Diversity of photosynthetic Paulinella species including a comparative plastid genome analysis.

Abstract

The thecate filose amoeba Paulinella chromatophora is a good model organism for understanding plastid organellogenesis because its plastid was derived from a Synechococcus-Cyanobium type of alphacyanobacterium. Recent studies have shown species-level of divergence after the acquisition of the organelle however, a full investigation has not been conducted for the photosynthetic species. We surveyed the biodiversity of this interesting alga using samples collected from around the world. Using four gene markers (18S rRNA, 16S rRNA, dnaK1, psaL), two distinct lineages with high genetic variation were identified, including one new species candidate (i.e., P. microporus). In addition, the chromatophore genome was fully sequenced from P. microporus strain KR01 and the recently reported marine P. longichromatophora. Comparative genomic analysis showed 0.17% of sequence divergence between the Korean strain KR01 and the Japanese strain FK01. Among 1,626 variable sites, the divergence was converged on noncoding regions at a rate seven times higher than for coding regions. The chromatophore genome of P. longichromatophora, when compared to other photosynthetic Paulinella species, showed a higher mutation rate. These results suggest that the diversification of the photosynthetic Paulinella species has occurred at a rapid rate and that the diversification is still ongoing.cies-level of divergence after the acquisition of the organelle however, a full investigation has not been conducted for the photosynthetic species. We surveyed the biodiversity of this interesting alga using samples collected from around the world. Using four gene markers (18S rRNA, 16S rRNA, dnaK1, psaL), two distinct lineages with high genetic variation were identified, including one new species candidate (i.e., P. microporus). In addition, the chromatophore genome was fully sequenced from P. microporus strain KR01 and the recently reported marine P. longichromatophora. Comparative genomic analysis showed 0.17% of sequence divergence between the Korean strain KR01 and the Japanese strain FK01. Among 1,626 variable sites, the divergence was converged on noncoding regions at a rate seven times higher than for coding regions. The chromatophore genome of P. longichromatophora, when compared to other photosynthetic Paulinella species, showed a higher mutation rate. These results suggest that the diversification of the photosynthetic Paulinella species has occurred at a rapid rate and that the diversification is still ongoing.