Characterization of a short form Peridinin-chlorophyll-protein (PCP) cDNA and protein from the symbiotic dinoflagellate Symbiodinium muscatinei (Dinophyceae) from the sea anemone Anthopleura elegantissima (Cnidaria)

Peridinin-chl-proteins (PCPs) are highly abundant light harvesting pigment proteins unique to the photosynthetic dinoflagellates. Although extensive studies have examined PCP proteins, only four complete pcp nucleotide sequences have been reported to date. PCPs occur in two different forms, a short form with a molecular mass of 14-16 kDa and a long form with a mass of 30-35 kDa, which is thought to have arisen by a gene duplication event. This study describes PCP and its cDNA from Symbiodinium muscatinei (LaJeunesse and Trench), a symbiotic dinoflagellate resident in the sea anemone Anthopleura elegantissima (Brandt). Two-dimensional PAGE of S. muscatinei proteins revealed numerous strongly staining spots at a molecular mass of 15.7 and varying pIs. The N-terminal peptide sequence from one of these spots could be successfully aligned with PCPs from other dinoflagellates, and a complete cDNA sequence was generated by reverse transcriptase PCR, using primers based on the peptide sequence. Northern analyses of RNA revealed a single 1.0-kb band, suggesting that only the short form of the gene is expressed. The S. muscatinei pcp predicted amino acid sequence displayed a 50%-70% identity with the other known pcp sequences. Interestingly, S. muscatinei PCP was best aligned with the only other short form sequence known, that from Heterocapsa pygmaea, and not with the long form from the congener Symbiodinium sp. from the coral Acropora formosa. Phylogenetic analysis of the five pcp sequences suggests that the PCP gene family is divided into two distinct clades, a short form and a long form, and indicates the existence of two separate genes for the two forms.