Conservation and divergence of OsGSTU9 and OsGSTU19 in cadmium detoxification and accumulation in rice

Cadmium (Cd) is one of the heavy metals highly toxic to organisms and the increase of Cd contamination in crops forms an urgent issue to food safety and human health. Overproduction of Reactive Oxygen Species (ROS) is the primary response in plant cells subjected to Cd, which could be partially alleviated by Glutathione S-transferases (GSTs). Here, two rice GST genes, OsGSTU9 and OsGSTU19 belonging to the same GST subfamily, were identified due to their preferential expression in root and their significantly Cd-induced upregulation. Knockout of OsGSTU19 dramatically increased Cd sensitivity, although Cd accumulation in the shoots was largely decreased compared to that of the wild type (WT). Loss-of-function of OsGSTU9 and OsGSTU19 increased Cd concentration in the soluble fraction and nucleus but decreased the Cd deposition in cell wall. Under Cd treatment, increased GSH/GSSG ratio and remarkably decreased cell viability was observed in the roots of osgstu9 and osgstu19 mutant lines. Furthermore, Cd-induced ROS was almost abolished in the root tip of osgstu19, but increased ROS was observed in the root tip of osgstu9 compared to that of control. Collectively, OsGSTU9 and OsGSTU19 showed similar expression pattern in rice plants and increased Cd concentration when expressed in yeast cells. However, their roles in Cd detoxification are significantly different, which potentially relies on their distinguished functions in Cd accumulation, redistribution among subcellular fractions, and ROS homeostasis.