OsHMA3 overexpression works more efficiently in generating low-Cd rice grain than OsNramp5 knockout mutation.

Abstract

Objective: Cadmium (Cd) is a highly toxic metal element and a carcinogen to humans. Rice is prone to taking up Cd from paddy fields and accumulating it in grain, which raises health concerns for rice consumers. OsNramp5 is a major transporter for Cd and manganese (Mn) uptake in rice, whereas OsHMA3 is a tonoplast-localized transporter involved in Cd detoxification in vacuoles. In this study, we compared the efficiency of OsNramp5 knockout mutation and OsHMA3 overexpression in reducing Cd content in rice grain.

Results: The grain Cd content of the OsNramp5 knockout mutants was significantly lower than that of the wild-type rice T5105. However, these mutants still had much higher grain Cd content than the previously reported OsNramp5 mutants or the OsHMA3 overexpression lines developed in our previous study. Pyramiding the OsNramp5 mutant allele and the OsHMA3 transgene in a single line did not result in an additional reduction in grain Cd content. The OsNramp5 gene in T5105 has a haplotype II promoter, and its knockout mutation also partially reduced Mn content in rice grain. Our results demonstrate that OsHMA3 overexpression works more efficiently in generating low-Cd rice grain than OsNramp5 knockout mutation without affecting Mn uptake in rice.