Dimethylmonothioarsenate Is a Key Arsenic Species Driving Rice Straighthead Disease

Dimethylmonothioarsenate (DMMTA) is a methylated thioarsenate species that was recently found to be present in paddy soil and rice grain. Despite its high cytotoxicity in mammalian cells, the impact of DMMTA on rice plants is poorly understood. Here, we investigated the toxicity of DMMTA to rice plants during both the vegetative and reproductive stages. Compared with arsenite (As[III]), arsenate (As[V]), and dimethylarsenate (DMA), DMMTA exhibited markedly higher toxicity to rice primary root growth, with a half-maximal inhibitory concentration (IC₅₀) approximately 1 order of magnitude lower. Rice roots took up DMMTA approximately 10 times more efficiently than DMA. DMMTA was converted to DMA prior to xylem translocation to rice shoots. DMMTA exposure at the rice booting stage induced severe symptoms of straighthead disease, with a potency being >5 times of DMA exposure. Most of the arsenic accumulated in the husks of DMMTA-exposed plants was in the form of DMA. Application of silicon decreased the uptake of DMMTA and alleviated straighthead disease. This study underscores the significant threat posed by DMMTA to rice reproduction and food safety, emphasizing the need for increased attention to this overlooked arsenic species in paddy soil environments.