Composite Auxin Response Elements and the Auxin Signal Transduction Pathway

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9604208 Guilfoyle The plant hormone auxin is involved in or controls a wide variety of developmental processes. Auxin-induced cell division, cell elongation and cell differentiation all involve distinct patterns of gene expression. A variety of early or primary response genes that are specifically induced by auxin have been identified in these growth and developmental processes. Most of the early auxin response genes are expressed in a tissue-specific and organ-specific manner in the absence of exogenous auxin application. To observe a substantial induction of these genes by exogenous auxin, it generally is necessary first to deplete auxin by bathing excised organs in auxin-free medium. Soybean GH3 is an early auxin response gene that differs from others in four important ways. First, it is expressed at very low levels in the absence of exogenous auxin application. Second, GH3 mRNA can be induced at least 50-fold in seedlings and plants without subjecting excised organs to the auxin depletion protocol. Third, the gene is induced in virtually every cell, tissue or organ of a seedling or plant. Fourth, the GH3 promoter is highly responsive to auxin in a variety of heterologous plant species whether assayed transiently in protoplasts or in stable transformants. The GH3 gene promoter consists of at least three separate auxin response elements (AuxRE) within 250 base pairs of the transcription start site, which have been characterized with respect to independent function, tissue/organ-specific expression, DNA sequence, and auxin responsiveness. Moreover, novel AuxREs have been constructed that are equivalent or several fold more inducible by auxin than natural AuxREs or the entire GH3 promoter, and transcription factors have been cloned that bind specifically to composite AuxREs. This research will use both natural composite and more active synthetic AuxREs to precisely determine how AuxREs function in auxin-responsive promoters, and to identify transcription factors that interact with composite AuxREs and determine their mechanism of action. The plant hormone auxin is involved in or controls a wide variety of developmental processes. Auxin-induced cell division, cell elongation and cell differentiation all involve distinct patterns of gene expression. A variety of early or primary response genes that are specifically induced by auxin have been identified in these growth and developmental processes. Soybean GH3 is an early auxin response gene that is induced in virtually every cell, tissue or organ of a seedling or plant. The regulatory region (promoter) of the GH3 gene consists of at least three separate auxin response elements (AuxRE) which have been characterized with respect to independent function, tissue/organ-specific expression, DNA sequence, and auxin responsiveness. Moreover, novel AuxREs have been constructed that are equivalent or several fold more active than natural AuxREs. This research will use both natural composite and more active synthetic AuxREs to precisely determine how AuxREs function, and to identify transcription factors that interact with AuxREs and determine their mechanism of action.