PARENT SESSION
Posters P2D Marine photosynthesis and production. Abstracts (711-719)

Functional diversity of the PsbA (D1) protein family in cyanobacteria. Douglas Campbell^*,1, Sarah Appleton¹, Chris Brown¹, Cosmin Sicora¹, ¹ Department of Biology, Sackville, NB, Canada

ABSTRACT- Those cyanobacteria for which genomic sequences have been determined contain genes encoding 1 to 5 members of the PsbA family (D1 protein subunit of PSII), and some cyanophages have now been shown to encode a PsbA protein as well. In contrast, known chloroplasts encode only one functional copy of the PsbA protein. The model species Synechocystis PCC 6803 modulates expression from two active genes to provide supplemental expression of identical PsbA/D1 proteins under excitation or UVB stress. In contrast, Synechococcus elongatus (PCC 7942) constitutively expresses a D1:1 protein isoform, which is transiently replaced by expression of a functionally distinct D1:2 form under excitation or UVB stress. The functional diversity of the PsbA protein family has been less explored in other cyanobacteria, although a bioinformatic analyses of protein sequences shows that many cyanobacteria contain isoforms of the protein which fall into two classes based on the sequence of a key, conserved region of the protein, where position 130 is either glutamine or glutamate. This position has been shown to alter D1 protein function upon an artifical change from glutamine to glutamate. We are now evaluating the roles and functional diversity of the PsbA protein family in mediating UVB resistance across a range of cyanobacteria species with diverse metabolisms and habitats. In particular we are searching for sequence motifs cross-correlated with protein expression under particular conditions. We will report our initial work on an Anabaena strain and the deeply branching Gloeobacter strain, which each encode PsbA proteins, and the marine Trichodesmium strain, which encodes only 2 PsbA proteins. In parallel we are using the same strains and treatments for a broad survey of macromolecular allocation patterns across cyanobacterial taxa.

KEY WORDS: UVB, PSII, Gloeobacter, Anabaena