Overexpression of the RAV Transcription Factor <i>OsAAT1</i> Confers Enhanced Arsenic Tolerance by Modulating Auxin Hemostasis in Rice

Characterization of arsenic (As)-responsive genes is fundamental to solving the issue of As contamination in rice. Herein, we establish the involvement of an RAV transcription factor OsAAT1 (<i>Arsenic Accumulation and Tolerance 1</i>) in regulating As response in rice. The expression of <i>OsAAT1</i> is significantly higher in roots and stems of rice seedlings and is clearly upregulated by higher concentrations of arsenite [As(III)]. Compared with wild-type (WT) plants, <i>OsAAT1</i>-overexpressed transgenic lines (OE-<i>OsAAT1</i>) exhibit tolerance, while <i>OsAAT1</i>-knockout mutants (<i>Osaat1</i>) are sensitive to As(III) stress. Notably, the application of exogenous 1-naphthylacetic acid (NAA) greatly enhances the As tolerance of WT and transgenic lines, with stronger effects on OE-<i>OsAAT1</i>. The change in <i>OsAAT1</i> expression leads to the alteration of As and auxin accumulation in transgenic plants by regulating the expression of <i>OsLsi1</i>, <i>OsLsi2</i>, <i>OsCRL4</i>, and <i>OsAUX1</i> genes. Moreover, overexpression of <i>OsAAT1</i> accelerates ROS scavenging and phytochelatins (PCs) synthesis, especially with the addition of exogenous NAA. OsAAT1 localizes in the nucleus and works as a transcriptional suppressor. <i>OsGH3-12,</i> belonging to the auxin-responsive <i>GH3</i> gene family, is the downstream target gene of OsAAT1, whose expression is extensively downregulated by As(III). These findings provide new insights into As response via auxin signaling pathway in rice.