Developmental Regulation of Auxin Biosynthesis in Arabidopsis thaliana

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9870798NormanlyThe long range goal of this project is to understand the developmental regulation of auxin biosynthesis. Auxin is a key regulator of plant growth and development, and it is known that the maintenance of auxin levels (auxin homeostasis) in the plant is a dynamic process that responds dramatically to developmental as well as environmental cues. The interplay between auxin homeostasis and the growth and developmental effects of auxin is still unclear since most aspects of auxin biosynthesis, metabolism, and signal transduction are poorly defined. The problem of auxin biosynthesis has been particularly vexing, and to date, none of the pathways that have been postulated for biosynthesis of the primary plant auxin, indole-3-acetic acid (IAA), has been proven definitively in any plant species. Arabidopsis thaliana is an excellent model system for the study of many aspects of plant growth and development and this project employs a combination of genetic, molecular, and biochemical techniques to define IAA biosynthesis and characterize its developmental regulation in this plant. In vivo labeling techniques will be used to determine synthesis and turnover rates for IAA and those compounds that are identified as IAA precursors. Additionally, the cellular distribution of IAA and precursor pools will be examined. This basic information will enable the investigator to characterize the candidates obtained in genetic screens for IAA biosynthetic mutants, as well as other mutants with apparent defects in IAA homeostasis. These will be valuable tools with which to define the role of IAA biosynthesis in the control of growth and development, and ultimately to manipulate IAA biosynthesis in agriculturally useful ways.There are multiple IAA biosynthetic pathways that utilize as a precursor either tryptophan (Trp-dependent pathways) or some other compound (Trp-independent pathways). These pathways appear to be utilized differentially during development. Since neither the Trp-dependent nor Trp-independent pathway is known, the immediate goals of this project are as follows:1. Quantify rates of IAA synthesis and turnover at different developmental time points and quantify metabolic activity of subcellular precursor and product pools.2. Establish whether indole-pyruvic acid (IPA) and /or indole-3-acetaldehyde (IAAld) are intermediates in IAA biosynthesis.3. Identify other intermediates in IAA biosynthesis.4. Initiate a screen for mutants defective in either Trp-dependent or Trp-independent IAA biosynthesis.5. Screen pools of yeast transformed with Arabidopsis cDNAs for indole-metabolizing genes.