Expansin gene TaEXPA2 positively regulates drought tolerance in transgenic wheat (Triticum aestivum L.)

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.