title: The root-colonizing endophyte Pirifomospora indica confers drought tolerance in Arabidopsis by stimulating the expression of drought stress-related genes in leaves.
abstract: Piriformospora indica is an endophytic fungus that colonizes the roots of many plant species, including Arabidopsis. We exposed 18-day-old Arabidopsis seedlings, which were either cocultivated with the fungus or mock-treated for the last 9 days, to mild drought stress for 84 h. During the first 36 to 48 h, seedlings cocultivated with the fungus continued to grow, while the uncolonized controls did not. This results in a threefold difference in the fresh weight and a more than twofold difference in the chlorophyll content. The photosynthetic efficiency was only slightly reduced in the colonized (F variable/F maximum [Fv/Fm] at t(0 h) = 0.82 and t(36 h) = 0.79) and was severely impaired in the uncolonized (Fv/Fm at t(0 h) = 0.81 and (t)(36 h) = 0.49) seedlings, which also showed symptoms of withering. When seedlings exposed to drought stress for 72 or 84 h were transferred to soil, 10% (72 h) and none (84 h) of uncolonized seedlings reached the flowering stage and produced seeds, while 59% (72 h) and 47% (84 h) of the colonized seedlings flowered and produced seeds. After exposure to drought stress for 3 h, the message levels for RESPONSE TO DEHYDRATION 29A, EARLY RESPONSE TO DEHYDRATION1, ANAC072, DEHYDRATION-RESPONSE ELEMENT BINDING PROTEIN2A, SALT-, AND DROUGHT-INDUCED RING FINGER1, phospholipase Ddelta, CALCINEURIN B-LIKE PROTEIN (CBL)1, CBL-INTERACTING PROTEIN KINASE3, and the histone acetyltransferase (HAT) were upregulated in the leaves of P. indica-colonized seedlings. Uncolonized seedlings responded 3 to 6 h later, and the message levels increased much less. We identified an Arabidopsis ethylmethane-sulfonate mutant that is less resistant to drought stress and in which the stress-related genes were not upregulated in the presence of P. indica. Thus, P. indica confers drought-stress tolerance to Arabidopsis, and this is associated with the priming of the expression of a quite diverse set of stress-related genes in the leaves. Transfer to soil was again associated with a faster and stronger upregulation of the message levels for phospholipase Ddelta, CBL1, and HAT in P. indica-colonized seedlings, indicating that this response might also contribute to better survival on soil.
authors.affiliation: Friedrich-Schiller-Universität Jena, Institut für Allgemeine Botanik und Pflanzenphysiologie, Dornburger Str. 159, 07743 Jena, Germany.
authors.forename: Irena
authors.initials: I
authors.lastname: Sherameti
authors.forename: Swati
authors.initials: S
authors.lastname: Tripathi
authors.forename: Ajit
authors.initials: A
authors.lastname: Varma
authors.forename: Ralf
authors.initials: R
authors.lastname: Oelmüller
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology; D001487:Basidiomycota / Q000254:growth & development / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism; D004190:Disasters; D018506:Gene Expression Regulation, Plant; D054884:Host-Pathogen Interactions; D018515:Plant Leaves / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D018517:Plant Roots / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D036226:Seedlings / Q000235:genetics / Q000382:microbiology / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D002734:Chlorophyll