Functional analysis of hydrophobin Hydph16 in the aerial mycelium of Pleurotus ostreatus
Junxian Han1, Moriyuki Kawauchi1*, Yuki Terauchi2, Kenya Tsuji1, Akira Yoshimi1, Chihiro Tanaka1, Takehito Nakazawa1 and Yoichi Honda1
1Graduate School of Agriculture, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
2Research Center for Thermotolerant Microbial Resources, Yamaguchi University, Ube 755-8611, Japan
Hydrophobins are small-secreted proteins with both hydrophobic and hydrophilic parts, which help the mycelium to break through the air-medium interface by reducing the surface tension of the medium. In the agaricomycete Pleurotus ostreatus, over 20 putative hydrophobin genes have been predicted. 3 hydrophobin genes vmh2, vmh3 and hydph16 are predominantly expressed in the aerial mycelium. In this study single disruption of hydph16 was conducted and showed obvious defects in aerial mycelium formation, which was not found in the deletion mutants of vmh2 and vmh3 in previous studies. Hence, the objective is to understand the mechanism of how hydrophobin Hydph16 affects aerial mycelium formation and other physiological functions. Based on the observation by transmission electron microscopy, the cell wall thickness of Δhydph16 strains reduced by 40% to wild-type strains. Additionally, the relative inhibitory rates of Δhydph16 strains were 1.7 and 4 times higher than wild-type strains to cell wall synthesis inhibitors calcofluor-white and micafungin on agar plates, respectively. No significant differences were found in the relative percentages of chitin and glucan or the relative expression level of putative cell wall synthesis genes. Interestingly, unlike vmh2 and vmh3, the deletion of hydph16 did not change the hydrophobicity of aerial mycelium. This study revealed multiple distinct roles for Hydph16 compared to other hydrophobin genes in the aerial mycelium. These results suggest that Agaricomycetes, including P. ostreatus, have evolved to possess multiple different hydrophobins as a means of adapting to various environments.