The multicluster regulator A (McrA) C6 factor acts as a global repressor of secondary metabolism in diverse filamentous fungi. Here, we report that the mcrA gene is positively regulated by the velvet regulators VosA/VelB during conidiogenesis and McrA governs cellular and metabolic integrity of conidia in Aspergillus nidulans. An mcrA promoter region contains a VosA responsive element, TGGCTTGGGCTGG, and its mRNA accumulation in conidia requires both VosA and VelB. The deletion (Δ) of mcrA results in a reduced number of conidia and decreased mRNA levels of the key asexual developmental activator brlA. In 138 conidia, ΔmcrA causes a rapid loss of conidia viability, which is likely associated with the lack of trehalose accumulation and increased the ß-(1,3)-glucan levels. In supporting its repressive role, ΔmcrA results in about 4-fold increased production of the mycotoxin sterigmatocystin (ST) and an unknown metabolite in conidia. While overexpression (OE) of mcrA causes fluffy-autolytic and accelerated cell death phenotypes, ΔmcrA does not suppress the developmental defects caused by the lack of the RGS protein FlbA. However, ST production is restored in the ΔflbA ΔmcrA double mutant, and OEmcrA completely blocked the production of ST and many secondary metabolites, corroborating the global repressive role of McrA in secondary metabolism. A genetic model depicting the roles of McrA in governing cellular and metabolic integrity is presented.
Full conference title:
- Fungal Genetics Conference 30th (2019)