New Insight Into Pathogenicity and Secondary Metabolism of the Plant Pathogen Penicillium expansum Through Deletion of the Epigenetic Reader SntB.

Joanna Tannous,Nancy P Keller,Dianiris Luciano-Rosario,Dov B Prusky,Omer Barda,Edward Sionov

doi:10.3389/fmicb.2020.00610

Abstract

Penicillium expansum is one of the most harmful post-harvest pathogens of pomaceous fruits and the causal agent of blue rot disease. During infection, P. expansum produces the toxic secondary metabolites patulin and citrinin that can impact virulence and, further, render the fruit inedible. Several studies have shown that epigenetic machinery controls synthesis of secondary metabolites in fungi. In this regard, the epigenetic reader, SntB, has been reported to govern the production of multiple toxins in Aspergillus species, and impact virulence of plant pathogenic fungi. Here we show that deletion of sntB in P. expansum results in several phenotypic changes in the fungus including stunted vegetative growth, reduced conidiation, but enhanced germination rates as well as decreased virulence on Golden Delicious apples. In addition, a decrease in both patulin and citrinin biosynthesis in vitro and patulin in apples, was observed. SntB positively regulates expression of three global regulators of virulence and secondary metabolism (LaeA, CreA, and PacC) which may explain in part some of the phenotypic and virulence defects of the PeΔsntB strain. Lastly, results from this study revealed that the controlled environmental factors (low temperatures and high CO2 levels) to which P. expansum is commonly exposed during fruit storage, resulted in a significant reduction of sntB expression and consequent patulin and citrinin reduction. These data identify the epigenetic reader SntB as critical factor regulated in post-harvest pathogens under storage conditions and a potential target to control fungal colonization and decaying of stored fruit.

Highlights

The ubiquitous fungus Penicillium expansum is the dominant post-harvest pathogen among fruits and vegetables, mainly pome fruits (Tannous et al, 2017a)
Screening of fungal transformants was done on sorbitol minimal medium (SMM) agar supplemented with the appropriate antibiotic
To screen for secondary metabolite production in vitro, strains were cultivated on four different agar media chosen to represent a broad range of nutrient source, which are: Potato Dextrose Agar (PDA), Yeast Extract Sucrose Agar (YES), Czapek Yeast Extract Agar (CYA) and glucose minimal medium (GMM), at 25◦C for 10 days

Summary

Introduction

The ubiquitous fungus Penicillium expansum is the dominant post-harvest pathogen among fruits and vegetables, mainly pome fruits (Tannous et al, 2017a). Besides the aesthetic aspect of its presence, contamination by P. expansum poses a health hazard due to the production of toxic secondary metabolites (mycotoxins) in contaminated fruit. Among the mycotoxins produced by P. expansum, the polyketide patulin is the most notable contaminant, given its long-established toxicity and prevalence during fruit infection (Puel et al, 2010; Tannous et al, 2017a). Citrinin is another polyketide mycotoxin reported to often co-occur with patulin on apples (Martins et al, 2002). Due to the agricultural losses and serious health risks associated with the occurrence of these mycotoxins, a deeper understanding of what triggers their production is needed

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Conclusion