Biochemical and Molecular Analysis of Ethylene Signal Transduction- The Role of Phospholipase D.

磷脂酶D(PLD)是一种关键酶，它启动一系列磷脂分解代谢事件，最终导致膜的劣化和衰老。磷脂酸是PLD作用的直接产物，也被认为是干旱和低温胁迫、病原菌侵染等生理事件中的关键信号分子。调控乙烯刺激、果实成熟衰老、胁迫等膜劣化过程激活的分子事件尚未完全揭开。在衰老过程中，磷脂酶D的活性增加，假设乙烯启动衰老导致胞内钙的增加，从而驱动胞浆中定位的磷脂酶D迁移到膜上，在那里它启动了磷脂的分解代谢。磷脂酶D属于多基因家族，目前已克隆出几种具有独特性质和生理作用的异构体。磷脂酶D亚型的特征是在N-末端存在一个~130个氨基酸的C2结构域。不同的PLD亚型在果实成熟衰老过程中的生理作用还不完全清楚。我们在本次发现拨款期间的研究揭示了PLD A C2结构域的独特特征，这些特征有别于从拟南芥克隆的唯一其他C2结构域。这些结果表明PLD在乙烯信号转导中的作用具有生理意义。在接下来的五年里，将对PLDü亚型的C2结构域进行进一步的研究，以描绘它们在乙烯信号转导事件中的作用。了解这些分子事件的性质对于设计提高水果、蔬菜和其他园艺产品的货架期和质量的策略和技术非常重要。

Phospholipase D (PLD) is a key enzyme that initiates a cascade of phospholipid catabolic events that ultimately lead to membrane deterioration and senescence. Phosphatidic acid, the immediate product of PLD action has also been identified as a key signaling molecule in several physiological events including drought and cold stress, pathogen infection etc. The molecular events that regulate the activation of membrane deterioration processes after ethylene stimulation, fruit ripening and senescence, imposition of stress etc., are not fully unraveled. Phospholipase D activity increases during senescence and it has been hypothesized that the initiation of senescence by ethylene leads to an increase in cytosolic calcium which drives the cytosol-localized phospholipase D to migrate to the membrane where it initiates the phospholipid catabolism. Phospholipase D belongs to a multigene family and several isoforms with characteristic properties and physiological roles have been cloned. Phospholipase D isoforms a, ß, and gamma are characterized by the presence of a ~ 130 amino acid long C2 domain at the N-terminal end. The physiological roles of various PLD isoforms in the fruit ripening and senescence process are not fully understood. Our research during the tenure of the current Discovery grant, have revealed unique characteristics of PLD a C2 domain that are distinct from the only other cloned C2 domains from Arabidopsis. These results show the physiological implications of PLD action in ethylene signal transduction events. During the next five years, further studies will be performed on the C2 domains of PLD ß isoform to delineate their role in ethylene signal transduction events. Understanding the nature of these molecular events is important to design strategies and technologies for enhancing the shelf life and quality of fruits, vegetables and other horticultural produce.