REICHMAN, J.R.; WILCOX, T.P.; VIZE, P.D.: Characterization and evolution of diverse peridinin chlorophyll-a protein gene families within symbiotic dinoflagellates.

Photosynthetic dinoflagellates have evolved unique light harvesting complexes that combine the accessory pigment peridinin and chlorophyll-a within the hydrophobic center of water soluble proteins known as PCPs. PCPs allow the efficient harvesting of light in the 480-500 um wavelength that normally would not be absorbed. PCPs also provide photoprotection by dissipating excess light energy as heat and thereby reducing the formation of damaging singlet oxygen. PCP apoproteins have been well studied and shown to occur in two molecular weight classes: 15 and 35 kD. Both PCP sizes come in multiple isoforms with distinct isoelectric focusing points (IP) and individual species of dinoflagellates express stable combinations of these isoforms. The source of different isoforms (post-translational modification or genetic) and the significance of the variation has remained unclear. PCP genes occur in tandem arrays with large copy number and are thought to be highly conserved. In this paper we present characterization and comparison PCP genes of Symbiodinium from ribosomal clades A, B and C. For every PCP gene family examined, there is considerable sequence variation among gene copies within a single genome. The resulting proteins are predicted to vary in IPs. At least some of the variability between PCP isoforms can thus be accounted for by genetic differences. These substitutions are mapped onto the crystal structure of PCP from Amphidinium carterae to estimate possible functional significance. PCP gene families in symbiotic dinoflagellates have a high amount of diversity and do not appear to be evolving under concerted evolution.