Genetic control of low arsenic accumulation in rice

Arsenic contamination in groundwater and the food chain is a major global health concern, particularly in South East Asia, where rice is a dietary staple (Begum et al., 2016). In regions like West Bengal and Bangladesh, rice contributes up to 50% of total dietary arsenic intake, while in China, this figure rises to 60%. Asian adults consume 400–600 grams of rice daily, making them vulnerable to arsenic exposure. Even trace amounts of arsenic (0.2 mg/kg) in rice pose significant health risks, as arsenic is a non-threshold carcinogen (Zhao et al., 2010). Arsenic levels in rice often exceed the safe limit of 0.2 mg/kg recommended by the Codex Alimentarius Commission, with some varieties containing up to 0.5–0.6 mg/kg depending on the cultivar and environmental conditions. Climate change is expected to worsen this issue by increasing the levels of arsenite (AsIII) in the rhizosphere of rice, leading to higher arsenic accumulation in grains and potentially reducing productivity. Rice is particularly prone to arsenic accumulation due to its traditional cultivation under submerged conditions. Flooding creates anaerobic soil environments that convert arsenate (AsV) into arsenite (AsIII), which is more readily absorbed by rice roots through silicon transporters like Lsi1 and Lsi2, given the similarity in properties between arsenite and silicon below pH 8. Once inside the plant, arsenate is further reduced to arsenite by OsHAC genes, leading to either efflux into the soil or sequestration in vacuoles as complexes with phytochelatins (PCs).