REU: Glycerol Metabolism and Its Role in Biotrophy Versus Necrotrophy in an Arabidopsis/Fungal Hemibiotroph Model System

Plant diseases have a devastating impact on agricultural production and our food supply every year. Most fungal plant pathogens are either biotrophic (able to infect only live host cells) or necrotrophic (colonizing only host tissues that have already been killed). Members of the fungal genus Colletotrichum are unique because they are hemibiotrophs, initially infecting as biotrophs, but switching later to necrotrophy. Thus, one can compare and contrast factors relevant to necrotrophy and biotrophy in a single Colletotrichum pathosystem. In the proposed research, we intend to utilize a newly described Arabidopsis-Colletotrichum model disease interaction to dissect a novel aspect of host-pathogen signaling. Inoculation of Arabidopsis with Colletotrichum is associated with a -50% reduction in host glycerol levels, and a concomitant increase in the levels of glycerol-3-phosphate (G3P). Mutations affecting synthesis of host G3P result in enhanced susceptibility to Colletotrichum. Fungal mutants impaired in synthesis of glycerol and G3P are avirulent on the wild type host, but can cause disease on Arabidopsis mutants affected in G3P biosynthesis. Our results demonstrate that the effectiveness of basal disease resistance does not rely solely on the host genotype, and that it can be altered by changes in the pathogen genotype. Based on our preliminary data, we hypothesize that there is a link between host defense and glycerol metabolism during the host-pathogen interaction. Such a link has not been described previously for plant-pathogen interactions, but an ability of the plant to detect alterations in metabolite levels that result from pathogen activity, and to respond by activating defense pathways, would undoubtedly be evolutionarily advantageous. We propose to use molecular and biochemical approaches, targeting both Arabidopsis and Colletotrichum, to test the hypothesis that glycerol metabolism in host and pathogen plays an important role in the successful establishment of the infection court and signaling related to defense responses during biotrophy and necrotrophy.