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.