Abstract
Mycelia of white-rot fungi are recently applied to eco-friendly alternative materials, such as mushroom leather. As a novel approach to modify the physical properties of mushroom materials, molecular breeding targeting the cell wall—which significantly contributes to mycelial strength and water repellency—is gaining more attentions. Efficient modification of the cell wall through molecular breeding requires a understanding of its biosynthetic regulatory systems. Therefore, in this study, we conducted functional analyses of the APSES-family transcription factors Mbp1 and Swi6, which regulate cell wall synthesis, using the white-rot fungus Pleurotus ostreatus. Furthermore, we evaluated the impact of mbp1 disruption on the physical properties of mushroom materials. Δmbp1 and Δswi6 strains exhibited reduced growth rates and impaired aerial hypha formation compared to the Wild type (WT), indicating that these transcription factors are essential for normal mycelial growth. In Δmbp1 strains, the cell wall thickness, the relative percentage of β-glucan, and expression levels of β-glucan synthase genes were decreased. mbp1 disruption altered the expression levels of several chitin synthase genes despite almost no differences in the relative percentage of chitin between the WT and Δmbp1 strains. These results suggest that Mbp1 is required for the normal regulation of β-glucan and chitin synthesis. On the other hand, Δswi6 strains showed abnormal distribution of cell wall thickness, slightly increased relative percentage of chitin, and altered expression of chitin synthase genes, whereas no significant differences in the relative percentage of β-glucan and the expression of β-glucan synthase genes were observed. Thus, Swi6 does not contribute to β-glucan synthesis regulation but is responsible for regulating chitin synthesis. Moreover, mbp1 disruption led to increased Young's modulus and tensile strength of the mycelial mats, indicating a shift toward stiffer and less deformable material properties. Mycelium-based composites from mbp1 disruption strains exhibited smoother surfaces and higher compressive strength than those from the WT. This study is the first to elucidate the functional overlap and differences between Mbp1 and Swi6 in the regulation of cell wall synthesis in white-rot fungi, and it highlights the potential of cell wall as a target for the improvement of mushroom materials.
