Arbuscular mycorrhizal (AM) fungi form a root endosymbiosis with many agronomically important crop species and both enhance the ability of their host to obtain nutrients from the soil and increase host tolerance to biotic and abiotic stressors. However, AM fungal species differ in the benefits they provide to their host plants. Here, we examined the putative molecular mechanisms involved in the regulation of the physiological response of Medicago truncatula to either Rhizophagus irregularis or Glomus aggregatum, a high or a low benefit AM fungus, respectively. Colonization with R. irregularis led to higher growth and nutrient uptake benefits than the colonization with G. aggregatum. These benefits were linked to an elevated expression in the roots of genes involved in strigolactone biosynthesis (NSP1, NSP2, CCD7, and MAX1a), mycorrhiza-induced phosphate (PT8), ammonium (AMT2;3), and nitrate (NPF4.12) transporters and the putative ammonium transporter NIP1;5. R. irregularis also stimulated the expression of photosynthesis-related genes in the shoot and the upregulation of the sugar transporters SWEET1.2, SWEET3.3 and SWEET 12 and the lipid biosynthesis gene RAM2 in the roots. In contrast, G. aggregatum induced the expression of biotic stress defense response genes in the shoots and several genes associated with abiotic stress in the roots. This suggests that either the host perceives colonization by G. aggregatum as a pathogen attack or that G. aggregatum can prime host defense responses. Our findings reveal novel insights into the molecular mechanisms that control the host plant response to colonization with high- and low-benefit arbuscular mycorrhizal fungal symbionts.

中文翻译：

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紫花苜蓿对高、低益丛枝菌根真菌定植的生理和转录组学反应

丛枝菌根 (AM) 真菌与许多重要的农艺作物物种形成根内共生，既增强了宿主从土壤中获取养分的能力，又增加了宿主对生物和非生物胁迫的耐受性。然而，AM 真菌物种在为寄主植物提供的益处方面有所不同。在这里，我们研究了参与调节蒺藜苜蓿对不规则根瘤菌或团聚球花（一种高或低效益的 AM 真菌）生理反应的推定分子机制。定植R. irregularis导致更高的增长和养分吸收的好处比殖民G. aggregatum. 这些益处与参与独脚金内酯生物合成（NSP1、NSP2、CCD7和MAX1a）、菌根诱导的磷酸盐（PT8）、铵（AMT2;3）和硝酸盐（NPF4.12）的基因在根中的表达升高有关。转运蛋白和假定的铵转运蛋白NIP1;5。R. irregularis也刺激的在拍摄光合作用有关的基因的表达和糖转运的上调SWEET1.2，SWEET3.3和SWEET 12和脂质生物合成基因RAM2在根部。相比之下，G. agregatum诱导芽中生物胁迫防御反应基因和根中几种与非生物胁迫相关的基因的表达。这表明宿主将G. aggregatum 的定植视为病原体攻击，或者G. agregatum可以引发宿主防御反应。我们的研究结果揭示了对控制寄主植物对高效益和低效益丛枝菌根真菌共生体定植反应的分子机制的新见解。