Arabidopsis CFD is an ortholog of Chlamydomonas Ccs1 that is required for c-type heme assembly in chloroplasts

Abstract

The Arabidopsis thaliana cfd (cytochrome f deficient) mutant was isolated by the sensitivity of its photosystem II to low temperature using a chlorophyll fluorescence imaging technique. The cfd mutant is defective in intersystem electron transport even at 23°C, secondarily leading to photodamage of PSII at 4°C. Map-based cloning revealed that the cfd phenotype is due to a mutation in At1g49380, which encodes a putative plastid-targeting protein with high similarity to Ccs1 in Chlamydomonas reinhardtii. Ccs1 is required for c-type cytochrome (Cyt) assembly in chloroplasts. Consistent with the high sequence similarity of At1g49380 and Ccs1, the levels of Cyt f heme and Cyt f were low in the cfd mutant. We conclude that CFD is an ortholog of Chlamydomonas Ccs1. In vitro ferredoxin-dependent plastoquinone reduction activity was not affected in cfd, suggesting that system II c-type Cyt biogenesis is required for the machinery of photosystem I cyclic electron transport.