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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

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

Almuth Hammerbacher, Bettina Raguschke, Louwrance P Wright, Jonathan Gershenzon

Phytochemistry. 2018 Apr;148:78-86.

PMID: 29421514

Abstract:

One 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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP3371275	(−)-Gallocatechin		3371-27-5	Price

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