Jasmonic acid (JA) and related octadecanoid-derivatives are key plant signals that are involved in development, defense against pathogens and insects, and in protecting plants from harmful environmental agents such as ozone. Despite the importance of these signaling molecules, their mechanism of action at the molecular genetic and biochemical level is largely unknown. Mutations in the JAR1 gene in Arabidopsis thaliana impair many JA-signaled responses, suggesting this gene is associated with JA function. The JAR1 protein was recently found to be a member of the adenylate-forming firefly luciferase superfamily. These enzymes adenylate substrate carboxyl groups, thereby activating them for further biochemical modification. Importantly, JAR1 appears to adenylate JA. This finding is unique among known plant hormone response pathways, because it suggests that covalent modification of the signal (JA) by JAR1 positively affects JA response. Arabidopsis also has 18 other genes that are closely related to JAR1 and some of these act on other plant hormones. This project intends to: 1. Determine how the adenylating activity of JAR1 affects JA signaling in Arabidopsis. 2. Understand the role of JAR1 in controlling plant gene expression. 3. Compare and contrast the expression pattern of JAR1 and related genes. 4. Isolate and characterize suppressors of the jar1 phenotype. 5. Determine the biochemical and physiological function of other Arabidopsis genes that are related to JAR1. Methods to achieve these objectives will include the in vitro assay of enzyme activity of JAR1-like genes using GST-fusion proteins expressed in E. coli. Extracts from jar1 mutants and wild type plants will be analyzed by GC/MS to determine if levels of JA, JA precursors or JA derivatives are altered. JAR1-related gene function will be explored in knockout mutants and by gene overexpression. The developmental and tissue-specific expression pattern of JAR1 and the 18 related Arabidopsis genes also will be analyzed to determine where and when each gene acts. Finally, suppressors of the jar1 phenotype will be isolated and characterized. Together these approaches will yield a comprehensive understanding of the role that covalent modification of hormones by adenylation plays in controlling hormone function.
A gene family that influences plant development and helps to protect plants from disease and other environmental damage will be investigated. Some of these genes encode enzymes that biochemically modify the plant hormones jasmonic acid and indole acetic acid. This is important to study because the control of plant hormone activity by chemical modification is poorly understood. The project will increase our understanding of how hormones regulate growth and protect plants from damage. The results from this study of the model plant Arabidopsis thaliana will have a fundamental and broad impact because similar genes are found in many if not all plant species.
