Abstract
BackgroundHydrophobins are small secreted cysteine-rich proteins that play diverse roles during different phases of fungal life cycle. In basidiomycetes, hydrophobin-encoding genes often form large multigene families with up to 40 members. The evolutionary forces driving hydrophobin gene expansion and diversification in basidiomycetes are poorly understood. The functional roles of individual genes within such gene families also remain unclear. The relationship between the hydrophobin gene number, the genome size and the lifestyle of respective fungal species has not yet been thoroughly investigated. Here, we present results of our survey of hydrophobin gene families in two species of wood-degrading basidiomycetes, Phlebia brevispora and Heterobasidion annosum s.l. We have also investigated the regulatory pattern of hydrophobin-encoding genes from H. annosum s.s. during saprotrophic growth on pine wood as well as on culture filtrate from Phlebiopsis gigantea using micro-arrays. These data are supplemented by results of the protein structure modeling for a representative set of hydrophobins.ResultsWe have identified hydrophobin genes from the genomes of two wood-degrading species of basidiomycetes, Heterobasidion irregulare, representing one of the microspecies within the aggregate H. annosum s.l., and Phlebia brevispora. Although a high number of hydrophobin-encoding genes were observed in H. irregulare (16 copies), a remarkable expansion of these genes was recorded in P. brevispora (26 copies). A significant expansion of hydrophobin-encoding genes in other analyzed basidiomycetes was also documented (1–40 copies), whereas contraction through gene loss was observed among the analyzed ascomycetes (1–11 copies). Our phylogenetic analysis confirmed the important role of gene duplication events in the evolution of hydrophobins in basidiomycetes. Increased number of hydrophobin-encoding genes appears to have been linked to the species’ ecological strategy, with the non-pathogenic fungi having increased numbers of hydrophobins compared with their pathogenic counterparts. However, there was no significant relationship between the number of hydrophobin-encoding genes and genome size. Furthermore, our results revealed significant differences in the expression levels of the 16 H. annosum s.s. hydrophobin-encoding genes which suggest possible differences in their regulatory patterns.ConclusionsA considerable expansion of the hydrophobin-encoding genes in basidiomycetes has been observed. The distribution and number of hydrophobin-encoding genes in the analyzed species may be connected to their ecological preferences. Results of our analysis also have shown that H. annosum s.l. hydrophobin-encoding genes may be under positive selection. Our gene expression analysis revealed differential expression of H. annosum s.s. hydrophobin genes under different growth conditions, indicating their possible functional diversification.
Highlights
Hydrophobins are small secreted cysteine-rich proteins that play diverse roles during different phases of fungal life cycle
Previous studies have demonstrated a high level of sequence divergence in P. gigantea hydrophobin-encoding genes Pgh1 and Pgh2 [20] and the hydrophobins from the pathogenic fungus H. irregulare Hah1 and Hah2 [12]
The hydrophobins from the thermophilic fungus Thielavia terrestris and the corn smut fungus Ustilago maydis deviated from the remaining analyzed hydrophobins in the length of the region between cysteine residues C3 and C4
Summary
Hydrophobins are small secreted cysteine-rich proteins that play diverse roles during different phases of fungal life cycle. Studies have shown that hydrophobins play important role in fungal pathogenesis where they act as virulence factors to enhance fungal infection [11,12,13,14,15] They have been reported to be involved in the attachment of fungal structures [16,17] and the emergence of aerial hyphae from submerged conditions [18,19,20]. Previous studies have demonstrated a high level of sequence divergence in P. gigantea hydrophobin-encoding genes Pgh and Pgh2 [20] and the hydrophobins from the pathogenic fungus H. irregulare Hah and Hah2 [12] These observations raised crucial questions on the evolutionary forces driving the rapid differentiation of this gene family. This may suggest that hydrophobin genes could be under a dynamic evolutionary process across most fungal taxa
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
