MOLECULAR MECHANISM OF POLLEN TUBE ELONGATION

本提案的目标是了解分子机制。 下面的花粉管伸长。花粉管的伸长是一个过程 植物有性繁殖的中心。在花粉沉积在植物上之后 雌性生殖器官雌蕊的接受柱头表面， 雄配子通过花粉管的伸长运输到子房 使卵细胞受精。花粉管的伸长是定向的副产物 从柱头表面的花粉粒到子房 位于雌蕊的基端，成百上千倍于雌蕊 花粉粒直径变小。人们经常把花粉管的伸长与 对动物系统中轴突的生长，因为它是定向的细胞运动 基于雌蕊细胞外基质中尖端的生长过程 纸巾。类似于理解轴突生长的机制， 花粉管伸长的研究面临同样的挑战 在基于特定机制的机制中很难破译 趋化性引诱剂，或对表面结构粘合，或以缺乏 刻意的吸引和花粉管沿着阻力最小的路径前进。 我们已经分离并鉴定了第一个蛋白质组分(TTS 蛋白质)及其cDNA从烟草的雌蕊组织中提取，可以 促进花粉管的伸长和显示特性表明它可能 有助于整个雌蕊机制引导花粉管走向 卵巢。TTS蛋白是一种特殊定位的阿拉伯半乳糖蛋白 在花柱传递组织的细胞间基质中， 花粉管从柱头向外延伸的特殊介质 卵巢。我们的结果表明TTS蛋白达到了它的花粉管 贴近表面、贴近成长的促成长活动 花粉管顶端，能吸收和水解糖残留物 这些蛋白质。TTS蛋白也显示出一个递增的梯度 从柱头到卵巢末端的糖基化水平 传递组织，与花粉管的生长方向相同。这个 拟议中的研究特别侧重于阐明分子 TTS蛋白与花粉相互作用的机制 测定其花粉管表面粘附力的贡献 花粉管对其糖组分的性质及其动员作用 其促进花粉管伸长的活性，以及在检测 相关糖基化水平梯度的功能意义 有了这种蛋白质。分子、细胞、生化和 将使用转基因方法。涉及到的生化参数 TTS蛋白与花粉管的相互作用将被确定。 TTS蛋白的结构-功能关系将通过以下方式进行研究 产生修饰的TTS蛋白并确定这些变化如何影响 它们的花粉管促生长活性及其与花粉管的相互作用 花粉管。TTS蛋白在花粉定向中的作用 还将在体内和体外检查管子的伸长情况。建议数 共同的实验应该会清楚地理解一个主要的 传递组织蛋白调节其功能，并证明 与这种蛋白质相关的糖梯度在化学上是 定向花粉管伸长显著。了解花粉 一般说来，管的延长应该会扩展我们对细胞迁移的认识。

The goal for the present proposal is to understand the molecular mechanism underlying pollen tube elongation. Pollen tube elongation is a process central to plant sexual reproduction. After pollen is deposited on the receptive stigmatic surface of the female reproductive organ pistil, the male gametes are transported by pollen tube elongation to the ovary to fertilize the egg cell. Pollen tube elongation is a directed outgrowth from the pollen grain on the stigmatic surface toward the ovary which is located at the basal end of the pistil, hundreds to thousand times the diameter of pollen grains away. Pollen tube elongation is often compared to axon outgrowth in animal systems since it is a directed cell movement based on a tip growth process in the extracellular matrix of pistillate tissues. Similar to understanding the mechanism underlying axon outgrowth, studies on pollen tube elongation face the same challenges of the difficulty to decipher among mechanisms that are based on specific chemotactic attractants, or to surface structure adhesion, or to a lack of deliberate attraction and pollen tubes follow a path of least resistance. We have isolated and characterized the first protein component (TTS protein) and its cDNAs from pistillate tissues of tobacco which can promote pollen tube elongation and display properties suggesting it may contribute to the overall pistil mechanism of guiding pollen tubes towards the ovary. TTS protein is an arabinogalactan protein specifically located in the intercellular matrix of the stylar transmitting tissue, a specialized medium through which pollen tubes elongate from the stigma to the ovary. Our results show that TTS protein attains its pollen tube growth promotion activity by adhering to the surface and to the growth tips of pollen tubes which uptake and hydrolyze the sugar residues on these proteins. TTS proteins also display a gradient of increasing glycosylation levels from the stigmatic to the ovarian end of the transmitting tissue, the same direction as pollen tube growth. The proposed research focuses specifically on elucidating the molecular mechanism underlying the interactions between TTS protein and pollen tubes, on determining the contribution of its pollen tube surface adhesion properties and the mobilization of its sugar components by pollen tubes to its activity in promoting pollen tube elongation, and on examining the functional significance of the gradient of glycosylation levels associated with this protein. A combination of molecular, cellular, biochemical and transgenic approaches will be used. The biochemical parameters involved in the interaction between TTS protein and pollen tubes will be determined. The structure-functional relationship of TTS protein will be examined by generating modified TTS proteins and determining how these changes affect their pollen tube growth promoting activity and their interactions with pollen tubes. The participation of TTS proteins in the direction of pollen tube elongation will also be examined in vivo and in vitro. The proposed experiments together should yield a clear understanding of how a major transmitting tissue protein mediates its functions and demonstrate whether a sugar_gradient associated with this protein is chemotactically significant in directional pollen tube elongation. Understanding pollen tube elongation should extend our knowledge on cell migration in general.