Downregulation of a pathogen-responsive tobacco UDP-Glc:phenylpropanoid glucosyltransferase reduces scopoletin glucoside accumulation, enhances oxidative stress, and weakens virus resistance.

Abstract

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.

• Authors: Julie Chong, Rachel Baltz, Corinne Schmitt, Roland Beffa, Bernard Fritig, Patrick Saindrenan
• Journal: The Plant cell (Plant Cell) Vol. 14 Issue 5 Pg. 1093-107 (May 2002) ISSN: 1040-4651 [Print] England
• PMID: 12034899 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Coumarins
• Glucosides
• scopolin
• Chlorogenic Acid
• Hydrogen Peroxide
• Glucosyltransferases
• Phenylalanine Ammonia-Lyase
• Scopoletin
• Salicylic Acid

Topics

• Chlorogenic Acid (metabolism, pharmacology)
• Coumarins (metabolism, pharmacology)
• Down-Regulation
• Enzyme Induction (drug effects)
• Gene Expression Regulation, Enzymologic (drug effects)
• Gene Expression Regulation, Plant (drug effects)
• Glucosides (metabolism, pharmacology)
• Glucosyltransferases (biosynthesis, genetics)
• Hydrogen Peroxide (metabolism)
• Immunity, Innate (genetics)
• Molecular Sequence Data
• Mutation
• Oxidative Stress
• Phenylalanine Ammonia-Lyase (biosynthesis, genetics)
• Plant Diseases (genetics, virology)
• Plant Leaves (virology)
• Plants, Genetically Modified
• Salicylic Acid (metabolism, pharmacology)
• Scopoletin (metabolism, pharmacology)
• Signal Transduction
• Tobacco (enzymology, genetics, virology)
• Tobacco Mosaic Virus (drug effects, growth & development)