Molecular Characterization of the AXR2 Gene of Arabidopsis

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9307134 Estelle The plant hormone auxin or indole acetic acid (IAA) plays a central role in plant growth and development. To understand the molecular mechanism of auxin action Dr. Estelle and his colleagues are studying a group of genes in Arabidopsis thaliana called the auxin- resistance genes. Mutations in these genes cause auxin resistance and an array of developmental defects which appear to be related to a reduction in auxin sensitivity. In addition, mutations in each of the auxin-resistance genes alter sensitivity to at least one additional plant hormone. It is hypothesized that this cross resistance is a reflection of the integrated nature of plant hormone action. In this award, Dr. Estelle describes experiments which investigate the function of the auxin-resistance gene AXR2. Two dominant mutations in this gene have been identified. The prior studies suggest that the AXR2 gene functions early in auxin response. In addition, histological studies on axr2 mutant plants suggest that the AXR2 gene has an important role in auxin-regulated cell elongation. Three specific aims are defined. First, the investigators will analyze two rapid auxin responses which are thought to be important in auxin-induced cell elongation. Second, they will isolate and characterize new alleles of the AXR2 gene. They use these mutants to gain new insight into the function of the wild-type gene. Third, they will isolate the AXR2 gene by positional cloning and characterize both wild-type and mutant alleles at the molecular level. In recent years, molecular and biochemical studies have resulted in the identification and partial characterization of several proteins which may function in auxin action. However, it has been difficult to determine the physiological role of these proteins. A genetic approach promises to make a unique contribution to our understanding of this complex problem. It is expected that the genetic and molecular characterization of auxin-resi stance genes like AXR2 will provide important new information on the mechanism of hormone action. ***