Abstract
The photosynthetic apparatus is constantly damaged by photooxidation. To minimize the photodamage, quality control of chloroplast proteins in which a damaged protein is rapidly replaced with a newly synthesized protein is crucial. This is especially important in quality control of reaction center protein D1 in Photosystem II that is located in thylakoid membranes and highly photodamaged during photosynthetic electron transfer. FtsH is a membrane-bound ATP-dependent metalloprotease and is involved in this cycle. We have recently shown that loss of chloroplastic homologues FtsH2 and FtsH5 in Arabidopsis reduces PSII activity upon exposure to high light and results in leaf-variegated phenotype. While our observation demonstrates the importance of FtsH in the PSII repair cycle, the mechanism leading to leaf variegation remains unclear. We propose that the formation of variegated sectors is an adaptive response of plants to potentially lethal environmental conditions, and our attempt to isolate the regulatory factors will be presented.
