Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2009
Publication Date: 6/1/2009
Citation: Jurick II, W.M., Vico, I., Mcevoy, J.L., Whitaker, B.D., Janisiewicz, W.J., Conway, W.S. 2009. Isolation, purification, and characterization of a polygalacturonase produced in Penicillium solitum-decayed 'Golden Delicious' apple fruit. Journal of Phytopathology. 99:636-641. Interpretive Summary: Penicillium solitum is a blue mold fungus that can cause losses of apples in storage due to decay. We investigated the presence of possible virulence factors produced by this pathogen leading to cell wall degradation and resulting decay. We have purified and characterized a cell wall degrading enzyme produced by P. solitum in infected apple fruit. By targeting this enzyme, non-fungicidal control strategies can be developed to reduce postharvest losses caused by this pathogen. This information will be of use to researchers as well as members of the apple storage industry that are exploring alternative methods of blue mold decay control.
Technical Abstract: Polygalacturonase (PG) was extracted and purified from decayed Golden Delicious apple fruit inoculated with Penicillium solitum. Gel filtration and cation exchange chromatography were used to purify the enzyme. Both methods revealed a single peak corresponding to PG activity and analysis of cation exchange-purified material using SDS-PAGE revealed a 50 kDa band. The enzyme was active over a broad range pH (3 to 7) with optimal activity between pH 4 and 5. PG was highly active at 20 and 37 °C but was also detectable at 2, 50 and 75 °C. Divalent and monovalent cations affected PG enzyme activity where Na, Mg, Fe and K increased whereas Ca and Mn reduced activity in vitro. Thin layer chromatographic separation of PG hydrolysis products revealed that the enzyme has both endo and exo activity. Purified PG macerated apple fruit tissue in vitro and caused a significant reduction in weight (~30 %) after 48 hours. Data from this study show for the first time that PG is a virulence factor in the P. solitum-apple fruit interaction which enables the fungus to colonize the host.