Chloroplast proteases are required for fine regulation of the plastid proteome, which controls a wide set of physiological processes. Eukaryotic AAA/FtsH proteases play a key role in protein quality control of membrane-inserted proteins in mitochondria and chloroplasts. In Arabidopsis thaliana, the thylakoidal FtsH proteases form a heterohexameric complex responsible for turnover of the photo-damaged PSII reaction center protein D1. In previous experiments, our group identified an FtsH-interacting protein named FIP (FtsH5 Interacting Protein), which localizes to the thylakoid membranes. FIP displays a Zinc-finger domain in the C-terminal region which is essential for the interaction with FtsH5. Phylogenetic analysis revealed the coevolution of FIP-like proteins and type A but not type B FtsH proteases. The fip knockdown mutants, or FIP-overexpressing (OE) lines could not be phenotypically distinguished from wild-type under normal conditions. However, under abiotic stress conditions such as, high salt, increased oxidative stress and high light intensity the fip mutant plants were considerably more tolerant to the different stresses. This study aims to elaborate the role of the FIP protein that we postulate is a negative regulator of the FtsH complex in the thylakoid membrane. Specifically, we will study the consequences due to over or under-expression of FIP on photosynthesis and test if the Zinc finger domain of FIP is redox active.
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