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O-methyltransferase(s)-suppressed plants produce lower amounts of phenolic vir inducers and are less susceptible to Agrobacterium tumefaciens infection.

Abstract
The first step of Agrobacterium tumefaciens/plant interaction corresponds to the activation of a transduction pathway of the bacterium by plant exudate. Phenolic compounds rapidly secreted by wounded plant cells induce the expression of bacterial virulence (vir) genes; however, little is known about their biosynthesis in plant. Here we show that inoculation of an Agrobacterium tumefaciens virulent strain on orthodiphenol-O-methyltransferases-suppressed tobacco plants leads to significantly smaller tumors compared to control plants. These transgenic plants are inhibited for caffeic acid O-methyltransferase class I or II (OMT; EC 2.1.1.6) and/or caffeoyl-coenzyme A O-methyltransferase (CCoAOMT; EC 2.1.1.104) that are involved in monolignol biosynthesis. The significant decrease of tumor size could be suppressed by the pre-activation of bacterial virulence, before inoculation, using acetosyringone a known vir inducer. Total soluble phenolic amounts and cell wall composition analyzed by FT-IR analysis did not show significant differences between transgenic and control plants. The potential of phenolic extracts from control and OMT-suppressed plants to induce virulence was evaluated using an Agrobacterium tumefaciens reporter strain carrying a vir::LacZ gene fusion plasmid. Lower vir-inducing activities were recorded for plants that show inhibition to caffeic acid O-methyltransferase activity. HPLC analysis confirmed that the levels of several phenolic compounds were differently affected by wounding and/or by bacterial inoculation. Statistical correlations were established between tumor sizes, vir-inducing activities, O-methyltransferases proteins accumulations and the levels of various soluble phenolic compounds such as acetosyringone. These results demonstrate the role of the O-methyltransferases of the phenylpropanoid pathway in the early production of soluble Agrobacterium tumefaciens vir inducers.
AuthorsStéphane Maury, A Delaunay, F Mesnard, D Crônier, B Chabbert, P Geoffroy, M Legrand
JournalPlanta (Planta) Vol. 232 Issue 4 Pg. 975-86 (Sep 2010) ISSN: 1432-2048 [Electronic] Germany
PMID20652308 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Plant Proteins
  • Methyltransferases
  • caffeoyl-CoA O-methyltransferase
  • caffeate O-methyltransferase
Topics
  • Agrobacterium tumefaciens (pathogenicity)
  • Chromatography, High Pressure Liquid
  • Electrophoresis, Polyacrylamide Gel
  • Immunoblotting
  • Methyltransferases (genetics, metabolism)
  • Plant Proteins (genetics, metabolism)
  • Plants, Genetically Modified (genetics, metabolism, microbiology)
  • Tobacco (genetics, metabolism, microbiology)
  • Virulence (genetics)

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