Phosphate Transport in the Arbuscular Mycorrhizal Symbiosis: Functional Analysis of a Medicago Truncatula Mycorrhiza-Specific Phosphate Transporter

摘要在自然生态系统中，大多数维管束开花植物与丛枝菌根真菌共生。这些互惠互利的组合在根系统中发展，真菌在那里定居根细胞，从植物中获得碳，同时帮助植物从土壤中获得矿物质营养，特别是磷。丛枝菌根共生体是几乎所有维管束开花植物形成的共生体，对生态系统的生物多样性和功能起着重要作用。其潜在的机制尚不清楚，但AM真菌对植物磷营养的贡献，以及由此对植物健康的影响，显然是一个主要的促成因素。这个项目的总体目标是剖析植物在丛枝菌根共生中从真菌中获得磷酸盐的机制。模式豆科植物，紫花苜蓿，将被用于这些分析。丛枝菌根共生是一种高度共同进化的伙伴关系，在这种伙伴关系中，两种共生体的分化导致了特殊的共生界面，使碳和磷的交换成为可能。在根细胞内，真菌形成高度分枝的菌丝，称为丛生菌丝，被一种特殊的植物膜所包裹，即丛枝周膜。以前的研究发现了一种独特的磷酸转运蛋白(MtPT4)，该转运蛋白仅位于茎周膜上。目前的目标是评估MtPT4靶向茎周膜的基序，并确定MtPT4在共生中磷酸盐运输中的作用。利用MtPT4表达被干扰的转基因品系，或通过耕作获得的MtPT4功能丧失的等位基因，将检验MtPT4对于从真菌释放的磷酸盐的获取是必不可少的假设。此外，突变的MtPT4品系将被用来探索关于磷运输和丛枝菌根共生的基本问题，包括不同共生界面的作用和双向营养交换在互惠共生中的重要性。目前，丛生植物发育的分子事件尚不清楚。对MtPT4突变系和一个丛枝突变体的比较转录图谱将提供与丛枝发育的结构和功能成分相关的转录事件的洞察力，以及共生中的磷酸盐运输。由于磷酸盐限制了植物的产量，因此了解AM/豆科植物的共生具有重要的农业和生态意义。其他更广泛的影响包括对研究生和博士后研究员以及本科生和高中生的培训。

IBN: 0343975AbstractIn natural ecosystems, most vascular flowering plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. These mutually beneficial associations develop in the root system, where the fungus colonizes the root cells to obtain carbon from the plant, while assisting the plant with the acquisition of mineral nutrients, particularly phosphorus, from the soil. Arbuscular mycorrhizal symbioses are formed by almost all vascular flowering plant species and play a significant role in ecosystem biodiversity and functioning. The underlying mechanisms are not yet understood, but the contribution of AM fungi to plant phosphorus nutrition, and the resulting impact on plant health, is clearly a major contributing factor. The overall objectives of this project are to dissect the mechanisms via which the plant obtains phosphate from the fungus in an arbuscular mycorrhizal symbiosis. A model legume, Medicago truncatula, will be used for these analyses. The arbuscular mycorrhizal symbiosis is a highly co-evolved partnership, in which the differentiation of both symbionts results in specialized symbiotic interfaces that enable the exchange of carbon and phosphate. Within the root cells, the fungus forms highly branched hyphae, called arbuscules, which are enveloped in a specialized plant membrane, the peri-arbuscular membrane. Previous studies led to the identification of a unique phosphate transporter (MtPT4) from Medicago truncatula that is located exclusively in the peri-arbuscular membrane. Current objectives are to evaluate motifs implicated in targeting MtPT4 to the peri-arbuscular membrane and to determine the role of MtPT4 in phosphate transport in the symbiosis. Using transgenic lines in which MtPT4 expression is disrupted, or loss-of-function alleles of MtPT4 obtained via TILLING, the hypothesis that MtPT4 is essential for the acquisition of phosphate released from the fungus will be tested. In addition, the mutant MtPT4 lines will be used to explore fundamental questions about phosphate transport and the arbuscular mycorrhizal symbiosis, including the role of the different symbiotic interfaces and the importance of bi-directional nutrient exchange in a mutualistic symbiosis. Currently, the molecular events underlying arbuscule development are unknown. Comparative transcriptional profiling of the MtPT4 mutant lines and a M. truncatula arbuscule development mutant, will provide insights into the transcriptional events associated with structural and functional components of arbuscule development and phosphate transport in the symbiosis. Because phosphate limits plant production, an understanding of the AM/legume symbiosis has significant agricultural and ecological implications. Other Broader Impacts include the training of graduate students and postdoctoral fellows, as well as undergraduates and high school students.