The objectives are to understand how hormones regulate gene expression and to correlate hormone-induced changes in gene expression with hormone-mediated changes in growth and development. The specific research aims are to analyze the role(s) of auxin-regulated gene expression in the growth responses mediated by this hormone in soybean seedling tissues. The growth responses of major interest are the control of cell elongation by auxin and the induction of massive tissue proliferation by auxin. A number of cDNA clones have been isolated, and additional clones will be identified, which are representative of mRNAs whose cytoplasmic concentrations increase or decrease rapidly and selectively following auxin treatment. The expression of these mRNAs will be assessed during various developmental stages, auxin-induced growth, and interactions of auxin with other hormones and growth regulators which result in altered and/or aberrant growth responses. Genes that encode these auxin-responsive mRNAs will be sequenced in order a) to determine the amino acid sequence and some properties of the encoded protein, b) to identify conserved regions which may be important to the regulation of their expression, and c) to define antigenic regions of the protein for peptide synthesis and antibody production. Antibodies will be used to identify the cellular localization of the relevant proteins and to quantify their abundance during the noted growth transitions. Auxin responsive genes will be cloned into T-DNA vectors and used in transformation experiments. These experiments are designed to evaluate which sequences are important to the developmental and hormone-regulated pattern of gene expression. Additionally, they will assess the physiological consequences of over expression of the gene (using very strong constitutive or inducible promoters) or of under expression of the gene (using these same promoters to express the negative strand to suppress translation of the mRNA). As progress is made in understanding the role of auxin-regulated gene expression during physiological responses to auxin (e.g. cell elongation or cell proliferation) and in defining cis-elements important in controlling the expression of these genes, analyses of trans-acting factors essential in the selective regulation of these genes will be initiated.
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