Analysis of symbiotic mineral nutrient transport and mechanisms underlying regulation of the arbuscular mycorrhizal (AM) symbiosis

80%以上的维管开花植物能够与丛枝菌根真菌形成共生关系。这些联系在根中发展，真菌共生体在根中交换碳，将磷和氮从土壤转移到植物中。在共生关系中，AM真菌栖息在根皮质细胞中，在那里它们形成分枝菌丝，称为丛枝。丛枝负责向根细胞输送营养。以往的研究表明，一种共生特异性磷酸盐转运蛋白MtPT4对共生磷酸盐运输至关重要。在这个项目中，研究人员将进一步分析MtPT4，此外，开始表征第二种磷酸盐转运蛋白MtPT8和一种新型铵转运蛋白MtAMT2的作用。将产生缺乏这些转运体的单、双和三突变体植株，它们将用于确定共生磷酸盐和氮转运对AM共生的调节程度。实验将解决潜在的机制和信号通路所涉及的。该项目的第二个方面侧重于共生中的蛋白质靶向。MtPT4蛋白仅位于一种特殊的膜上，称为丛枝周围膜，它包围着丛枝。利用免疫学方法和荧光蛋白标记MtPT4的活细胞成像，研究人员将分析蛋白靶向丛枝周围膜的机制。AM共生是由几乎所有维管开花植物形成的，但介导共生磷酸盐和铵运输的蛋白质，调节关键共生界面维持的机制，以及将调节机制与植物矿物质营养状况相结合的信号通路，在很大程度上都是未知的。在这些实验中产生的数据将促进我们对共生的这些方面的理解。该项目包括本科生获得共聚焦显微镜经验的机会。

Over 80% of the vascular flowering plants are capable of forming mutualistic symbioses with arbuscular mycorrhizal (AM) fungi. These associations develop in the roots, where in exchange for carbon, the fungal symbionts transfer phosphorus and nitrogen from the soil to the plant. In the symbiosis, the AM fungi inhabit the root cortical cells where they form branched hyphae called arbuscules. The arbuscules are responsible for nutrient delivery to the root cells. Previous studies in Medicago truncatula indicated that a symbiosis-specific phosphate transporter, MtPT4, is essential for symbiotic phosphate transport. In this project the investigators will further analyze MtPT4 and in addition, begin to characterize the roles of a second phosphate transporter, MtPT8, and a novel ammonium transporter, MtAMT2. Single, double and triple mutant plants lacking these transporters will be generated and they will be used to determine the extent to which symbiotic phosphate and nitrogen transport regulate the AM symbiosis. Experiments will address the underlying mechanisms and signaling pathways involved. A second aspect of the project focuses on protein targeting in the symbiosis. The MtPT4 protein is located exclusively on a specialized membrane called the peri-arbuscular membrane, which surrounds the arbuscule. Using immunological approaches, and live cell imaging of MtPT4 tagged with fluorescent proteins, the investigators will analyze the mechanisms underlying protein targeting to the peri-arbuscular membrane. The AM symbiosis is formed by almost all vascular flowering plants but the proteins that mediate symbiotic phosphate and ammonium transport, the mechanisms that regulate maintenance of key symbiotic interfaces, and the signaling pathways that integrate regulatory mechanisms with the mineral nutrient status of the plant, are all largely unknown. The data generated in these experiments will advance our understanding of these aspects of the symbiosis. The project includes opportunities for undergraduate students to obtain experience with confocal microscopy.