Belowground interactions of plants with other organisms in the rhizosphere rely on extensive small-molecule communication. Chemical signals released from host plant roots ensure the development of beneficial arbuscular mycorrhizal (AM) fungi which in turn modulate host plant growth and stress tolerance. However, parasitic plants have adopted the capacity to sense the same signaling molecules and to trigger their own seed germination in the immediate vicinity of host roots. The contribution of AM fungi and parasitic plants to the regulation of phytohormone levels in host plant roots and root exudates remains largely obscure. Here, we studied the hormonome in the model system comprising tobacco as a host plant, Phelipanche spp. as a holoparasitic plant, and the AM fungus Rhizophagus irregularis. Co-cultivation of tobacco with broomrape and AM fungi alone or in combination led to characteristic changes in the levels of endogenous and exuded abscisic acid, indole-3-acetic acid, cytokinins, salicylic acid, and orobanchol-type strigolactones. The hormonal content in exudates of broomrape-infested mycorrhizal roots resembled that in exudates of infested non-mycorrhizal roots and differed from that observed in exudates of non-infested mycorrhizal roots. Moreover, we observed a significant reduction in AM colonization of infested tobacco plants, pointing to a dominant role of the holoparasite within the tripartite system.

• Keywords
• mycorrhizal fungi, parasitic plants, plant hormones, rhizosphere, root exudates, small-molecule communication, strigolactones,
• MeSH
• Chromatography, Liquid MeSH
• Cytokinins metabolism   MeSH
• Heterocyclic Compounds, 3-Ring metabolism   MeSH
• Mass Spectrometry MeSH
• Fungi physiology   MeSH
• Host-Pathogen Interactions MeSH
• Plant Roots metabolism   microbiology   MeSH
• Abscisic Acid metabolism   MeSH
• Salicylic Acid metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Lactones metabolism   MeSH
• Mycorrhizae physiology   MeSH
• Orobanche growth & development   microbiology   MeSH
• Nicotiana growth & development   microbiology   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins MeSH
• GR24 strigolactone MeSH Browser
• Heterocyclic Compounds, 3-Ring MeSH
• indoleacetic acid MeSH Browser
• Abscisic Acid MeSH
• Salicylic Acid MeSH
• Indoleacetic Acids MeSH
• Lactones MeSH