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

Summary

Researchers studied proteins called hydrophobins in a corn fungal pathogen to understand what they do. Surprisingly, even when they removed all four hydrophobin genes from the fungus, it grew normally and remained just as water-repellent as wild-type. However, when these same proteins were placed into a different fungus species that lacks its own hydrophobins, they worked perfectly to restore water repellency. This suggests that hydrophobins have different roles depending on which fungus they’re in.

Background

Hydrophobins are small amphiphilic proteins secreted by filamentous fungi that confer hydrophobic properties to hyphae and conidia. Bipolaris maydis is the causal agent of southern corn leaf blight, but the biological functions of its hydrophobins remain unclear. Previous studies suggested the B. maydis genome encodes at least four hydrophobins, though their specific roles in this fungus have not been thoroughly analyzed.

Objective

This study aimed to identify all hydrophobin genes in B. maydis, characterize their expression, and determine their functional roles in fungal growth, pathogenicity, and colony hydrophobicity. The researchers also investigated whether B. maydis hydrophobins could functionally complement a hydrophobin-deficient mutant of Aspergillus nidulans.

Results

Four hydrophobin genes were identified: HYP1 (class I) and HYP2-HYP4 (class II). All four genes were expressed under different conditions. Disruptant strains showed no significant phenotypic differences from wild-type in growth, conidiation, stress tolerance, virulence, sexual reproduction, or colony hydrophobicity. However, when B. maydis hydrophobin genes were introduced into a dewA-deficient A. nidulans mutant, all four hydrophobins restored colony hydrophobicity, though to varying degrees.

Conclusion

Although B. maydis hydrophobins retain their biochemical function in hydrophobicity, they do not contribute to colony hydrophobicity in their native fungus, suggesting their role may differ from that of hydrophobins in other fungi. The study demonstrates functional redundancy and indicates that hydrophobin functions are species-dependent, with colony hydrophobicity in B. maydis likely controlled by other factors such as Nps4.
  • Published in:Frontiers in Fungal Biology,
  • Study Type:Experimental Study,
  • Source: PMID: 41356074, DOI: 10.3389/ffunb.2025.1604903
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