Neolecta - a fungal dinosaur? Evidence from beta-tubulin amino acid sequences

Were the first ascomycetes yeast-like (unicellular) or filamentous with com plex multicellular growths Molecular studies have indicated that the earlie st lineages of ascomycetes were mostly yeast-like and without complex, mult icellular fruit bodies. The genus Neolecta stands out as an exception. Neol ecta spp. have filamentous growth and discomycete-type of fruit bodies, but constitute one of the basal lineages both in rRNA and RPB2 gene trees. In this paper, we have used 10 previously unpublished and 30 GenBank beta -tub ulin genes to test the phylogenetic position of Neolecta spp. We compared t he phylogenetic information from the amino acid sequences (485 characters) with the phylogenetic information content of 33 characters from intron gain s and losses. Due to gene duplications, two paralogous versions of beta -tu bulin genes occurred in four species included in our analysis. Although phy logenetic interpretation of beta -tubulin gene trees was complicated by a h istory of gene duplications, intron gains and losses, and by unequal rates of amino acid substitution, Neolecta species never formed a monophyletic gr oup with any of the sequences from the filamentous ascomycetes in the Peziz omycotina (euascomycetes) in parsimony or distance analyses. Like the RPB2 and rRNA genes, the P-tubulin genes support the hypotheses of an early dive rgence of Neolecta from superficially similar filamentous ascomycetes. Neol ecta could become a key taxon particularly in comparative studies between t he fungal model organisms in the mainly unicellular (=yeast-like) taxa Sacc haromyces and Schizosaccharomyces and the filamentous fruit-body forming ta xa Neurospora and Aspergillus.