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

磷脂酶D（PLD）是启动磷脂分解代谢级联反应的关键酶，最终导致膜的退化和衰老。磷脂酶D（PLD）作用的直接产物磷脂酸（Phosphatidic acid）也被认为是干旱、低温胁迫、病原菌感染等生理事件中的关键信号分子。在乙烯刺激、果实成熟和衰老、胁迫等后，还没有完全解开磷脂酶D活性在衰老过程中增加，并且已经假设由乙烯引发的衰老导致胞质钙的增加，其驱动胞质定位的磷脂酶D迁移到膜，在膜处其引发磷脂催化剂。磷脂酶D是一个多基因家族，目前已克隆出几种具有特异性和生理功能的同工酶。磷脂酶D亚型a、a和y的特征在于在N-末端存在约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还不完全清楚。我们的研究在任期内的当前发现补助金，揭示了独特的特征PLD的C2结构域，是不同于唯一的其他克隆的C2结构域从拟南芥。这些结果表明PLD作用在乙烯信号转导事件的生理意义。在未来的五年中，将进行进一步的研究PLD的C2结构域的异构体，以描绘其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以提高水果、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.