Mn tolerance in rice is mediated by MTP8.1, a member of the cation diffusion facilitator family

Manganese (Mn) is an essential micronutrient for plants, but is toxic when present in excess. The rice plant (Oryza sativa L.) accumulates high concentrations of Mn in the aerial parts; however, the molecular basis for Mn tolerance is poorly understood. In the present study, genes encoding Mn tolerance were screened for by expressing cDNAs of genes from rice shoots in Saccharomyces cerevisiae. A gene encoding a cation diffusion facilitator (CDF) family member, OsMTP8.1, was isolated, and its expression was found to enhance Mn accumulation and tolerance in S. cerevisiae. In plants, OsMTP8.1 and its transcript were mainly detected in shoots. High or low supply of Mn moderately induced an increase or decrease in the accumulation of OsMTP8.1, respectively. OsMTP8.1 was detected in all cells of leaf blades through immunohistochemistry. OsMTP8.1 fused to green fluorescent protein was localized to the tonoplast. Disruption of OsMTP8.1 resulted in decreased chlorophyll levels, growth inhibition in the presence of high concentrations of Mn, and decreased accumulation of Mn in shoots and roots. However, there was no difference in the accumulation of other metals, including Zn, Cu, Fe, Mg, Ca, and K. These results suggest that OsMTP8.1 is an Mn-specific transporter that sequesters Mn into vacuoles in rice and is required for Mn tolerance in shoots.