The gene homologous to OsCd1, designated as ABNORMAL SHOOT IN YOUTH (OsASY), functions as a cadmium influx transporter in rice.

Abstract

Cadmium (Cd) contamination in rice threatens food security and public health. Identifying and characterizing key genes governing Cd uptake and translocation is crucial for breeding low-Cd varieties. In this study, we characterized a Cd-responsive member of major facilitator superfamily (MFS), ABNORMAL SHOOT IN YOUTH (OsASY), which shares high sequence homology with the known Cd transporter OsCd1. Functional analysis revealed that OsASY localizes to the plasma membrane and functions as an influx transporter mediating Cd uptake and translocation. OsASY is constitutively expressed in rice, and its transcript and protein levels were both downregulated by Cd stress. Loss of OsASY function significantly reduced Cd accumulation and enhanced Cd tolerance in rice, whereas overexpression produced opposite effects. The Cd influx activity of OsASY was confirmed by heterologous expression in yeast and Cd kinetic assays using osasy mutants. Alterations in OsASY function may trigger secondary regulatory effects by directly or indirectly affecting the expression of other Cd-responsive genes. Notably, OsASY interacts with OsCd1, and their co-expression in yeast increases cellular Cd concentrations. Collectively, these findings demonstrate that OsASY acts as a membrane-localized transporter that positively regulates Cd accumulation. Moreover, our preliminary evidence indicates that targeted editing of OsASY offers a promising strategy to reduce grain Cd content without adversely affecting major agronomic traits or yield, highlighting its potential as a molecular target for breeding low-Cd-accumulating rice varieties.