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

转录因子DREB1A/CBF3和DREB2A与一个顺式作用元件DRE相互作用，参与拟南芥寒冷和干旱胁迫响应基因的表达。在正常生长条件下，完整的DREB2A表达不会激活下游基因，这表明DREB2A需要翻译后修饰才能激活。利用原生质体对DREB2A结构域进行分析，发现在254和335残基之间存在转录激活结构域，删除136和165残基之间的区域可将DREB2A转化为组成活性形式。过表达构成活性DREB2A使转基因植株具有显著的抗旱性，但仅具有轻微的抗冻性。基因芯片显示，DREB2A调控许多水分胁迫诱导基因的表达。然而，DREB2A下游的一些基因不在DREB1A的下游，DREB1A也识别DRE，但在冷应激应答基因表达中起作用。在非胁迫条件下，绿色荧光蛋白与构成型活性DREB2A融合时在细胞核中表现出较强的信号，而与全长DREB2A融合时则表现出较弱的信号。DREB2A残基136和165之间的区域对该蛋白在细胞核内的稳定性起着重要作用，对蛋白的活化具有重要意义。对过表达DREB2A CA的转基因基因的芯片分析也表明，过表达DREB2A CA可诱导热休克相关基因。此外，我们发现HS胁迫对DREB2A的瞬时诱导发生迅速，并且sgp -DREB2A蛋白在HS胁迫细胞的细胞核中积累。根据DREB2A上调基因的表达模式，将其分为HS诱导的基因、干旱胁迫诱导的基因和HS +干旱胁迫共同诱导的基因3组。DREB2A基因敲除突变体在应激条件下下调DREB2A基因的表达。过表达DREB2A CA的植株的耐热性显著提高，而敲除DREB2A的植株的耐热性显著降低。综上所述，这些结果表明DREB2A在水和HS胁迫响应中都起作用。少

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