Molecular Aspects of Ethylene-Regulated Gene Expression in Phaseolus

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Molecular Aspects of Ethylene-Regulated Gene Expression in Phaseolus: The objectives of this project are two-fold: 1) to characterize the hormonal regulation of the genomic clones of chitinase from bean (Phaseolus vulgaris); and 2) to map and define the ethylene sensitive elements (i.e., promoter) of these clones. The phytohormone ethylene has long been known to exert powerful effects on physiological and developmental processes in higher plants. The chitinase gene family from Phaseolus is used as a paradigm for ethylene regulated gene expression in higher plants. Under normal growth conditions, when ethylene levels are low, chitinase expression is minimal; when ethylene levels are high, however, such as when plants are subjected to physical or biological stresses, or by normal developmental processes connected with aging or senescence, the level of chitinase expression can increase as much as 75- to 100-fold over controls. The exact role of chitinase in the physiology and biochemistry of the plant is unknown. Chitin is, however, a major component of fungal cell walls and insect exoskeletons and, thus, it has been postulated to have a protective function. Using cDNA clones of chitinase isolated from Phaseolus vulgaris, this agronomically important gene family will be characterized. Since ethylene is intimately involved in numerous processes in the normal growth and development of higher plants, knowledge of how vanishingly small amounts of ethylene affect gene transcription may yield insights into the molecular aspects of senescence, fruit ripening, wound response, as well as the mechanism(s) of response to stress and pathogen attack. Considering the magnitude of crop losses each year by pathogenic fungi and insect pests, chitinase stands out as an excellent candidate for genetic transfer to plants with the possible aim of incresing resistance to chitinous pathogens. Likewise, further characterization of the putative ethylene promoter could be of immeasurable practical use for regulating the expression of foreign genes at times of high stress.