Dissection of Plant Defense Mechanisms Using Chemical and Molecular Genomics

year billions of dollars are spent on pesticides which can be harmful to consumers and the environment. Off-target effects make the study of interactions between plants and pathogens an integral field for the reduction of conventional pesticide use. Using model pathosystems, such as Arabidopsis thaliana (Arabidopsis) and Hyaloperonospora arabidopsidis (Hpa), important plant disease questions are being addressed. Plant defense-inducing molecules (synthetic elicitors) identified and characterized using chemical genomics will be valuable tools for the dissection of the plant defense network and will serve as leads for the development of environmentally-safe pesticides.;Genes from the Arabidopsis ACID (Associated with Chemically Induced Defense) cluster are coordinately inducible by the synthetic elicitors DCA and INA. I demonstrated that 10 of 16 ACID members tested are required for basal immunity of Arabidopsis against Hpa. In addition, nine novel synthetic elicitors were reported on here.;2-(5-bromo-2-hydroxy-phenyl)-thiazolidine-4-carboxylic acid (CMP442) is able to quickly and transiently induce disease resistance, has a distinct mode-of-action, is structurally unique, and can be easily synthesized. At low doses CMP442 enhances the growth of roots and aerial parts of Arabidopsis and Solanum lycopersicum, while high concentrations inhibited growth. These effects are reminiscent of the hormetic-like response, which is characterized by a low dose stimulatory or beneficial effect of a wide range of stimuli that are toxic or inhibitory at higher concentrations.;Salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) are known to coordinate plant defense responses to combat pathogens. Most documented interactions between JA- and SA-dependent signaling processes are antagonistic, but their interactions are complex. Here I report on the development of a screening procedure to identify synthetic elicitors that activate the JA-/ET-dependent branch of the defense network. A set of genes, termed the Jasmonic acid and Ethylene Dependently Induced (JEDI) genes, were identified that display SA-independent upregulation in response to infection with Hpa. Additionally, efforts to create Arabidopsis lines containing RNA silencing transgenes co-silencing closely related PDF family members is described.