Characterization and evolution of peridinin-chlorophyll a binding protein gene families in symbiotic dinoflagellates
Abstract (Summary)Photosynthetic dinoflagellates have evolved unique light harvesting complexes that combine the accessory pigment peridinin and chlorophyll a within the hydrophobic center of water-soluble peridinin-chlorophyll a binding proteins (PCPs). Most species of dinoflagellates express either 14-17 & 32-35 kDa mature PCP apoproteins and do so in stable combinations of isoforms that differ in isoelectric point (pI). The source (post-translational modification, protein degradation or genetic) and functional significance of PCP isoform variation has remained unclear. PCPs are coded for by multi-gene families. However, previous reports on free-living dinoflagellates conflict over the diversity of PCP genes within gene arrays. I present the first genomic characterization of the PCP gene family from a symbiotic dinoflagellate. Symbiodinium sp. from the Pacific bivalve Hippopus hippopus (RK Trench culture collection # 203) contains genes for 33 kDa PCP apoproteins that are organized in tandem arrays like those of free-living dinoflagellates Lingulodinium (Gonyaulax) polyedra and Heterocapsa pygmaea. The Symbiodinium 203 PCP cassette consists of 1098 bp coding regions separated 1 by spacers of variable length that are approximately 900 bp. The spacers contain a conserved upstream sequence similar to the promoter in L. polyedra. There is surprising diversity between cloned genomic coding regions. Ka/Ks divergence analyses between paired coding regions generally had values < 1. These differences are not accounted for by recombinations or errors introduced during PCR. Reverse Transcription PCR cDNA clones also show the same pattern of diversity. Quantitative Real-Time PCR and flow cytometry indicate that the Symbiodinium 203 genome has 36 ± 12 PCP genes per genome. Thus the PCP gene family of Symbiodinium 203 appears to be evolving under little or no of concerted evolution. The predicted proteins have pIs that are within the range of those published for other species of Symbiodinium. Post-translational modifications are not necessary to explain the multiple PCP isoforms. Amino acid substitutions were mapped onto the Amphidinium carterae PCP crystal structure and identified several polymorphic sites that may influence spectral absorption tuning of chromophores.
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:protein binding dinoflagellates chlorophyll
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