Characterization of OsLCT1, a cadmium transporter from indica rice (Oryza sativa)

Molecular understanding of cadmium (Cd) transport in indica rice (Oryza sativa) is still insufficient, although indica rice generally has a potential to accumulate higher Cd in shoots and grains than japonica rice. We have previously demonstrated that OsLCT1 is a Cd transporter gene responsible for grain Cd accumulation in the japonica model cultivar Nipponbare. In this study, we isolated OsLCT1 cDNA from Kasalath, a model indica (aus subgroup) cultivar and conducted cation transport activity assays in yeast and mRNA expression analysis in plants. The deduced amino acid sequence of Kasalath OsLCT1 is 91.2% identical and 93.8% similar to that of Nipponbare OsLCT1. We established the yeast heterologous system expressing the Kasalath allele of OsLCT1. Elemental profiling of the yeast cells suggested an efflux activity of Kasalath OsLCT1 for Cd, K, Mg, Ca and Mn, but not for Fe, Zn, Cu and Na. This substrate specificity was identical to that of the Nipponbare version. Quantitative real time-polymerase chain reaction (RT-PCR) showed that expression of OsLCT1 in Kasalath was higher in reproductive stage than in vegetative stage. The expression level of OsLCT1 was significantly higher in Kasalath than in Nipponbare. Phylogenetic analysis found several LCT1-like genes only in grass plants. OsLCT1 is the sole copy in the rice genome and is conserved among each rice subgroup. These newly found low-affinity cation transporter (LCT) homologs will provide a basis for further understanding of LCT-mediated Cd transport.