Rice plants absorb cadmium and manganese from the roots simultaneously by using OsNRAMP5, a protein localized in the cell membrane. National Agriculture and Food Research Organization (NARO) identified the 337th amino acid, which constitutes the OsNRAMP5 protein, as an important site for the regulation of cadmium and manganese transport. Rice plants, in which the amino acid at this site has been changed from glutamine to lysine due to mutation, the uptake of both elements is suppressed, but the amount of manganese necessary for growth can be secured. This result will be useful for the development of rice cultivars with improved safety and productivity.
Overview
NARO has developed Koshihikari Kan No.1, a low-cadmium-absorbing cultivar that dramatically reduces the concentration of cadmium in rice, which accounts for about 40% of the cadmium consumed by Japanese people. Since this cultivar lacks the function of the OsNRAMP5 gene, which controls cadmium absorption, cadmium absorption is remarkably suppressed. However, the absorption of manganese, which is necessary for growth is also suppressed simultaneously, so there is a tendency to be susceptible to brown spot disease due to manganese deficiency. Therefore, attention was required in the rice cultivation.
Therefore, NARO by combining mutation breeding and genetic analysis technology, selected mutant rice plants with a new mutant OsNRAMP5 gene in which the transport of cadmium and manganese was moderately reduced. We identified the 337th amino acid from the N-terminus of the mutated OsNRAMP5 protein as an important site for the regulation of cadmium and manganese transport. The 337th amino acid of OsNRAMP5 in commonly cultivated rice is glutamine whereas in this mutant rice it was replaced by lysine by mutation.
In the mutant rice, even though the cadmium concentration in rice was suppressed and the absorption of manganese was also suppressed simultaneously, the amount of manganese necessary for growth was secured. Moreover, the onset of brown spot disease due to manganese deficiency was clearly suppressed compared to Koshihikari Kan No.1.
In conjunction with the identification of this amino acid mutation, we developed a DNA marker that can detect the OsNRAMP5-Q337K gene in which the 337th amino acid of OsNRAMP5 is mutated from glutamine to lysine. By using this marker in rice breeding, it is possible to develop new rice cultivars with reduced cadmium absorption while avoiding manganese deficiency.
From experiments in which the amino acid at this site was replaced with another amino acid, it was also found that the transport of both elements changed greatly depending on the type of amino acid.
Publication
Kuramata M, Abe T, Tanikawa H, Sugimoto K and Ishikawa S (2022) A weak allele of OsNRAMP5 confers moderate cadmium uptake while avoiding manganese deficiency in rice. Journal of Experimental Botany https:/doi.org/10.1093/jxb/erac302
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