抄録
Hydrophobins are small amphiphilic proteins secreted by filamentous fungi. These proteins confer hydrophobic properties to hyphae and conidia. They have also been reported to be involved in various biological processes. In this study, we investigated the biological functions of hydrophobins in the plant pathogenic fungus Bipolaris maydis. The genome of B. maydis contains four hydrophobin genes: Hyp1, which belongs to class I, and Hyp2, Hyp3, and Hyp4, which belong to class II. All four genes were confirmed to be expressed. We generated single gene deletion mutants as well as triple and quadruple mutants. However, no significant differences were observed between the wild-type strain and all mutants in terms of radial growth, conidiation, stress tolerance, virulence, or sexual reproduction. Furthermore, colony hydrophobicity of all the mutants was similar to that of the wild-type strain. In contrast, the colony hydrophobicity of the ΔdewA mutant of Aspergillus nidulans was significantly reduced. However, when the HYP1 gene from B. maydis was introduced into this mutant, its hydrophobicity was restored to the level of the control strain. Taken together, these results suggest that hydrophobins in B. maydis are not significantly involved in its biological processes, although Hyp1 retains its functional activity. Our data further provide additional evidence that the functions of hydrophobins depend on the fungal species. Additionary, through screening of collections of mutants of B. maydis, we identified found a strain that formed markedly hydrophilic colonies. Genome comparison analysis showed that this phenotype was caused by a mutation in the NPS4 gene. The NPS4 gene disruptants also formed the hydrophilic colony. These results indicate that colony hydrophobicity in B. maydis depends not on hydrophobins, but on a compound produced by Nps4.
