ARS | Publication request: Carbon, nitrogen and pH regulate the production and activity of a polygalacturonase isozyme produced by Penicillium expansum

Submitted to: Archives of Phytopathology and Plant Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 12, 2012
Publication Date: February 13, 2012
Citation: Jurick Ii, W.M., Vico, I., Gaskins, V.L., Peter, K.A., Park, E., Janisiewicz, W.J. 2012. Carbon, nitrogen and pH regulate the production and activity of a polygalacturonase isozyme produced by Penicillium expansum. Archives of Phytopathology and Plant Protection. DOI:10.1080/03235408.2012.657893.

Interpretive Summary: Blue mold decay of apple and pear fruit is caused by the fungus Penicillium expansum. It is one of the most economically important diseases causing postharvest decay in storage and produces carcinogenic toxins that contaminate processed fruit products. We have chosen to study a protein that is secreted by the fungus that degrades fruit during storage. We have determined that the fungus is capable of growing on a wide variety of nutrient sources. We have also demonstrated that pH regulates activity of the protein and have obtained a portion of the corresponding gene. Understanding how this protein functions and the conditions that the fungus uses to regulate its activity may lead to new methods of decay control. Many different audiences will benefit from this information such as apple and pear fruit growers, fruit packing industry, and other scientists.

Technical Abstract: The influence of carbon, nitrogen and pH on polygalacturonase activity produced by Penicillium expansum were investigated. P. expansum mycelial growth was greatest on lyophilized fruit tissue and the highest PG activity occurred in apple pectin medium. Nitrogen source influenced PG activity and was highest with ammonia while the greatest mycelial mass was supported by glutamate or glutamine. PG activity and mycelial mass peaked 5 days after inoculation as polyuronide content decreased and the pH and ammonium levels increased in apple pectin medium. A single active PG isozyme with an isoelectric point of ~7.6 was produced in apple pectin medium and a partial cDNA clone was obtained that was most homologous to the pggII gene from P. griseoroseum. The results from this study indicate that P. expansum can modulate the activity of PG in response to nutrient sources and ambient pH through signaling pathways that modulate nutrient acquisition, uptake and metabolism.