Nouri Eva, Breuillin-Sessoms Florence, Feller Urs, Reinhardt Didier
Dept. of Biology, University of Fribourg, Fribourg, Switzerland.
Institute of Plant Science, University of Bern, Bern, Switzerland.
PLoS One. 2014 Mar 7;9(6):e90841. doi: 10.1371/journal.pone.0090841. eCollection 2014.
Phosphorus and nitrogen are essential nutrient elements that are needed by plants in large amounts. The arbuscular mycorrhizal symbiosis between plants and soil fungi improves phosphorus and nitrogen acquisition under limiting conditions. On the other hand, these nutrients influence root colonization by mycorrhizal fungi and symbiotic functioning. This represents a feedback mechanism that allows plants to control the fungal symbiont depending on nutrient requirements and supply. Elevated phosphorus supply has previously been shown to exert strong inhibition of arbuscular mycorrhizal development. Here, we address to what extent inhibition by phosphorus is influenced by other nutritional pathways in the interaction between Petunia hybrida and R. irregularis. We show that phosphorus and nitrogen are the major nutritional determinants of the interaction. Interestingly, the symbiosis-promoting effect of nitrogen starvation dominantly overruled the suppressive effect of high phosphorus nutrition onto arbuscular mycorrhiza, suggesting that plants promote the symbiosis as long as they are limited by one of the two major nutrients. Our results also show that in a given pair of symbiotic partners (Petunia hybrida and R. irregularis), the entire range from mutually symbiotic to parasitic can be observed depending on the nutritional conditions. Taken together, these results reveal complex nutritional feedback mechanisms in the control of root colonization by arbuscular mycorrhizal fungi.
磷和氮是植物大量需要的必需营养元素。植物与土壤真菌之间的丛枝菌根共生关系可在有限条件下提高磷和氮的获取。另一方面，这些养分影响菌根真菌的根系定殖和共生功能。这代表了一种反馈机制，使植物能够根据养分需求和供应情况来控制真菌共生体。先前的研究表明，高磷供应对丛枝菌根的发育有强烈抑制作用。在此，我们探讨在矮牵牛与不规则球囊霉的相互作用中，磷的抑制作用在多大程度上受其他营养途径的影响。我们发现磷和氮是这种相互作用的主要营养决定因素。有趣的是，氮饥饿促进共生的作用显著超过了高磷营养对丛枝菌根的抑制作用，这表明只要植物受到这两种主要养分之一的限制，它们就会促进共生关系。我们的研究结果还表明，在特定的一对共生伙伴（矮牵牛和不规则球囊霉）中，根据营养条件可以观察到从互利共生到寄生的整个范围。综上所述，这些结果揭示了在丛枝菌根真菌控制根系定殖过程中复杂的营养反馈机制。
