Mechanism of Asymmetric Growth of the Bacterial Plant Pathogen Agrobacterium tumefaciens

细菌细胞通过细胞壁的扩张而生长。由于细菌细胞壁是重要的抗生素靶标并触发免疫反应，因此了解细菌的生长具有广泛的基础意义。这项拟议的工作将揭示植物病原体根癌农杆菌生长的分子机制。根癌农杆菌是数百种开花植物冠瘤的病原菌，对苹果、李子和樱桃等苗圃植物来说是一个特别的问题。值得注意的是，根癌农杆菌表现出一种非典型的细菌生长形式，其中新的生长被限制在细胞的一端(不对称生长)。细菌细胞的不对称生长相对知之甚少，但在不同的土壤细菌中经常观察到。因此，拟议的科学工作有望提供关于细菌生长机制的关键见解，这可能导致重要的应用，如限制冠胆疾病。最后，与科学教育专家合作，将开发一个关于细菌中出现抗生素耐药性的动手、基于探究的实验室模块。本单元将为高中生提供参与研究的机会，并将提供对进化过程的理解。关于细胞壁生物发生的机制和调节仍有许多重要的问题。细胞壁生物发生是如何在时间和空间上被控制的？单元格的长度和宽度是如何维护的？这些问题主要是在模型细菌中解决的，如大肠杆菌和枯草芽孢杆菌，它们利用分散的细胞壁生长模式。将细菌细胞生长的分析扩展到具有不对称生长的生物体，将揭示细胞壁生物发生的生物合成、组装和调节的新机制。在这个项目中，目标是以根癌农杆菌为模型，阐明属于变形杆菌根瘤菌分支的细菌单极生长的机制。以下问题将用于指导这项工作。在伸长过程中，细胞壁的生物发生如何被限制在新的极点上？如何将细胞壁生物发生重定向到中间细胞以使细胞分裂并使新的极点成为细胞壁生物发生的活性部位？成像细胞壁生物发生的最新进展将被用来探索单极生长的机制。使用系统的方法，候选蛋白质在生物合成、组装或调节细胞壁生物发生中的作用将被表征。基因筛查将被用来揭示参与细菌细胞生长过程的其他蛋白质。拟议的研究将改善目前对细胞壁生物发生如何在空间和时间上进行调控的理解，并将为一种相对未被探索但普遍存在的细菌细胞生长模式提供关键见解。

Bacterial cells grow through expansion of their cell walls. Since the bacterial cell wall is an important antibiotic target and triggers immune responses, understanding bacterial growth is of broad fundamental interest. The proposed work will reveal the molecular mechanisms underlying growth of the plant pathogen, Agrobacterium tumefaciens. A. tumefaciens is the causative agent of crown gall disease in hundreds of flowering plants and is a particular problem for nursery plants such as apple, plum, and cherry. Remarkably, A. tumefaciens exhibits an atypical form of bacterial growth, in which new growth is restricted to one end of the cell (asymmetric growth). Asymmetric bacterial cell growth is relatively poorly understood, but has been observed frequently in diverse soil dwelling bacteria. Thus, the proposed scientific work is expected to provide key insights regarding mechanisms of bacterial growth, which may lead to important applications such as limiting crown gall disease. Finally, in collaboration with experts in science education, a hands-on, inquiry based lab module on the emergence of antibiotic resistance in bacteria will be developed. This module will provide high school students with an opportunity to participate in research and will provide an understanding of evolutionary processes.Many important questions remain about the mechanism and regulation of cell wall biogenesis. How is cell wall biogenesis controlled in time and space? How are cell lengths and widths maintained? These questions have been primarily addressed in model bacteria, such as Escherichia coli and Bacillus subtilis, which utilize a dispersed mode of cell wall growth. Expanding the analysis of bacterial cell growth into organisms with asymmetric growth will reveal new mechanisms for the biosynthesis, assembly, and regulation of cell wall biogenesis. In this project, the objective is to elucidate the mechanisms underlying unipolar growth of bacteria belonging to the Rhizobiales clade of Alphaproteobacteria using A. tumefaciens as a model. The following questions will be used to guide this work. How is cell wall biogenesis restricted to the new pole during elongation? How is cell wall biogenesis redirected to mid-cell to enable cell division and prime the new poles to serve as active sites for cell wall biogenesis? Recent advances in imaging cell wall biogenesis will be used to probe the mechanism of unipolar growth. Using a systematic approach, the role of candidate proteins in the biosynthesis, assembly, or regulation of cell wall biogenesis will be characterized. Genetic screens will be utilized to reveal additional proteins involved in bacterial cell growth processes. The proposed studies will improve the current understanding of how cell wall biogenesis is spatially and temporally regulated and will provide key insights into a relatively unexplored, but prevalent mode of bacterial cell growth.