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

磷脂酶D （PLD）是启动一系列磷脂分解代谢事件的关键酶，最终导致膜退化和衰老。磷脂酸是PLD作用的直接产物，在干旱和寒冷胁迫、病原体感染等生理事件中也被认为是一个关键的信号分子。调控乙烯刺激、果实成熟和衰老、施加胁迫等后膜退化过程激活的分子事件尚未完全解开。磷脂酶D的活性在衰老过程中增加，据推测，乙烯引发的衰老导致细胞质钙的增加，从而驱动细胞质定位的磷脂酶D迁移到膜上，在那里它启动磷脂分解代谢。磷脂酶D属于一个多基因家族，已克隆出多个具有特性和生理作用的同工异构体。磷脂酶D同工型a、β和γ的特征是在n端存在约130个氨基酸长的C2结构域。各种PLD异构体在果实成熟和衰老过程中的生理作用尚不完全清楚。我们的研究在目前的发现资助的任期内，已经揭示了PLD的C2结构域的独特特征，不同于其他克隆的拟南芥C2结构域。这些结果表明PLD作用在乙烯信号转导事件中的生理意义。在接下来的五年中，将对PLD β亚型的C2结构域进行进一步的研究，以描述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策略和技术来延长水果、蔬菜和其他园艺产品的保质期和质量是重要的。

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.