A novel fungal arsenic methyltransferase, WaarsM reduces grain arsenic accumulation in transgenic rice (Oryza sativa L.)

Rice (Oryza sativa L.) grown on arsenic-containing soil and water become a primary dietary source of arsenic and pose a significant health risk. Gene modification is an important and practical approach to reduce arsenic accumulation in rice grains. Here, we reported a WaarsM gene of soil fungus Westerdykella aurantiaca, expressed in rice able to convert toxic inorganic arsenicals to methylated arsenic species, therefore, reduce arsenic accumulation in rice grains. In response to arsenic treatment in hydroponics, WaarsM expressing transgenic lines showed a marked increase in arsenic resistance and reduces its accumulation compared to NT. Also, WaarsM expressing transgenic Line 1 evolved ca. 157 ng and ca. 43 ng volatile arsenicals (mg⁻¹ fresh weight) after 72 h of exposure to 25 μM AsIII and 250 μM AsV, respectively. Transgenic Line 1, grown in soil irrigated with arsenic-containing water accumulates about 50% and 52% lower arsenic than NT in shoot and root, respectively; while arsenic concentration in polished seeds and husk of the transgenic line was reduced by 52% compared to NT. Thus, the present study demonstrates that the expression of WaarsM in rice induces arsenic methylation and volatilization, provides a potential strategy to reduce arsenic accumulation in rice grain.