Heteroexpression of the wheat phytochelatin synthase gene (TaPCS1) in rice enhances cadmium sensitivity

Phytochelatin synthase (PCS) (EC 2.3.2.15) catalyzes the final step of phytochelatins (PCs) biosynthesis. PCs are a family of cysteine-rich thiol-reactive and heavy metal-binding peptides that play an important role in sequestration and detoxification of heavy metals in plants. Previous studies have indicated that plants that overexpressed PCS displayed contrasting phenotypes, ranging from enhanced cadmium (Cd) tolerance to Cd hypersensitivity in Arabidopsis thaliana. In this study, the wheat phytochelatin synthase gene, TaPCS1, was heteroexpressed in wild-type rice (Oryza sativa L., cv. Zhonghua 11) to evaluate the relationship between synthesis of PCs and Cd tolerance in rice. Data showed that the heteroexpression of TaPCS1 in rice enhanced Cd sensitivity and significantly increased Cd accumulation in shoots, but not in roots. Additionally, the PCS line exhibited a much higher content of PCs and non-protein thiols (NPTs) in shoots. Prominent changes in NPT composition led to reduced glutathione pool depletion and higher Cd content in cell organelles in shoots, followed by higher oxidative stress, which might result in Cd sensitivity. Therefore, the heteroexpression of TaPCS1 in rice is capable of increasing Cd accumulation in rice shoots and enhancing Cd sensitivity.