Approximately one fifth of the agricultural soils in China is contaminated,mainly by heavy metals or metalloids such as cadmium (Cd) and arsenic (As),which are the class-one carcinogens.Rice produced in some areas of southern China often exceeds the maximum permissible limits of Cd and As,posing a significant risk to food safety.Contamination in soil and irrigation water,soil acidification and growing cultivars with a high accumulation ability are the main reasons for high levels of heavy metals in rice grain.There are large genetic variations among rice cultivars and germplasms in both grain Cd and As concentrations.OsHMA3 is a Cd transporter on the tonoplast functioning to sequester Cd into the vacuole of rice roots.We have recently identified a new loss-of-function allele of OsHMA3 associated with high Cd accumulation in rice grain.This allele has a predicted amino acid mutation at the 380th position from Ser to Arg and is present only in some Japonica cultivars.Cultivars possessing this allele have markedly increased root to shoot translocation of Cd.Paddy rice also accumulates As because of the elevated availability of As in flooded paddy soil.We have previously discovered that arsenite is taken up by silicon transporters in rice.In contrast,arsenate is taken up by phosphate transporters.Plants are able to reduce arsenate to arsenite efficiently and to extrude arsenite to the external medium,thus avoiding excessive buildup of As in plant tissues.We have recently characterized two arsenate reductases in rice (OsHAC1;1 and OsHAC1;2).Mutations in the two genes result in decreased arsenate reduction and arsenite efflux,and increased As accumulation in rice plants.Overexpression of either gene increases arsenate reduction and arsenite efflux,leading to lower As accumulation in rice plants and increased tolerance to arsenate.