Molecular Aspects of Ethylene-Regulated Gene Expression in Phaseolus

菜豆中乙烯调节基因表达的分子方面：本项目的目标有两个：1)表征菜豆几丁质酶基因组克隆的激素调节；2)定位和确定这些克隆的乙烯敏感元件(即启动子)。长期以来，植物激素乙烯在高等植物的生理和发育过程中发挥着重要作用。来自菜豆的几丁质酶基因家族被用来作为乙烯调控高等植物基因表达的范例。在正常生长条件下，当乙烯水平较低时，几丁质酶的表达很低；然而，当乙烯水平较高时，如植物受到物理或生物胁迫，或受到与衰老或衰老有关的正常发育过程的影响，几丁质酶的表达水平可以比对照增加75-100倍。几丁质酶在植物生理和生化中的确切作用尚不清楚。然而，甲壳素是真菌细胞壁和昆虫外骨骼的主要成分，因此，它被认为具有保护功能。利用从菜豆中分离的几丁质酶基因克隆，将对这个重要的农艺基因家族进行鉴定。由于乙烯密切参与高等植物正常生长和发育的许多过程，了解极少量的乙烯如何影响基因转录可能有助于深入了解衰老、果实成熟、伤口反应的分子方面，以及对胁迫和病原体攻击的反应机制(S)。考虑到每年由病原真菌和病虫害造成的作物损失，几丁质酶是一种很好的植物遗传转移候选者，其目的可能是提高对几丁质病原菌的抗性。同样，进一步鉴定可能的乙烯启动子对于调控外源基因在高胁迫时的表达具有不可估量的实用价值。

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.