Expansins loosen plant cell walls and are involved in cell enlargement and various abiotic stresses. In previous studies, we cloned the expansin gene TaEXPA2 from the wheat cultivar HF9703. Here, we studied its function and regulation in wheat drought stress tolerance. The results indicated that TaEXPA2-overexpressing wheat plants (OE) exhibited drought tolerant phenotypes, whereas down-regulation of TaEXPA2 by RNA interference (RNAi) resulted in elevated drought sensitivity, as measured by survival rate, photosynthetic rate and water containing ability under drought stress. Overexpression of TaEXPA2 enhanced the antioxidant capacity in wheat plants, via elevation of antioxidant enzyme activity and the increase of the transcripts of some ROS scavenging enzyme-related genes. Further investigation revealed that TaEXPA2 positively influenced lateral root formation under drought conditions. A MYB transcription factor of wheat named TaMPS activates TaEXPA2 expression directly by binding to its promoter. Overexpression of TaMPS in Arabidopsis conferred drought tolerance associated with improved lateral root number, and the close homolog genes of TaEXPA2 were up-regulated in Arabidopsis roots overexpressing TaMPS, which suggest that TaMPS may function as one of the regulator of TaEXPA2 gene expression in the root lateral development under drought stress. These findings suggest that TaEXPA2 positively regulates drought stress tolerance in wheat.

中文翻译：

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扩展蛋白基因 TaEXPA2 正调控转基因小麦 (Triticum aestivum L.) 的耐旱性

扩展蛋白使植物细胞壁松散并参与细胞增大和各种非生物胁迫。在之前的研究中，我们从小麦品种 HF9703 中克隆了扩展蛋白基因 TaEXPA2。在这里，我们研究了其在小麦干旱胁迫耐受性中的功能和调控。结果表明，过表达 TaEXPA2 的小麦植物 (OE) 表现出耐旱表型，而通过 RNA 干扰 (RNAi) 下调 TaEXPA2 导致干旱敏感性升高，如干旱胁迫下的存活率、光合速率和含水能力所衡量的. TaEXPA2 的过表达通过提高抗氧化酶活性和增加一些 ROS 清除酶相关基因的转录本来增强小麦植株的抗氧化能力。进一步研究表明，TaEXPA2 在干旱条件下对侧根形成有积极影响。一种名为 TaMPS 的小麦 MYB 转录因子通过与其启动子结合直接激活 TaEXPA2 表达。TaMPS 在拟南芥中的过表达赋予了与侧根数增加相关的耐旱性，TaEXPA2 的近亲基因在过表达 TaMPS 的拟南芥根中上调，这表明 TaMPS 可能作为根中 TaEXPA2 基因表达的调节因子之一干旱胁迫下的横向发育。这些发现表明 TaEXPA2 正调节小麦的干旱胁迫耐受性。TaMPS 在拟南芥中的过表达赋予了与侧根数增加相关的耐旱性，TaEXPA2 的近亲基因在过表达 TaMPS 的拟南芥根中上调，这表明 TaMPS 可能作为根中 TaEXPA2 基因表达的调节因子之一干旱胁迫下的横向发育。这些发现表明 TaEXPA2 正调节小麦的干旱胁迫耐受性。拟南芥中TaMPS的过表达赋予了与侧根数量增加相关的耐旱性，并且TaEXPA2的近同源基因在过表达TaMPS的拟南芥根中上调，这表明TaMPS可能是根中TaEXPA2基因表达的调节因子之一干旱胁迫下的横向发育。这些发现表明 TaEXPA2 正调节小麦的干旱胁迫耐受性。