Cyanobacterial contribution to the genomes of the plastid-lacking protists

Abstract

BackgroundEukaryotic 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.ResultsWe 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.ConclusionOur 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.

Evolution of enzymes involved in the photorespiratory 2-phosphoglycolate cycle from cyanobacteria via algae toward plants

“…The close relationship among the algal GLYKs could result from a cryptic green endosymbiont (e.g., Prasinophyte) in the ancestor of the Chromalveolates before the secondary endosymbiosis with a red alga (Frommolt et al 2008;Moustafa et al 2009). In this study, we cannot distinguish whether the GLYKs in the Chromalveolates came from a green or a red algal endosymbiont, whereas Maruyama et al (2009) postulated a red algal origin of GLYK for the Chromalveolate Phytophthora.…”

“…The presence of GLYK proteins in other Chromalveolates such as Emiliania huxleyii (Haptophyta) or Ectocarpus siliculosus (Phaeophyceae; Accession number CBN78958) point to a loss of this gene in diatoms. It should be noted that GLYKencoding genes are frequently present in fungal genomes, where they probably originate from a HGT event (Maruyama et al 2009). …”

Cytokinins - recent news and views of evolutionally old molecules

“…This demonstrates the potentially significant contributions of ancestral or extant cyanobacteria to the eukaryotic genomes, which probably occurred via HGT or ancient primary endosymbiotic gene transfer events, followed by retention of the transferred genes in the nuclear genomes after the plastid loss (Maruyama et al 2009). This can explain the presence of CK-related genes in Dictyostelium discoideum, an early eukaryote slime mould that diverged from the line leading to Fig.…”

“…Comparative analyses identified several 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); Maruyama et al 2009). This demonstrates the potentially significant contributions of ancestral or extant cyanobacteria to the eukaryotic genomes, which probably occurred via HGT or ancient primary endosymbiotic gene transfer events, followed by retention of the transferred genes in the nuclear genomes after the plastid loss (Maruyama et al 2009).…”

Dynamics and Innovations within Oomycete Genomes: Insights into Biology, Pathology, and Evolution

“…Diatom and oomycete genes having affinity with red alga have limited overlap, so some researchers suggested that separate endosymbiotic events occurred before and after they diverged from their common ancestor (5,57,62,80). Support for endosymbiosis in the diatom lineage appears solid, but its occurrence prior to their divergence from oomycetes was challenged by a study that argued that other evolutionary events provide better explanations for the presence of red alga-like genes in oomycetes (80).…”