The Clp protease system is required for copper ion‐dependent turnover of the PAA 2/ HMA 8 copper transporter in chloroplasts
Wiebke Tapkena b, Jitae Kimc d, Kenji J. Nishimurac d, Klaas Jan van Wijkc d, Marinus Pilona b✉
- aBiology Department Colorado State University Fort Collins CO 80523 USA
- bBiology Department, Colorado State University, Fort Collins, CO, 80523 USA
- cDepartment of Plant Biology Cornell University Ithaca NY 14853 USA
- dDepartment of Plant Biology, Cornell University, Ithaca, NY, 14853 USA
- ✉Corresponding author
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Abstract
The distribution of essential metal ions over subcellular compartments for use as cofactors requires control of membrane transporters. PAA2/HMA8 is a copper-transporting P1B -type ATPase in the thylakoid membrane, required for the maturation of plastocyanin. When copper is highly available to the plant this transporter is degraded, which implies the action of a protease. In order to identify the proteolytic machinery responsible for PAA2/HMA8 turnover in Arabidopsis, mutant lines defective in five different chloroplast protease systems were analyzed. Plants defective in the chloroplast caseinolytic protease (Clp) system were specifically impaired in PAA2/HMA8 protein turnover on media containing elevated copper concentrations. However, the abundance of a core Clp component was not directly affected by copper. Furthermore, the expression and activity of both cytosolic and chloroplast-localized superoxide dismutases (SODs), which are known to be dependent on copper, were not altered in the clp mutants, indicating that the loss of PAA2/HMA8 turnover in these lines was not caused by a lack of stromal copper. The results suggest that copper excess in the stroma triggers selection of the thylakoid-localized PAA2 transporter for degradation by the Clp protease, but not several other chloroplast proteases, and support a novel role for this proteolytic system in cellular copper homeostasis.
TL;DRIt is suggested that copper excess in the stroma triggers selection of the thylakoid-localized PAA2 transporter for degradation by the Clp protease, but not several other chloroplast proteases, and support a novel role for this proteolytic system in cellular copper homeostasis. (Semantic Scholar)