Rice Aluminum Tolerance – Multiple Genes to Exploit for Enhancing Production on Acid Soils

Aluminum (Al) toxicity is the primary limitation to crop production on approximately 50% of the world's potentially arable lands, with significant areas of acid soils in developing countries of the tropics and subtropics, where food security is most tenuous. Rice is a staple crop for half the world’s population and is the most Al tolerant cereal species. Furthermore, necause of its abundant genetic and genomic resources, rice is a good model to investigate cereal Al tolerance. The results from genome-wide association (GWA) studies on rice Al tolerance identified a large number of Al tolerance loci; we are now focusing on several different of these loci. One of these loci explains 40% of the variation aus Al tolerance and is due to, Nrat1, which encodes a root Al uptake transporter from the Nramp family of metal transporters. Comparative sequence analysis of Nrat1 from a panel of 24 rice lines representing the aus, indica, temperate and tropical japonica rice subpopulations led to the identification of a sensitive Nrat1 haplotype in the Al sensitive aus lines and several Al tolerant Nrat1 haplotypes in Al tolerant lines from all subpopulations Sequence variation in the promoter and coding regions identified differences in expression (higher expression) and function (greater Al uptake) for the Al tolerant Nrat1 variant. This variation underlies a key rice Al tolerance mechanism where the level of toxic Al in the cell wall is reduced by transporting Al into the root symplasm, where it is sequestered in the vacuole.