UC Riverside

Plants are subject to attack by microbial pathogens. This research utilized four distinct plant-pathosystems combined with methods of phytopathology, molecular genetics and chemical biology to study mechanisms of plant immunity against microbial phytopathogens. Chemical biology is the use of small molecule compounds to study biological processes. A previous chemical screen identified 114 compounds, called synthetic elicitors, that activate innate immune responses in the model plant Arabidopsis thaliana (Arabidopsis). Here, experiments conducted with three synthetic elicitors were found to provide disease protection in one or more of the following plant-pathogen interactions: Solanum lycopersicum (tomato) and Pseudomonas syringae pathovar tomato (Pst), Vigna unguiculata (cowpea) and Fusarium oxysporum formae speciales tracheiphilum race 3 (Fot3) or Arabidopsis and Hyaloperonospora arabidopsidis (Hpa). The results of these studies demonstrated the potential power of synthetic elicitors as both tools for molecular/chemical biology research and for direct protection of agricultural crop plants. In addition to synthetic elicitor-applied research, innovative agar plate-based infection assays were developed to study defense responses in Arabidopsis against Macrophomina phaseolina (Mp). Dubbed as a “global destroyer of crops”, the necrotrophic, soil-borne fungus Mp infects more than 500 plant species including many economically important crops. Plant defenses against this powerful pathogen are poorly understood. The novel model phyto-pathosystem was used to quantify Mp biomass growth in roots and to analyze shoot disease severity in different Arabidopsis genotypes, quantitatively assessing host factors affecting the outcome of Mp infections. By comparative profiling of host transcripts in roots of the wild type Arabidopsis accession Col-0, with and without Mp infection, expression changes were uncovered in hundreds of genes potentially contributing to Mp defense mechanisms or putative effector targeting schemes. The results established the Mp-Arabidopsis interaction as a useful model pathosystem, which allowed for application of the vast genomics-related resources of this versatile model plant to the systematic investigation of previously understudied host defenses against a major broad host-spectrum plant pathogen.