Research article

Cyanobacterial contribution to the genomes of the plastid-lacking protists

Shinichiro Maruyama¹ , Motomichi Matsuzaki^1,2,3 , Kazuharu Misawa^1,3,3 and Hisayoshi Nozaki¹

¹Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

²Current address: Department of Biomedical Chemistry, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

³Current address: Research Program for Computational Science, Riken, 4-6-1 Shirokane-dai, Minato-ku, Tokyo 108-8639, Japan

author email corresponding author email

BMC Evolutionary Biology 2009, 9:197doi:10.1186/1471-2148-9-197

Published:	11 August 2009

Abstract

Background

Eukaryotic genes with cyanobacterial ancestry in plastid-lacking protists have been regarded as important evolutionary markers implicating the presence of plastids in the early evolution of eukaryotes. Although recent genomic surveys demonstrated the presence of cyanobacterial and algal ancestry genes in the genomes of plastid-lacking protists, comparative analyses on the origin and distribution of those genes are still limited.

Results

We identified 12 gene families with cyanobacterial ancestry in the genomes of a taxonomically wide range of plastid-lacking eukaryotes (Phytophthora [Chromalveolata], Naegleria [Excavata], Dictyostelium [Amoebozoa], Saccharomyces and Monosiga [Opisthokonta]) using a novel phylogenetic pipeline. The eukaryotic gene clades with cyanobacterial ancestry were mostly composed of genes from bikonts (Archaeplastida, Chromalveolata, Rhizaria and Excavata). We failed to find genes with cyanobacterial ancestry in Saccharomyces and Dictyostelium, except for a photorespiratory enzyme conserved among fungi. Meanwhile, we found several Monosiga genes with cyanobacterial ancestry, which were unrelated to other Opisthokonta genes.

Conclusion

Our data demonstrate that a considerable number of genes with cyanobacterial ancestry have contributed to the genome composition of the plastid-lacking protists, especially bikonts. The origins of those genes might be due to lateral gene transfer events, or an ancient primary or secondary endosymbiosis before the diversification of bikonts. Our data also show that all genes identified in this study constitute multi-gene families with punctate distribution among eukaryotes, suggesting that the transferred genes could have survived through rounds of gene family expansion and differential reduction.