Adenylyl cyclase is required for cAMP production, growth, conidial germination, and virulence in the citrus green mold pathogen Penicillium digitatum

Penicillium digitatum is the causative agent of green mold decay on citrus fruit. The cAMP-mediated signaling pathway plays an important role in the transduction of extracellular signals and has been shown to regulate a wide range of developmental processes and pathogenicity in fungal pathogens. We cloned and characterized a Pdacl gene of P. digitatum, which encodes a polypeptide similar to fungal adenylyl cyclases. Using a loss-of-function mutation in the Pdacl gene we demonstrated a critical requirement for hyphal growth and conidial germination. Deletion of Pdacl resulted in decreased accumulation of cAMP and down-regulation of genes encoding a G protein cc subunit, both catalytic and regulatory subunits of PICA, and two transcriptional regulators StuA and Soml. Fungal mutants lacking Pdacl produced abundant conidia, which failed to germinate effectively and displayed an elevated sensitivity to heat treatment. Pdacl mutant failed to utilize carbohydrates effectively and thus displayed severe growth retardation on rich and synthetic media. Slow growth seen in the Pdacl mutants could be due to a defect in nutrient sensing and acquisition. Quantitative RT-PCR analysis revealed that Pdacl was primarily expressed at the early stage of infection. Fungal pathogenicity assayed on citrus fruit revealed that P. digitatum strains impaired for Pdacl delayed lesion formation. Our results highlight important regulatory roles of adenylyl cyclase-mediated cAMP production in P. digitatum and provide insights into the critical role of cAMP in fungal growth, development and virulence. (C) 2016 Elsevier GmbH. All rights reserved.