Evolution, surface properties and nomenclature of Trichoderma hydrophobins

Hydrophobins are surface active amphiphilic proteins secreted by filamentous fungi. They contain eight conserved cysteine residues that stabilize their structure. Despite this, their primary structure is highly polymorphic. Fungi from mycoparasitic genus Trichoderma (Hypocreales, Pezizomycotina) have expanded number of hydrophobins compared to other Ascomycota. We mined whole genome sequences of eleven Trichoderma species and nine other Hypocreales fungi. We identified 128 hydrophobin encoding genes, among which 90% (115) belonged to Trichoderma genomes. The number of individual genes varied from seven (T. reesei) to twelve (T. virens or T. harzianum). Multivariate data clustering performed based on the hydropathy scores revealed two distinct clusters of HFBs in Hypocreales. The larger and more diverse cluster corresponded to class II and the smaller combined proteins with unique profiles similar to class I. In accordance with the differences in surface properties, phylogenetic analysis also revealed two clades. Class II HFBs contained 14 monophyletic subclades and three lone lineages; class I was represented by three clades. Thus, HFBome of 11 Trichoderma species comprises of 20 genes. Among them, six were found in core Trichoderma genomes while others were present only in individual clades or species (orphan genes). Evolutionary analysis also revealed history of gene duplication and gene loss events. NOTUNG analysis also confirmed that at least eleven hfb genes were gained by Trichoderma through the horizontal gene transfer from other Pezizomycotina fungi. Statistical analysis for natural selection pressure revealed that HFBs appeared to be under strong pressure of either purifying or positive selection while respective orthologous genes evolved neutrally in other taxa. Similar analyses were performed on another group of small secreted cysteine-rich proteins; cerato-platanins that also have surface modulation properties. The study highlighted role of surface-active proteins in evolution of Trichoderma species. It also allowed development of updated nomenclature of hydrophobin-encoding genes in Hypocreales.