Masuda Shinji Takamiya Ken-Ichiro 10 Mori Kazuki Ogura Kan 17921316 Mochizuki Mariko Shimada Hiroshi et al. 2007 Oct. Plant Cell 19(10):3157-69. Shimada Hiroshi Chloroplast development in cotyledons differs in a number of ways from that in true leaves, but the cotyledon-specific program of chloroplast biogenesis has not been clarified. The cyo1 mutant in Arabidopsis thaliana has albino cotyledons but normal green true leaves. Chloroplasts develop abnormally in cyo1 mutant plants grown in the light, but etioplasts are normal in mutants grown in the dark. We isolated CYO1 by T-DNA tagging and verified that the mutant allele was responsible for the albino cotyledon phenotype by complementation. CYO1 has a C(4)-type zinc finger domain similar to that of Escherichia coli DnaJ. CYO1 is expressed mainly in young plants under light conditions, and the CYO1 protein localizes to the thylakoid membrane in chloroplasts. Transcription of nuclear photosynthetic genes is generally unaffected by the cyo1 mutation, but the level of photosynthetic proteins is decreased in cyo1 mutants. Recombinant CYO1 accelerates disulfide bond reduction in the model substrate insulin and renatures RNase A, indicating that CYO1 has protein disulfide isomerase activity. These results suggest that CYO1 has a chaperone-like activity required for thylakoid biogenesis in cotyledons. Shirano Yumiko Shibata Daisuke 2007 Oct 19 Arabidopsis cotyledon-specific chloroplast biogenesis factor CYO1 is a protein disulfide isomerase. Osteryoung Katherine W Froehlich John E 3157-69