Comparative Regulation of Genes Involved in Plant Disease Resistance and Pigment Biosynthesis

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In plants, specific branch pathways diverge from the central phenylpropanoid pathway which leads to the synthesis of lignins, UV-absorbing flavonoids, as well as isoflavonoid and coumarin antibiotics. Environmental stresses such as UV light and pathogens induce the selective synthesis of protective compounds by particular branches. While coordinate changes in gene regulation in the central pathway have been demonstrated to underlie these physiological responses, the mechanisms controlling differential activation of branch pathways is unknown. As a model for understanding the coordinate and selective controls regulating synthesis within these pathways, this research focuses on the comparative regulation of genes encoding enzymes in the central and branch pathways for synthesis of flavonoids and isoflavonoid antibiotics. Chalcone isomerase, a possible regulatory enzyme, will be studied as a representative of the central pathway. The research will identify the DNA sequences regulating the expression of the chalcone isomerase and branch pathway P-450 genes. This will be accomplished by: identifying branch pathway P-450 genes and characterizing their expression in response to environmental inducers as well as during development; mapping the transcription units on genomic clones; localizing regulatory regions by construction of chimeric genes; and sequencing the functionally important regions.%%% It is expected that this research will reveal distinct promoter elements responsive to particular environmental or developmental signals. This study of the organization of these elements in the phenylpropanoid pathway genes may lead to a general model for differential regulation of metabolically related genes in plants. Furthermore, a fundamental understanding of the genetic regulation of phytoalexin biosynthesis is essential if this trait is to be genetically manipulated to enhance disease resistance in plants.***//