Systematic Characterization of the Nine Components Involved in the MAPK Cascades in Peach Shoot Blight Fungus Diaporthe amygdali.

Abstract

As a causative agent of peach shoot blight, Diaporthe amygdali poses a substantial threat to the peach industry. However, no molecular studies on this pathogen have been reported to date. The three mitogen-activated protein kinase (MAPK) cascades are highly conserved among fungal species, and exert a considerable influence on the developmental and pathogenic processes of these organisms. Here, the genome of D. amygdali strain ZN32 was sequenced performed and compared with that of four other Diaporthe isolates. Nine proteins involved in the three MAPK cascades were identified: Mst11-Mst7-Pmk1 (Pmk1-MAPK cascade), Mck1-Mkk1-Mps1(Mps1-MAPK cascade), and Ssk2-Pbs2-Osm1(Osm1-MAPK cascade). Deletion of the genes encoding the Pmk1- and Mps1-MAPK cascade proteins and an adaptor protein DaMst50 significantly attenuated vegetative growth, abolished asexual reproduction, compromised the stress response, impacted surface hydrophobicity, and markedly reduced pathogenicity of D. amygdali. However, deletion of the genes encoding the Osm1-MAPK cascade proteins only affected stress response regulation. Additionally, DaMst11 interacted with both DaMst7 and DaMst50, and no interactions were observed between other proteins in Pmk1- and Mps1-MAPK cascades using yeast two-hybrid system. Finally, heterologous expression of Pmk1-encoding genes from Magnaporthe oryzae and Valsa mali completely rescued the asexual reproduction and virulence defects in the ΔDapmk1 mutants, but only partially restored its vegetative growth. Overall, our findings expand the existing knowledge about the role of the MAPK cascades in plant pathogenic fungi. The genomic information and genetic transformation system by this study will greatly contribute to help toward elucidating the pathogenic mechanism of D. amygdali and effectively managing orchard diseases.