Arbuscular mycorrhizal fungi increase growth and phenolics synthesis in Poncirus trifoliata under iron deficiency

- AM fungi enhanced the Poncirus trifoliate growth.
- AMF induced higher phenolics content and enzymatic activity.
- AMF up regulated the pal1 gene expression in response to Fe deficiency.
- Phenolics played a crucial role in AMF-mediated alleviation of iron stress in P. trifoliata.

In order to reveal the changes phenolics involved in symbiotic process between arbuscular mycorrhizal fungi (AMF) and host plant, the impacts of arbuscular mycorrhizal (AM) fungus on growth and phenolic synthesis in Poncirus trifoliata under iron deficiency were investigated. The P. trifoliata seedlings were inoculated with or without AM fungus Glomus versiforme irrigated with Fe-deficient (0 μM o,o-FeEDDHA) or Fe-sufficient (50 μM o,o-FeEDDHA) nutrient solution twice a week. Three months later, we monitored biomass, the contents of phenolics, the activities of phenylalanine ammonia-lyase (PAL) and the expression of pal1 gene. Mycorrhizal colonization significantly promoted P. trifoliata growth and phenolic synthesis compared with the non-AMF control, in parallel with the increase in PAL enzyme activity and pal1 gene expression. Mycorrhization significantly increased ferulic acid, gallic acid, phlorizin and salicylic acid. Caffeic acid, chlorogenic acid, coumaric acid, protocatechuic, rutin, syringic acid, vanillin and vanilloid were not detected in both AMF and non-AMF inoculated treatments. However, phloretin was only present in Fe-deficient groups whether it was inoculated with AMF or not. In conclusion, phenolics changes and integrated transcriptional regulation might play a crucial role in AMF-mediated alleviation of iron stress in P. trifoliata.