CONICET | Buscador de Institutos y Recursos Humanos

The increasing number of complete sequenced genomes of oxygenic photosynthetic organisms let us to continue our study on sucrose (Suc) metabolism proteins. Searches for homologs to sps and spp, sus and inv (genes encoding proteins of Suc synthesis, cleavage and hydrolysis) allowed to retrieve sequences of new putative genes. They were functionally characterized by expression in E. coli and studies of the native proteins from cyanobacteria of the genera Synechococcus, Thermosynechococcus, Prochorococcus, Gloebacter, Microcystis, and Nostoc. The deduced aminoacid sequences of the characterized SPS, SPP and SuS were used to expand our phylogenetical analysis on Suc metabolism evolution. The presence of SuS proteins in G. violaceus and M. aeruginosa as the unique proteins responsible for Suc degradation allows to support the hypothesis of a distinct role for that enzyme in unicellular than in filamentous strains. By two different lines of evidence we conclude that the sus genes of those strains might have been acquired by lateral gene transfer. We conclude that whereas Suc seems to be essential in vascular plants, at least in some photosynthetic oxygenic microrganisms it is likely to be dispensable. Gene expression analyses suggest that its role in some microorganisms is related to environmental conditions.

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