Botany and Plant Pathology Seminar Series
Speaker: Dr. Eric Schmelz - USDA - University of Florida
Topic: New insights on maize defense against insects and pathogens
When: Wednesday, October 10, 2012 at 3:30 pm in WSLR 116

Plants perceive and respond to biotic stress through a complex series of transcriptional, proteomic and metabolic changes which often improve subsequent resistance. On going CMAVE projects in maize include the investigation of effectors present in insect and pathogens (defense modulators), activation of phytohormone cascades, role of Plant Elicitor Peptides as endogenous signal amplifiers, and induction of terpenoid-based plant defenses. Significant overlap in insect and pathogen-induced maize defense responses occur during stem attack by the European corn borer (ECB; Ostrinia nubilalis). Investigation of this system lead to the recent discovery of a complex series of acidic ent-kaurene-related diterpenoid and b-macrocarpene-derived sesquiterpenoid phytoalexins. Despite broad activation of maize stem defenses, subsequent ECB larval growth actually improves. This relationship strongly contrasts the expectation of induced plant resistance. Improved performance on previously attacked stem tissues is attributable to greatly increased total protein levels and large scale metabolic changes. Unlike other Lepidoptera pests examined, European corn borer larvae excrete high levels of the phytohormone indole-3-acetic acid (IAA) into the feeding tunnel through frass contact. While maize plants rapidly conjugate and remove exogenous IAA, stem tissue concentrations remain elevated during European corn borer attack. Consistent with an effector that promotes plant susceptibility, application of stable IAA analogs trigger significant increases in stem protein levels. The tailoring of plant responses to any biotic attacker is limited in specificity and vulnerable to manipulation by specialists; however, mechanistic biochemical knowledge creates testable approaches for targeted improvements in plant resistance.

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