December 21, 2012

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Cd uptake mechanisms in Koshihikari and low-Cd mutant lcd-kmt1.
Because mutant osnaramp5-1 protein does not take up Cd, Cd content in grains and straw is greatly decreased.
© Satoru Ishikawa and Hiromi Nakanishi

A group led by Project Associate Professor Hiromi Nakanishi and Project Professor Naoko K. Nishizawa in the University of Tokyo's Graduate School of Agricultural and Life Sciences, and Dr. Satoru Ishikawa, Senior Researcher in the National Institute for Agro-Environmental Sciences Soil Environment Division, has identified three rice mutants with grains containing less than 0.05 mg cadmium (Cd) per kilogram. The group produced the mutants by carbon ion-beam irradiation and also identified the responsible gene for reduced Cd uptake.

Rice (Oryza sativa L.) grain is a major dietary source of Cd, which is toxic to humans, but no practical technique exists to substantially reduce Cd contamination. The mutants have different mutations in the OsNRAMP5 gene, which encodes a Mn, Fe and Cd transporter. The defective transporter protein encoded by the mutant osnramp5 genes greatly decreases Cd uptake by roots and Cd content in the straw and grain. When grown in Cd-contaminated paddy fields, the mutants have nearly undetectable Cd in their grains and exhibit no agriculturally or economically adverse traits. DNA markers have been developed to transfer the low-Cd trait into other cultivars. Because the mutants produced by ion beam radiation are not transgenic plants, they represent a practical choice for rice production worldwide. This result will contribute to reducing the Cd content in rice and Cd risk via the food-chain.

Paper information

Satoru Ishikawa, Yasuhiro Ishimaru, Masato Igura, Masato Kuramata, Tadashi Abe, Takeshi Senoura, Yoshihiro Hase, Tomohito Arao, Naoko K. Nishizawa and Hiromi Nakanishi, "Ion-beam irradiation, gene identification, and marker-assisted breeding in the development of low cadmium rice.," Proceedings of the National Academy of Sciences of the United States of America Online Edition: 2012/11/5 (Japan time), doi: 10.1073/pnas.1211132109.
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