Downregulation of a Pathogen-Responsive Tobacco UDP-Glc:Phenylpropanoid Glucosyltransferase Reduces Scopoletin Glucoside Accumulation, Enhances Oxidative Stress, and Weakens Virus Resistance

• Published in: The Plant cell 2002-05, Vol.14 (5), p.1093-1107
• Main Authors: Chong, Julie, Baltz, Rachel, Schmitt, Corinne, Beffa, Roland, Fritig, Bernard, Saindrenan, Patrick
• Format: Article
• Language: English
• Subjects: Accumulation; Chlorogenic Acid - metabolism; Chlorogenic Acid - pharmacology; Coumarins - metabolism; Coumarins - pharmacology; Down-Regulation; Enzyme Induction - drug effects; Fluorescence; Gels; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Plant - drug effects; Glucosides - metabolism; Glucosides - pharmacology; Glucosyltransferases - biosynthesis; Glucosyltransferases - genetics; Hydrogen Peroxide - metabolism; Immunity, Innate - genetics; Infections; Inoculation; Leaves; Lesions; Life Sciences; Molecular Sequence Data; Mutation; Nicotiana - enzymology; Nicotiana - genetics; Nicotiana - virology; Oxidative Stress; Pathogens; Phenylalanine Ammonia-Lyase - biosynthesis; Phenylalanine Ammonia-Lyase - genetics; Plant cells; Plant Diseases - genetics; Plant Diseases - virology; Plant Leaves - virology; Plants; Plants, Genetically Modified; Protoplasts; Salicylic Acid - metabolism; Salicylic Acid - pharmacology; Scopoletin - metabolism; Scopoletin - pharmacology; Signal Transduction; Tobacco; Tobacco Mosaic Virus - drug effects; Tobacco Mosaic Virus - growth & development; Vegetal Biology; Viruses
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.010436

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.