Molecular Aspects of Ethylene-Regulated Gene Expression in Phaseolus

菜豆中乙烯调控基因表达的分子研究：本项目的目的有两个方面：1)研究大豆几丁质酶基因组克隆的激素调控；2)绘制和定义这些克隆的乙烯敏感元件（即启动子）。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。菜豆几丁质酶基因家族被用作高等植物乙烯调控基因表达的范例。在正常生长条件下，当乙烯水平较低时，几丁质酶的表达量最小；然而，当乙烯水平较高时，例如当植物受到物理或生物胁迫时，或通过与衰老或衰老相关的正常发育过程时，几丁质酶的表达水平可比对照增加75至100倍。几丁质酶在植物生理生化中的确切作用尚不清楚。然而，几丁质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。利用从菜豆中分离得到的几丁质酶cDNA克隆，对这一具有重要农艺学意义的基因家族进行了分析。由于乙烯与高等植物正常生长发育的许多过程密切相关，因此了解少量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，伤口反应以及对胁迫和病原体攻击的反应机制的分子方面。考虑到每年由致病真菌和害虫造成的作物损失的程度，几丁质酶作为遗传转移到植物上的一个极好的候选者脱颖而出，其可能目的是增加对几丁质病原体的抗性。同样，对乙烯启动子的进一步表征可能对调节外源基因在高胁迫下的表达具有不可估量的实际用途。

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.