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Front. Plant Sci. | doi: 10.3389/fpls.2019.00208

Flavanone-3-hydroxylase plays an important role in the biosynthesis of spruce phenolic defenses against bark beetles and their fungal associates

  • 1University of Pretoria, South Africa
  • 2Max Planck Institute for Chemical Ecology, Germany

Conifer forests worldwide are becoming increasingly vulnerable to attacks by bark beetles and their fungal associates due to the effects of global warming. Attack by the bark beetle Ips typographus and the blue-stain fungus it vectors (Endoconidiophora polonica) on Norway spruce (Picea abies) is well known to induce increased production of terpene oleoresin and polyphenolic compounds. However, it is not clear whether specific compounds are important in resisting attack. In this study, we observed a significant increase in dihydroflavonol and flavan-3-ol content after inoculating Norway spruce with the bark beetle vectored fungus. A bioassay revealed that the dihydroflavonol taxifolin and the flavan-3-ol catechin negatively affected both I. typographus and E. polonica. The biosynthesis of flavan-3-ols is well studied in Norway spruce, but little is known about dihydroflavonol formation in this species. A flavanone-3-hydroxylase (F3H) was identified that catalyzed the conversion of eriodictyol to taxifolin and was highly expressed after E. polonica infection. Down-regulating F3H gene expression by RNA interference in transgenic Norway spruce resulted in significantly lower levels of both dihydroflavonols and flavan-3-ols. Therefore F3H plays a key role in the biosynthesis of defense compounds in Norway spruce that act against the bark beetle-fungus complex. This enzyme forms a defensive product, taxifolin, which is also a metabolic precursor of another defensive product, catechin, which in turn synergizes the toxicity of taxifolin to the bark beetle associated fungus.

Keywords: Taxifolin, Catechin, F3H, Flavonoids, Picea abies, Endoconidiophora polonica, Ips typhographus

Received: 03 Sep 2018; Accepted: 07 Feb 2019.

Edited by:

Bartosz Adamczyk, Natural Resources Institute Finland (Luke), Finland

Reviewed by:

Elizabeth H. Neilson, University of Copenhagen, Denmark
Françoise MARTZ, Natural Resources Institute Finland (Luke), Finland  

Copyright: © 2019 Hammerbacher, Kandasamy, Ullah, Schmidt, Wright and Gershenzon. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Almuth Hammerbacher, University of Pretoria, Pretoria, South Africa, almuth.hammerbacher@fabi.up.ac.za