Isolation and characterization of rice cesium transporter genes from a rice-transporter-enriched yeast expression library

A considerable portion of agricultural land in central-east Japan has been contaminated by radioactive material, particularly radioactive Cs, due to the industrial accident at the Fukushima Daiichi nuclear power plant. Understanding the mechanism of absorption, translocation and accumulation of Cs+ in plants will greatly assist in developing approaches to help reduce the radioactive contamination of agricultural products. At present, however, little is known regarding the Cs+ transporters in rice. A transporter-enriched yeast expression library was constructed and the library was screened for Cs+ transporter genes. The 1452 full length cDNAs encoding transporter genes were obtained from the Rice Genome Resource Center and 1358 clones of these transporter genes were successively subcloned into yeast expression vectors; which were then transferred into yeast. Using this library, both positive and negative selection screens can be performed, which have not been previously possible. The constructed library is an excellent tool for the isolation of novel transporter genes. This library was screened for clones that were sensitive to Cs+ using a SD-Gal medium containing either 30 or 70 mM CsCl; resulting in the isolation of 13 Cs+ sensitive clones. Cs-137 absorption experiments were conducted and confirmed that all of the identified clones were able to absorb Cs-137. A total of 3 potassium transporters, 2 ABC transporters and 1 NRAMP transporter were among the 13 identified clones.