Defining Whole-Plant Phloem Function with Molecular Studies of Anatomy

要将植物韧皮部维管系统中糖运输的长距离流体力学行为与韧皮部与周围组织之间糖交换的短距离调节联系起来，需要比目前可用的更深入的韧皮部数量解剖知识。利用转基因拟南芥植物的活细胞成像技术对韧皮部解剖结构进行精确测量是可能的，这些转基因植物在韧皮部筛选分子中表达mCitine(单体黄色荧光蛋白，YFP)标记的质膜蛋白。其中一些转基因药物(由PI开发)为共聚焦激光扫描显微镜(甚至通过活组织)提供了极佳的筛选元件照明。筛板和孔洞显示了彻底的YFP标记，为固定和切片组织的免疫组织荧光成像提供了希望。PI目前正在将成功的构建结构输出到其他物种，包括烟草、烟草和杨树，用于韧皮部解剖的跨物种比较。这些结果将有助于PI预测韧皮部在一组物种和植物器官中的宏观物理化学行为，这将为其他实验提供背景，例如使用局部和化学诱导的沉默韧皮部特定转运蛋白的局部和化学诱导沉默来操纵全植物的源和库强度。对这些结构的分析也将有助于理解在有核伴胞中表达的蛋白质是如何被贩运到去核筛子元素的。这项研究的更广泛影响包括，利用应用数学、系统生物学和分子遗传学，对美国韧皮部生物学进行了跨学科的“重新发明”，以及为本科生培训提供了一个真正的跨学科机会。这项工作可能对我们理解韧皮部传播的植物疾病的运动、植物资源分配以及树木在全球碳循环中的作用非常重要。

To link the long-distance fluid mechanical behavior of sugar transport in the phloem vasculature of plants with the short-distance regulation of sugar exchange between the phloem and surrounding tissue requires much deeper knowledge of the phloem's quantitative anatomy than is currently available. Accurate measurements of phloem anatomy are now possible with live-cell imaging of transgenic Arabidopsis plants that express mCitrine (monomeric yellow fluorescent protein, YFP)-labeled plasma membrane proteins in phloem sieve elements. Some of these transgenics (developed by the PI) provide excellent illumination of sieve elements for confocal laser scanning microscopy (even through live tissue). Sieve plates and pores show thorough YFP labeling, holding out the promise for immunohistochemical fluorescence imaging of fixed and sectioned tissues. The PI is currently exporting successful constructs to other species, including Nicotiana benthamiana, N. tabacum, and Populus, for cross-species comparisons of phloem anatomy. The results will help the PI to predict the gross-scale physicochemical behavior of the phloem across a set of species and plant organs, which will provide the context for other experiments, such as "black-box" manipulations of whole-plant source and sink strength using local and chemically inducible silencing of phloem-specific transporters. Analysis of the constructs will also aid in understanding how proteins expressed in nucleate companion cells are trafficked to enucleate sieve elements.The broader impacts of this study include a "re-invention" of American phloem biology to cut across disciplines, drawing from applied mathematics, systems biology, and molecular genetics, as well as a truly interdisciplinary opportunity for undergraduate training. The work could be very important for our understanding of the movement of phloem-borne plant diseases, plant resource allocation, and the role of trees in the global carbon cycle.