Knockout of a rice K5.2 gene increases Ca accumulation in the grain.

Rice is a staple food for half world's population, but it is a poor dietary source of calcium (Ca) due to its low concentration. Therefore, it is an important issue to boost the Ca concentration in the grain for improving Ca deficiency risk, but the mechanisms underlying the Ca accumulation are poorly understood. Here, we obtained a rice (Oryza sativa) mutant with high shoot Ca accumulation. The mutant exhibited 26-53% higher Ca in the shoots than that in wild-type rice (WT) at different Ca supplies. The Ca concentration in the xylem sap was 36% higher in the mutant than in the WT. There was no difference in agronomic traits between the WT and mutant, but the mutant showed 25% higher Ca in the polished grain compared with the WT. Map-based cloning combined with complementation test revealed that the mutant phenotype was caused by an 18-bp deletion of a gene, OsK5.2 belonging to Shaker-like K + channel family. OsK.2 was highly expressed in the mature region of the roots and its expression in the roots was not affected by Ca levels, but up-regulated by low K. Immunostaining showed that OsK.2 was mainly expressed in pericycle of the roots. Taken together, our results revealed a novel role of OsK.2 in Ca translocation in rice, which will be a good target for Ca biofortification in rice. This article is protected by copyright. All rights reserved.