The Glutathione S‐Transferase OsGSTU50 Is Involved in Dimethylarsenate Reduction and Straighthead Disease Susceptibility in Rice

Straighthead disease, a physiological disorder leading to sterility in rice, is caused by over-accumulation of dimethylarsenate [DMAs(V)]. However, the genetic and molecular mechanisms underlying rice responses to DMAs(V) stress remain poorly understood. In this study, we showed that OsGSTU50, a Tau-class glutathione S-transferase (GST), is a key enzyme mediating the reduction of DMAs(V) to its more toxic trivalent form, dimethylarsenite [DMAs(III)] in rice. OsGSTU50 was predominantly expressed in the above-ground tissues, especially during reproductive stages, and the protein is localized to the cytoplasm. Enzymatic assays confirmed its ability to catalyze the glutathione-dependent reduction of DMAs(V) in vitro, following Michaelis-Menten kinetics. Knockout of OsGSTU50 led to reduced DMAs(III) accumulation, alleviated DMAs(V) toxicity, decreased DNA damage and apoptosis in rice seedlings, while also mitigating straighthead symptoms at maturity. In contrast, overexpression of OsGSTU50 elevated DMAs(III) levels, increased genotoxicity, and enhanced straighthead severity. The increased GSH/GSSG ratio in the OsGSTU50 knockout lines and its decrease in the overexpression lines further supported the GSH-dependent enzymatic mechanism of OsGSTU50. Together, these findings demonstrate that OsGSTU50 mediates the enzymatic reduction of DMAs(V) to DMAs(III), contributing to DMAs(III)-induced genotoxicity and straighthead disease in rice. Targeted suppression or manipulation of OsGSTU50 offers a promising genetic approach for breeding rice cultivars with enhanced resistance to DMAs(V) toxicity and straighthead disease.