Genetic interaction between the septation initiation network component SepM and the cell wall integrity transcription...

We previously reported that SepL and SepM, components of the septation initiation network (SIN) complex, are involved in the activation of the ManR-dependent cellobiose-responsive expression in the cellulase-producing fungus Aspergillus aculeatus. The SIN pathway regulates septation and cytokinesis, processes that require extensive cell wall remodeling and are tightly coupled to cell wall integrity signaling. Because cell wall remodeling and homeostasis are monitored by the cell wall integrity (CWI) pathway, we hypothesized that CWI signaling may contribute to the SIN-dependent regulation of CAZyme genes. To investigate this hypothesis, we analyzed the roles of RlmA, a downstream transcription factor of the CWI pathway, and SepM in regulating cellobiose-responsive CAZyme expression in A. aculeatus. Under the cellobiose-inducing conditions, ΔsepM showed reduced expression of cbhI, cmc2, and cel7b, whereas ΔrlmA did not at all; however, ΔsepMΔrlmA exhibited the loss of the inducible expression of their genes, which was restored in the complemented strain, whereas their genes were induced in response to β-1,4-mannobiose in all test strains. These data demonstrate that SepM and RlmA function through genetically interacting pathways. Notably, transcription responses displayed distinct patterns, suggesting partially overlapping but non-redundant regulatory roles. Our findings reveal that SIN and CWI signaling pathways cooperatively regulate CAZyme gene expression in response to cellobiose, providing new insights into the integration of morphogenetic and cellobiose-responsive signaling in filamentous fungi.