Govindarajulu Manjula, Pfeffer Philip E, Jin Hairu, Abubaker Jehad, Douds David D, Allen James W, Bücking Heike, Lammers Peter J, Shachar-Hill Yair
Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA.
Nature. 2005 Jun 9;435(7043):819-23. doi: 10.1038/nature03610.
Most land plants are symbiotic with arbuscular mycorrhizal fungi (AMF), which take up mineral nutrients from the soil and exchange them with plants for photosynthetically fixed carbon. This exchange is a significant factor in global nutrient cycles as well as in the ecology, evolution and physiology of plants. Despite its importance as a nutrient, very little is known about how AMF take up nitrogen and transfer it to their host plants. Here we report the results of stable isotope labelling experiments showing that inorganic nitrogen taken up by the fungus outside the roots is incorporated into amino acids, translocated from the extraradical to the intraradical mycelium as arginine, but transferred to the plant without carbon. Consistent with this mechanism, the genes of primary nitrogen assimilation are preferentially expressed in the extraradical tissues, whereas genes associated with arginine breakdown are more highly expressed in the intraradical mycelium. Strong changes in the expression of these genes in response to nitrogen availability and form also support the operation of this novel metabolic pathway in the arbuscular mycorrhizal symbiosis.
大多数陆地植物与丛枝菌根真菌（AMF）形成共生关系，AMF从土壤中吸收矿物质养分，并与植物交换这些养分以获取光合固定碳。这种交换是全球养分循环以及植物生态学、进化和生理学中的一个重要因素。尽管氮作为一种养分很重要，但对于AMF如何吸收氮并将其转移到宿主植物中却知之甚少。在此，我们报告了稳定同位素标记实验的结果，这些结果表明，真菌在根外吸收的无机氮被整合到氨基酸中，以精氨酸的形式从根外菌丝体转运到根内菌丝体，但在没有碳的情况下转移到植物中。与这种机制一致，初级氮同化基因在根外组织中优先表达，而与精氨酸分解相关的基因在根内菌丝体中表达更高。这些基因的表达因氮的可用性和形态而发生强烈变化，这也支持了这种新的代谢途径在丛枝菌根共生中的运作。
