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All the members of our research group who went to Stockholm enjoyed the city as the location for the 5th European Workshop on the Molecular Biology of Cyanobacteria. The weather was perfect and we took every opportunity to walk around the city or, even better, get on a boat. But work wasn’t too bad either: the conference venue was very smart and there were some excellent talks. Highlights were the presentations by William Martin – one of the most charismatic as well as one of the most interesting speakers – and by David Adams. Although this was a conference for cyanobacteriologists, similarities and interactions between plant and cyanobacterial proteins were discussed right from the beginning, with Jim Barber’s description of antenna systems. But after the football results on the final day of the conference, John Allen summarised, ‘Anabaena three–Arabidopsis nil’.
David Adams (University of Leeds, UK) gave a summary of the many symbiotic associations between cyanobacteria and eukaryotes. It was illuminating to discover how many of these involved Nostoc – the importance of which was a recurring theme during the meeting. For those of us working mostly on Synechocystis it is always interesting to hear about its (equally) important relatives. After an entertaining video clip of the response of hormogonia to plant chemoattractant, David summarised some of his lab’s work on mutants in hormogonium formation, one of a number of presentations highlighting aspects of protein expression control in cyanobacteria.
Kept in suspense until the very end of the talk by William Martin (Heinrich-Heine University, Düsseldorf, Germany), we finally found out that the answer was 18% – that is the proportion of genes in Arabidopsis that appear to have originated in the cyanobacterial precursor of the chloroplast. Of nearly 9400 proteins from the plant that gave a hit in a sequence database, about 1700 (most of them chromosomally encoded) appear to have a cyanobacterial origin. All functional categories are represented by these proteins: as is well-known, the chloroplast only managed to hang onto the bulk of one group, the photosynthesis and respiration genes. Even this is very variable, of course. This presentation also included a summary of the difference in the extent of the reduction of the chloroplast genome. Whereas the Porphyra chloroplast encodes about 200 proteins, Euglena appears to have retained genes for only 58. Once again, Nostoc appeared as a very likely close relative of the much-discussed chloroplast ancestor. Lateral gene transfer as ever complicates the picture, however. Interestingly, the similarity between Gram-positive bacterial genes and plant genes may be due to the similarity between cyanobacteria and the Gram-positive bacteria. The final figure for plant genes originating in cyanobacteria may rise again.
Christiane Funk (Umeå University, Sweden) and Iwona Adamska (Stockholm University, Sweden) are working on members of the Deg serine protease family, a group of proteins that are present in both chloroplasts and cyanobacteria. Even though the genes for Clp proteases are apparently the only ones retained in plant chloroplasts, other chromosomally-encoded proteases have very important roles in maintenance of the photosynthetic apparatus. DegP2 is one of the Arabidopsis proteases implicated in the repair of the D1 protein of photosystem II after photoinhibitory damage in vitro. This presentation, however, showed that DegP2's closest homologue in Synechocystis (HtrA) appears not to have the same role. Deletion mutants of htrA, hhoA (degQ equivalent) and hhoB (degS) in fact demonstrated a role for HtrA in heat shock, and only under oxidative stress. It was the hhoA protease mutant that impeded D1 repair in Synechocystis after high light, although the most dramatic effect was only after heat shock. All of the protease genes showed light-activated transcription but, again in contrast to the plant versions, the level of transcription was not affected by heat shock in the cyanobacterium. Clearly, the roles of the numerous chloroplast and cyanobacterial proteases still require clarification.