title: The role of auxins and cytokinins in the mutualistic interaction between Arabidopsis and Piriformospora indica.
abstract: Arabidopsis growth and reproduction are stimulated by the endophytic fungus Piriformospora indica. The fungus produces low amounts of auxins, but the auxin levels and the expression of auxin-regulated genes are not altered in colonized roots. Also, mutants with reduced auxin levels (ilr1-1, nit1-3, tfl2, cyp79 b2b3) respond to P. indica. However, the fungus rescues the dwarf phenotype of the auxin overproducer sur1-1 by converting free auxin into conjugates, which also results in the downregulation of the auxin-induced IAA6 and the upregulation of the P. indica-induced LRR1 gene. The fungus produces relatively high levels of cytokinins, and the cytokinin levels are higher in colonized roots compared with the uncolonized controls. trans-Zeatin cytokinin biosynthesis and the CRE1/AHK2 receptor combination are crucial for P. indica-mediated growth stimulation, while mutants lacking cis-zeatin, impaired in other cytokinin receptor combinations, or containing reduced cytokinin levels respond to the fungus. Since root colonization is not affected in the cytokinin mutants, we propose that cytokinins are required for P. indica-induced growth promotion. Finally, a comparative analysis of the phytohormone mutants allows the conclusion that the response to P. indica is independent of the architecture and size of the roots.
authors.affiliation: Friedrich-Schiller-Universitat Jena, Jena Germany.
authors.forename: Jyothilakshmi
authors.initials: J
authors.lastname: Vadassery
authors.forename: Claudia
authors.initials: C
authors.lastname: Ritter
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Venus
authors.forename: Iris
authors.initials: I
authors.lastname: Camehl
authors.forename: Ajit
authors.initials: A
authors.lastname: Varma
authors.forename: Bationa
authors.initials: B
authors.lastname: Shahollari
authors.forename: Ondrej
authors.initials: O
authors.lastname: Novák
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Jutta
authors.initials: J
authors.lastname: Ludwig-Müller
authors.forename: Ralf
authors.initials: R
authors.lastname: Oelmüller
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D001487:Basidiomycota / Q000502:physiology*; D003583:Cytokinins / Q000378:metabolism* / Q000502:physiology; D054884:Host-Pathogen Interactions; D007210:Indoleacetic Acids / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000382:microbiology
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids