Molecular Assessment of Metabolome Alterations in Lotus japonicus Roots Induced by Arbuscular Mycorrhiza

Abstract

An arbuscular mycorrhiza symbiosis, which is established by 80% of all vascular plants and Glomeromycota fungi, can boost the growth, stress tolerance, and yield of agricultural crop plants by increasing the mineral supply of the host plant [1]. Mineral nutrients absorbed by the fungus are exchanged for photoassimilates from the plant via highly branched fungal structures called arbuscules which are formed within root cortex cells [2]. The process of arbuscule formation and degradation is highly dynamic and accompanied by considerable cell reprogramming [3], but there is only limited knowledge on the influence of arbuscular mycorrhiza on the host metabolome. We investigated alterations of the host plant's root metabolome induced by arbuscular mycorrhizal symbiosis using the model legume Lotus japonicus. Methanol extracts of mycorrhizal (myc) and non‐mycorrhizal roots (mock) were analyzed employing ultra‐highperformance liquid chromatography–electrospray ionization–time‐of‐flight–ion mobility–mass spectrometry (UPLC–ESI–ToF–IM–MS) in an untargeted metabolomics approach. Up‐regulated marker metabolites were identified via principal components analysis (PCA) and orthogonal partial least squares–discriminant analysis (OPLS–DA) depicted as S‐plots, and their structures elucidated by co‐chromatography with authentic standards or by isolation from L. japonicus roots using preparative HPLC and one‐ and two‐dimensional nuclear magnetic resonance spectroscopy (NMR) experiments. We isolated three previously unknown mycorrhizal marker polyphenols from L. japonicus roots, one being a coumaronochromone, one pterocarp‐6a‐ene, and one aryl benzofuran carboxaldehyde. Additionally, we identified three more coumaronochromones, three flavonoids, three isoflavonoids, and one coumestan in mycorrhized L. japonicus.