Abstract
The mycotoxin patulin is produced in colonized tissue by Penicillium expansum during storage of apples and is significantly affected by environmental factors that contribute to its accumulation. Few reports have, however, examined the effect of natural intrinsic factors associated with the fruit on the production of patulin. Here, we find that with advancing maturity, Golden Delicious apples show increased concentrations of total soluble solids (TSS) from 14 to 17% associated with the increased expression of the global transcription factor involved in regulation of secondary metabolite biosynthesis in filamentous fungi, laeA expression and patulin accumulation. However, the apple cultivar Granny Smith, with similar TSS values but differing in pH levels and malic acid concentrations, showed reduced expression levels of laeA and the patulin biosynthesis gene cluster (pat genes) and patulin accumulation, suggesting a complexity of host factors contribution to patulin accumulation during P. expansum colonization. To start elucidating these apple intrinsic factors, we examined their in vitro impact on laeA and pat gene expression concomitant with patulin synthesis. Increasing sucrose concentrations from 15 to 175 mM repressed laeA and pat gene expression and patulin production. However, this affect was modified and often reversed and sometimes accentuated by changes in pH, or the addition of malic acid or the major apple phenolic compounds, chlorogenic acid and epicatechin. While the increase in malic acid from 0 to 1% increased laeA and pat gene expression, the decrease in pH from 3.5 to 2.5 reduced their expression. Also the increased laeA and pat genes expressions at increasing epicatechin concentrations from 0 to 1 mM, was reversed by increasing sucrose concentrations, all together suggesting the complexity of the interactions in vivo.
Highlights
Penicillium expansum is a destructive phytopathogen, capable of causing decay in many deciduous fruits during postharvest handling and storage (Prusky et al, 2004)
To determine the effect of dynamic changes occurring during fruit maturation on patulin accumulation by P. expansum in Golden Delicious (GD) fruits, apples were inoculated at different periods during fruit maturation (Table 1)
These results showed that a relatively higher amount of patulin was observed in more mature fruits
Summary
Penicillium expansum is a destructive phytopathogen, capable of causing decay in many deciduous fruits during postharvest handling and storage (Prusky et al, 2004). Patulin is produced by several species belonging to the genera Penicillium, Aspergillus, Paecilomyces, and Byssochlamys (Puel et al, 2007). P. expansum is generally regarded as the major producer of patulin (McKinley and Carlton, 1991; Andersen et al, 2004; Pitt et al, 2009). Apple juice and other derived fruit products from P. expansum infected apples are the major source of patulin. Long-term exposure to patulin contaminated fruit juices can cause serious health issues as patulin is believed to be mutagenic, neurotoxic, genotoxic, and immunotoxic to animals (Wouters and Speijers, 1996; Moake et al, 2005)
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