Blistering1 Modulates Penicillium expansum Virulence Via Vesicle-mediated Protein Secretion

A TDNA mutant, in the single copy Blistering1 locus, was created in Penicillium expansum. The mutant showed reduced decay in apple fruit, undetectable levels of patulin, and blistered hyphae. Mass spectrometry of proteins in liquid medium and mycelia revealed that it failed to secrete degrative enzymes and ones involved in patulin synthesis. Quantitative mass spectrometry of mycelial proteins revealed altered cellular networks controlling protein processing. These data show that Blistering1 affects internal and external protein processing involving vesicle-mediated transport. [Display omitted] Highlights •The Blistering1 locus in Penicillium expansum encodes a novel protein with a DnaJ domain.•A single T-DNA insertion was generated in the blistering1 gene which manifested in reduced decay in apple and nearly undetectable levels of the mycotoxin patulin in the T625 mutant.•T625 failed to secrete a set of enzymes that degrade plant cell walls and the three final biosynthetic enzymes of patulin synthesis.•Quantitative mass spectrometry of mycelial proteins revealed that the mutant had altered cellular networks controlling protein processing in the endoplasmic reticulum, protein export, vesicle-mediated transport, and endocytosis.•Transmission electron microscopy of hyphal cross sections confirmed that the mutant formed abnormally enlarged endosomes or vacuoles.•These data reveal that Blistering1 affects internal and external protein processing involving vesicle-mediated transport in a family of fungi with medical, commercial, and agricultural importance. The blue mold fungus, Penicillium expansum, is a postharvest apple pathogen that contributes to food waste by rotting fruit and by producing harmful mycotoxins (e.g. patulin). To identify genes controlling pathogen virulence, a random T-DNA insertional library was created from wild-type P. expansum strain R19. One transformant, T625, had reduced virulence in apples, blistered mycelial hyphae, and a T-DNA insertion that abolished transcription of the single copy locus in which it was inserted. The gene, Blistering1, encodes a protein with a DnaJ domain, but otherwise has little homology outside the Aspergillaceae, a family of fungi known for producing antibiotics, mycotoxins, and cheese. Because protein secretion is critical for these processes and for host infection, mass spectrometry was used to monitor proteins secreted into liquid media during fungal growth. T625 failed to secrete a set of enzymes that deg