S5.2 Jan. 5 The evolutionary transition from protists to Metazoa: mitochondrial genome organization and phylogenomic analyses based on nuclear and mitochondrial genes. LIU, Yu; STEENKAMP, Emma; DARMON, Daniel; BURGER, Gertraud; LANG, B. Franz*; 1; 2 Department of Microbiology and Plant Pathology, University of Pretoria, South Africa; 1; 1; 1 Robert Cedergren Centre for Bioinformatics and Genomics, Canadian Institute for Advanced Research, Departement de biochimie, Universite de Montreal, Quebec, Canada Franz.Lang@Umontreal.ca
Key events in eukaryotic evolution such as the divergence of major lineages such as animals, Fungi and plants occurred a billion or more years ago. Hence, their phylogenetic inference is difficult, and analyses based on a single or few genes are usually insufficient to provide statistically significant results. Therefore, we perform phylogenomic analyses either based on complete sets of mtDNA-encoded proteins, or on large collections of nucleus-encoded proteins derived from ESTs. We are interested in the phylogenetic position of protists that are suspected to branch close to the animal-fungus divergence including Monosiga, Capsaspora, Nuclearia, Amoebidium and members of the Apusozoa (Amastigomonas and Ancyromonas). The analysis of complete mtDNA sequences reveals that all of these species have extra genes (several for ribosomal proteins) compared to the animal set (now including atp9 and 25 standard tRNAs in sponges). Phylogenomic analyses with mt and nuclear data show that Amoebidium, Capsaspora and Monosiga branch at the base of animals and Nuclearia at the base of Fungi. However, we have difficulties to place Apusozoa. Contrary to results by others who position them close to the animal-fungus divergence, our mt data tend to group them with malawimonads (jakobid-related bacterivorous flagellates), yet without significant support. Nuclear data so far do not resolve this question.