The calcineurin-responsive transcription factor Crz1 is required for regulation of infection structure differentiation, calcium homeostasis and cell wall integrity in Alternaria alternata

Ca2+/calcineurin signaling pathway is crucial in regulating growth, stress response and pathogenicity of phytopathogenic fungi. However, there is little information about the downstream calcineurin-responsive zinc finger transcription factor Crz1 in Alternaria alternata, the pathogenic factors of pear black spot. Here, AaCrz1 was identified in A. alternata and its function was characterized by generating target gene knockout strains. The results showed that ΔAaCrz1 was impaired in vegetative growth and spore morphology. The infection structures in the ΔAaCrz1 inhibited on hydrophobic and pear wax extract coated surface. Deletion of AaCrz1 increased sensitivity to different stresses, especially the hypersensitivity to Ca2+. In addition, AaPMC1 and AaPMR1 genes were regulated by AaCrz1 in response to Ca2+ level. CFW staining indicated that the cell wall of ΔAaCrz1 was damaged, and the ΔAaCrz1 displayed a reduction in the expression of genes related to cell wall biosynthesis, such as chitin synthases (CHS) and β-1,3-glucan synthase (FKS). Furthermore, AaCrz1 was involved in the full virulence of A. alternata on pear fruit. Collectively, this study suggests that identified AaCrz1 is essential for the development, infection structure formation, calcium homeostasis, cell wall integrity and virulence of A. alternata.