菌根特异铵转运蛋白介导的植物-AM真菌共生界面上的氮素转运机制研究

丛枝菌根真菌（AM）与植物根系形成互惠互利的菌根共生体，实现植物和真菌之间的资源交换。有证据表明AM真菌对植物氮素吸收有重要作用，但其生理贡献大小及共生界面上的氮素转运机制尚不清楚。我们前期研究建立了土培条件下菌根室15N标记的实验体系，证实了玉米菌根氮素吸收途径的显著贡献；并筛选分离到菌根特异诱导的玉米铵转运蛋白（AMT）和水通道蛋白（NIP）基因，可能介导了铵从菌根向根系的传递。本项目拟深入研究两个候选基因在根中的组织和亚细胞定位；在卵母细胞、酵母和拟南芥AMT多缺失突变体中异源表达来研究铵转运特性；在玉米RNAi转基因系中沉默基因的表达，利用建立的玉米毛根-菌根培养体系和土培菌根室体系，研究它们在介导菌根氮素吸收过程中的作用。研究结果将最终明确氮素在根系-菌根共生界面上以铵的方式运输，及其菌根特异诱导的AMT和NIP 蛋白的功能机理，从而在分子上阐明植物根系菌根氮素吸收途径的机理

Arbuscular mycorrhizal (AM) symbiosis brings together the roots of plant and the fungi of the phylum Glomeromycota, and improves their mutual benefits for exchanges of mineral nutrients and photosynthetically fixed carbon. Besides phosphorus (P) nutrient, AM can play an important role for the acquisition of nitrogen (N) by plant roots. However, the solid evidences at the physiological and molecular levels are still missing to support the contribution of mycorrhizal pathway to plant N uptake (Myc-N pathway). In the previous work, we established an advanced system to evaluate the Myc-N pathway in soil-cultured maize plants based on 15N-labelling N strategy in AM-compartments, and showed that a significantly higher 15N abundances in shoots of maize plants grown with 15N- mycorrhizal compartment. This suggested an important contribution of mycorrhizal to N transport into maize plants. Meanwhile, we isolated the myc-specific each of AMT and NIP gene, which might be involved in N transport from mycorrhizal to plant root cells in a form of ammonium. Here, we aim to characterize these two candidate genes by investigating 1) the cellular and sub-cellular location in maize roots when colonized by AM; 2) the transport properties in terms of ammonium substrate when heterogously expressed in oocytes, and yeast or Arabidospsis in which the multiple AMTs were disrupted; 3) the function for N-transport from AM to plant cells in vivo using the transgenic maize RNAi lines in which the target genes expression were silenced. There results will not only provide the physiological evidence to support the contribution of N transport during mycorrhizal symbiosis, and also reveal the essential roles of plasma-membrane localized membrane transporters in arbusculated cortical cells in NH3/NH4+ transport to plant roots.