The Protistan Origins of Animals and Fungi

Abstract

Recent molecular studies suggest that Opisthokonta, the eukaryotic supergroup including animals and fungi, should be expanded to include a diverse collection of primitively single-celled eukaryotes previously classified as Protozoa. These taxa include corallochytreans, nucleariids, ministeriids, choanoflagellates, and ichthyosporeans. Assignment of many of these taxa to Opisthokonta remains uncorroborated as it is based solely on small subunit ribosomal RNA trees lacking resolution and significant bootstrap support for critical nodes. Therefore, important details of the phylogenetic relationships of these putative opisthokonts with each other and with animals and fungi remain unclear. We have sequenced elongation factor 1-alpha (EF-1alpha), actin, beta-tubulin, and HSP70, and/or alpha-tubulin from representatives of each of the proposed protistan opisthokont lineages, constituting the first protein-coding gene data for some of them. Our results show that members of all opisthokont protist groups encode a approximately 12-amino acid insertion in EF-1alpha, previously found exclusively in animals and fungi. Phylogenetic analyses of combined multigene data sets including a diverse set of opisthokont and nonopisthokont taxa place all of the proposed opisthokont protists unequivocally in an exclusive clade with animals and fungi. Within this clade, the nucleariid appears as the closest sister taxon to fungi, while the corallochytrean and ichthyosporean form a group which, together with the ministeriid and choanoflagellates, form two to three separate sister lineages to animals. These results further establish Opisthokonta as a bona fide taxonomic group and suggest that any further testing of the legitimacy of this taxon should, at the least, include data from opisthokont protists. Our results also underline the critical position of these "animal-fungal allies" with respect to the origin and early evolution of animals and fungi.

The Environmental Clade LKM11 and Rozella Form the Deepest Branching Clade of Fungi

“…''Rozellida'' appears to be the sister clade of all other true fungi (PP of 1, BV of 97%). The Nucleariida, the group of phagotrophic eukaryotes that has been found to be the closest relatives of Fungi (Steenkamp et al 2005), appears as the only deeper branch in holofungi than ''Rozellida''.…”

The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans

“…Over the past decade or so, evidence supporting this relationship has accumulated from phylogenetic analyses of nuclear and mitochondrial genes [3][4][5][6] , comparative genomics between the mitochondrial genomes of choanoflagellates, sponges and other metazoans 7,8 , and the finding that choanoflagellates express homologues of metazoan signalling and adhesion genes 9-12 . Furthermore, species-rich phylogenetic analyses demonstrate that choanoflagellates are not derived from metazoans, but instead represent a distinct lineage that evolved before the origin and diversification of metazoans (Fig.…”

Mutualism and asexual reproduction influence recognition genes in a fungal symbiont

“…The resulting PCR products were purified using polyethylene glycol (PEG) precipitation (Steenkamp et al, 2006) and the purified PCR products were cloned using the pGEM-T Easy vector System I (Promega Corporation, Madison, USA).…”

“…The cloned products were amplified from individual colonies with plasmid-specific primers (Steenkamp et al, 2006), after which the PCR products were purified using PEG precipitation. The purified products were then sequenced with the plasmid-specific primers, Big Dye Cycle Sequencing kit version 3.1 (Perkin-Elmer, Warrington, UK) and an ABI3700 DNA analyzer (Applied Biosystems, Foster City, USA).…”