Root-to-Shoot Translocation of Dimethylarsenate and Reduction of Dimethylarsenate to Dimethylarsenite are the Key Factors Controlling Rice Resistance to Dimethylarsenate Toxicity

Dimethylarsenate [DMAs(V)] is a common methylated arsenic (As) species in paddy soils and rice plants. It is more toxic to plants than inorganic As and can cause the physiological disorder straighthead disease in rice. The mechanisms underlying different resistance to DMAs(V) among rice cultivars are unclear. Here, we investigated the differences in DMAs(V) uptake, translocation and reduction, as well as the effects on the metabolome, between two rice cultivars. We found that the cultivar Mars was 11-times more resistant to DMAs(V) than Zhe733. Mars accumulated more DMAs(V) in the roots, whereas Zhe733 translocated more DMAs(V) to the shoots and reduced more DMAs(V) to DMAs(III). DMAs(III) was more toxic than DMAs(V). Using heterologous expression and in vitro enzyme assays, we showed that the glutathione-S-transferases OsGSTU17 and OsGSTU50 were able to reduce DMAs(V) to DMAs(III), and the two genes were expressed at higher levels in the shoot of Zhe733 than Mars. Metabolomic analysis of rice shoots indicated that glutathione (GSH) metabolism was perturbed by DMAs(V) toxicity in Zhe733. Addition of exogenous GSH significantly alleviated the toxicity of DMAs(V) to Zhe733. Taken together, the results suggest that root-to-shoot translocation and reduction of DMAs(V) to DMAs(III) are key factors underlying the cultivar difference in the resistance to DMAs(V) toxicity.