Abstract
Antifungal proteins (AFPs) from ascomycete fungi could help the development of antimycotics. However, little is known about their biological role or functional interactions with other fungal biomolecules. We previously reported that AfpB from the postharvest pathogen Penicillium digitatum cannot be detected in the parental fungus yet is abundantly produced biotechnologically. While aiming to detect AfpB, we identified a conserved and novel small Secreted Cysteine-rich Anionic (Sca) protein, encoded by the gene PDIG_23520 from P. digitatum CECT 20796. The sca gene is expressed during culture and early during citrus fruit infection. Both null mutant (Δsca) and Sca overproducer (Scaop) strains show no phenotypic differences from the wild type. Sca is not antimicrobial but potentiates P. digitatum growth when added in high amounts and enhances the in vitro antifungal activity of AfpB. The Scaop strain shows increased incidence of infection in citrus fruit, similar to the addition of purified Sca to the wild-type inoculum. Sca compensates and overcomes the protective effect of AfpB and the antifungal protein PeAfpA from the apple pathogen Penicillium expansum in fruit inoculations. Our study shows that Sca is a novel protein that enhances the growth and virulence of its parental fungus and modulates the activity of AFPs.
Highlights
Infections caused by fungal pathogens pose a serious risk to human health, food production and security [1,2]
CECT 20796, a faint band of a protein of about 12 kDa was detected by SDS-PAGE after 11 days of growth in potato dextrose broth (PDB) (Figure 1a), which was more evident after tenfold concentration of the supernatant samples (Figure 1b)
In order to identify this protein, a Matrix-assisted laser desorption/ionization (MALDI)-TOF/TOF analysis was performed and the results revealed that this protein was encoded by the PDIG_23520 gene
Summary
Infections caused by fungal pathogens pose a serious risk to human health, food production and security [1,2]. Fungal plant pathogens are of great economic importance because they threaten the production of crops and can cause severe postharvest diseases, with an increasing incidence trend in the last decades [1,3]. Multiple chemical fungicide treatments are widely applied, which have negative effects on animal and human health and the environment. There are very few classes of fungicides available to treat (and prevent) fungal infections, leading to a rapid increase in resistance against the existing compounds [4].
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