Programmed cell death in plant development

程序性细胞死亡（PCD）是一种基因激活的过程，在这个过程中，选定的细胞组织自己的毁灭。PCD在所有真核生物王国中普遍存在，单细胞和多细胞生物都利用它作为正常发育的一部分或对外界刺激的反应。在植物中，PCD是生长和生存所必需的，可以由发育调节或环境诱导。发育性PCD的一个独特例子是蕾丝植物叶片的穿孔（孔）形成。这些孔位于纵脉和横脉之间，使叶子呈格状。在穿孔形成过程中，离散的细胞亚群经历PCD，而相邻的细胞保持完整。蕾丝植物原产于马达加斯加，在水族馆条件下很难生长。我成功地开发了一种组织培养系统来研究蕾丝植物的PCD发育。就信号通路和分子机制而言，我们仍然不知道在叶片发育的特定阶段是什么线索触发了PCD。我描述了水生植物穿孔形成过程中的细胞死亡过程，并表明这种水生植物是研究体内发育性PCD的理想模型系统。因此，我研究的长期目标是利用花边植物叶片形态发生作为模型系统，对发育性PCD的机制有一个基本的了解。这将通过以下目标实现：1)利用活细胞成像技术表征PCD事件的顺序并生成三维模型；2)研究蕾丝植物PCD过程中肌动蛋白细胞骨架的变化；3)探讨钙和线粒体内膜间隙蛋白在PCD发病初期的作用；4)评价乙烯作为诱导信号在蕾丝植物PCD中的作用；5)利用简并引物鉴定乙烯受体基因。这些结果将帮助我们确定动物和植物PCD之间是否存在共同的机制，或者它们是否独立进化。

Programmed cell death (PCD) is a genetically-enabled process in which select cells organize their own destruction. PCD is ubiquitous in all eukaryotic kingdoms and is employed by both unicellular and multicellular organisms as part of normal development or in response to external stimuli. In plants, PCD is necessary for growth and survival and can either be developmentally regulated or environmentally induced. A unique example of developmental PCD is perforation (holes) formation in lace plant leaves. These holes are situated equidistantly between longitudinal and transverse veins, giving leaves a lattice-like pattern. During perforation formation, discrete subpopulations of cells undergo PCD while adjacent cells remain intact. Lace plant is native to Madagascar and difficult to grow in aquarium conditions. I have successfully developed a tissue culture system to work on developmental PCD in lace plant. We still do not know what cues trigger PCD at a specific stage of leaf development, as far as the signaling pathways and the molecular mechanisms are concerned. I have characterized the cell death process during perforation formation in lace plant and showed that this aquatic plant is an ideal model system to study developmental PCD in vivo. Therefore, the long term objective of my research is to achieve a fundamental understanding of the mechanisms involved in developmental PCD using lace plant leaf morphogenesis as a model system. This will be achieved through the following objectives: 1) Characterize the order of PCD events using live cell imaging techniques and generate 3-D models; 2) Investigate changes in the actin cytoskeleton during lace plant PCD; 3) Investigate the roles of calcium and mitochondrial inner membrane space proteins in the initial stages of PCD; 4) Evaluate the role of ethylene as an induction signal in lace plant PCD; 5) Identify ethylene receptor genes using degenerate primers. These results will help us to determine whether there are common mechanisms between animal and plant PCD or whether they evolved independently.