The metallochaperone OsHIPP56 gene is required for cadmium detoxification in rice crops

Abstract

Rice (Oryza sativa), a paddy crop, is the major target of Cd contamination in farmland. Limiting Cd accumulation in rice crop and environment is a great challenge for managing cleaner production and food security. This report describes an uncharacterized metallochaperone family gene OsHIPP56 in mediating Cd detoxification and accumulation in the plant. OsHIPP56 resides in the nucleus and plasma membrane, and sufficiently expresses in roots by Cd exposure. Mutation of OsHIPP56 by CRISPR/Cas9 approach leads to compromised growth responses, while transgenic rice overexpressing OsHIPP56 displays phenotypes comparable to the wild-type control. In hydroponic studies with Cd exposure, the knockout mutants had a significantly higher level of Cd in rice tissues, whereas the less Cd was accumulated in the transgenic lines. When the varieties were exposed to 0.5 μM Cd for 30 days, the Cd concentrations in the mutant lines were increased by 16.9–21.3 % in shoots and 22.6–55.6 % in roots; in contrast, those in the overexpression lines were reduced by 28.1–34.8 % in shoots and 13.5–231 % roots compared to the wild-type. The contrasting Cd accumulation in the two genotypes was well confirmed by the study with rice growing in the soil (0.21 mg/kg Cd) under natural condition. Mutation caused by CRISPR/Cas9 accumulated similarly more Cd in rice straws, seeds and brown rice, whereas the Cd concentrations in the overexpression lines were relatively lower. These results signify that the metal chaperone gene OsHIPP56 is able to repress the cadmium toxicity by reducing Cd accumulation in the crops. Overall, our work contributes to the understanding the functional role of OsHIPP56 in rice detoxification of Cd, which would be potentially applicable for the clean-up of Cd-contaminated wetland and generating cleaner crops with minimal Cd accumulation.