in plants is largely unknown. We previously demonstrated that the chickpea TLP, CaTLP1, participates in osmotic stress response and might be associated with ABA-dependent network. However, how CaTLP1 is connected to ABA signaling remains unclear. The CaTLP1 was found to be engaged in ABA-mediated gene expression and stomatal closure. Complementation of the yeast yap1 mutant with CaTLP1 revealed its role in ROS scavenging. Furthermore, complementation of Arabidopsis attlp2 mutant displayed enhanced stress tolerance, indicating the functional conservation of TLPs across the species. The presence of ABA-responsive element along with other motifs in the proximal promoter regions of TLPs firmly established their involvement in stress signalling pathways. The CaTLP1 promoter driven GUS expression was restricted to the vegetative organs, especially stem and rosette leaves. Global protein expression profiling of wild-type, attlp2 and complemented Arabidopsis plants revealed 95 differentially expressed proteins, presumably involved in maintaining physiological and biological processes under dehydration. Immunoprecipitation assay revealed that protein kinases are most likely to interact with CaTLP1. This study provides the first demonstration that the TLPs act as module for ABA-mediated stomatal closure possibly via interaction with protein kinase.

Gene expression and physiological responses associated to stomatal functioning in Rosa×hybrida grown at high relative air humidity

High relative air humidity (RH≥85%) during growth disturbs stomatal functioning, resulting in excessive water loss in conditions of high evaporative demand. We investigated the expression of nine abscisic acid (ABA)-related genes (involved in ABA biosynthesis, oxidation and conjugation) and two non-ABA related genes (involved in the water stress response) aiming to better understand the mechanisms underlying contrasting stomatal functioning in plants grown at high RH. Four rose genotypes with contrasting sensitivity to high RH (one sensitive, one tolerant and two intermediate) were grown at moderate (62±3%) or high (89±4%) RH. The sensitive genotype grown at high RH showed a significantly higher stomatal conductance (g_s) and water loss in response to closing stimuli as compared to the other genotypes. Moreover, high RH reduced the leaf ABA concentration and its metabolites to a greater extent in the sensitive genotype as compared to the tolerant one. The large majority of the studied genes had a relevant role on stomatal functioning (NCED1, UGT75B2, BG2, OST1, ABF3 and Rh-APX) while two others showed a minor contribution (CYP707A3 and BG1) and AAO3, CYP707A1 and DREB1B did not contribute to the tolerance trait. These results show that multiple genes form a highly complex regulatory network acting together towards the genotypic tolerance to high RH.

Abscisic acid controlled sex before transpiration in vascular plants

Sexual reproduction in animals and plants shares common elements, including sperm and egg production, but unlike animals, little is known about the regulatory pathways that determine the sex of plants. Here we use mutants and gene silencing in a fern species to identify a core regulatory mechanism in plant sexual differentiation. A key player in fern sex differentiation is the phytohormone abscisic acid (ABA), which regulates the sex ratio of male to hermaphrodite tissues during the reproductive cycle. Our analysis shows that in the fern Ceratopteris richardii, a gene homologous to core ABA transduction genes in flowering plants [SNF1-related kinase2s (SnRK2s)] is primarily responsible for the hormonal control of sex determination. Furthermore, we provide evidence that this ABA-SnRK2 signaling pathway has transitioned from determining the sex of ferns to controlling seed dormancy in the earliest seed plants before being co-opted to control transpiration and CO₂ exchange in derived seed plants. By tracing the evolutionary history of this ABA signaling pathway from plant reproduction through to its role in the global regulation of plant-atmosphere gas exchange during the last 450 million years, we highlight the extraordinary effect of the ABA-SnRK2 signaling pathway in plant evolution and vegetation function.

Genome-wide identification of the expansin gene family in tobacco (Nicotiana tabacum)

Expansins are pH-dependent cell wall loosening proteins which form a large family in plants. They have been shown to be involved in various developmental processes and been implicated in enabling plants' ability to absorb nutrients from the soil as well as conferring biotic and abiotic stress resistances. It is therefore clear that they can be potential targets in genetic engineering for crop improvement. Tobacco (Nicotiana tabacum) is a major crop species as well as a model organism. Considering that only a few tobacco expansins have been studied, a genome-wide analysis of the tobacco expansin gene family is necessary. In this study, we identified 52 expansins in tobacco, which were classified into four subfamilies: 36 NtEXPAs, 6 NtEXPBs, 3 NtEXLAs and 7 NtEXLBs. Compared to other species, the NtEXLB subfamily size was relatively larger. Phylogenetic analysis showed that the 52 tobacco expansins were divided into 13 subgroups. Gene structure analysis revealed that genes within subfamilies/subgroups exhibited similar characteristics such as gene structure and protein motif arrangement. Whole-genome duplication and tandem duplication events may have played important roles in the expanding of tobacco expansins. Cis-Acting element analysis revealed that each expansin gene was regulated or several expansin genes were co-regulated by both internal and environmental factors. 35 of these genes were identified as being expressed according to a microarray analysis. In contrast to most NtEXPAs which had higher expression levels in young organs, NtEXLAs and NtEXLBs were preferentially expressed in mature or senescent tissues, suggesting that they might play different roles in different organs or at different developmental stages. As the first step towards genome-wide analysis of the tobacco expansin gene family, our work provides solid background information related to structure, evolution and expression as well as regulatory cis-acting elements of the tobacco expansins. This information will provide a strong foundation for cloning and functional exploration of expansin genes in tobacco.

Involvement of ABA- and H2O2-dependent cytosolic glucose-6-phosphate dehydrogenase in maintaining redox homeostasis in soybean roots under drought stress

The roles of abscisic acid (ABA) and hydrogen peroxide (H2O2) in inducing glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) activity and the possible roles of G6PDH in regulating ascorbate-glutathione (AsA-GSH) cycle were investigated in soybean (Glycine max L.) roots under drought stress. Drought caused a marked increase of the total and cytosolic G6PDH activities and triggered a rapid ABA and H2O2 accumulation in soybean roots. Exogenous ABA or H2O2 treatment elevated the total and cytosolic G6PDH activities, whereas suppressing ABA or H2O2 production inhibited the drought-induced increase in total and cytosolic G6PDH activities, suggesting that ABA and H2O2 are required for drought-induced increase of total G6PDH activity, namely cytosolic G6PDH activity. Furthermore, ABA induced H2O2 production by stimulating NADPH oxidase activity under drought stress. Moreover, drought significantly increased the contents of AsA and GSH and the activities of key enzymes in AsA-GSH cycle, while application of G6PDH inhibitor to seedlings significantly reduced the above effect induced by drought. Taken together, these results indicate that H2O2 acting as a downstream signaling molecule of ABA mediates drought-induced increase in cytosolic G6PDH activity, and that enhanced cytosolic G6PDH activity maintains cellular redox homeostasis by regulating AsA-GSH cycle in soybean roots.

Overexpression of an Arabidopsis cysteine-rich receptor-like protein kinase, CRK5, enhances abscisic acid sensitivity and confers drought tolerance

Receptor-like kinases (RLKs) have been reported to regulate many developmental and defense process, but only a few members have been functionally characterized. In the present study, our observations suggest that one of the RLKs, a membrane-localized cysteine-rich receptor-like protein kinase, CRK5, is involved in abscisic acid (ABA) signaling in Arabidopsis thaliana Overexpression of CRK5 increases ABA sensitivity in ABA-induced early seedling growth arrest and promotion of stomatal closure and inhibition of stomatal opening. Interestingly, and importantly, overexpression of CRK5 enhances plant drought tolerance without affecting plant growth at the mature stages and plant productivity. Transgenic lines overexpressing a mutated form of CRK5, CRK5 (K372E) with the change of the 372nd conserved amino acid residue from lysine to glutamic acid in its kinase domain, result in wild-type ABA and drought responses, supporting the role of CRK5 in ABA signaling. The loss-of-function mutation of the CRK5 gene does not affect the ABA response, while overexpression of two homologs of CRK5, CRK4 and CRK19, confers ABA responses, suggesting that these CRK members function redundantly. We further showed that WRKY18, WRKY40 and WRKY60 transcription factors repress the expression of CRK5, and that CRK5 likely functions upstream of ABI2 in ABA signaling. These findings help in understanding the complex ABA signaling network.

AsHSP17, a creeping bentgrass small heat shock protein modulates plant photosynthesis and ABA-dependent and independent signalling to attenuate plant response to abiotic stress

Heat shock proteins (HSPs) are molecular chaperones that accumulate in response to heat and other abiotic stressors. Small HSPs (sHSPs) belong to the most ubiquitous HSP subgroup with molecular weights ranging from 12 to 42 kDa. We have cloned a new sHSP gene, AsHSP17 from creeping bentgrass (Agrostis stolonifera) and studied its role in plant response to environmental stress. AsHSP17 encodes a protein of 17 kDa. Its expression was strongly induced by heat in both leaf and root tissues, and by salt and abscisic acid (ABA) in roots. Transgenic Arabidopsis plants constitutively expressing AsHSP17 exhibited enhanced sensitivity to heat and salt stress accompanied by reduced leaf chlorophyll content and decreased photosynthesis under both normal and stressed conditions compared to wild type. Overexpression of AsHSP17 also led to hypersensitivity to exogenous ABA and salinity during germination and post-germinative growth. Gene expression analysis indicated that AsHSP17 modulates expression of photosynthesis-related genes and regulates ABA biosynthesis, metabolism and ABA signalling as well as ABA-independent stress signalling. Our results suggest that AsHSP17 may function as a protein chaperone to negatively regulate plant responses to adverse environmental stresses through modulating photosynthesis and ABA-dependent and independent signalling pathways.

Effects of exogenous abscisic acid on phenolic characteristics of red Vitis vinifera grapes and wines

The effects of exogenous abscisic acid (ABA) on phenolic characteristics of grapes and wines were investigated in Vitis vinifera cvs. Merlot and Cabernet Sauvignon. Exogenous ABA treatment at veraison significantly improved phenolic contents, mainly anthocyanins and flavonols, and antioxidant properties of the grape skins, but had no effects on total phenolics and antioxidant activities in the seeds or on basic fruit qualities. The wines made from ABA-treated grapes were also consequently enhanced in total phenolics, anthocyanins, flavonols and antioxidant activities. The proportions of methylated anthocyanins in the skins and acylated anthocyanins and derived pigments in the wines were decreased to some degree by exogenous ABA treatment. No distinct relationships were observed between ABA concentrations and phenolic characteristics, and the effects were observed even with 200 mg/L ABA. The results revealed that exogenous ABA applied at veraison offered opportunities to improve phenolic contents and nutritional values of grape skins and wines.

The Craterostigma plantagineum glycine-rich protein CpGRP1 interacts with a cell wall-associated protein kinase 1 (CpWAK1) and accumulates in leaf cell walls during dehydration

Craterostigma plantagineum tolerates extreme desiccation. Leaves of this plant shrink and extensively fold during dehydration and expand again during rehydration, preserving their structural integrity. Genes were analysed that may participate in the reversible folding mechanism. Analysis of transcripts abundantly expressed in desiccated leaves identified a gene putatively coding for an apoplastic glycine-rich protein (CpGRP1). We studied the expression, regulation and subcellular localization of CpGRP1 and its ability to interact with a cell wall-associated protein kinase (CpWAK1) to understand the role of CpGRP1 in the cell wall during dehydration. The CpGRP1 protein accumulates in the apoplast of desiccated leaves. Analysis of the promoter revealed that the gene expression is mainly regulated at the transcriptional level, is independent of abscisic acid (ABA) and involves a drought-responsive cis-element (DRE). CpGRP1 interacts with CpWAK1 which is down-regulated in response to dehydration. Our data suggest a role of the CpGRP1-CpWAK1 complex in dehydration-induced morphological changes in the cell wall during dehydration in C. plantagineum. Cell wall pectins and dehydration-induced pectin modifications are predicted to be involved in the activity of the CpGRP1-CpWAK1 complex.

Overexpression of human peroxisomal enoyl-CoA delta isomerase2 HsPECI2, an ortholog of bamboo expressed during gregarious flowering alters salinity stress responses and polar lipid content in tobacco

Peroxisomal enoyl-CoA delta isomerase2 (PECI2) is one of the key enzymes that has critical role in lipid metabolism and plant development during salt stress. Seven out of ten tobacco plants overexpressing human PECI2 (HsPECI2) with PTS1-sequence showed hypersensitivity to salt. Under salt-stress, T2 transformed plants (HsPECI2) displayed reduced primary root, delayed shoot-growth, and visibly smaller rosette leaves turning pale yellow as compared to the pKYLX71 vector control plant. Also, we found altered reactive oxygen species (ROS) levels and reduced catalase activity in 100mM sodium chloride (NaCl) treated HsPECI2 transformed plant compared with the pKYLX71 counterpart. ESI-MS/MS data showed that the polar lipids were differentially modulated upon salt treatment in HsPECI2 transformed and pKYLX71 plants as compared with the respective untreated counterpart. Notably, the levels of monogalactosyldiacylglycerol and phosphatidic acid varied significantly, whereas phosphatidylcholine, phosphatidylserine and digalactosyldiacylglycerol contents were moderately upregulated. In parallel, abscisic acid (ABA) responsiveness assay confirmed insensitivity of HsPECI2 transformed plant towards ABA. Overall our data proclaim that HsPECI2 play multifunctional role in normal development and response to salinity stress apart from its primary role in β-oxidation.

Global Plant Stress Signaling: Reactive Oxygen Species at the Cross-Road

Current technologies have changed biology into a data-intensive field and significantly increased our understanding of signal transduction pathways in plants. However, global defense signaling networks in plants have not been established yet. Considering the apparent intricate nature of signaling mechanisms in plants (due to their sessile nature), studying the points at which different signaling pathways converge, rather than the branches, represents a good start to unravel global plant signaling networks. In this regard, growing evidence shows that the generation of reactive oxygen species (ROS) is one of the most common plant responses to different stresses, representing a point at which various signaling pathways come together. In this review, the complex nature of plant stress signaling networks will be discussed. An emphasis on different signaling players with a specific attention to ROS as the primary source of the signaling battery in plants will be presented. The interactions between ROS and other signaling components, e.g., calcium, redox homeostasis, membranes, G-proteins, MAPKs, plant hormones, and transcription factors will be assessed. A better understanding of the vital roles ROS are playing in plant signaling would help innovate new strategies to improve plant productivity under the circumstances of the increasing severity of environmental conditions and the high demand of food and energy worldwide.

Overexpression of the NDR1/HIN1-Like Gene NHL6 Modifies Seed Germination in Response to Abscisic Acid and Abiotic Stresses in Arabidopsis

NHL (NDR1/HIN1-like) genes play crucial roles in pathogen induced plant responses to biotic stress. Here, we report the possible function of NHL6 in plant response to abscisic acid (ABA) and abiotic stress. NHL6 was highly expressed in non-germinated seeds, and its expression was strongly induced by ABA and multiple abiotic stress signals. Loss-of-function of NHL6 decreased sensitivity to ABA in the early developmental stages including seed germination and post-germination seedling growth of the nhl6 mutants. However, overexpression of NHL6 increased sensitivity to ABA, salt and osmotic stress of the transgenic plants. Further studies indicated that the increased sensitivity in the 35S::NHL6 overexpressing plants could be a result of both ABA hypersensitivity and increased endogenous ABA accumulation under the stress conditions. It was also seen that the ABA-responsive element binding factors AREB1, AREB2 and ABF3 could regulate NHL6 expression at transcriptional level. Our results indicate that NHL6 plays an important role in the abiotic stresses-induced ABA signaling and biosynthesis, particularly during seed germination and early seedling development in Arabidopsis.

Overexpression of the MYB37 transcription factor enhances abscisic acid sensitivity, and improves both drought tolerance and seed productivity in Arabidopsis thaliana

Although a lot of genes have been revealed to participate in abscisic acid (ABA) signaling, many of the additional components involved in ABA signaling remain to be discovered. Here we report that overexpression of MYB37, a R2R3 MYB subgroup 14 transcription factor in Arabidopsis thaliana, confers hypersensitive phenotypes to exogenous ABA in all the major ABA responses, including ABA-induced inhibition of seed germination, cotyledon greening and early seedling growth, and ABA-induced stomatal closure and inhibition of stomatal opening. Interestingly and importantly, MYB37-overexpression improves plant tolerance to drought, enhances growth of mature plants and seed productivity, thought it delays flowering, which suggests that this gene may be used for improving crop adaptability to drought environment and productivity. However, a myb37-1 knockout mutant displays wild-type ABA responses most likely due to a functional redundancy of the multiple MYB members. Real-time PCR analysis shows that upregulation of the MYB37 expression changes expression of a subset of ABA-responsive genes. Together, these findings suggest that the MYB37 transcription factor plays an important, positive role in plant response to ABA and drought stress, and meanwhile, it plays a positive role in the regulation of seed production.

Phosphonamide pyrabactin analogues as abscisic acid agonists

A four step synthesis towards novel phosphonic pyrabactin analogues is presented. Via a stomatal closure and germination assay, the ability of the analogues to selectively induce the ABA-signaling pathway was demonstrated.

Molecular and Functional Characterization of a Wheat B2 Protein Imparting Adverse Temperature Tolerance and Influencing Plant Growth

Genomic attempts were undertaken to elucidate the plant developmental responses to heat stress, and to characterize the roles of B2 protein in mediating those responses. A wheat expressed sequence tag for B2 protein was identified which was cloned and characterized to assess its functional relevance causing plant growth and development during stress adaptation. Here, we show that wheat B2 protein is highly expressed in root and shoot tissues as well as in developing seed tissues under high temperature stress conditions. Morphological studies of transgenic Arabidopsis overexpressing gene encoding wheat B2 protein and Δb2 mutant plants were studied at major developmental stages. The stunted growth phenotype of mutant plants, together with hypocotyl and root elongation analysis of transgenic plants showed that B2 protein exhibits a crucial role in plant growth and development. Additional physiological analyses highlights the role of B2 protein in increased tolerance to heat and cold stresses by maintaining high chlorophyll content, strong activity of photosystem II and less membrane damage of overexpression transgenics as compared with the wild-type. Furthermore, the constitutive overexpression of TaB2 in Arabidopsis resulted in ABA hypersensitivity. Taken together, these studies suggest a novel perspectives of B2 protein in plant development and in mediating the thermal stress tolerance.

The Arabidopsis LYST INTERACTING PROTEIN 5 Acts in Regulating Abscisic Acid Signaling and Drought Response

Multivesicular bodies (MVBs) are unique endosomes containing vesicles in the lumens and play essential roles in many eukaryotic cellular processes. The Arabidopsis LYST INTERACTING PROTEIN 5 (LIP5), a positive regulator of MVB biogenesis, has critical roles in biotic and abiotic stress responses. However, whether the abscisic acid (ABA) signaling is involved in LIP5-mediated stress response is largely unknown. Here, we report that LIP5 functions in regulating ABA signaling and drought response in Arabidopsis. Analyses of a LIP5 promoter-β-glucuronidase (GUS) construct revealed substantial GUS activity in whole seedlings. The expression of LIP5 was induced by ABA and drought, and overexpression of LIP5 led to ABA hypersensitivity, enhanced stomatal closure, reduced water loss, and, therefore, increased drought tolerance. On the contrary, LIP5 knockdown mutants showed ABA-insensitive phenotypes and reduced drought tolerance; suggesting that LIP5 acts in regulating ABA response. Further analysis using a fluorescent dye revealed that ABA and water stress induced cell endocytosis or vesicle trafficking in a largely LIP5-dependent manner. Furthermore, expression of several drought- or ABA-inducible marker genes was significantly down-regulated in the lip5 mutant seedlings. Collectively, our data suggest that LIP5 positively regulates drought tolerance through ABA-mediated cell signaling.

The E-Subgroup Pentatricopeptide Repeat Protein Family in Arabidopsis thaliana and Confirmation of the Responsiveness PPR96 to Abiotic Stresses

Pentatricopeptide repeat (PPR) proteins are extensive in all eukaryotes. Their functions remain as yet largely unknown. Mining potential stress responsive PPRs, and checking whether known PPR editing factors are affected in the stress treatments. It is beneficial to elucidate the regulation mechanism of PPRs involved in biotic and abiotic stress. Here, we explored the characteristics and origin of the 105 E subgroup PPRs in Arabidopsis thaliana. Phylogenetic analysis categorized the E subgroup PPRs into five discrete groups (Cluster I to V), and they may have a common origin in both A. thaliana and rice. An in silico expression analysis of the 105 E subgroup PPRs in A. thaliana was performed using available microarray data. Thirty-four PPRs were differentially expressed during A. thaliana seed imbibition, seed development stage(s), and flowers development processes. To explore potential stress responsive PPRs, differential expression of 92 PPRs was observed in A. thaliana seedlings subjected to different abiotic stresses. qPCR data of E subgroup PPRs under stress conditions revealed that the expression of 5 PPRs was responsive to abiotic stresses. In addition, PPR96 is involved in plant responses to salt, abscisic acid (ABA), and oxidative stress. The T-DNA insertion mutation inactivating PPR96 expression results in plant insensitivity to salt, ABA, and oxidative stress. The PPR96 protein is localized in the mitochondria, and altered transcription levels of several stress-responsive genes under abiotic stress treatments. Our results suggest that PPR96 may important function in a role connecting the regulation of oxidative respiration and environmental responses in A. thaliana.

Overexpression of AtEDT1/HDG11 in Chinese Kale (Brassica oleracea var. alboglabra) Enhances Drought and Osmotic Stress Tolerance

Plants are constantly challenged by environmental stresses, including drought and high salinity. Improvement of drought and osmotic stress tolerance without yield decrease has been a great challenge in crop improvement. The Arabidopsis ENHANCED DROUGHT TOLERANCE1/HOMEODOMAIN GLABROUS11 (AtEDT1/HDG11), a protein of the class IV HD-Zip family, has been demonstrated to significantly improve drought tolerance in Arabidopsis, rice, and pepper. Here, we report that AtEDT1/HDG11 confers drought and osmotic stress tolerance in the Chinese kale. AtEDT1/HDG11-overexpression lines exhibit auxin-overproduction phenotypes, such as long hypocotyls, tall stems, more root hairs, and a larger root system architecture. Compared with the untransformed control, transgenic lines have significantly reduced stomatal density. In the leaves of transgenic Chinese kale plants, proline (Pro) content and reactive oxygen species-scavenging enzyme activity was significantly increased after drought and osmotic stress, particularly compared to wild kale. More importantly, AtEDT1/HDG11-overexpression leads to abscisic acid (ABA) hypersensitivity, resulting in ABA inhibitor germination and induced stomatal closure. Consistent with observed phenotypes, the expression levels of auxin, ABA, and stress-related genes were also altered under both normal and/or stress conditions. Further analysis showed that AtEDT1/HDG11, as a transcription factor, can target the auxin biosynthesis gene YUCC6 and ABA response genes ABI3 and ABI5. Collectively, our results provide a new insight into the role of AtEDT1/HDG11 in enhancing abiotic stress resistance through auxin- and ABA-mediated signaling response in Chinese kale.

Arabidopsis C3HC4-RING finger E3 ubiquitin ligase AtAIRP4 positively regulates stress-responsive abscisic acid signaling

Degradation of proteins via the ubiquitin system is an important step in many stress signaling pathways in plants. E3 ligases recognize ligand proteins and dictate the high specificity of protein degradation, and thus, play a pivotal role in ubiquitination. Here, we identified a gene, named Arabidopsis thaliana abscisic acid (ABA)-insensitive RING protein 4 (AtAIRP4), which is induced by ABA and other stress treatments. AtAIRP4 encodes a cellular protein with a C3HC4-RING finger domain in its C-terminal side, which has in vitro E3 ligase activity. Loss of AtAIRP4 leads to a decrease in sensitivity of root elongation and stomatal closure to ABA, whereas overexpression of this gene in the T-DNA insertion mutant atairp4 effectively recovered the ABA-associated phenotypes. AtAIRP4 overexpression plants were hypersensitive to salt and osmotic stresses during seed germination, and showed drought avoidance compared with the wild-type and atairp4 mutant plants. In addition, the expression levels of ABA- and drought-induced marker genes in AtAIRP4 overexpression plants were markedly higher than those in the wild-type and atairp4 mutant plants. Hence, these results indicate that AtAIRP4 may act as a positive regulator of ABA-mediated drought avoidance and a negative regulator of salt tolerance in Arabidopsis.

Abscisic Acid as an Internal Integrator of Multiple Physiological Processes Modulates Leaf Senescence Onset in Arabidopsis thaliana

Many studies have shown that exogenous abscisic acid (ABA) promotes leaf abscission and senescence. However, owing to a lack of genetic evidence, ABA function in plant senescence has not been clearly defined. Here, two-leaf early-senescence mutants (eas) that were screened by chlorophyll fluorescence imaging and named eas1-1 and eas1-2 showed high photosynthetic capacity in the early stage of plant growth compared with the wild type. Gene mapping showed that eas1-1 and eas1-2 are two novel ABA2 allelic mutants. Under unstressed conditions, the eas1 mutations caused plant dwarf, early germination, larger stomatal apertures, and early leaf senescence compared with those of the wild type. Flow cytometry assays showed that the cell apoptosis rate in eas1 mutant leaves was higher than that of the wild type after day 30. A significant increase in the transcript levels of several senescence-associated genes, especially SAG12, was observed in eas1 mutant plants in the early stage of plant growth. More importantly, ABA-activated calcium channel activity in plasma membrane and induced the increase of cytoplasmic calcium concentration in guard cells are suppressed due to the mutation of EAS1. In contrast, the eas1 mutants lost chlorophyll and ion leakage significant faster than in the wild type under treatment with calcium channel blocker. Hence, our results indicate that endogenous ABA level is an important factor controlling the onset of leaf senescence through Ca(2+) signaling.

Induced drought tolerance through wild and mutant bacterial strain Pseudomonas simiae in mung bean (Vigna radiata L.)

The present study focused on the overproducing mutant of a plant growth promoting rhizobacterium (PGPR) Pseudomonas simiae strain AU (MTCC-12057) for significant drought tolerance in mung bean plants. Five mutants namely AU-M1, AU-M2, AU-M3, AU-M4 and AU-M5 were made after treatment of wild type strain with N-methyl-N-nitro-N-nitrosoguanidine. Mutant strain AU-M4 was recorded for enhanced ACC deaminase (ACC-D) activity, indole acetic acid (IAA) production and inorganic phosphate (Pi) solubilization compared to wild strain and other four mutant strains under drought condition. AU-M4 showed higher phosphate solubilization index (8.17) together with higher ACC-D activity (98 nmol/mg/h) and IAA concentration (69.35 µg/ml) compared with the wild type P. simiae strain AU ACC-D activity (79 nmol/mg/h) and IAA concentration (38.98 µg/ml) respectively. In this report, we investigated the effect of both wild and mutant type bacterial strain on mung bean plants under drought stress. Results showed that mutant AU-M4 and wild type strain AU inoculated plants exhibited superior tolerance against drought stress, as shown by their enhanced plant biomass (fresh weight), higher water content, higher proline accumulation and lower osmotic stress injury. Mutant AU-M4 and wild strain AU inoculated plants reduced the ethylene level by 59 and 45% respectively, compared to the control under stress condition. Furthermore, bacterial inoculated plants showed enhanced induced systemic drought tolerance by reducing stomata size and net photosynthesis resulting higher water content in mung bean plants that may help in survival of plants during drought condition. To mitigate the effects of drought stress, use of PGPR will be needed to ensure sufficient production of food from crop plants. Taking current leads available, concerted future research is needed in this area, particularly on field evaluation with application of potential microorganisms.

Functional Characterization and Substrate Promiscuity of UGT71 Glycosyltransferases from Strawberry (Fragaria × ananassa)

Glycosylation determines the complexity and diversity of plant natural products. To characterize fruit ripening-related UDP-dependent glycosyltransferases (UGTs) functionally in strawberry, we mined the publicly available Fragaria vesca genome sequence and found 199 putative UGT genes. Candidate UGTs whose expression levels were strongly up-regulated during fruit ripening were cloned from F.×ananassa and six were successfully expressed in Escherichia coli and biochemically characterized. UGT75T1 showed very strict substrate specificity and glucosylated only galangin out of 33 compounds. The other recombinant enzymes exhibited broad substrate tolerance, accepting numerous flavonoids, hydroxycoumarins, naphthols and the plant hormone, (+)-S-abscisic acid (ABA). UGT71W2 showed the highest activity towards 1-naphthol, while UGT71A33, UGT71A34a/b and UGT71A35 preferred 3-hydroxycoumarin and formed 3- and 7-O-glucosides as well as a diglucoside from flavonols. Screening of a strawberry physiological aglycone library identified kaempferol, quercetin, ABA and three unknown natural compounds as putative in planta substrates of UGT71A33, UGT71A34a and UGT71W2. Metabolite analyses of RNA interference (RNAi)-mediated silenced fruits demonstrated that UGT71W2 contributes to the glycosylation of flavonols, xenobiotics and, to a minor extent, of ABA, in planta. The study showed that both specialist and generalist UGTs were expressed during strawberry fruit ripening and the latter were probably not restricted to only one function in plants.

Genome-wide expression analysis offers new insights into the origin and evolution of Physcomitrella patens stress response

Changes in the environment, such as those caused by climate change, can exert stress on plant growth, diversity and ultimately global food security. Thus, focused efforts to fully understand plant response to stress are urgently needed in order to develop strategies to cope with the effects of climate change. Because Physcomitrella patens holds a key evolutionary position bridging the gap between green algae and higher plants, and because it exhibits a well-developed stress tolerance, it is an excellent model for such exploration. Here, we have used Physcomitrella patens to study genome-wide responses to abiotic stress through transcriptomic analysis by a high-throughput sequencing platform. We report a comprehensive analysis of transcriptome dynamics, defining profiles of elicited gene regulation responses to abiotic stress-associated hormone Abscisic Acid (ABA), cold, drought, and salt treatments. We identified more than 20,000 genes expressed under each aforementioned stress treatments, of which 9,668 display differential expression in response to stress. The comparison of Physcomitrella patens stress regulated genes with unicellular algae, vascular and flowering plants revealed genomic delineation concomitant with the evolutionary movement to land, including a general gene family complexity and loss of genes associated with different functional groups.

The Calcium Sensor CBL-CIPK Is Involved in Plant's Response to Abiotic Stresses

Abiotic stress halts the physiological and developmental process of plant. During stress condition, CBL-CIPK complex is identified as a primary element of calcium sensor to perceive environmental signals. Recent studies established that this complex regulates downstream targets like ion channels and transporters in adverse stages conditions. Crosstalks between the CBL-CIPK complex and different abiotic stresses can extend our research area, which can improve and increase the production of genetically modified crops in response to abiotic stresses. How this complex links with environmental signals and creates adjustable circumstances under unfavorable conditions is now one of the burning issues. Diverse studies are already underway to delineate this signalling mechanism underlying different interactions. Therefore, up to date experimental results should be concisely published, thus paving the way for further research. The present review will concisely recapitulate the recent and ongoing research progress of positive ions (Mg(2+), Na(+), and K(+)), negative ions (NO3 (-), PO4 (-)), and hormonal signalling, which are evolving from accumulating results of analyses of CBL and CIPK loss- or gain-of-function experiments in different species along with some progress and perspectives of our works. In a word, this review will give one step forward direction for more functional studies in this area.

Functional roles of the pepper RING finger protein gene, CaRING1, in abscisic acid signaling and dehydration tolerance

Plants are constantly exposed to a variety of biotic and abiotic stresses, which include pathogens and conditions of high salinity, low temperature, and drought. Abscisic acid (ABA) is a major plant hormone involved in signal transduction pathways that mediate the defense response of plants to abiotic stress. Previously, we isolated Ring finger protein gene (CaRING1) from pepper (Capsicum annuum), which is associated with resistance to bacterial pathogens, accompanied by hypersensitive cell death. Here, we report a new function of the CaRING1 gene product in the ABA-mediated defense responses of plants to dehydration stress. The expression of the CaRING1 gene was induced in pepper leaves treated with ABA or exposed to dehydration or NaCl. Virus-induced gene silencing of CaRING1 in pepper plants exhibited low degree of ABA-induced stomatal closure and high levels of transpirational water loss in dehydrated leaves. These led to be more vulnerable to dehydration stress in CaRING1-silenced pepper than in the control pepper, accompanied by reduction of ABA-regulated gene expression and low accumulation of ABA and H2O2. In contrast, CaRING1-overexpressing transgenic plants showed enhanced sensitivity to ABA during the seedling growth and establishment. These plants were also more tolerant to dehydration stress than the wild-type plants because of high ABA accumulation, enhanced stomatal closure and increased expression of stress-responsive genes. Together, these results suggest that the CaRING1 acts as positive factor for dehydration tolerance in Arabidopsis by modulating ABA biosynthesis and ABA-mediated stomatal closing and gene expression.

Long-term impact of deficit irrigation on the physical quality of berries in 'Crimson Seedless' table grapes

BACKGROUND

In table grapes, berry firmness influences consumer acceptance so it is important to avoid berry shattering and dehydration during their post-harvest life. Since studies of irrigation effects on table grape quality are comparatively rare, sensory evaluation aimed to identify high-quality berries obtained under different deficit irrigation treatments. A 3-year study examined the effects of deficit irrigation strategies on some physical quality attributes at harvest, after 28 days of cold storage at 0 °C and after an additional shelf-life period of 3 days at 15 °C. Control vines were irrigated to ensure non-limiting water conditions (110% of crop evapo-transpiration), while both regulated deficit irrigation treatment (RDI) and partial root-zone drying (PRD) treatments applied 35% less water post-veraison. The null irrigation treatment (NI) only received natural precipitation (72% less water than control vines).

RESULTS

Total yield and physical quality at harvest were not significantly affected by RDI or PRD. Only severe deficit (NI) decreased berry size, and this treatment had the most dehydrated berries and the worst sensory scores post-harvest. After cold storage, increased berry shattering of the PRD treatment was correlated with lower leaf xylem abscisic acid (ABA) concentration at the time of harvest. Overall quality, especially stem browning, determined the shelf-life, and longer storage duration tended to diminish treatment differences.

CONCLUSIONS

Only NI clusters showed lower quality than their irrigated counterparts. Neither RDI nor PRD had any noticeable effect on berry quality at the end of cold storage and shelf-life, with the slight differences detected between these treatments related to stem browning and dehydration. Sensory results were similar in RDI and PRD, which provided grapes that were more acceptable to consumers than the control. Thus, it is possible to decrease irrigation of table grapes without adversely affecting the physical quality of the berries.

The pepper late embryogenesis abundant protein CaLEA1 acts in regulating abscisic acid signaling, drought and salt stress response

As sessile organisms, plants are constantly challenged by environmental stresses, including drought and high salinity. Among the various abiotic stresses, osmotic stress is one of the most important factors for growth and significantly reduces crop productivity in agriculture. Here, we report a function of the CaLEA1 protein in the defense responses of plants to osmotic stress. Our analyses showed that the CaLEA1 gene was strongly induced in pepper leaves exposed to drought and increased salinity. Furthermore, we determined that the CaLEA1 protein has a late embryogenesis abundant (LEA)_3 homolog domain highly conserved among other known group 5 LEA proteins and is localized in the processing body. We generated CaLEA1-silenced peppers and CaLEA1-overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to dehydration and high salinity. Virus-induced gene silencing of CaLEA1 in pepper plants conferred enhanced sensitivity to drought and salt stresses, which was accompanied by high levels of lipid peroxidation in dehydrated and NaCl-treated leaves. CaLEA1-OX plants exhibited enhanced sensitivity to abscisic acid (ABA) during seed germination and in the seedling stage; furthermore, these plants were more tolerant to drought and salt stress than the wild-type plants because of enhanced stomatal closure and increased expression of stress-responsive genes. Collectively, our data suggest that CaLEA1 positively regulates drought and salinity tolerance through ABA-mediated cell signaling.

Activated expression of AtWRKY53 negatively regulates drought tolerance by mediating stomatal movement

AtWRKY53 is an early factor in drought response and activated expression of AtWRKY53 regulates stomatal movement via reduction of H 2 O 2 content and promotion of starch metabolism in guard cells. Drought is one of the most serious environmental factors limiting the productivity of agricultural crops worldwide. However, the mechanisms underlying drought tolerance in plants remain unclear. AtWRKY53 belongs to the group III of WRKY transcription factors. In this study, we observed both the mRNA and protein products of this gene are rapidly induced under drought conditions. Phenotypic analysis showed AtWRKY53 overexpression lines were hypersensitive to drought stress compared with Col-0 plants. The results of stomatal movement assays and abscisic acid (ABA) content detection indicated that the impaired stomatal closure of 53OV lines was independent of ABA. Further analysis found that WRKY53 regulated stomatal movement via reducing the H2O2 content and promoting the starch metabolism in guard cells. The results of quantitative real-time reverse transcriptase PCR showed that the expression levels of CAT2, CAT3 and QQS were up-regulated in 53OV lines. Chromatin immunoprecipitation assays demonstrated that AtWRKY53 can directly bind to the QQS promoter sequences, thus led to increased starch metabolism. In summary, our results indicated that the activated expression of AtWRKY53 inhibited stomatal closure by reducing H2O2 content and facilitated stomatal opening by promoting starch degradation.

Analyzing the Expression Profile of AREB/ABF and DREB/CBF Genes under Drought and Salinity Stresses in Grape (Vitis vinifera L.)

Expression patterns of four candidate AREB/ABF genes and four DREB/CBF genes were evaluated in leaf and root tissues of five grape varieties (‘Qalati’, ‘Kaj Angoor’, ‘Sabz Angoor’, ‘Siahe Zarghan’, ‘Bidane Safid’) with differential response to drought stress. Among the AREB/ABF genes, AREB1 and ABF2 showed up-regulation in response to drought stress in leaf and root tissues of all varieties while AREB2 and ABF1 showed down-regulation in both leaf and root tissues of the sensitive variety ‘Bidane Sefid’ in response to drought and salt stress. Among the DREB/CBF genes, CBF4 was the most responsive to drought stress in both leaf and root tissues. CBF2 and CBF3 showed up-regulation in all varieties in response to drought stress in leaf except in ‘Bidane Sefid’. Under salinity stress, AREB2 and ABF2 showed up-regulation in response to the increasing level of salinity in the leaf tissues but in the root tissues ABF2 was up-regulated in response to increasing NaCl concentration while AREB2 was down-regulated. Therefore, it seems AREB2 has tissue-specific response to salinity stress. All CBF genes were up-regulated in response to salinity stress in the leaf and root tissues. Expression data suggested that CBF2 is more responsive to NaCl stress. Among all four promising and stress tolerant varieties ‘Siah Zarghan’ and ‘Kaj Angoor’ were more tolerant than ‘Qalati’ and ‘Sabz Angoor’ to drought and salinity.

Genetic analyses of the interaction between abscisic acid and gibberellins in the control of leaf development in Arabidopsis thaliana

Although abscisic acid (ABA) and gibberellins (GAs) play pivotal roles in many physiological processes in plants, their interaction in the control of leaf growth remains elusive. In this study, genetic analyses of ABA and GA interplay in leaf growth were performed in Arabidopsis thaliana. The results indicate that for the ABA and GA interaction, leaf growth of both the aba2/ga20ox1 and aba2/GA20ox1 plants, which were derived from the crosses of aba2×ga20ox1 and aba2×GA20ox1 overexpressor, respectively, exhibits partially additive effects but is similar to the aba2 mutant. Consistently, the transcriptome analysis suggests that a substantial proportion (45-65%) of the gene expression profile of aba2/ga20ox1 and aba2/GA20ox1 plants overlap and share a pattern similar to the aba2 mutant. Thus, these data suggest that ABA deficiency dominates leaf growth regardless of GA levels. Moreover, the gene ontology (GO) analysis indicates gene enrichment in the categories of hormone response, developmental and metabolic processes, and cell wall organization in these three genotypes. Leaf developmental genes are also involved in the ABA-GA interaction. Collectively, these data support that the genetic relationship of ABA and GA interaction involves multiple coordinated pathways rather than a simple linear pathway for the regulation of leaf growth.

Analysis of phylogenetic and functional diverge in plant nine-cis epoxycarotenoid dioxygenase gene family

During different environmental stress conditions, plant growth is regulated by the hormone abscisic acid (an apocarotenoid). In the biosynthesis of abscisic acid, the oxidative cleavage of cis-epoxycarotenoid catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is the crucial step. The NCED genes were isolated in numerous plant species and those genes were phylogenetically investigated to understand the evolution of NCED genes in various plant lineages comprising lycophyte, gymnosperm, dicot and monocot. A total of 93 genes were obtained from 48 plant species to statistically estimate their sequence conservation and functional divergence. Selaginella moellendorffii appeared to be evolutionarily distinct from those of the angiosperms, insisting the substantial influence of natural selection pressure on NCED genes. Further, using exon-intron structure analysis, the gene structures of NCED were found to be conserved across some species. In addition, the substitution rate ratio of non-synonymous (Ka) versus synonymous (Ks) mutations using the Bayesian inference approach, depicted the critical amino acid residues for functional divergence. A significant functional divergence was found between some subgroups through the co-efficient of type-I functional divergence. Our results suggest that the evolution of NCED genes occurred by duplication, diversification and exon intron loss events. The site-specific profile and functional diverge analysis revealed NCED genes might facilitate the tissue-specific functional divergence in NCED sub-families, that could combat different environmental stress conditions aiding plant survival.

Identification of genes induced by Fusarium graminearum inoculation in the resistant durum wheat line Langdon(Dic-3A)10 and the susceptible parental line Langdon

The wheat recombinant chromosome inbred line LDN(Dic-3A)10, obtained through introgression of a Triticum dicoccoides disomic chromosome 3A fragment into Triticum turgidum spp. durum var. Langdon, is resistant to fusarium head blight (FHB) caused by Fusarium graminearum. To identify genes involved in FHB resistance, we used a cDNA-AFLP approach to compare gene expression between LDN(Dic-3A)10 and the susceptible parental line LDN at different time points post-inoculation. In total, 85 out of the ∼ 500 transcript-derived fragments (TDFs) were found to be differentially expressed: 36 and 19% were upregulated in LDN(Dic-3A)10 and LDN, respectively, whereas 45% were induced in both genotypes. Several of the cloned TDFs showed similarity to proteins involved in specific recognition of plant pathogens or associated with early responses to infection. Some TDFs specific to the inoculation response did not show similarity to characterized proteins. The availability of T. aestivum genome sequences allowed the in silico mapping of 28 TDFs and the acquirement of the corresponding gene sequences and, in some cases, their regulatory regions. Analysis of promoter regions revealed the potential existence of shared transcription regulation mechanisms. For instance, three TDF-associated genes contained binding sites for WRKY transcription factors, which have been implicated in the regulation of genes associated with pathogen defense, and three for abscisic acid-responsive element (ABRE). Collectively, our results revealed specific pathogen recognition in the interactions of LDN and LDN(Dic-3A)10 with F. graminearum. Such recognition leads to changes in the expression of several transcripts, attributable to the presence of the wheat QTL Qfhs.ndsu-3AS.

Sequence and expression variations suggest an adaptive role for the DA1-like gene family in the evolution of soybeans

BACKGROUND

The DA1 gene family is plant-specific and Arabidopsis DA1 regulates seed and organ size, but the functions in soybeans are unknown. The cultivated soybean (Glycine max) is believed to be domesticated from the annual wild soybeans (Glycine soja). To evaluate whether DA1-like genes were involved in the evolution of soybeans, we compared variation at both sequence and expression levels of DA1-like genes from G. max (GmaDA1) and G. soja (GsoDA1).

RESULTS

Sequence identities were extremely high between the orthologous pairs between soybeans, while the paralogous copies in a soybean species showed a relatively high divergence. Moreover, the expression variation of DA1-like paralogous genes in soybean was much greater than the orthologous gene pairs between the wild and cultivated soybeans during development and challenging abiotic stresses such as salinity. We further found that overexpressing GsoDA1 genes did not affect seed size. Nevertheless, overexpressing them reduced transgenic Arabidopsis seed germination sensitivity to salt stress. Moreover, most of these genes could improve salt tolerance of the transgenic Arabidopsis plants, corroborated by a detection of expression variation of several key genes in the salt-tolerance pathways.

CONCLUSIONS

Our work suggested that expression diversification of DA1-like genes is functionally associated with adaptive radiation of soybeans, reinforcing that the plant-specific DA1 gene family might have contributed to the successful adaption to complex environments and radiation of the plants.

ABA inducible rice protein phosphatase 2C confers ABA insensitivity and abiotic stress tolerance in Arabidopsis

Arabidopsis PP2C belonging to group A have been extensively worked out and known to negatively regulate ABA signaling. However, rice (Oryza sativa) orthologs of Arabidopsis group A PP2C are scarcely characterized functionally. We have identified a group A PP2C from rice (OsPP108), which is highly inducible under ABA, salt and drought stresses and localized predominantly in the nucleus. Genetic analysis revealed that Arabidopsis plants overexpressing OsPP108 are highly insensitive to ABA and tolerant to high salt and mannitol stresses during seed germination, root growth and overall seedling growth. At adult stage, OsPP108 overexpression leads to high tolerance to salt, mannitol and drought stresses with far better physiological parameters such as water loss, fresh weight, chlorophyll content and photosynthetic potential (Fv/Fm) in transgenic Arabidopsis plants. Expression profile of various stress marker genes in OsPP108 overexpressing plants revealed interplay of ABA dependent and independent pathway for abiotic stress tolerance. Overall, this study has identified a potential rice group A PP2C, which regulates ABA signaling negatively and abiotic stress signaling positively. Transgenic rice plants overexpressing this gene might provide an answer to the problem of low crop yield and productivity during adverse environmental conditions.