Heavy metals are toxic to living organisms even at trace levels and persist in the environment due to their non-degradability. Understanding the mechanisms of heavy metal response and adaptation is therefore crucial. As a key stress defense system, the chloroplast Clp protease complex plays a central role in degrading damaged proteins within chloroplasts. This study characterized the molecular responses of the Clp complex to nickel (Ni) and cadmium (Cd) stress in Chlamydomonas reinhardtii , revealing significant upregulation of CrClpP5 specifically under Ni stress. Subsequently, a CrClpP5 -overexpressing transgenic strain (OE-CrClpP5) was generated to investigate its role in Ni stress regulation. Phenotypic analysis demonstrated that OE-CrClpP5 cells exhibited significantly higher Ni tolerance than wild-type (WT) controls, evidenced by enhanced chlorophyll retention, increased biomass accumulation, and elevated antioxidant enzyme activities. Ultrastructural examination revealed the presence of autophagosome-like structures in unstressed OE-CrClpP5 cells. Furthermore, the up-regulated expression pattern of autophagy-related genes in OE-CrClpP5 confirmed the activation of autophagy, indicating that chloroplast CrClpP5 overexpression activates cytoplasmic ATG pathway associated with autophagy formation. These findings elucidate a novel mechanism of chloroplast-protease-mediated autophagy activation for heavy metal stress mitigation and provide a theoretical foundation for developing microalgae-based bioremediation technologies for heavy metal pollution. • The novel role of CrClp P5 in tolerance to the nickel stress has been revealed. • The overexpression of CrClpP5 increased the nickel tolerance in C. reinhardtii . • The overexpression of CrClpP5 triggered the autophagy-like morphology in C. reinhardtii .
Huang et al. (Sat,) studied this question.
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