title: Compromising early salicylic acid accumulation delays the hypersensitive response and increases viral dispersal during lesion establishment in TMV-infected tobacco.
abstract: To investigate the role of salicylic acid (SA) in the hypersensitive response (HR) its accumulation was compromised during different phases of lesion development by differential expression of a salicylate hydroxylase gene (SH-L). Constitutive suppression of SA accumulation was achieved by expression of a gene fusion between the CaMV35S promoter (35S) and SH-L. Using the H2O2-responsive AoPR1 promoter to drive SH-L SA accumulation could be compromised at an early stage, on lesion formation and possibly prior to visible necrosis, whilst use of the salicylate-responsive PR1a promoter reduced SA accumulation at a later stage as lesions expand. TMV infection of 35S-SH-L and AoPR1-SH-L, but not PR1a-SH-L, tobacco resulted in significantly greater rates of lesion growth than in wild-type tobacco. TMV was detected in asymptomatic tissue surrounding lesions only in 35S-SH-L and AoPR1-SH-L lines; subsequently these transgenic lines exhibited a 'spreading-necrosis' originating from the lesion which entered the stem and eventually other leaves, a phenotype which could be correlated with the presence of TMV particles. Analysis of TMV-infected and 'temperature-shifted' tobacco indicated that both 35S-SH-L and AoPR1-SH-L, but not PR1a-SH-L, transgenics exhibited delayed cell-death compared to wild-type infections. We propose that the SH-L phenotypes indicate that early SA accumulation is a major factor in preventing viral escape, via mechanism(s) which may include influencing the rate of host-cell death and, possibly, an effect on viral function.
authors.affiliation: Botany Department, University of Leicester, UK.
authors.forename: L A
authors.initials: LA
authors.lastname: Mur
authors.forename: Y M
authors.initials: YM
authors.lastname: Bi
authors.forename: R M
authors.initials: RM
authors.lastname: Darby
authors.forename: S
authors.initials: S
authors.lastname: Firek
authors.forename: J
authors.initials: J
authors.lastname: Draper
mesh_terms: D019677:Artificial Gene Fusion; D002470:Cell Survival; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000096:biosynthesis; D006899:Mixed Function Oxygenases / Q000096:biosynthesis*; D010935:Plant Diseases; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012459:Salicylates / Q000378:metabolism*; D020156:Salicylic Acid; D013997:Time Factors; D014026:Nicotiana / Q000502:physiology* / Q000821:virology*; D014027:Tobacco Mosaic Virus / Q000472:pathogenicity / Q000502:physiology*
chemical_list: D017931:DNA Primers; D011993:Recombinant Fusion Proteins; D012459:Salicylates; D006899:Mixed Function Oxygenases; C022619:salicylate 1-monooxygenase; D005966:Glucuronidase; D020156:Salicylic Acid