Exploring Factors Conferring Hydrophobicity on Hyphal Surfaces in Bipolaris maydis: Rethinking the Role of Hydrophobins as the Primary Factor

Exploring Factors Conferring Hydrophobicity on Hyphal Surfaces in Bipolaris maydis: Rethinking the Role of Hydrophobins as the Primary Factor

Akira Yoshimi1,2*, Kenya Tsuji2, Masafumi Saba2, Yuki Terauchi1,2, Diana Cecilia Ruiz-Nava1, Moriyuki Kawauchi2, Yoichi Honda2, Chihiro Tanaka1,2

1Graduate School of Global Environmental Studies, Kyoto University

2 Graduate School of Agriculture, Kyoto University

*Email: yoshimi.akira.8c@kyoto-u.ac.jp

In phytopathogenic fungi, the surface hydrophobicity of conidia and hyphae is a critical physical property that determines conidial dispersion and plant colonization. Previously, we obtained two wettable mutants (Wet86 and WetR2) of the maize pathogen Bipolaris maydis, which lacked hyphal surface hydrophobicity. In this study, we aimed to genetically identify the factor(s) for hyphal wettability in these two mutants and to clarify the relationship, if any, between the factor(s) and hydrophobins, known contributors to hyphal surface hydrophobicity. Through crossing experiments between the wild-type and mutant strains, we confirmed that the wettable phenotype observed in each mutant was attributable to a single alteration at a locus. Subsequently, we compared the whole genome sequences of the wild-type and mutant strains, identifying specific polymorphisms in ORFs unique to each mutant. Furthermore, linkage analysis of these extracted polymorphisms and wettability in the offspring of the crosses revealed that a NPS4 (nonribosomal peptide synthetase 4) gene mutation was associated with the wettability of Wet86 strain. Analysis of the WetR2 strain is still ongoing. We also identified four hydrophobin genes and developed a strain lacking all four of them. Intriguingly, unlike the NPS4 disruptant, the hydrophobin-deficient B. maydis strain did not exhibit a significant difference in hydrophobicity compared to the wild-type strain. This suggests that cell surface hydrophobicity in this fungus depends on cyclic peptide compounds rather than hydrophobins. Currently, we are analyzing strains that overexpress hydrophobin in the NPS4 disruptant and would like to discuss the relationship between NPS and hydrophobins.