Targeted expression of OsHMA3 driven by the OsYSL16 promoter decreases Cd accumulation in grains

Abstract

Reducing cadmium (Cd) levels in rice grains through genetic improvement is an effective strategy for rice production in Cd-contaminated soils. In this study, we developed transgenic rice lines from Zhongzao39, featuring targeted expression of OsHMA3 driven by the OsYSL16 promoter. We conducted a comparative analysis to evaluate the phenotypic and physiological responses of transgenic rice lines versus wild-type (WT) plants under Cd treatment. Under 0.1, 1, and 10 μM Cd treatment conditions, transgenic rice plants exhibited a reduction of over 30 % in shoot Cd content. Notably, at 10 μM Cd treatment, Cd levels in the xylem sap of transgenic rice plants were significantly lower than those in WT plants. Additionally, shoot fresh weight and dry weight of the transgenic lines were increased by more than 60 %, while the corresponding root fresh weight and dry weight increased by 22.6–29.7 %. Furthermore, levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and activities of peroxidase (POD) and superoxide dismutase (SOD) were significantly lower in the transgenic lines compared to WT plants. Importantly, expression levels of OsCAL1, OsIRT1, OsIRT2, OsNRAMP1, and OsHMA2 in the roots of transgenic rice plants were significantly reduced compared to those in WT plants. The Cd contents in grains and leaves, as well as the transport of Cd from leaves to grains, were significantly lower in the transgenic rice plants, achieving a reduction in grain Cd content of over 70 %. Together, these results indicate that OsHMA3 expression driven by the OsYSL16 promoter effectively inhibits Cd translocation from roots to shoots and from leaves to grains, ultimately reducing Cd accumulation in grains. This provides a novel strategy for rice cultivation in Cd-contaminated soils, enhancing food safety and agricultural sustainability.