CYO1/ABC2 protein, a cotyledon-specific chloroplast development factor of Arabidopsis, had thiol-disulfide reduction activity

Abstract

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/abc2 mutant in Arabidopsis thaliana has albino cotyledons but normal green true leaves. Chloroplasts develop abnormally in cyo1/abc2 mutant plants grown in the light, but etioplasts are normal in mutants grown in the dark. CYO1/ABC2 protein localizes to the thylakoid membrane in chloroplasts, and CYO1/ABC2 protein copurified with the PSI/LHCI and PSII/LHCII complexes. CYO1/ABC2 has a C4-type zinc finger domain similar to that of Escherichia coli DnaJ. Recombinant CYO1 accelerates disulfide bond reduction in the model substrate insulin and renatures RNase A, indicating that CYO1/ABC2 has protein disulfide isomerase activity. These results suggest that CYO1/ABC2 has a chaperone-like activity required for thylakoid biogenesis in cotyledons.