Arabidopsis mtHSC70-1 physically interacts with the Cox2 subunit of cytochrome c oxidase.

The 70-kD heat shock proteins (HSP70s or HSC70s) function as molecular chaperones and are involved in diverse cellular processes. We recently demonstrated the roles of mitochondrial HSC70-1 (mtHSC70-1) in the establishment of cytochrome c oxidase (COX)-dependent respiration and redox homeostasis in Arabidopsis thaliana. Defects in COX assembly were observed in the mtHSC70-1 knockout lines. The levels of Cox2 (COX subunit 2) proteins in COX complex were markedly lower in the mutants than in wild-type plants; however, the levels of total Cox2 proteins in the mutants were not obviously different from those in wild-type plants, suggesting that the stability of COX or the availability of Cox2 was impaired in the mtHSC70-1 mutants. Here, we further detected the interaction between mtHSC70-1 and Cox2 proteins through co-immunoprecipitation, pull-down and firefly luciferase complementation imaging assays. The results showed that mtHSC70-1 could directly combine Cox2 in vivo and in vitro, providing supporting evidence for the role of mtHSC70-1 in COX assembly.