title: The Rhizobium sp. strain NGR234 systemically suppresses arbuscular mycorrhizal root colonization in a split-root system of barley (Hordeum vulgare).
abstract: Nitrogen-fixing bacteria (rhizobia) form a nodule symbiosis with legumes, but also induce certain effects on non-host plants. Here, we used a split-root system of barley to examine whether inoculation with Rhizobium sp. strain NGR234 on one side of a split-root system systemically affects arbuscular mycorrhizal (AM) root colonization on the other side. Mutant strains of NGR234 deficient in Nod factor production (strain NGRΔnodABC), perception of flavonoids (strain NGRΔnodD1) and secretion of type 3 effector proteins (strain NGRΩrhcN) were included in this study. Inoculation resulted in a systemic reduction of AM root colonization with all tested strains. However, the suppressive effect of strain NGRΩrhcN was less pronounced. Moreover, levels of salicylic acid, an endogenous molecule related to plant defense, were increased in roots challenged with rhizobia. These data indicate that barley roots perceived NGR234 and that a systemic regulatory mechanism of AM root colonization was activated. The suppressive effect appears to be Nod factor independent, but enhanced by type 3 effector proteins of NGR234.
authors.affiliation: Faculty of Sciences, Department of Biotechnology, Ramkhamhaeng University, Bangkok 10240, Thailand.
authors.forename: Thanasan
authors.initials: T
authors.lastname: Khaosaad
authors.forename: Christian
authors.initials: C
authors.lastname: Staehelin
authors.forename: Siegrid
authors.initials: S
authors.lastname: Steinkellner
authors.forename: Karin
authors.initials: K
authors.lastname: Hage-Ahmed
authors.forename: Juan Antonio
authors.initials: JA
authors.lastname: Ocampo
authors.forename: Jose Manuel
authors.initials: JM
authors.lastname: Garcia-Garrido
authors.forename: Horst
authors.initials: H
authors.lastname: Vierheilig
mesh_terms: D000898:Antibiosis; D001467:Hordeum / Q000378:metabolism / Q000382:microbiology*; D038821:Mycorrhizae / Q000502:physiology*; D018517:Plant Roots / Q000382:microbiology*; D012231:Rhizobium / Q000502:physiology*; D020156:Salicylic Acid / Q000032:analysis
chemical_list: D020156:Salicylic Acid