Tubulin Polymerization Promoting Protein (TPPP) paralogs of flagellated fungi

Tubulin Polymerization Promoting Proteins (TPPPs) are a family of proteins whose occurrence is closely correlated with the presence of eukaryotic flagellum/cilium. This relationship is also observed in fungi, where these proteins are only found in species of early-branching, non-terrestrial phyla that usually reproduce by flagellated zoospores. The defining structural unit of these proteins is the p25alpha domain. TPPP paralogs differ in the length of this domain and the number of times it occurs in the protein. The paper systematically examines the occurrence of different types of TPPPs in the phyla of fungi, discussing the phylogenetic relationships between them. The types found in fungi are long TPPP, which has one full-length p25alpha domain; double long TPPP, which has two copies of the domain; and fungal type, in which the second p25alpha domain has only the C-terminal part. Of the latter, two different paralogs exist; one is found in several fungal phyla, while the other is found only in the order Chytridiales (phylum Chytridiomycota). Phylogenetic analysis has shown that although the second fungal type paralog occurs only in this single order, it is not the result of a duplication within the order. Furthermore, the phylogenetic trees of TPPPs generally agree with the species phylogeny. In several cases where the classification of individual species has been disputed, the phylogenetic tree of TPPPs confirms recent phylogenomic results (e.g., in Blyttiomyces, Entophlyctis, Cladochytrium, Phlyctochytrium genera). Finally, it can be noted that TPPPs are present in the early diverging lineages of fungi, mostly associated with the presence of a flagellum, but they are absent in terrestrial (non-flagellated) fungi.