The Arabidopsis APR2 positively regulates cadmium tolerance through glutathione-dependent pathway

Cadmium (Cd) is a dangerous environmental pollutant with high toxicity to plants. The adenosine 5'-phosphosulfate reductase 2 (APR2) is the dominant APRs in Arabidopsis and plays an important role in reductive sulfate assimilation pathway. However, whether the involvement of plant APRs in Cd stress response is largely unclear. Herein, we report that APR2 functions in Cd accumulation and tolerance in Arabidopsis. The transcript levels of APR2 were markedly induced by Cd exposure. Transgenic plants overexpressing APR2 improved Cd tolerance, whereas knockout of APR2 reduced Cd tolerance. APR2-overexpressing plants with increased Cd accumulation and tolerance showed higher glutathione (GSH) and phytochelatin (PC) levels than the wild type and apr2 mutant plants, but lower H₂O₂ and TBARS contents upon Cd exposure. Moreover, exogenous GSH application effectively rescued Cd hypersensitivity in APR2-knockout plants. Further analysis showed that buthionine sulfoximine (BSO, an inhibitor of GSH synthesis) treatment completely eliminated the enhanced Cd tolerance phenotypes of APR2-overexpressing plants, implying that APR2-mediated enhanced Cd tolerance is GSH dependent. In addition, over-expression of the APR2 led to elevated expressions of the GSH/PC synthesis-related genes under Cd stress. Taken together, our results indicated that APR2 regulated Cd accumulation and tolerance possibly through modulating GSH-dependent antioxidant capability and Cd-chelation machinery in Arabidopsis. APR2 could be exploited for engineering heavy metal-tolerant plants in phytoremediation.