title: Cytokinins mediate resistance against Pseudomonas syringae in tobacco through increased antimicrobial phytoalexin synthesis independent of salicylic acid signaling.
abstract: Cytokinins are phytohormones that are involved in various regulatory processes throughout plant development, but they are also produced by pathogens and known to modulate plant immunity. A novel transgenic approach enabling autoregulated cytokinin synthesis in response to pathogen infection showed that cytokinins mediate enhanced resistance against the virulent hemibiotrophic pathogen Pseudomonas syringae pv tabaci. This was confirmed by two additional independent transgenic approaches to increase endogenous cytokinin production and by exogenous supply of adenine- and phenylurea-derived cytokinins. The cytokinin-mediated resistance strongly correlated with an increased level of bactericidal activities and up-regulated synthesis of the two major antimicrobial phytoalexins in tobacco (Nicotiana tabacum), scopoletin and capsidiol. The key role of these phytoalexins in the underlying mechanism was functionally proven by the finding that scopoletin and capsidiol substitute in planta for the cytokinin signal: phytoalexin pretreatment increased resistance against P. syringae. In contrast to a cytokinin defense mechanism in Arabidopsis (Arabidopsis thaliana) based on salicylic acid-dependent transcriptional control, the cytokinin-mediated resistance in tobacco is essentially independent from salicylic acid and differs in pathogen specificity. It is also independent of jasmonate levels, reactive oxygen species, and high sugar resistance. The novel function of cytokinins in the primary defense response of solanaceous plant species is rather mediated through a high phytoalexin-pathogen ratio in the early phase of infection, which efficiently restricts pathogen growth. The implications of this mechanism for the coevolution of host plants and cytokinin-producing pathogens and the practical application in agriculture are discussed.
authors.affiliation: Institute for Plant Sciences, Department of Plant Physiology, University of Graz, 8010 Graz, Austria.
authors.forename: Dominik K
authors.initials: DK
authors.lastname: Grosskinsky
authors.forename: Muhammad
authors.initials: M
authors.lastname: Naseem
authors.forename: Usama Ramadan
authors.initials: UR
authors.lastname: Abdelmohsen
authors.forename: Nicole
authors.initials: N
authors.lastname: Plickert
authors.forename: Thomas
authors.initials: T
authors.lastname: Engelke
authors.forename: Thomas
authors.initials: T
authors.lastname: Griebel
authors.forename: Jürgen
authors.initials: J
authors.lastname: Zeier
authors.forename: Ondrej
authors.initials: O
authors.lastname: Novák
authors.forename: Miroslav
authors.initials: M
authors.lastname: Strnad
authors.forename: Hartwig
authors.initials: H
authors.lastname: Pfeifhofer
authors.forename: Eric
authors.initials: E
authors.lastname: van der Graaff
authors.forename: Uwe
authors.initials: U
authors.lastname: Simon
authors.forename: Thomas
authors.initials: T
authors.lastname: Roitsch
mesh_terms: D000890:Anti-Infective Agents / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D003583:Cytokinins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D060467:Disease Resistance; D054884:Host-Pathogen Interactions; D054883:Oxylipins / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D057865:Plant Immunity; D018515:Plant Leaves / Q000382:microbiology; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D020156:Salicylic Acid / Q000378:metabolism*; D012603:Scopoletin / Q000378:metabolism; D012717:Sesquiterpenes / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000382:microbiology* / Q000502:physiology*; D043324:beta-Fructofuranosidase / Q000378:metabolism; D000094162:Phytoalexins
chemical_list: D000890:Anti-Infective Agents; D003517:Cyclopentanes; D003583:Cytokinins; D054883:Oxylipins; D012717:Sesquiterpenes; C081843:capsidiol; C011006:jasmonic acid; D043324:beta-Fructofuranosidase; D012603:Scopoletin; D020156:Salicylic Acid; D000094162:Phytoalexins