PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Cytochrome b₆ in redox regulation of the photosynthesis and chloroplast gene function. Jörgen Ström^*,1, Jens Forsberg², Sujith Puthiyaveetil¹, John Allen¹, ¹ Plant Biochemistry, Lund University, Sweden² Medical Biochemistry and Microbiology, Uppsala, Sweden

ABSTRACT- Cytochrome b6 is a component of the cytochrome b6f complex of chloroplast thylakoid membranes. The recent structure of cytochrome b6f [1,2] have provided insight to the function of the complex [3] We suggest, on the basis of our data, that cytochrome b6, apart from being important to both linear and cyclic electron transport, holds another key function, namely signaling in redox regulation of chloroplast function. This suggestion is supported by the observation that cytochrome b6 is phosphosphorylated [4], and by work from other laboratories showing that occupancy of the Qo quinol-binding site of the cytochrome b6f-complex is the factor governing activation of a thylakoid protein kinase. Sequence comparisons reveal homology of an N-terminal segment of cytochrome b6 with receptors (phytochrome) and sensors (bacterial histidine kinases). Recent phylogenetic analysis of Xiong and Bauer [5] shows that cytochrome b6 is likely to be homologous with photosynthetic reaction centres, where the non-heme iron of type II centres (e.g. photosystem II) is coordinated by amino-acid side chains originally responsible for ligation of the bH-heme. We propose that redox signals from primary and secondary electron transfer events in photosynthesis have been of over-riding importance in cell evolution, and that conserved redox signalling pathways, including that from cytochrome b6, support the primary function of the chloroplast genetic system [6,7]. 1. Kurisu, G., Zhang H., Smith J. L. and Cramer A. W. (2003) . Science: Vol 302, 1009-1014. 2. Stroebe1 D, Choquet Y., Popot J. and Picot D. (2003) . Nature: 426, 413-418. 3. Allen, J.F (2004) TRENDS.in Plant Sciences: Vol. 9 No.3 130-137. 4. Gal, A., Herrmann, R. G., Lottspeich, F. and Ohad, I. (1992) FEBS Lett: 298, 33-35. 5. Xiong, J. and Bauer, C. E. (2002) J. Mol. Biol. 322, 1025-1037. 6. Allen, J. F. (2003) Philos. Trans. R. Soc. Lond. B 358, 19-38. 7. Allen, J. F. (2003) Comp. Funct. Genomics. vol. 4, pages: 31-36.

KEY WORDS: redox regulation, cytochrome b6