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Separate introns gained within short and long soluble peridinin-chlorophyll a-protein genes during radiation of Symbiodinium (Dinophyceae) clade A and B lineages
Citation:
REICHMAN, J. R. Separate introns gained within short and long soluble peridinin-chlorophyll a-protein genes during radiation of Symbiodinium (Dinophyceae) clade A and B lineages. Presented at OSU Botany & Plant Pathology Seminar, Corvallis, OR, December 01, 2011.
Impact/Purpose:
Peridinin-containing dinoflagellates express short (15-17 kD) and/or long (32-35kD) soluble peridinin-chlorophyll a-proteins (sPCP) that harvest blue-green light within chloroplast thylacoid lumens.
Description:
Peridinin-containing dinoflagellates express short (15-17 kD) and/or long (32-35kD) soluble peridinin-chlorophyll a-proteins (sPCP) that harvest blue-green light within chloroplast thylacoid lumens. The previously described pseudo-axis of symmetry in long sPCPs and phylogenetic evidence suggested that evolution of sPCP genes included duplication and fusion of short sPCP genes. To date, all nuclear genes for short and long sPCPs from Amphidinium carterae, Heterocapsa pygmaea, Lingulodinium polyedra and Symbiodinium sp. 203 (clade C) have been intronless. In contrast, we observed that long sPCP genes from Symbiodinium clade B isolates from two Caribbean coral species each contained two spliceosomal introns. To test the hypothesis that these introns were gained during radiation of clade B, we compared sPCP genomic and cDNA sequences for ten genetically distinct Symbiodinium clade B isolates collected from Caribbean and Pacific invertebrate hosts. In all cases except S. muscatinei which had intronless short sPCP genes, two distinct introns were spliced into phase one sites of conserved glycine codons within long sPCP genes. There was no evidence that alternative splicing of clade B large sPCP transcripts would have coded for small sPCPs. Sampling of additional Symbiodinium species confirmed that short sPCP genes from S. pilosum (clade A) plus long sPCP genes from S. microadriaticum (clade A) and S. kawagutii (clade F) are intronless. However, short sPCP genes of S. microadriaticum contained a third, unique intron spliced into a phase zero site of an alanine codon. All three introns are flanked by different exon junctions and are located in the 5’ half of coding sequences. The long sPCP genomic locus appears to be useful for assessing divergence among most clade B taxa. In a broader comparison of dinoflagellate sPCP coding sequences, the phylogenetic position of taxa containing sPCP introns and presence of cryptic splice sites within intronless sPCP cds of other species support our intron gain hypothesis. Comparisons of predicted sPCP amino acids across five genera yielded very high statistical support for short and long sPCP sister clades, each containing corresponding S. microadriaticum sequences. Overall, our results indicate that sPCP introns were gained independently during the radiation of Symbiodinium clades A and B. In addition, we confirmed that duplication and fusion of short sPCP genes occurred once earlier in dinoflagellate evolution.