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New Phytol

Title:		The saponin bomb: a nucleolar-localized beta-glucosidase hydrolyzes triterpene saponins in Medicago truncatula
Author(s):		Lacchini E; Erffelinck ML; Mertens J; Marcou S; Molina-Hidalgo FJ; Tzfadia O; Venegas-Molina J; Cardenas PD; Pollier J; Tava A; Bak S; Hofte M; Goossens A;
Address:		"Department of Plant Biotechnology and Bioinformatics, Ghent University, Ghent, B-9052, Belgium. VIB Center for Plant Systems Biology, Ghent, B-9052, Belgium. Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, B-9000, Belgium. Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg C, DK-1871, Denmark. CREA Research Centre for Animal Production and Aquaculture, Lodi, 26900, Italy"
Journal Title:		New Phytol
Year:		2023
Volume:		20230312
Issue:		2
Page Number:		705 - 719
DOI:		10.1111/nph.18763
ISSN/ISBN:		1469-8137 (Electronic) 0028-646X (Linking)
Abstract:		"Plants often protect themselves from their own bioactive defense metabolites by storing them in less active forms. Consequently, plants also need systems allowing correct spatiotemporal reactivation of such metabolites, for instance under pathogen or herbivore attack. Via co-expression analysis with public transcriptomes, we determined that the model legume Medicago truncatula has evolved a two-component system composed of a beta-glucosidase, denominated G1, and triterpene saponins, which are physically separated from each other in intact cells. G1 expression is root-specific, stress-inducible, and coregulated with that of the genes encoding the triterpene saponin biosynthetic enzymes. However, the G1 protein is stored in the nucleolus and is released and united with its typically vacuolar-stored substrates only upon tissue damage, partly mediated by the surfactant action of the saponins themselves. Subsequently, enzymatic removal of carbohydrate groups from the saponins creates a pool of metabolites with an increased broad-spectrum antimicrobial activity. The evolution of this defense system benefited from both the intrinsic condensation abilities of the enzyme and the bioactivity properties of its substrates. We dub this two-component system the saponin bomb, in analogy with the mustard oil and cyanide bombs, commonly used to describe the renowned beta-glucosidase-dependent defense systems for glucosinolates and cyanogenic glucosides"
Keywords:		*Triterpenes/metabolism *Medicago truncatula/genetics *Saponins/chemistry beta-Glucosidase/metabolism Medicago truncatula bioactive triterpenes jasmonate liquid-liquid phase plant defense saponins specialized metabolism beta-glucosidase;
Notes:		"MedlineLacchini, Elia Erffelinck, Marie-Laure Mertens, Jan Marcou, Shirley Molina-Hidalgo, Francisco Javier Tzfadia, Oren Venegas-Molina, Jhon Cardenas, Pablo D Pollier, Jacob Tava, Aldo Bak, Soren Hofte, Monica Goossens, Alain eng Research Support, Non-U.S. Gov't England 2023/01/24 New Phytol. 2023 Jul; 239(2):705-719. doi: 10.1111/nph.18763. Epub 2023 Mar 12"