IMPROVED KNOWLEDGE OF VIRULENCE FACTORS TO DEVELOP POSTHARVEST DECAY CONTROL STRATEGIES
Title: Penicillium solitum produces a polygalacturonase isozyme in decayed ‘Anjou’ pear fruit capable of macerating host tissue in vitro
Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 2011
Publication Date: January 6, 2012
Citation: Jurick Ii, W.M., Vico, I., Gaskins, V.L., Whitaker, B.D., Garrett, W.M., Janisiewicz, W.J., Conway, W.S. 2012. Penicillium solitum produces a polygalacturonase isozyme in decayed ‘Anjou’ pear fruit capable of macerating host tissue in vitro. Mycologia. DOI:10.3852/11.119.
Interpretive Summary: Blue mold decay of pears is caused by the fungus Penicillium solitum. It is the one of the most economically important diseases of pear fruit, causes significant losses in storage, and is controlled by the use of fungicides. However, consumers desire alternatives to controlling this disease without using chemicals. Therefore, we have studied a major protein that is secreted by the fungus during pear decay. Understanding how this protein functions during pear fruit decay may lead to better control strategies that do not involve fungicides. Many different audiences will benefit from this information such as growers, packers, and consumers.
A polygalacturonase (PG) isozyme was isolated from Penicillium solitum-decayed ‘Anjou’ pear fruit and purified to homogeneity using a multistep process. Both gel filtration and cation exchange chromatography revealed a single PG activity peak and analysis of the purified protein showed a single band with a molecular mass of 43 kDa. The purified enzyme was active from pH 3.5 to 6, with an optimum at pH 4.5. PG activity was detectable from 0 to 70°C with a maximum at 50°C. The purified isozyme was inhibited by the divalent cations Ca2+, Mg2+, Mn2+, and Fe2+ and analysis of enzymatic hydrolysis products revealed polyagalacturonic acid monomers and oligomers. The purified enzyme has an isoelectric point of 5.3 and is not associated with a glycosylated protein. The purified PG isozyme macerated fruit tissue plugs in vitro and produced ~1.2 fold more soluble polyuronides from pear than from apple tissue which further substantiates the role of PG in pear fruit decay. Data from this study show for the first time that the purified PG isozyme produced in decayed ‘Anjou’ pear is different from that PG produced by the same fungus in decayed apple.