Flavanone-3-Hydroxylase Plays an Important Role in the Biosynthesis of Spruce Phenolic Defenses Against Bark Beetles and Their Fungal Associates

Abstract

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.

Localization of (+)-Catechin in Picea abies Phloem: Responses to Wounding and Fungal Inoculation

“…[31,34]. Additionally, in vitro studies indicate that stilbene glucosides inhibit the fungal growth of E. polonica [52,55,56]. This supports the idea that (+)-catechin has an important role in conifer defense against fungal pathogens.…”

Phytochemical Shift from Condensed Tannins to Flavonoids in Transgenic Betula pendula Decreases Consumption and Growth but Improves Growth Efficiency of Epirrita autumnata Larvae

“…Molecular-genetic methods for up-or downregulation of gene expression in plants provide numerous opportunities for exp er i m en t al m an i p u l a t i on of p l a n t bi o ch e m i s t r y (Hammerbacher et al 2019;Tian et al 2015), but also for investigating the effects of specific plant compounds on feeding behavior and performance of associated herbivores (Kosonen et al 2012;Müller et al 2015;Sasse et al 2016). In our study, inhibition of DFR and ANR activity altered the chemo-and phenotype of young B. pendula.…”

Accumulation of Catechin and Proanthocyanidins in Black Poplar Stems After Infection by Plectosphaerella populi: Hormonal Regulation, Biosynthesis and Antifungal Activity

“…In previous work, leaf infection by the rust fungus, M. larici-populina , also resulted in the accumulation of flavan-3-ols which reached a maximum level during the sporulation phase of the fungus (Ullah et al, 2017). Other studies have also shown that catechin and PAs accumulate in tree stems upon pathogen infection as anti-microbial defenses (Barry et al, 2002; Danielsson et al, 2011; Hammerbacher et al, 2019). In agreement, catechin and PAs accumulated densely around the point of inoculation in the bark and cambium tissues of P. populi -infected poplar stems compared to the adjacent stem internodes.…”