This research examines phenolic metabolism in disease development in corn. Hosts will provide genetically differential resistance and susceptibility to the fungus Helminthosporium maydis, race O. Changes in phenolic metabolism after infection include a significant increase in hydroxycinnamic acid: CoA ligase activity, and resistant and susceptible interactions are distinguishable by the CoA ligase isozyme response after infection. The goals of this study are to: (1) characterize these isozymes, (2) define the isozyme response in resistant and susceptible interactions, (3) purify the enzyme for polyclonal antiserum production, (4) clone and characterize the CoA ligase genes, and (5) characterize antisera for CoA ligase specificity. Symptoms of resistance suggest the involvement of phenols in response to infection in plants. Blocking phenolic synthesis at the level of phenylalanine ammonia-lyase (an enzyme of phenylpropanoid metabolism) changes a normally resistant interaction into one of susceptibility. Significant changes in phenols are detected throughout the infection and disease development processes, and the changes in resistance differ from those in susceptibility. This research will examine expression and regulation of phenolic metabolism in the fungal pathogen, Helminthosporium maydis. This research will provide important information about the infection response processes in corn as well as new insights into disease resistance in general.
