Identification of pathogenicity-related genes and the role of a subtilisin-related peptidase S8 (PePRT) in authophagy and virulence of Penicilium expansum on apples

Authors: LEVIN, ELENA - Volcani Center (ARO); KISHORE, AMIT - Volcani Center (ARO); BALLESTER, ANA ROSA - Instituto De Agroquimica Y Technologia De Alimentos; RAPHAEL, GINAT - Volcani Center (ARO); FEIGENBERG, OLEG - Volcani Center (ARO); LIU, YONGSBENG - Hefei University Of Technology; Norelli, John; GONZALES-CANDELAS, LUIS - Instituto De Agroquimica Y Technologia De Alimentos; Wisniewski, Michael; DROBY, SAMIR - Volcani Center (ARO)

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2018
Publication Date: 12/15/2018
Citation: Levin, E., Kishore, A., Ballester, A., Raphael, G., Feigenberg, O., Liu, Y., Norelli, J.L., Gonzales-Candelas, L., Wisniewski, M.E., Droby, S. 2018. Identification of pathogenicity-related genes and the role of a subtilisin-related peptidase S8 (PePRT) in authophagy and virulence of Penicilium expansum on apples. Postharvest Biology and Technology. 149:209-220. https://doi.org/10.1016/j.postharvbio.2018.10.011.
DOI: https://doi.org/10.1016/j.postharvbio.2018.10.011

Interpretive Summary: Blue mold is a major postharvest disease of apple and is responsible for causing significant economic losses. In order to develop effective management strategies to control this postharvest disease, it is critical to develop an understanding of how the pathogen overcomes the natural defense mechanisms of apple fruit. The current study identified proteins secreted by the pathogen that may potentially play a role in overcoming host defense mechansisms. A bioinformatics approach was also used to identify a wide-array of potential pathogenicity factors in the blue mold pathogen. Particular focus was placed on a proteolytic enzyme, a subtilisin-related peptidase. When the gene for this protein was deleted from the blue mold genome, the pathogen exhibited a reduced ability to infect apple fruit. The bioinformatic analysis conducted in the current study, along with the conducted experiments, increases our knowledge of the factors that allow the blue mold fungus, Penicillium expansum, to infect apple fruit and will serve as a basis for developing more effective management strategies.

Technical Abstract: Blue mold caused by Penicillium expansum is a major postharvest disease of pome fruit. Several mechanisms possibly involved in P. expansum pathogenicity and virulence. However, factors that mediate pathogenicity and virulence are largely not yet characterized. In this work we analyzed P. expansum predicted secretome to reveal potential effectors that have a role in host-pathogen interaction. An effector-prediction pipeline was designed using an approach that combines common effector features, transcriptomic data and homology to proteins reported to be involved in pathogenicity of other pytopathogenic fungi. Among 297 genes predicted in P. expansum secretome, 103 genes (35%) were found to code for hydrolytic enzymes. The majority of the secreted enzymes are carbohydrate-degrading enzymes among which five coding for pectin-degrading enzymes are highly induced during the infection and decay of apple fruit by P. expansum, indicating that they may represent an important aspect of pathogenicity and virulence. Applying the pipeline we have predicted 17 candidate genes coding for putative effectors that are likely involved in pathogenicity and virulence. One of the top effector candidates is a subtilisin-related peptidase, S8 (PePRT), proteolytic enzyme highly expressed in planta, and potentially involved in authophagy process. Deletion of PePRT-coding gene resulted in reduced virulence of P. expansum on apples. Moreover, 'Peprt exhibited decreased sporulation as well as affected mycelial morphology and internal mycelial cell structure.