Downregulation of a pathogen-responsive tobacco UDP-Glc:phenylpropanoid glucosyltransferase reduces scopoletin glucoside accumulation, enhances oxidative stress, and weakens virus resistance.
Plant UDP-Glc:phenylpropanoid glucosyltransferases (UGTs) catalyze the transfer of Glc from UDP-Glc to numerous substrates and regulate the activity of compounds that play important roles in plant defense against pathogens. We previously characterized two tobacco salicylic acid- and pathogen-inducible UGTs (TOGTs) that act very efficiently on the hydroxycoumarin scopoletin and on hydroxycinnamic acids. To identify the physiological roles of these UGTs in plant defense, we generated TOGT-depleted tobacco plants by antisense expression. After inoculation with Tobacco mosaic virus (TMV), TOGT-inhibited plants exhibited a significant decrease in the glucoside form of scopoletin (scopolin) and a decrease in scopoletin UGT activity. Unexpectedly, free scopoletin levels also were reduced in TOGT antisense lines. Scopolin and scopoletin reduction in TOGT-depleted lines resulted in a strong decrease of the blue fluorescence in cells surrounding TMV lesions and was associated with weakened resistance to infection with TMV. Consistent with the proposed role of scopoletin as a reactive oxygen intermediate (ROI) scavenger, TMV also triggered a more sustained ROI accumulation in TOGT-downregulated lines. Our results demonstrate the involvement of TOGT in scopoletin glucosylation in planta and provide evidence of the crucial role of a UGT in plant defense responses. We propose that TOGT-mediated glucosylation is required for scopoletin accumulation in cells surrounding TMV lesions, where this compound could both exert a direct antiviral effect and participate in ROI buffering.
Chong
Julie
J
Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, Université Louis Pasteur, 12 rue du Général Zimmer, 67084 Strasbourg Cedex, France.
Baltz
Rachel
R
Schmitt
Corinne
C
Beffa
Roland
R
Fritig
Bernard
B
Saindrenan
Patrick
P
D002726:Chlorogenic Acid / Q000378:metabolism / Q000494:pharmacology; D003374:Coumarins / Q000378:metabolism / Q000494:pharmacology; D015536:Down-Regulation; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005960:Glucosides / Q000378:metabolism / Q000494:pharmacology; D005964:Glucosyltransferases / Q000096:biosynthesis / Q000235:genetics*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007113:Immunity, Innate / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D018384:Oxidative Stress; D010650:Phenylalanine Ammonia-Lyase / Q000096:biosynthesis / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics / Q000821:virology*; D018515:Plant Leaves / Q000821:virology; D030821:Plants, Genetically Modified; D020156:Salicylic Acid / Q000378:metabolism / Q000494:pharmacology; D012603:Scopoletin / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000187:drug effects / Q000254:growth & development
D003374:Coumarins; D005960:Glucosides; C417572:scopolin; D002726:Chlorogenic Acid; D006861:Hydrogen Peroxide; D005964:Glucosyltransferases; D010650:Phenylalanine Ammonia-Lyase; D012603:Scopoletin; D020156:Salicylic Acid