Abstract
The Arabidopsis thaliana mutant chlorina5 (ch5) showed reduced chlorophyll and carotenoids contents in an age-dependent manner. Ch5 encodes a metalloprotease located in chloroplasts that is required for development of thylakoid membrane. This protease is predicted to have a seven-transmembrane domain and a putative zinc-binding site. We studied the function of CH5 by analyzing the phenotype of the ch5 mutant, and focusing on its age-dependent pigment reduction. Ch5 gene expression was gradually increased by age in wild type and the mutant. Mutant chloroplasts had reduced stacking of thylakoid membrane because of pigment reduction and LHC degradation. Protein profiles were not different between wild type and ch5 except for LHC. Therefore, substrates of CH5 were predicted to be some minor thylakoid proteins. We discuss the functions of CH5 and other chloroplast proteases.
