The chloroplast metalloproteases VAR2 and EGY1 act synergistically to regulate chloroplast development in Arabidopsis
Yafei Qi, Xiaomin Wang, Pei Lei, Huimin Li, Liru Yan, Jun Zhao, Jingjing Meng, Jingxia Shao, Lijun An, Fei Yu, Xiayan Liu
Journal of Biological Chemistry
Abstract Chloroplast development and photosynthesis require the proper assembly and turnover of photosynthetic protein complexes. Chloroplasts harbor a repertoire of proteases to facilitate proteostasis and development. We previously have used an Arabidopsis leaf variegation mutant, yellow variegated2 (var2), defective in thylakoid FtsH protease complexes, as a tool to dissect the genetic regulation of chloroplast development. Here, we report a new genetic enhancer mutant of var2, enhancer of variegation3-1 (evr3-1). We confirm that EVR3 encodes a chloroplast metalloprotease, previously reported as ETHYLENE-DEPENDENT GRAVITROPISM-DEFICIENT AND YELLOW-GREEN1 (EGY1)/AMMONIUM OVERLY SENSITIVE1 (AMOS1). We observed that mutations in EVR3/EGY1/AMOS1 cause more severe leaf variegation in var2-5 and synthetic lethality in var2-4. Using a modified blue-native PAGE system, we revealed abnormal accumulations of photosystem I, photosystem II, and light-harvesting antenna complexes in EVR3/EGY1/AMOS1 mutants. Moreover, we discover distinct roles of VAR2 and EVR3/EGY1/AMOS1 in the turnover of photosystem II reaction center under high light stress. In summary, our findings indicate that two chloroplast metalloproteases, VAR2/AtFtsH2 and EVR3/EGY1/AMOS1, function coordinately to regulate chloroplast development and reveal new roles of EVR3/EGY1/AMOS1 in regulating chloroplast proteostasis in Arabidopsis.