Mitogen-activated protein kinase (MAPK) signaling pathway plays key roles in sensing extracellular signals and transmitting them from the cell membrane to the nucleus in response to various environmental stimuli. A MAPKKK protein CgMck1 in Colletotrichum gloeosporioides was characterized. Phenotypic analyses of the ∆Cgmck1 mutant showed that the CgMck1 was required for vegetative growth, fruiting body development, and sporulation. Additionally, the CgMCK1 deletion mutant showed significant defects in cell wall integrity, and responses to osmotic stresses. The mutant abolished the ability to develop appressorium, and lost pathogenicity to host plants. The ∆Cgmck1 mutant also exhibited a higher sensitivity to antifungal bacterium agent Bacillus velezensis. The deletion mutants of downstream MAPK cascades components CgMkk1 and CgMps1 showed similar defects to the ∆Cgmck1 mutant. In conclusion, CgMck1 is involved in the regulation of vegetative growth, asexual development, cell wall integrity, stresses resistance, and infection morphogenesis in C. gloeosporioides.

Potassium has an important role to play in multiple cellular processes. In Saccharomyces cerevisiae, the serine/threonine (S/T) kinase Sat4/Hal4 is required for potassium accumulation, and thus, regulates the resistance to sodium salts and helps in the stabilization of other plasma membrane transporters. However, the functions of Sat4 in filamentous phytopathogenic fungi are largely unknown. In this study, ChSat4, the yeast Sat4p homolog in Colletotrichum higginsianum, has been identified. Target deletion of ChSAT4 resulted in defects in mycelial growth and sporulation. Intracellular K+ accumulation was significantly decreased in the ChSAT4 deletion mutant. Additionally, the ΔChsat4 mutant showed defects in cell wall integrity, hyperoxide stress response, and pathogenicity. Localization pattern analysis indicated ChSat4 was localized in the cytoplasm. Furthermore, ChSat4 showed high functional conservation with the homolog FgSat4 in Fusarium graminearum. Taken together, our data indicated that ChSat4 was important for intracellular K+ accumulation and infection morphogenesis in C. higginsianum.

Anthracnose caused by Colletotrichum gloeosporioides is one of most serious fungal diseases on Chinese fir (Cunninghamia lanceolata). Eight fungal endophytes were isolated from a young heathy branch of Chinese fir and screened against the pathogen in vitro. One isolate, designated as SMEL1 and subsequently identified as Epicoccum dendrobii based on morphological and phylogenetic analyses, suppressed mycelial growth of C. gloeosporioides on dual culture plates. Additionally, the metabolites of E. dendrobii significantly decreased the biomass of C. gloeosporioides. E. dendrobii was able to enter the internal tissues of the host plant via stomatal cells. The metabolites of E. dendrobii significantly inhibited conidial germination and appressorium formation, which at least partly explained why the endophyte significantly inhibited lesion development caused by C. gloeosporioides on various host plants. We further confirmed that some components with antifungal activity could be extracted from E. dendrobii using ethyl acetate as an organic solvent. To our knowledge, this is the first report of E. dendrobii as a potential biocontrol agent against a fungal phytopathogen.

Protein phosphatases (PPs) play important roles in the regulation of various cellular processes in eukaryotes. The ascomycete Colletotrichum gloeosporioides is a causal agent of anthracnose disease on some important crops and trees. In this study, CgPPZ1, a protein phosphate gene and a homolog of yeast PPZ1, was identified in C. gloeosporioides. Targeted gene deletion showed that CgPpz1 was important for vegetative growth and asexual development, conidial germination, and plant infection. Cytological examinations revealed that CgPpz1 was localized to the cytoplasm. The Cgppz1 mutant was hypersensitive to osmotic stresses, cell wall stressors, and oxidative stressors. Taken together, our results indicated that CgPpz1 plays important role in fungal development and virulence of C. gloeosporioides and multiple stress responses.

The authors wish to make the following correction to this paper [...]