Novel insights in the production, activity and protective effect of Penicillium expansum antifungal proteins.

Antifungal proteins (AFPs) offer a great potential as new biofungicides to control deleterious fungi. The phytopathogenic fungus Penicillium expansum encodes three phylogenetically distinct AFPs, PeAfpA, PeAfpB and PeAfpC. Here, PeAfpA, a potent in vitro self-inhibitory protein, was demonstrated to control the infection caused by P. expansum in Golden apple fruits. We determined the production of the three proteins in different growth media. PeAfpA and PeAfpC were simultaneously produced by P. expansum in three out of the eight media tested as detected by Western blot, whereas PeAfpB was not detected even in those described for class B AFP production. Regardless of the culture medium, the carbon source affected Peafp expression. Notably, the production of PeAfpA was strain-dependent, but analyses of PeafpA regulatory sequences in the three strains studied could not explain differences in protein production. None of the PeAFPs was produced during apple infection, suggesting no relevant role in pathogenesis. PeAfpA together with PeAfpB and also with Penicillium digitatum PdAfpB showed synergistic interaction. The highly active antifungal PeAfpA also showed moderate antibacterial activity. We conclude that there is not a general pattern for Peafp gene expression, protein production or antimicrobial activity and confirm PeAfpA as a promising compound for postharvest conservation.