Auxin-Responsive Promoters and Auxin-Induced Growth

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9303956 Guilfoyle The plant hormone, auxin, plays roles in cell division, extension, and differentiation. Dr. Guillfoyle has cloned a number of auxin responsive genes (GH1, GH2/4, GH3, and SAURs) from soybean, pea and Arabidopsis that are expressed in meristems, epidermal and cortical cells within elongation zones, vascular tissues, and/or developing xylem elements. Each of these gene families shows distinct tissue, organ, and developmental specific patterns of expression. The functions of the auxin responsive gene products are under investigation. The GH2/4 gene encodes a putative glutathione S- transferase. The promoters for these genes are being analyzed in transgenic plants and by particle gun bombardment of soybean and transient expression in carrot cells. Putative auxin responsive elements (AuxREs) have been identified and transcription factors that bind to the AuxREs are being cloned. The auxin responsive promoters have been used to monitor auxin regulated gene expression during tropisms, xylogenesis, rooting, flowering, and seed formation. These promoters have also been used to drive expression of auxin and cytokinin biosynthetic genes and a gene encoding an auxin conjugating enzyme in transgenic plants. The tissue and organ specific expression of these hormone modifying genes produces a number of changes in plant growth and development, as well as changes in cell fate. The transgenic plants with altered hormone levels are being used along with Arabidopsis gravitropic mutants to study alterations in expression of auxin responsive genes. Dr. Guilfoyle is proposing to 1) determine precisely what sequence elements make a gene auxin responsive; to determine if more than one type of AuxRE exists in different auxin responsive genes and to clone and analyze the transcription factors that interact with the AuxREs; 2) to use the AuxREs or auxin responsive promoters as molecular probes to study gene expression during auxin regulated growth and development; to use transgenic plants that overproduce or conjugate auxin or overproduce cytokinins as tools to study auxin regulated gene expression; 3) to gain insight into the functions of the auxin responsive gene products and their possible roles in auxin action; and 4) to take advantage of the chimeric constructs to identify auxin responsive mutants; to search for mutants in the auxin signal transduction pathway(s). The long range goals of this research are to understand how auxin regulates gene expression and how signals are transduced from the auxin receptor to events such as cell expansion, cell division, and plant development; to manipulate auxin responsive promoters, auxin responsive gene products and/or auxin or cytokinin biosynthetic genes to modify plant growth and development in beneficial ways. ***