ReichmanJayBotanyPlantPathologySeparateIntronsGained.pdf
- Publication date
- Publisher
Abstract
Here we document introns in two Symbiodinium clades that were most likely gained following divergence of this genus
from other peridinin-containing dinoflagellate lineages. Soluble peridinin-chlorophyll a-proteins (sPCP) occur in short and
long forms in different species. Duplication and fusion of short sPCP genes produced long sPCP genes. All short and long
sPCP genes characterized to date, including those from free living species and Symbiodinium sp. 203 (clade C/type C2) are
intronless. However, we observed that long sPCP genes from two Caribbean Symbiodinium clade B isolates each contained
two introns. To test the hypothesis that introns were gained during radiation of clade B, we compared sPCP genomic and
cDNA sequences from 13 additional distinct Caribbean and Pacific Symbiodinium clade A, B, and F isolates. Long sPCP genes
from all clade B/B1 and B/B19 descendants contain orthologs of both introns. Short sPCP genes from S. pilosum (A/A2) and S.
muscatinei (B/B4) plus long sPCP genes from S. microadriaticum (A/A1) and S. kawagutii (F/F1) are intronless. Short sPCP
genes of S. microadriaticum have a third unique intron. Symbiodinium clade B long sPCP sequences are useful for assessing
divergence among B1 and B19 descendants. Phylogenetic analyses of coding sequences from four dinoflagellate orders
indicate that introns were gained independently during radiation of Symbiodinium clades A and B. Long sPCP introns were
present in the most recent common ancestor of Symbiodinium clade B core types B1 and B19, which apparently diverged
sometime during the Miocene. The clade A short sPCP intron was either gained by S. microadriaticum or possibly by the
ancestor of Symbiodinium types A/A1, A3, A4 and A5. The timing of short sPCP intron gain in Symbiodinium clade A is less
certain. But, all sPCP introns were gained after fusion of ancestral short sPCP genes, which we confirm as occurring once in
dinoflagellate evolution