The calcineurin-responsive transcription factor Crz1 is required for conidation, full virulence and DMI resistance in Penicillium digitatum

The Ca2+/calmodulin-dependent pathway is a critical signal transduction pathway that mediates various cellular responses in multiple organisms. Calcineurin acts through zinc finger transcription factor Crz1 in fungi. In the present study, we identified an ortholog of Crz1, PdCrz1, in Penicillium digitatum, the most important pathogen of postharvest citrus. To determine the function(s) of PdCrz1, a gene-disruption mutant was generated using an Agrobacterium tumefaciens-mediated transformation (ATMT) procedure. The PdCrz1 disruption (ΔPdCrz1) mutant was defective in conidiation, cell wall integrity and virulence, and was hypersensitivity to stresses caused by Ca2+, H2O2 or 14α-demethylation inhibitor (DMI) fungicides. Expressions of cell wall synthase genes (CHS2, CHS3 and FKS1) and P-type ATPase genes (PMR1 and PMC1) were defective in the ΔPdCrz1 mutant when compared with the wild type. Calcineurin inhibitors were shown to enhance the effect of imazalil on P. digitatum. In contrast, Ca2+ (≤0.2 mol l−1) could alleviate the antifungal activity by imazalil. These results indicate that PdCrz1 has important roles in conidiation, virulence and DMI resistance in P. digitatum. In addition, this study also indicates that specific calcium signaling pathway inhibitors could be used as adjuvants in the conventional DMI fungicides.