OsDi19‐4 acts downstream of OsCDPK14 to positively regulate ABA response in rice

The drought‐induced 19 protein family consists of several atypical Cys2/His2‐type zinc finger proteins in plants and plays an important role in abiotic stress. In this study, we found that overexpressing OsDi19‐4 in rice altered the expression of a series of abscisic acid (ABA)‐responsive genes, resulting in strong ABA‐hypersensitive phenotypes including ABA‐induced seed germination inhibition, early seedling growth inhibition and stomatal closure. On the contrary, OsDi19‐4 knockdown lines were less sensitive to ABA. Additionally, OsCDPK14 was identified to interact with OsDi19‐4 and be responsible for the phosphorylation of OsDi19‐4, and the phosphorylation of OsDi19‐4 was further enhanced after the treatment of ABA. Apart from these, OsDi19‐4 was shown to directly bind to the promoters of OsASPG1 and OsNAC18 genes, two ABA‐responsive genes, and regulate their expression. Transient expression assays confirmed the direct regulation role of OsDi19‐4, and the regulation was further enhanced by the increased phosphorylation of OsDi19‐4 after the treatment of ABA. Taken together, these data demonstrate that OsDi19‐4 acts downstream of OsCDPK14 to positively regulate ABA response by modulating the expression of ABA‐responsive genes in rice.     

Abscisic acid prevents pollen abortion under high‐temperature stress by mediating sugar metabolism in rice spikelets

Heat stress at the pollen mother cell (PMC) meiotic stage leads to pollen sterility in rice, in which the reactive oxygen species (ROS) and sugar homeostasis are always adversely affected. This damage is reversed by abscisic acid (ABA), but the mechanisms underlying the interactions among the ABA, sugar metabolism, ROS and heat shock proteins in rice spikelets under heat stress are unclear. Two rice genotypes, Zhefu802 (a recurrent parent) and fgl (its near‐isogenic line) were subjected to heat stress of 40°C after pre‐foliage sprayed with ABA and its biosynthetic inhibitor fluridone at the meiotic stage of PMC. The results revealed that exogenous application of ABA reduced pollen sterility caused by heat stress. This was achieved through various means, including: increased levels of soluble sugars, starch and non‐structural carbohydrates, markedly higher relative expression levels of heat shock proteins (HSP24.1 and HSP71.1) and genes related to sugar metabolism and transport, such as sucrose transporters (SUT) genes, sucrose synthase (SUS) genes and invertase (INV) genes as well as increased antioxidant activities and increased content of adenosine triphosphate and endogenous ABA in spikelets. In short, exogenous application of ABA prior to heat stress enhanced sucrose transport and accelerated sucrose metabolism to maintain the carbon balance and energy homeostasis, thus ABA contributed to heat tolerance in rice.     

Analysis of embryonic proteome modulation by GA and ABA from germinating rice seeds

The phytohormones gibberellic acid (GA) and abscisic acid (ABA) play essential and often antagonistic roles in regulating plant growth, development, and stress responses. Using a proteomics-based approach, we examined the role of GA and ABA in the modulation of protein expression levels during seed germination. Rice seeds were treated with GA (200 microM), ABA (10 microM), ABA followed by GA, GA followed by ABA, and water as a control and then incubated for 3 days. The embryo was dissected from germinated seeds, and proteins were subjected to 2-DE. Approximately, 665 total protein spots were resolved in the 2-D gels. Among them, 16 proteins notably modulated by either GA or ABA were identified by MALDI-TOF MS. Northern analyses demonstrated that expression patterns of 13 of these 16 genes were consistent with those of the proteome analysis. Further examination of two proteins, rice isoflavone resuctase (OsIFR) and rice PR10 (OsPR10), using Western blot and immunolocalization, revealed that both are specifically expressed in the embryo but not in the endosperm and are dramatically downregulated by ABA.     

Comprehensive sequence and expression profile analysis of PEX11 gene family in rice

PEX11 gene family has been shown to be involved in peroxisome biogenesis but very little is known about this gene family in rice. Here we show that five putative PEX11 genes (OsPEX11-1-5) present in rice genome and each contain three conserved motifs. The PEX11 sequences from rice and other species can be classified into three major groups. Among the five rice PEX11 genes, OsPEX11-2 and -3 are most likely duplicated. Expression profile and RT-PCR analysis suggested that the members of PEX11 family in rice had differential expression patterns: OsPEX11-1 and OsPEX11-4 had higher expression levels in leaf tissues than in the other tissues, OsPEX11-2 was detected only in germinated seeds, OsPEX11-3 was expressed predominantly in endosperm and germinated seeds, and OsPEX11-5 was expressed in all the tissues investigated. We also observed that the rice PEX11 genes had differential expression patterns under different abiotic stresses. OsPEX11-1 and OsPEX11-4 were induced by abscisic acid (ABA), hydrogen peroxide (H2O2), salt and low nitrogen stress conditions. OsPEX11-3 was responsive to ABA and H2O2 treatments, and OsPEX11-5 was responsive to ABA, H2O2, and salt treatments. However, OsPEX11-2 had no response to any of the stresses. Our results suggest that the rice PEX11 genes have diversification not only in sequences but also in expression patterns under normal and various stress conditions.     

The cytosolic/nuclear HSC70 and HSP90 molecular chaperones are important for stomatal closure and modulate abscisic acid-dependent physiological responses in Arabidopsis

Cytosolic/nuclear molecular chaperones of the heat shock protein families HSP90 and HSC70 are conserved and essential proteins in eukaryotes. These proteins have essentially been implicated in the innate immunity and abiotic stress tolerance in higher plants. Here, we demonstrate that both chaperones are recruited in Arabidopsis (Arabidopsis thaliana) for stomatal closure induced by several environmental signals. Plants overexpressing HSC70-1 or with reduced HSP90.2 activity are compromised in the dark-, CO(2)-, flagellin 22 peptide-, and abscisic acid (ABA)-induced stomatal closure. HSC70-1 and HSP90 proteins are needed to establish basal expression levels of several ABA-responsive genes, suggesting that these chaperones might also be involved in ABA signaling events. Plants overexpressing HSC70-1 or with reduced HSP90.2 activity are hypersensitive to ABA in seed germination assays, suggesting that several chaperone complexes with distinct substrates might tune tissue-specific responses to ABA and the other biotic and abiotic stimuli studied. This study demonstrates that the HSC70/HSP90 machinery is important for stomatal closure and serves essential functions in plants to integrate signals from their biotic and abiotic environments.     

热激对水稻幼苗耐冷性及热激蛋白合成的诱导

萌发的水稻种子经42℃热激处理后其幼苗的耐冷性明显增强,膜伤害程度降低,脯氨酸含量增加,超氧物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性和抗氧化物质抗坏血酸含量增加,而膜脂过氧化的关键酶脂氧合酶(LOX)活性及其产物丙二醛(MDA)含量下降.并且热激诱导萌发的水稻胚合成78、70、64、60、46、38、24、17、16kD的热激蛋白(HSP),其中属于HSP70的内质网结合蛋白(BiP)的合成与水稻幼苗耐寒性的提高有关.     

Enhancement of ABA responsiveness in wheat embryos by high temperature*†

Abstract. Mature wheat (Triticum aestivum L.) grain often possesses high-temperature dormancy which restricts the grain from germinating at warm temperatures (25–30°C). Isolated embryos from such grain exhibited little high-temperature dormancy when germinated in water. Dormancy was restored by the application of abscisic acid (ABA) to the embryos. The ability of ABA to block germination in isolated embryos was enhanced significantly by elevating the germination temperature. ABA was 100 times more effective in reducing embryonic germination at 30°C than at 15°C. These temperature effects on embryonic response to ABA are a useful system for studying the mechanism of ABA action in seed dormancy.     

Genomics approach to abscisic acid- and gibberellin-responsive genes in rice.

We used an 8987-EST collection to construct a cDNA microarray system with various genomics information (full-length cDNA, expression profile, high accuracy genome sequence, phenotype, genetic map, and physical map) in rice. This array was used as a probe to hybridize target RNAs prepared from normally grown callus of rice and from callus treated for 6 hr or 3 days with the hormones abscisic acid (ABA) or gibberellin (GA). We identified 509 clones, including many clones that had never been annotated as ABA-or GA-responsive. These genes included not only ABA- or GA-responsive genes but also genes responsive to other physiological conditions such as pathogen infection, heat shock, and metal ion stress. Comparison of ABA- and GA-responsive genes revealed antagonistic regulation for these genes by both hormones except for one defense-related gene, thionin. The gene for thionin was up-regulated by both hormone treatments for 3 days. The upstream regions of all the genes that were regulated by both hormones had cis-elements for ABA and GA response. We performed a clustering analysis of genes regulated by both hormones and various expression profiles that showed three notable clusters (seed tissues, low temperature and sugar starvation, and thionin-gene related). A comparison of the cis-elements for hormone response genes between rice and Arabidopsis thaliana, we identified cis-elements for dehydration-stress response or for expression of amylase gene as Arabidopsis gene-specific or rice gene-specific, respectively.