HCF164 Encodes a Thioredoxin-Like Protein Involved in the Biogenesis of the Cytochrome b 6 f Complex in Arabidopsis

Abstract

To understand the biogenesis of the plastid cytochrome b(6)f complex and to identify the underlying auxiliary factors, we have characterized the nuclear mutant hcf164 of Arabidopsis and isolated the affected gene. The mutant shows a high chlorophyll fluorescence phenotype and is severely deficient in the accumulation of the cytochrome b(6)f complex subunits. In vivo protein labeling experiments indicated that the mutation acts post-translationally by interfering with the assembly of the complex. Because of its T-DNA tag, the corresponding gene was cloned and its identity confirmed by complementation of homozygous mutant plants. HCF164 encodes a thioredoxin-like protein that possesses disulfide reductase activity. The protein was found in the chloroplast, where it is anchored to the thylakoid membrane at its lumenal side. HCF164 is closely related to the thioredoxin-like protein TxlA of Synechocystis sp PCC6803, most probably reflecting its evolutionary origin. The protein also shows a limited similarity to the eubacterial CcsX and CcmG proteins, which are required for the maturation of periplasmic c-type cytochromes. The putative roles of HCF164 for the assembly of the cytochrome b(6)f complex are discussed.

Activation of the Stt7/STN7 Kinase through Dynamic Interactions with the Cytochrome b6f Complex

“…This configuration of the kinase allows its catalytic domain to act on the substrate sites of the LHCII proteins, which are exposed to the stroma. Although in this model the conserved Cys residues in the lumen are on the opposite side from the stromal thioredoxins, it is possible that thiol-reducing equivalents are transferred across the thylakoid membrane through the CcdA and Hcf164 proteins, which have been shown to operate in this way during heme and Cyt b 6 f assembly (Lennartz et al, 2001;Page et al, 2004) or through the LTO1 protein (Du et al, 2015;Karamoko et al, 2011).…”

A Homolog of Prokaryotic Thiol Disulfide Transporter CcdA Is Required for the Assembly of the Cytochrome bf Complex in Arabidopsis Chloroplasts

“…Emergence of a Thioreduction Pathway in Plastid c-Type Cytochrome Biogenesis-The existence of a thio-reduction pathway in the chloroplast was also suggested recently with the discovery of HCF164, a thylakoid membrane-anchored thioredoxin-like protein with disulfide reductase activity which is required for cytochrome b 6 f biogenesis in Arabidopsis (62). HCF164 displays similarity to CcsX/ResA, a thioredoxin-like protein involved in system II bacterial cytochrome c assembly pathway (63,64).…”

Regulatory factors for the assembly of thylakoid membrane protein complexes

“…In Arabidopsis, the loss of CcdA and HCF164 (high chlorophyll fluorescence 164, an orthologue of CcSX) impairs photosynthesis and results in a cyt b 6 f assembly defect, suggesting that these proteins are required for cyt b 6 f biogenesis in plant chloroplasts [54,55]. The role of HCF164 was further investigated through a study of CCS5, its orthologue in Chlamydomonas [56].…”