title: Methyl salicylate is a critical mobile signal for plant systemic acquired resistance.
abstract: In plants, the mobile signal for systemic acquired resistance (SAR), an organism-wide state of enhanced defense to subsequent infections, has been elusive. By stimulating immune responses in mosaic tobacco plants created by grafting different genetic backgrounds, we showed that the methyl salicylate (MeSA) esterase activity of salicylic acid-binding protein 2 (SABP2), which converts MeSA into salicylic acid (SA), is required for SAR signal perception in systemic tissue, the tissue that does not receive the primary (initial) infection. Moreover, in plants expressing mutant SABP2 with unregulated MeSA esterase activity in SAR signal-generating, primary infected leaves, SAR was compromised and the associated increase in MeSA levels was suppressed in primary infected leaves, their phloem exudates, and systemic leaves. SAR was also blocked when SA methyl transferase (which converts SA to MeSA) was silenced in primary infected leaves, and MeSA treatment of lower leaves induced SAR in upper untreated leaves. Therefore, we conclude that MeSA is a SAR signal in tobacco.
authors.affiliation: Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853, USA.
authors.forename: Sang-Wook
authors.initials: SW
authors.lastname: Park
authors.forename: Evans
authors.initials: E
authors.lastname: Kaimoyo
authors.forename: Dhirendra
authors.initials: D
authors.lastname: Kumar
authors.forename: Stephen
authors.initials: S
authors.lastname: Mosher
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Klessig
mesh_terms: D004950:Esterases / Q000235:genetics / Q000378:metabolism; D025461:Feedback, Physiological; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D052585:Phloem / Q000378:metabolism; D010935:Plant Diseases / Q000276:immunology* / Q000821:virology; D018515:Plant Leaves / Q000378:metabolism / Q000821:virology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012459:Salicylates / Q000378:metabolism*; D020156:Salicylic Acid / Q000378:metabolism; D015398:Signal Transduction; D014026:Nicotiana / Q000276:immunology / Q000378:metabolism* / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000502:physiology*; D014779:Virus Replication
chemical_list: D010940:Plant Proteins; D012459:Salicylates; D006899:Mixed Function Oxygenases; C022619:salicylate 1-monooxygenase; C499506:SABP2 protein, Nicotiana tabacum; D004950:Esterases; C033069:methyl salicylate; D020156:Salicylic Acid