The Role of Actin Monomer Binding Proteins in Plant Cell Tip Growth

智力价值植物细胞生长的一个非常重要的方面是“尖端生长”。这个项目将解决肌动蛋白细丝网络调控的一些基本方面，肌动蛋白细丝网络是一种动态的细胞骨架结构，是植物细胞尖端生长的驱动力。贝扎尼拉博士将研究肌动蛋白结合蛋白ADF/cofilin(ADF)在苔藓模式生物Physcomitrella patens顶端生长过程中的作用。在植物系统中，Physcomitrella具有进行同源重组的独特能力，使其成为进行详细的体内互补研究的理想模式植物系统，这将是该项目的基石。ADF是一种促进肌动蛋白细丝分解的单体肌动蛋白结合蛋白。ADF在所有类群的真核物种中高度保守，存在于从酵母到动物再到植物的各种有机体中。在如此多样化的物种中，基于肌动蛋白的运动现象的种类也相当不同；然而，进化上高度保守的ADF蛋白被认为是所有这些物种中肌动蛋白动力学的关键调节因子。因此，通过研究ADF蛋白在植物细胞顶端生长中的作用，有可能开始解决这些基于肌动蛋白的过程中的一些根本差异。贝扎尼拉博士已经证明，ADF对于藻尖的生长是必不可少的。她将结合使用RNAi的条件性敲除和使用同源重组的基因替换来确定ADF功能在体内是如何调节的。此外，她还将研究ADF和其他进化保守的肌动蛋白单体结合蛋白之间潜在的分子和遗传相互作用，以控制肌动蛋白聚合。最后，她将开始建立一个体内蛋白质图谱，这些蛋白质是在藻类顶端生长过程中调节ADF和肌动蛋白动态所需的蛋白质。这些研究将为测试这些高度保守的蛋白质在其他植物系统中是否具有类似的功能奠定基础。了解叶尖生长的机制很重要，因为植物细胞中的叶尖生长是发育对植物至关重要的特定组织类型所必需的基本过程。例如，藻类的根状突起，开花植物的花粉管和根毛，以及苔藓和蕨类植物的原丝状体都表现出尖端生长。在所有情况下，这些顶端生长的组织都代表着植物发育的一个重要方面。在开花植物中，根毛的适当发育对于吸收生长发育所需的水分和矿物质至关重要。含有更多根毛的根系更健壮，更能承受干燥的环境条件。如果没有适当的花粉管生长来使精子核到达子房，受精就不可能发生，因此该物种的生存处于危险之中。同样，在苔藓和蕨类植物中，原丝体顶端的生长是物种生存所需的一个必要的发育阶段。因此，阐明调控顶端生长的机制将增加我们对各种进化上不同植物物种的植物活力和物种生存能力的了解。广泛的影响该项目具有潜在的农业社会效益。例如，这个项目将带来的知识和理解可能使我们能够增强作物形成根毛的能力，从而潜在地提高抗旱性，并最终导致作物产量的提高。该项目还将把研究与教学和培训结合起来，并将扩大未被充分代表的群体对科学的参与。贝扎尼拉博士本人是科学界代表性不足的少数族裔的一员，她对招募各级科学培训(本科生、研究生和博士后)代表性不足的少数民族非常感兴趣。她打算将这一研究项目的技术和发现整合到马萨诸塞大学阿默斯特分校的一门本科植物细胞生物学课程中。本课程将向本科生介绍这项研究，并鼓励他们参与实验室实践。此外，贝扎尼拉博士打算在暑期招募高中生参与这项研究，以此鼓励高中生探索科学。

Intellectual MeritOne very important aspect of the growth of plant cells is "tip growth." This project will address some fundamental aspects of the regulation of the actin filament network, a dynamic cytoskeletal structure which is the driving force behind plant cell tip growth. Dr. Bezanilla will study the role of an actin binding protein, ADF/cofilin (ADF), during tip growth in the moss model organism, Physcomitrella patens. Physcomitrella has the unique capacity among plant systems to undergo homologous recombination, making it an ideal model plant system for performing detailed in vivo complementation studies, which will be a cornerstone of the project. ADF is a monomeric actin binding protein that promotes actin filament disassembly. ADF is highly conserved across eukaryotic species of all taxa, and found in organisms ranging from yeast to animals to plants. Across such a diverse array of species, the kinds of actin-based motility phenomena are also quite diverse; yet the evolutionarily highly-conserved ADF protein has been implicated as a key regulator of actin dynamics in all of them. Thus, by studying the function of the ADF protein in plant cell tip growth, it may be possible to begin to address some of the fundamental differences among these actin-based processes. Dr. Bezanilla has already demonstrated that ADF is essential for tip growth in Physcomitrella. She will use a combination of conditional knockdowns employing RNAi, and gene replacements employing homologous recombination, to determine how ADF function is regulated in vivo. In addition she will investigate the potential molecular and genetic interactions between ADF and other evolutionarily conserved actin monomer binding proteins for controlling actin polymerization. Finally, she will begin to establish an in vivo map of the proteins required to regulate ADF and actin dynamics during tip growth in Physcomitrella. These studies will serve to lay groundwork for testing whether these highly conserved proteins function similarly in other plant systems. Understanding the mechanism of tip growth is important because tip growth in plant cells is a fundamental process required for the development of specific tissue types critical for the plant. As examples, rhizoids from algae, pollen tubes and root hairs from flowering plants, and protonemal filaments from mosses and ferns all exhibit tip growth. In all cases these tip-growing tissues represent an essential aspect of development for the plant. In flowering plants, proper development of root hairs is critical for the uptake of water and minerals required for growth and development. Root systems containing more abundant root hairs are more robust and are better able to withstand dryer environmental conditions. Without proper pollen tube growth to allow the sperm nucleus to reach the ovary, fertilization cannot occur and thus the very survival of the species is at risk. Similarly in mosses and ferns, protonemal tip growth is an essential developmental stage required for species viability. Thus, elucidating the mechanism that regulates tip growth will add to our understanding of plant vigor and species viability across a wide range of evolutionarily distinct plant species.Broader ImpactsThis project has potential agricultural benefits for society. For example, the knowledge and understanding that will result from this project may allow us to enhance the ability of crop plants to form root hairs and thus potentially increase drought tolerance and eventually lead to improving crop yields. The project also will integrate research with teaching and training and will broaden the participation of underrepresented groups in science. Dr. Bezanilla, herself a member of an underrepresented minority in science, is strongly interested in recruiting underrepresented minorities at all levels of scientific training (undergraduate, graduate and postdoctoral). She intends to integrate the techniques and findings from this research project into an undergraduate Plant Cell Biology course at the University of Massachusetts, Amherst. This course will serve to introduce undergraduate students to the research and encourage them to participate hands-on in the laboratory. In addition, Dr. Bezanilla intends to encourage high school students to explore science, by recruiting high school students to participate in the research during the summers.