Tian Hui, Yuan Xiaolei, Duan Jianfeng, Li Wenhu, Zhai Bingnian, Gao Yajun
Key Laboratory of Plant Nutrition and Agri-environment in Northwest China, Ministry of Agriculture, College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi, China.
PLoS One. 2017 Feb 16;12(2):e0172154. doi: 10.1371/journal.pone.0172154. eCollection 2017.
Arbuscular mycorrhizal (AM) colonization of plant roots causes the down-regulation of expression of phosphate (Pi) or nitrogen (N) transporter genes involved in direct nutrient uptake pathways. The mechanism of this effect remains unknown. In the present study, we sought to determine whether the expression of Pi or N transporter genes in roots of winter wheat colonized by AM fungus responded to (1) Pi or N nutrient signals transferred from the AM extra-radical hyphae, or (2) carbon allocation changes in the AM association. A three-compartment culture system, comprising a root compartment (RC), a root and AM hyphae compartment (RHC), and an AM hyphae compartment (HC), was used to test whether the expression of Pi or N transporter genes responded to nutrients (Pi, NH4+ and NO3-) added only to the HC. Different AM inoculation density treatments (roots were inoculated with 0, 20, 50 and 200 g AM inoculum) and light regime treatments (6 hours light and 18 hours light) were established to test the effects of carbon allocation on the expression of Pi or N transporter genes in wheat roots. The expression of two Pi transporter genes (TaPT4 and TaPHT1.2), five nitrate transporter genes (TaNRT1.1, TaNRT1.2, TaNRT2.1, TaNRT2.2, and TaNRT2.3), and an ammonium transporter gene (TaAMT1.2) was quantified using real-time polymerase chain reaction. The expression of TaPT4, TaNRT2.2, and TaAMT1.2 was down-regulated by AM colonization only when roots of host plants received Pi or N nutrient signals. However, the expression of TaPHT1.2, TaNRT2.1, and TaNRT2.3 was down-regulated by AM colonization, regardless of whether there was nutrient transfer from AM hyphae. The expression of TaNRT1.2 was also down-regulated by AM colonization even when there was no nutrient transfer from AM hyphae. The present study showed that an increase in carbon consumption by the AM fungi did not necessarily result in greater down-regulation of expression of Pi or N transporter genes.
丛枝菌根（AM）对植物根系的定殖会导致参与直接养分吸收途径的磷（Pi）或氮（N）转运蛋白基因的表达下调。这种效应的机制尚不清楚。在本研究中，我们试图确定被AM真菌定殖的冬小麦根系中Pi或N转运蛋白基因的表达是否响应（1）从AM根外菌丝传递的Pi或N养分信号，或（2）AM共生中碳分配的变化。使用三室培养系统，包括一个根系隔室（RC）、一个根系和AM菌丝隔室（RHC）以及一个AM菌丝隔室（HC），来测试Pi或N转运蛋白基因的表达是否对仅添加到HC中的养分（Pi、NH4+和NO3-）作出响应。建立了不同的AM接种密度处理（根系接种0、20、50和200 g AM接种物）和光照处理（6小时光照和18小时光照），以测试碳分配对小麦根系中Pi或N转运蛋白基因表达的影响。使用实时聚合酶链反应对两个Pi转运蛋白基因（TaPT4和TaPHT1.2）、五个硝酸盐转运蛋白基因（TaNRT1.1、TaNRT1.2、TaNRT2.1、TaNRT2.2和TaNRT2.3）以及一个铵转运蛋白基因（TaAMT1.2）的表达进行定量。仅当宿主植物根系接收到Pi或N养分信号时，AM定殖才会下调TaPT4、TaNRT2.2和TaAMT1.2的表达。然而，无论是否有来自AM菌丝的养分转移，AM定殖都会下调TaPHT1.2、TaNRT2.1和TaNRT2.3的表达。即使没有来自AM菌丝的养分转移，AM定殖也会下调TaNRT1.2的表达。本研究表明，AM真菌碳消耗的增加不一定会导致Pi或N转运蛋白基因表达的更大下调。
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