Plant and Cell Physiology Advance Access published online on October 29, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm146
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HCF208 - An homologue of Chlamydomonas CCB2 is required for accumulation of native cytochrome b6 in Arabidopsis thaliana
Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität, Universitätsstr. 1, 40225 Düsseldorf
Corresponding author: Dr. Karin Meierhoff, Heinrich-Heine-Universität Düsseldorf, Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Universitätsstr. 1, 40225 Düsseldorf, Phone: +49 (0)211 8113428, Fax: +49 (0)211 8114871, E-mail: karin.meierhoff{at}uni-duesseldorf.de
| Abstract |
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The cytochrome b6 subunit of the cytochrome b6f complex is a multiheme protein. Two b-type hemes are bound noncovalently to the protein whereas the third heme (heme cn) is covalently attached via an atypical thioether bond. To understand the maturation of cytochrome b6 and to identify the assisting factors we characterized the ethyl methanesulfonate induced nuclear mutant hcf208. This Arabidopsis mutant shows a high chlorophyll fluorescence phenotype and does not accumulate the major cytochrome b6f complex subunits. Transcript levels and patterns of the four major polypeptides of the complex are equal to the wild type. The mutant cytochrome b6 polypeptide shows a faster migration behaviour in SDS-PAGE compared to the wild type and it has no peroxidase activity. The HCF208 locus was mapped and the gene was cloned. Sequence analysis revealed that HCF208 is a homologue of the Chlamydomonas reinhardtii CCB2 protein, which is a factor mediating attachment of heme cn to the cytochrome b6 polypeptide as part of a novel heme biogenesis pathway, called system IV (Kuras et al., 2007). Blue Native PAGE revealed residual amounts of the cytochrome b6f complex dimer in hcf208 however this form is unable to participate in electron transport reactions.
Keywords: Arabidopsis - chloroplast - cytochrome b6f complex - heme attachment - heme cn
(Received August 10, 2007; Accepted October 23, 2007)
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