Plant signal transduction and gene expression in response to water stress condition

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Transcription factors DREB1A/CBF3 and DREB2A interact with a cis-acting element, DRE, involved in cold- and drought-stress-responsive gene expression in Arabidopsis. Intact DREB2A expression does not activate downstream genes under normal growth conditions, suggesting that DREB2A requires post-translational modification for activation. DREB2A domain analysis using protoplasts identified a transcriptional activation domain between residues 254 and 335, and deletion of a region between residues 136 and 165 transforms DREB2A to a constitutive active form. Overexpression of constitutive active DREB2A resulted in significant drought stress tolerance but only slight freezing tolerance in transgenic plants. Microarray revealed that DREB2A regulates expression of many water-stress-inducible genes. However, some genes downstream of DREB2A are not downstream of DREB1A, which also recognizes DRE but functions in cold-stress-responsive gene expression. Green fluorescent protein gave a strong signa … More l in the nucleus under unstressed control conditions when fused to constitutive active DREB2A but only a weak signal when fused to full-length DREB2A. The region between DREB2A residues 136 and 165 plays a role in the stability of this protein in the nucleus, which is important for protein activation.Microarray analysis of transgenics overexpressing DREB2A CA also indicated that the overexpression of DREB2A CA induces heat-shock (HS) related genes. Moreover, we found that transient induction of the DREB2A occurs rapidly by HS stress and that the sGFP-DREB2A protein accumulates in nuclei of HS stressed cells. DREB2A upregulated genes were classified into 3 groups based on their expression patterns : genes induced by HS, genes induced by drought stress and genes induced by both HS and drought stress. DREB2A upregulated genes were downregulated in DREB2A knockout mutants under stress conditions. Thermotolerance was significantly increased in the plants overexpressing DREB2A CA and decreased in the DREB2A knockout plants. Collectively, these results indicate that DREB2A functions in both water and HS stress responses. Less