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- KurzbeschreibungThe acquisition of photosynthesis by eukaryotes was undoubtedly a key step in the evolution of life,<br>shaping the face of this planet like no other evolutionary event. It is commonly accepted that a single<br>primary endosymbiosis, in which a cyanobacterium was engulfed by a heterotrophic host cell, gave<br>rise to the photosynthetic organelles of plants, the plastids, probably more than 1 billion years ago.<br>Recently, we presented evidence that the photosynthetic inclusions, termed &1187;hromatophores&1196;<br>present in the filose thecamoeba Paulinella chromatophora originated from an independent, more<br>recent primary endosymbiotic event, involving a cyanobacterium from the Prochlorococcus/<br>Synechococcus clade (=PSclade).<br>A subclade of the PSclade is known to have obtained a proteobacterial form 1A RubisCO by<br>horizontal gene transfer (HGT) and its members are therefore referred to as cyanobacteria. In<br>rDNAphylogenies, the chromatophore diverged basal to the PSclade, raising the question whether<br>the HGT occurred before or after the split of the chromatophore ancestor from the PSclade. By<br>sequence determination and phylogenetic analysis of the RubisCO large subunit gene of<br>P. chromatophora and several Synechococcus strains it was demonstrated in this thesis that the HGT<br>predated the divergence of the chromatophore. Thus, the whole PSclade plus the chromatophore<br>have to be regarded as cyanobacteria. The proteobacterium Nitrococcus mobilis was identified as<br>closest known relative to the donor of the HGT.<br>To clarify the chromatophore&1267; metabolic role and its state of integration into the host, the complete<br>genome sequence of the chromatophore was determined. The data presented here reveal a<br>fundamental reduction of the chromatophore genome. The single, circular chromosome of 1.02 Mb<br>encodes 867 proteincoding genes and is, therewith, the smallest cyanobacterial genome reported to<br>date. Although the chromatophore genome contains a complete set of photosynthesis genes, it lacks<br>not only genes thought to be dispensable for an intracellular lifestyle but also genes of essential<br>pathways for amino acid and cofactor biosynthesis, characterizing the chromatophore as a<br>photosynthetic entity that is absolutely dependent on its host for growth and survival.<br>The genome data were complemented with gene expression data obtained from a shotgun<br>proteome analysis as well as an RTPCR approach. The proteome analysis yielded semiquantitative<br>expression data for more than 50% of the chromatophoreencoded genes. The physiological profile<br>obtained highlights photosynthesis as the chromatophore&1267
- AutorEva Nowack
- Ausgabe1. Auflage
- VerlagCuvillier Verlag
- Seiten174 Seiten
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