PdbrlA, PdabaA and PdwetA control distinct stages of conidiogenesis in Penicillium digitatum

Penicillium digitatum is one of the most important citrus postharvest pathogens worldwide. Reproduction of massive asexual spores is the primary factor contributing to the epidemic of citrus green mold. To understand the molecular mechanisms underlying conidiogenesis in P. digitatum, we functionally characterized the Aspergillus nidulans orthologs of brlA, abaA and wetA. We showed that deletion of PdbrlA completely blocked formation of conidiophores, whereas deletion of PdabaA led to the formation of aberrant and non-functional phialides. The PdwetA mutant showed various defective phenotypes, such as abnormal conidia with loose cell walls, delayed germination and reduced tolerance to osmotic, detergent, heat shock and menadione stresses, but elevated resistance to H2O2. PdbrlA-influenced genes were identified by comparing global gene expression profiles between the wild-type and the PdbrlA deletion mutant during conidiation. Gene ontology analysis of these differentially expressed genes (DEGs) revealed the diverse roles of PdbrlA in metabolism, transportation and cell structure. Moreover, out of 39 genes previously reported to be involved in conidiogenesis in Aspergillus, mRNA levels of 14 genes were changed in ΔPdbrlA. Our results confirm the roles of brlA, abaA and wetA in P. digitatum conidiogenesis and provide new insights into the genetics of conidiation in filamentous fungi.