Characterization and Functional Analysis of a New Calcium/Calmodulin-Dependent Protein Kinase (CaMK1) in the Citrus Pathogenic Fungus Penicillium italicum

Calcium (Ca )/calmodulin-dependent protein kinases (CaMKs) act as a class of crucial elements in Ca -signal transduction pathways that regulate fungal growth, sporulation, virulence, and environmental stress tolerance. However, little is known about the function of such protein kinase in phytopathogenic species. In the present study, a new CaMK gene from the citrus pathogenic fungus , designated , was cloned and functionally characterized by gene knockout and transcriptome analysis. The open reading frame of is 1209 bp in full length, which encodes 402 amino acid residues (putative molecular weight ~45.2 KD) with the highest homologous (~96.3%) to the CaMK. The knockout mutant Δ showed a significant reduction in vegetative growth, conidiation, and virulence (i.e., to induce blue mold decay on citrus fruit). Δ was less sensitive to NaCl- or KCl-induced salinity stress and less resistant to mannitol-induced osmotic stress, indicating the functional involvement of in such environmental stress tolerance. In contrast, the -complemented strain Δ COM can restore all the defective phenotypes. Transcriptome analysis revealed that knockout of down-regulated expression of the genes involved in DNA replication and repair, cell cycle, meiosis, pyrimidine and purine metabolisms, and MAPK signaling pathway. Our results suggested the critical role of in regulating multiple physical and cellular processes of citrus postharvest pathogen , including growth, conidiation, virulence, and environmental stress tolerance.