title: Systemic resistance in Arabidopsis induced by biocontrol bacteria is independent of salicylic acid accumulation and pathogenesis-related gene expression.
abstract: Systemic acquired resistance is a pathogen-inducible defense mechanism in plants. The resistant state is dependent on endogenous accumulation of salicylic acid (SA) and is characterized by the activation of genes encoding pathogenesis-related (PR) proteins. Recently, selected nonpathogenic, root-colonizing biocontrol bacteria have been shown to trigger a systemic resistance response as well. To study the molecular basis underlying this type of systemic resistance, we developed an Arabidopsis-based model system using Fusarium oxysporum f sp raphani and Pseudomonas syringae pv tomato as challenging pathogens. Colonization of the rhizosphere by the biological control strain WCS417r of P. fluorescens resulted in a plant-mediated resistance response that significantly reduced symptoms elicited by both challenging pathogens. Moreover, growth of P. syringae in infected leaves was strongly inhibited in P. fluorescens WCS417r-treated plants. Transgenic Arabidopsis NahG plants, unable to accumulate SA, and wild-type plants were equally responsive to P. fluorescens WCS417r-mediated induction of resistance. Furthermore, P. fluorescens WCS417r-mediated systemic resistance did not coincide with the accumulation of PR mRNAs before challenge inoculation. These results indicate that P. fluorescens WCS417r induces a pathway different from the one that controls classic systemic acquired resistance and that this pathway leads to a form of systemic resistance independent of SA accumulation and PR gene expression.
authors.affiliation: Department of Plant Ecology and Evolutionary Biology, Utrecht University, The Netherlands.
authors.forename: C M
authors.initials: CM
authors.lastname: Pieterse
authors.forename: S C
authors.initials: SC
authors.lastname: van Wees
authors.forename: E
authors.initials: E
authors.lastname: Hoffland
authors.forename: J A
authors.initials: JA
authors.lastname: van Pelt
authors.forename: L C
authors.initials: LC
authors.lastname: van Loon
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism* / Q000382:microbiology; D001483:Base Sequence; D005670:Fusarium / Q000472:pathogenicity; D018506:Gene Expression Regulation, Plant; D010935:Plant Diseases / Q000209:etiology / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics*; D011549:Pseudomonas / Q000472:pathogenicity; D011551:Pseudomonas fluorescens / Q000472:pathogenicity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012459:Salicylates / Q000378:metabolism*; D020156:Salicylic Acid
chemical_list: D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D012459:Salicylates; C053376:pathogenesis-related proteins, plant; D020156:Salicylic Acid