Project description:IntroductionLow temperature is one of the major environmental factors that adversely affect plant growth and yield. Many cereal crops from tropical regions, such as rice, are chilling sensitive and, therefore, are affected already at <10 °C. Interestingly, it has been demonstrated that chilling susceptibility varies greatly among rice varieties, which indicates differences in the underlying molecular responses. Understanding these differences is vital for continued development of rational breeding and transgenic strategies for more tolerant varieties. Thus, in this study, we conducted a comparative global gene expression profiling analysis of the chilling tolerant varieties Sijung and Jumli Marshi (spp. Japonica) during early chilling stress (<24 h, 10 °C).Methods and resultsGlobal gene expression experiments were conducted with Agilent Rice Gene Expression Microarray 4 x 44 K. The analysed results showed that there was a relatively low (percentage or number) overlap in differentially expressed genes in the two varieties and that substantially more genes were up-regulated in Jumli Marshi than in Sijung but the number of down-regulated genes were higher in Sijung. In broad GO annotation terms, the activated response pathways in Sijung and Jumli Marshi were coherent, as a majority of the genes belonged to the catalytic, transcription regulator or transporter activity categories. However, a more detailed analysis revealed essential differences. For example, in Sijung, activation of calcium and phosphorylation signaling pathways, as well as of lipid transporters and exocytosis-related proteins take place very early in the stress response. Such responses can be coupled to processes aimed at strengthening the cell wall and plasma membrane against disruption. On the contrary, in Jumli Marshi, sugar production, detoxification, ROS scavenging, protection of chloroplast translation, and plausibly the activation of the jasmonic acid pathway were the very first response activities. These can instead be coupled to detoxification processes.ConclusionsBased on the results inferred from this study, we conclude that different, but overlapping, strategies are undertaken by the two varieties to cope with the chilling stress; in Sijung the initial molecular responses seem to be mainly targeted at strengthening the cell wall and plasma membrane, whereas in Jumli Marshi the protection of chloroplast translation and detoxification is prioritized.

Project description:The central role of transcriptional regulation in integrating various low temperature response mechanisms has been established in Arabidopsis, where the CBF/DREB regulon plays a prominent role during acclimation. Rice is sensitive to chilling but many japonica cultivars can survive continuous exposure to as low as 10oC for up to 7 days during the most critical stage of seedling establishment better than most indica cultivars. The transcriptional regulatory networks that define this variation have not been studied in detail as cold acclimation has been scrutinized in Arabidopsis. Towards the comparison of the compositional complexity of low temperature response regulons of rice and Arabidopsis, we used the cultivar Nipponbare for genome-wide survey of regulatory clusters by integrative analysis of promoter architectures and temporal expression profiles during exposure to 10oC at narrow time intervals. Temporal profiles revealed major clusters of genes that were induced within the initial 24 hours. These clusters were further defined by common features of having either CRT/DRE-like elements, as1/ocs-like elements or both in their promoters. Genes containing as1/ocs-like elements with or without CRT/DRE, but not those containing only CRT/DRE-like elements were induced by exogenous H2O2 but not by ABA at ambient temperature, suggesting that they belong to a potential regulon (ROS-bZIP – as1/ocs module) that responds to elevated levels of reactive oxygen species (ROS) during the initial stages of stress. Parallel analysis of transcription factors during the initial 12 hours revealed candidate regulator(s) of this putative early response regulon. Cultivar-specific expression signatures of selected members of this regulatory cluster were also positively correlated with genotypic variation in chilling tolerance. We hypothesized that the ROS-bZIP – as1/ocs cluster has important roles in configuring the transcriptome of rice seedlings during the early stages of chilling stress and it appears to be independent of ABA and functions in parallel to the CBF/DREB regulon. Keywords: time course (response to low temperature)

Project description:BackgroundChilling stress is a major factor limiting rice production. Rice genotypes differ greatly in their seedling chilling tolerance (CT), which is known to involve differential expression of large numbers of genes and proteins. To further understand the metabolomic responses of rice to chilling stress, profiles of the 106 primary metabolites of a CT japonica variety, Lijiangxintuanhegu (LTH) and a chilling sensitive indica line, IR29, were investigated under a time-series of chilling stress and non-stress control conditions at the seedling stage.ResultsWe identified 106 primary metabolites that were temporally and genotype-dependently regulated in LTH and IR29 under the time-series chilling stress and subsequent recovery. Three major groups of primary metabolites, amino acids (AAs), organic acids (OAs) and sugars, showed distinct change patterns in both genotypes in response to the chilling stress: a more general accumulation of most AAs, more dramatic decreased levels of most OAs, and greatly reduced levels for most sugars at early time points of stress but increased levels of specific sugars at the later time points of stress. Compared to IR29, LTH had more metabolites showing chilling induced changes, greater levels of these metabolomic changes and a greater ability to recover after stress, implying that LTH used a positive energy-saving strategy against chilling stress. During subsequent recovery, more metabolites were significantly and exclusively up-regulated in LTH, indicating their positive role in chilling tolerance. A comparative analysis of these metabolites data and differentially expressed genes data allowed identification of 7 AAs and related genes that were both chilling responsive and contributed greatly to the CT of LTH.ConclusionsThe metabolomic responses of rice to chilling stress at the seedling stage were dynamic and involved large numbers of the metabolites. The chilling induced changes of three major groups of metabolites, AAs, OAs and sugars, in rice were well coordinated. The high level seedling CT of LTH was apparently attributed to its increased levels of most AAs and reduced energy consumption that resulted in increased glycolysis and strong resilience on recovery. The results of this study extend our understanding of molecular mechanisms of chilling stress tolerance in rice.

Project description:The central role of transcriptional regulation in integrating various low temperature response mechanisms has been established in Arabidopsis, where the CBF/DREB regulon plays a prominent role during acclimation. Rice is sensitive to chilling but many japonica cultivars can survive continuous exposure to as low as 10oC for up to 7 days during the most critical stage of seedling establishment better than most indica cultivars. The transcriptional regulatory networks that define this variation have not been studied in detail as cold acclimation has been scrutinized in Arabidopsis. Towards the comparison of the compositional complexity of low temperature response regulons of rice and Arabidopsis, we used the cultivar Nipponbare for genome-wide survey of regulatory clusters by integrative analysis of promoter architectures and temporal expression profiles during exposure to 10oC at narrow time intervals. Temporal profiles revealed major clusters of genes that were induced within the initial 24 hours. These clusters were further defined by common features of having either CRT/DRE-like elements, as1/ocs-like elements or both in their promoters. Genes containing as1/ocs-like elements with or without CRT/DRE, but not those containing only CRT/DRE-like elements were induced by exogenous H2O2 but not by ABA at ambient temperature, suggesting that they belong to a potential regulon (ROS-bZIP – as1/ocs module) that responds to elevated levels of reactive oxygen species (ROS) during the initial stages of stress. Parallel analysis of transcription factors during the initial 12 hours revealed candidate regulator(s) of this putative early response regulon. Cultivar-specific expression signatures of selected members of this regulatory cluster were also positively correlated with genotypic variation in chilling tolerance. We hypothesized that the ROS-bZIP – as1/ocs cluster has important roles in configuring the transcriptome of rice seedlings during the early stages of chilling stress and it appears to be independent of ABA and functions in parallel to the CBF/DREB regulon. Keywords: time course (response to low temperature) This experiment describes the analysis of the temporal changes in gene expression in response to chilling temperature in Nipponbare rice. A total of 10 stress time points, i.e., 0.5, 2, 4, 6, 12, 18, 24, 36, 48, and 96 hrs after exposure to 10C in a growth chamber and one recovery time point, i.e., 96 hrs at 10C and then 24 hrs (24R) at ambient or control temperature (29C), were profiled with reference to a corresponding control, which was exposed to ambient temperature (29C) for the same length of time under cold stress (each stress time point has a corresponding control sample). Control and cold stress samples were labeled with Cy5 and Cy3, respectively. No dye swap replicate was performed in this experiment. The microarray platform used in this study was the 45K oligonucleotide microarray (www.ricearray.org) which comes in pairs of slides A and B (each containing about 50% of the total number of features). The data described in this series include all hybridizations with slide A and with slide B. All experiments were performed with two independent biological replicates (R1 and R2) for each time point.

Project description:Chilling stress is considered the major abiotic stress affecting the growth, development, and yield of rice. To understand the transcriptomic responses and methylation regulation of rice in response to chilling stress, we analyzed a cold-tolerant variety of rice (Oryza sativa L. cv. P427). The physiological properties, transcriptome, and methylation of cold-tolerant P427 seedlings under low-temperature stress (2-3 °C) were investigated. We found that P427 exhibited enhanced tolerance to low temperature, likely via increasing antioxidant enzyme activity and promoting the accumulation of abscisic acid (ABA). The Methylated DNA Immunoprecipitation Sequencing (MeDIP-seq) data showed that the number of methylation-altered genes was highest in P427 (5496) and slightly lower in Nipponbare (Nip) and 9311 (4528 and 3341, respectively), and only 2.7% (292) of methylation genes were detected as common differentially methylated genes (DMGs) related to cold tolerance in the three varieties. Transcriptome analyses revealed that 1654 genes had specifically altered expression in P427 under cold stress. These genes mainly belonged to transcription factor families, such as Myeloblastosis (MYB), APETALA2/ethylene-responsive element binding proteins (AP2-EREBP), NAM-ATAF-CUC (NAC) and WRKY. Fifty-one genes showed simultaneous methylation and expression level changes. Quantitative RT-PCR (qRT-PCR) results showed that genes involved in the ICE (inducer of CBF expression)-CBF (C-repeat binding factor)-COR (cold-regulated) pathway were highly expressed under cold stress, including the WRKY genes. The homologous gene Os03g0610900 of the open stomatal 1 (OST1) in rice was obtained by evolutionary tree analysis. Methylation in Os03g0610900 gene promoter region decreased, and the expression level of Os03g0610900 increased, suggesting that cold stress may lead to demethylation and increased gene expression of Os03g0610900. The ICE-CBF-COR pathway plays a vital role in the cold tolerance of the rice cultivar P427. Overall, this study demonstrates the differences in methylation and gene expression levels of P427 in response to low-temperature stress, providing a foundation for further investigations of the relationship between environmental stress, DNA methylation, and gene expression in rice.

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Glycosyltransferase OsUGT90A1 helps protect the plasma membrane during chilling stress in rice.

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Glycosyltransferase OsUGT90A1 helps protect the plasma membrane during chilling stress in rice.

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