Role of the putative transcription factor Rim101 in pH/oxidative stress response and cell wall structure formation in the white-rot fungus Pleurotus ostreatus

The transcription factor Rim101 regulates various cellular functions in fungi, including maintaining cell homeostasis, regulating redox processes, and transmembrane transport, in response to environmental pH changes and redox stress. White-rot fungi encounter various environmental stresses during wood degradation. In this study, the role of Rim101 in the stress response of white-rot fungi was investigated by analysing the phenotype of rim101-disrupted strains of Pleurotus ostreatus. The Δrim101 strains exhibited approximately a 15 % decrease in growth rate on agar medium and impaired growth under culture conditions at pH 5, compared to the wild-type (WT) strain. Disruption of Rim101 also increased sensitivity to oxidative stress induced by H₂O₂. Notably, RT-PCR analysis showed reduced expression of oxidative stress-related genes (cat1, cat2, gsh-px, and sod4), suggesting that Rim101 is essential for the normal oxidative stress response in P. ostreatus. Furthermore, the Δrim101 strains exhibited reduced resistance to cell wall synthesis inhibitors, such as Calcofluor White and Micafungin. While the Δrim101 strains showed no significant differences in the expression of cell wall polysaccharide synthesis enzyme genes or cell wall thickness compared to the WT strain, the content of α-glucan in the dried mycelia and the signal of α-glucan detected by a fluorescent protein probe in the inner layer of the cell wall were increased. Therefore, disruption of rim101 appears to affect cell wall integrity. This study provides evidence for the conserved function of Rim101 in pH and oxidative stress responses among basidiomycetes and ascomycetes. Additionally, a novel function of Rim101 was revealed, wherein it modulates the formation of the inner α-glucan layer in the cell wall of P. ostreatus.