Phylogenomic Revisit for Green Contribution to Diatoms

Talk - Phylogenomic Revisit for Green Contribution to Diatoms

Meeting - The molecular life of diatoms, 25 – 28 June 2013 | Paris, France

Abstract

According to Cavalier-Smith’s 1999 “chromalveolate hypothesis”, diatoms and other chlorophyll c-containing algae evolved through a secondary endosymbiosis event, in which a protist, probably a heterotroph, engulfed a red alga, which gave rise to the red plastid in the ancestor of this supergroup. Thus, a significant red algal contribution to the nuclear genome of the chromalveolates was expected as a result of endosymbiotic gene transfer. However, A few years ago, we reported the identification of more than 1000 genes of green algal origin in the nuclear genome of the two diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum using a phylogenomic approach. That was an intriguing and unexpected result with the contribution of the green lineage exceeding that of the red lineage by about 500 nuclear genes. We interpreted these data as a potential cryptic green endosymbiont that had once inhabited the chromalveolate host, donated genetic material, and then was lost. Our proposal has been criticized with a consensus argument suggesting that undersampling of red algal genomes back in 2009 led to an overestimation of the green contribution. Now, in the light of additional novel transcriptomic and genomic red algal datasets, we have reanalyzed the phylogeny of nuclear genes in diatoms and other chromalveolates to compare and contrast the red and green algal genetic footprints in these genomes. Here, we are going to show the results of a large-scale phylogenomic and manual analysis, providing insights into the “greening” of diatom and chromalveolate genomes.