Hydrophobins in Bipolaris maydis do not contribute to colony hydrophobicity, but their heterologous expressions alter colony hydrophobicity in Aspergillus nidulans

Kenya Tsuji¹Hiroshi Yoshida¹Masafumi Saba²Yuki Terauchi^1,3,4Moriyuki Kawauchi¹Yoichi Honda⁵Chihiro Tanaka^2,3Akira Yoshimi^1,2,3*

• ¹Laboratory of Environmental Interface Technology of Filamentous Fungi, Graduate School of Agriculture, Kyoto University,, Kyoto, Japan
• ²Laboratory of Terrestrial Microbiology, Graduate School of Agriculture, Kyoto University,, Kyoto, Japan
• ³Terrestrial Microbiology and Systematics, Global Environmental Studies, Kyoto University,, Kyoto, Japan
• ⁴Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi, Yamaguchi, Japan
• ⁵Laboratory of Forest Biochemistry, Graduate School of Agriculture, Kyoto University,, Kyoto, Japan

Hydrophobins are small amphiphilic proteins secreted by filamentous fungi. These proteins confer hydrophobic properties to the hyphae and conidia. Bipolaris maydis is the causal agent of southern corn leaf blight; the biological function of its hydrophobins is not clear. In the present study, we focused on the broad function of hydrophobins in the life cycle of this fungus. We found that the B. maydis genome encodes four hydrophobins—Hyp1 of class I, and Hyp2, Hyp3 and Hyp4 of class II—and all of them are expressed. We generated single disruptants of each gene, as well as triple and quadruple disruptants. No differences were detected between the wild type and any of disruptants in mycelial growth, conidiation, stress tolerance, virulence, or sexual reproduction. The colony hydrophobicity of all disruptant strains was similar to that of the wild-type strain. Complementation of a null Aspergillus nidulans mutant of dewA, which showed a significantly reduced colony hydrophobicity, with each of the four B. maydis hydrophobin genes restored the hydrophobic phenotype, although the degree of hydrophobicity varied among them. Despite the absence of any significant phenotypic changes in the B. maydis mutants generated, results strongly suggest that all four hydrophobins have retained their function in hydrophobicity. Furthermore, the results of this study suggest that the role of hydrophobins might change depending on the fungal species.