Molecular Genetic Dissection of Haustorium Development in Parasitic Angiosperms

与植物-微生物相互作用相比，研究植物-植物相互作用的分子机制的研究在很大程度上受到阻碍，因为缺乏简单的基于实验室的模型系统。 寄生玄参科与其宿主植物的相互作用提供了一个最好的机会，整合现代生物化学，生理学和遗传学的方法来了解植物如何在环境中沟通。 本研究的总体目标是了解植物寄生的起源和进化，了解化学信号如何启动寄生器官的发育并调节其功能，以及识别寄生植物如何识别和区分宿主，非宿主和自我。 这些研究集中在植物寄生的定义器官，即吸器。 这种专门的多功能结构识别到宿主的距离和方向，通过酶促和侵入性生长的组合穿透宿主血管组织，并形成一个传导桥梁，寄生虫通过该桥梁从宿主那里掠夺营养。 虽然在形态学水平的特点，几乎没有什么是已知的遗传机制控制吸器的启动，发展，或功能。 本实验利用玄参科寄生植物作为模式生物研究吸器的发育，其原因在于：植物寄生进化的所有阶段，从完全的自养生物到专性非光合异养生物，均为当代物种所代表，吸器诱导的生物化学和吸器个体发育的组织学是玄参科最先进的;兼性寄生玄参科植物在土壤和无菌培养中都能在有或无宿主的条件下生长;用纯化的宿主编码化合物离体处理幼苗，可以同步诱导这些物种的吸器;是研究植物发育的最佳模式系统之一金鱼草（Antirrhinum）是这个家族的成员;并且这个家族的寄生物种是世界上最具破坏性的杂草害虫之一。 这些实验采用两种互补的方法来研究寄生玄参科吸器的发育。 (1)吸器属特异性基因正在被分离和分析，以获得关于它们的起源、它们在寄生植物中的功能以及它们在非寄生亲属中的作用的线索。 表达研究将表明它们对异养植物的特异性，原位杂交将确定它们对吸器的特异性。 (2)一个用于确定吸器发育的遗传决定因素的模型系统正在开发中。 特别是，不同的半寄生玄参科正在评估其顺从性的遗传分析，包括易于生长的存在和不存在的主机，顺从性的寄生虫和主机的遗传分析，并在体外吸器诱导的保真度。 选择寄生玄参科和金鱼草之间的遗传共线性关系将被检查作为一个捷径，发展的寄生成员的遗传。 最后，将检查寄生物种的基因组中是否含有内源性TAM样转座因子，这些转座因子可以在以后纳入诱变实验。

Studies examining the molecular mechanisms of plant-plant interactions have been impeded compared to those in plant- microbe interactions in large part because simple laboratory based model systems are lacking. The interaction of parasitic Scrophulariaceae with their host plants offers one of the best opportunities for integrating modern biochemical, physiological, and genetic methodologies to understand how plants communicate in the environment. The overall objectives of this research are to learn how plant parasitism originates and evolves, to understand how chemical signals initiate the development of parasitic organs and mediate their functions, and to discern how parasitic plants recognize and distinguish hosts, non-hosts, and self. These studies are focused on the defining organ of plant parasitism, namely the haustorium. This specialized multi-functional structure recognizes the distance and direction to the host, penetrates host vascular tissue through a combination of enzymatic and invasive growth, and forms a conductive bridge through which the parasite robs nutrients from the host. While well characterized at the morphological level, almost nothing is known about the genetic mechanisms controlling haustorium initiation, development, or function. The experiments in this proposal make use of parasitic members of the Scrophulariaceae family as model organisms to study haustorium development because: all stages in the evolution of plant parasitism, ranging from complete autotrophs to obligate non-photosynthetic heterotrophs, are represented by contemporary species; the biochemistry of haustorium induction and histology of haustorium ontogeny are most advanced for this family; facultative parasitic Scrophulariaceae are readily grown in the presence or absence of host in both soil and axenic culture; haustoria of these species can be synchronously induced by in vitro treatment of seedlings with purified, host encoded compounds; one of the best devel oped model systems for studying plant development (Antirrhinum) is a member of this family; and parasitic species of this family are among the world's most devastating weed pests. These experiments take two complementary approaches to examine haustorium development in parasitic Scrophulariaceae. (1) Haustorium specific genes are being isolated and analyzed to obtain clues about their origin, their function in parasitic plants, and their role in non-parasitic relatives. Expression studies will indicate their specificity for heterotrophic plants and in situ hybridizations will determine their specificity for haustoria. (2) A model system for defining the genetic determinants of haustorium development is being developed. In particular, different hemiparasitic Scrophulariaceae are being evaluated for their amenability to genetic analyses including ease of growth in the presence and absence of host, amenability of both parasite and host to genetic analysis, and the fidelity of haustorium induction in vitro. Genetic colinearity relationships between selected parasitic Scrophulariaceae and Antirrhinum will be examined as a shortcut to developing the genetics of the parasitic member. Finally, the genomes of parasitic species will be examined for containing endogenous Tam-like transposable elements that can be later incorporated into mutagenesis experiments.