The role of pH signalling transcription factor PacC in pathogenicity and ochratoxin A biosynthesis by Aspergillus carbonarius

Pathogenic fungi must respond effectively to changes in environmental pH for successful host colonization, virulence and toxigenicity. Aspergillus carbonarius is a mycotoxigenic pathogen with the ability to colonize many plant hosts and secrete ochratoxin A (OTA). In this study we characterized the functions and addressed the role of PacC‐mediated pH signalling in A. carbonarius virulence using designed pacC gene knockout mutant. pacC mutant displayed an acidity-mimicking phenotype resulting in poor growth at neutral/alkaline pH, accompanied by reduced sporulation and conidial germination compared to the wild-type. The ΔAcpacC mutant was unable to effectively acidify the growth media as a direct result of poor gluconic and citric acid production. Furthermore, loss of AcpacC resulted in significant reduction of OTA production at acidic pH. Additionally, ΔAcpacC mutant was less virulent than the wild-type strain in grapes and nectarine fruits. Reintroduction of pacC gene into ΔAcpacC mutant restored the wild-type phenotype. Our results demonstrate important roles of PacC in OTA biosynthesis through regulation of the genes in the cluster, and in pathogenicity of A. carbonarius, possibly by controlling transcription of acid-expressed genes important for fungal infection.