Molecular Mechanism of Cadmium Accumulation in Rice
Rice (Oryza sativa L.) is a major dietary source of cadmium (Cd) intake, which accounts for about 50% of total Cd intake for populations consuming rice as the staple food. Therefore, it is a very important issue to reduce transfer of Cd from soil to rice grains for human health. Recently, great progresses have been made in understanding the molecular mechanisms of Cd accumulation in rice. OsNramp5, a member of Nramp (natural resistance-associated macrophage protein) transporter family, is a major transporter for Cd uptake in rice, which is localized at the distal side of both root exodermis and endodermis. On the other hand, OsHMA3 belonging to heavy metal ATPase family is responsible for sequestration of Cd into the root vacuoles. Subsequent translocation of Cd from the roots to the shoots is mediated by OsHMA2 localized at the pericycle cells in the roots. At least two transporters (OsHMA2 and OsLCT1) localized in the nodes are involved in distribution of Cd to the rice grains. In addition, several QTL for Cd accumulation, by using wide genotypic variation in Cd accumulation, have been detected although the responsible genes remain to be identified in the future. Further identification of useful alleles for Cd accumulation will contribute to breeding rice cultivars with low Cd accumulation.
KeywordsCadmium accumulation Distribution Molecular mechanism Rice grain Transporter Translocation Uptake Vacuolar sequestration
This work was supported by a Grant-in-Aid for Specially Promoted Research (JSPS KAKENHI grant 16H06296 to J.F.M.).
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