Hammerbacher, AlmuthRaguschke, BettinaWright, Louwrance P.Gershenzon, Jonathan2018-03-292018-04Hammerbacher, A., Raguschke, B., Wright, L.P. & Gershenzon, J. 2018, 'Gallocatechin biosynthesis via a flavonoid 3′,5′-hydroxylase is a defense response in Norway spruce against infection by the bark beetle-associated sap-staining fungus Endoconidiophora polonica', Phytochemistry, vol. 148, pp. 78-86.0031-9422 (print)1873-3700 (online)10.1016/j.phytochem.2018.01.017http://hdl.handle.net/2263/64351One of the best-studied defense responses to fungal infection in Norway spruce (Picea abies) is the biosynthesis of flavan-3-ols, which accumulate as monomers or polymers known as proanthocyanidins. The individual flavan-3-ol units consist of compounds with a 3′,4′-dihydroxylated B ring [2,3-(trans)-(+)-catechin or 2,3-(cis)-(−)-epicatechin] and compounds with a 3′,4′,5′-trihydroxylated B ring [2,3 (trans)-(+)-gallocatechin or 2,3-(cis)-(−)-epigallocatechin]. While much is known about the biosynthesis and biological activity of catechin in Norway spruce, there is little comparable information about gallocatechin or epigallocatechin. We found that there was a significant increase in the gallocatechin content of Norway spruce bark and wood after inoculation with the bark beetle-associated sap-staining fungus Endoconidiophora polonica. Gallocatechins increased proportionally more than catechins as both monomers and units of polymers. A flavonoid 3′,5′-hydroxylase gene identified in Norway spruce was shown by heterologous expression in Nicotiana benthamiana to be involved in the conversion of 2,3 (trans)-(+)-catechin to 2,3 (trans)-(+)-gallocatechin. The formation of the trihydroxylated B ring in Norway spruce occurs at the level of flavan-3-ols, rather than at the level of dihydroflavonols as in many angiosperms. The transcript abundance of the flavonoid 3′,5′-hydroxylase gene also increased significantly during fungal infection underlining its importance in gallocatechin biosynthesis. Comparisons of the effect of 2,3 (trans)-(+)-catechin and 2,3 (trans)-(+)-gallocatechin on fungal growth revealed that 2,3 (trans)-(+)-catechin is a stronger inhibitor of fungal growth, while 2,3 (trans)-(+)-gallocatechin is a stronger inhibitor of melanin biosynthesis.en© 2018 Elsevier Ltd.. All rights reserved. Notice : this is the author’s version of a work that was accepted for publication in Physiology and Behavior. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. A definitive version was subsequently published in Physiology and Behavior, vol. 148, pp. 78-86, 2018. doi : 10.1016/j.phytochem.2018.01.017.Anti-fungal defenseBlue-stain fungusEndoconidiophora polonicaGallocatechinFlavonoid 3′,5′-hydroxylaseNorway sprucePicea abiesPostprint Article