Functional Dissection of Plant-Plant Signaling in the Rhizosphere

虽然几个世纪以来人们已经知道，一些植物通过释放到土壤中的化学物质来抑制邻近植物的生长，但实际上，人们对植物之间地下相互作用的遗传或分子机制一无所知。这在很大程度上是由于难以分析不同植物之间传递的地下化学信号的影响。一种植物如何改变另一种植物的生长发育，最明显的表现是寄生植物。寄生植物直接侵入附近寄主植物的根部，以抢夺它们的水分和营养。这些寄生虫利用寄主根系释放的某些分子作为识别信号来识别潜在的寄主植物。受寄主根系信号影响的寄生植物根系的形态学变化之一是吸器的发育，吸器是寄主特有的根系器官，在寄主附着、渗透和养分从寄主转移到寄主中起作用。吸器的发育迅速，高度同步，完全依赖于外部宿主因素，并且可以很容易地在体外监测。分子遗传学方法被用来确定寄主植物的根因子是如何触发寄生植物三绒藻吸器的发育的。三绒藻是一种春季的一年生野花，在太平洋沿岸很常见，与毁灭性的寄生杂草Striga和Orobanche密切相关。自然种群调查和随后的遗传分析表明，在杂交种群中存在寄主因子识别的遗传变异。一组候选寄主识别基因在寄生植物和密切相关的非寄生植物中的表达正在被比较，以确定吸器发育的特异性遗传途径。将三根藻根暴露于纯化的吸器诱导因子或与结构相关的非活性分子中，将进一步定义这些过程。除了确定新植物器官如何产生的进化起源外，这项工作还应该导致基于生物学的控制有害杂草策略的发展。

While it has been known for centuries that some plants inhibit the growth of neighboring plants through chemicals released into the soil, virtually nothing is known about the genetic or molecular mechanisms associated with subterranean interactions between plants. This is due in large part to the difficulty of assaying the effects of underground chemical signal transferred between different plants. The clearest manifestations of how one plant can alter the growth and development of a second are displayed by parasitic plants. Parasitic plants in the Orobanchaceae directly invade the roots of nearby host plants in order to rob them of water and nutrients. These parasites recognize potential host plants using certain molecules released by host roots as identification signals. One of the morphologically obvious changes to parasitic plant roots exposed to host root signals is the development of haustoria, parasite specific root organs that function in host attachment, penetration, and nutrient transfer from host to parasite. Haustorium development is rapid, highly synchronous, completely dependent on external host factors, and can be readily monitored in vitro. Molecular genetic approaches are being taken to determine how root factors from host plants triggers the development of haustoria in the parasite Triphysaria, a spring time annual wildflower common throughout the Pacific Coast and closely related to the devastating parasitic weeds Striga and Orobanche. Surveys of natural populations and subsequent genetic analyses demonstrated the existence of heritable variation in host factor recognition within interbreeding populations. The expression of a candidate set of host recognition genes is being compared in parasitic and closely related non-parasitic plants to identify genetic pathways specific for haustorium development. Exposing Triphysaria roots to either purified haustorium-inducing factors or structurally related, non-active molecules will further define these processes. In addition to determining the evolutionary origins of how novel plant organs arise, this work should lead to the development of biologically based strategies for controlling unwanted weeds.