The accumulation of proanthocyanidins is regulated by a complex of transcription factors composed of R2R3 MYB, basic helix-loop-helix, and WD40 proteins that activate the promoters of biosynthetic genes. In poplar (genus Populus), MYB134 is known to regulate proanthocyanidin biosynthesis by activating key flavonoid genes. Here, we characterize a second MYB regulator of proanthocyanidins, MYB115. Transgenic poplar overexpressing MYB115 showed a highproanthocyanidin phenotype and reduced salicinoid accumulation, similar to the effects of MYB134 overexpression. Transcriptomic analysis of MYB115-and MYB134-overexpressing poplar plants identified a set of common up-regulated genes encoding proanthocyanidin biosynthetic enzymes and several novel uncharacterized MYB transcriptional repressors. Transient expression experiments demonstrated the capacity of both MYB134 and MYB115 to activate flavonoid promoters, but only in the presence of a basic helix-loop-helix cofactor. Yeast two-hybrid experiments confirmed the direct interaction of these transcription factors. The unexpected identification of dihydromyricetin in leaf extracts of both MYB115-and MYB134-overexpressing poplar led to the discovery of enhanced flavonoid B-ring hydroxylation and an increased proportion of prodelphinidins in proanthocyanidin of the transgenics. The dramatic hydroxylation phenotype of MYB115 overexpressors is likely due to the up-regulation of both flavonoid 39,59-hydroxylases and cytochrome b 5 . Overall, this work provides new insight into the complexity of the gene regulatory network for proanthocyanidin synthesis in poplar.Proanthocyanidins (PAs), also known as condensed tannins, are widespread polyphenols with diverse ecological functions. They are polymers of flavan-3-ols and, thus, end products of the phenylpropanoid and flavonoid pathways (Dixon et al., 2005). The PAs are the most broadly distributed secondary metabolites and are especially prominent in forest trees and woody plants ( Barbehenn and Constabel, 2011). PA accumulation in trees can be substantial; for example, in some species of poplar (genus Populus), PAs can constitute 25% of leaf dry weight. However, the accumulation of PAs also is highly plastic and varies with genotype and growth conditions (Hwang and Lindroth, 1997;Osier and Lindroth, 2006). In trees, PAs are common constituents of vegetative organs, including roots, leaves, bark, and flowers. Seasonal leaf drop in autumn and turnover of roots thus lead to substantial tannin input into forest soils, where it has been shown to slow litter decomposition and nutrient cycling (Schweitzer et al., 2008). In herbaceous plants, PAs are more restricted in distribution, but they can be found in leaves of legumes, 1 This work was supported by the Natural Sciences and Engineering Research Council of Canada, the Max Planck Society, the Academy of Finland, and the Canadian Genomics R&D Initiative.2 These authors contributed equally to the article. * Address correspondence to cpc@uvic.ca. The author responsible for distribution ...

Worldwide, parasitic gastrointestinal nematodes continue to threaten animal health, welfare, and production in outdoor breeding systems of small ruminants. For more than 50 years, the control of these parasitic worms has relied on the use of commercial synthetic anthelmintics. However, anthelmintic resistance in worm populations is nowadays widespread and requires novel solutions. The use of tannin-rich plants has been suggested as an alternative to synthetic anthelmintics to control gastrointestinal nematodes. The majority of previous studies have focused on the activity of proanthocyanidins (syn condensed tannins), and less is known about ellagitannins. In this study, the effects of 30 structurally unique ellagitannins on the exsheathment of third-stage infective larvae were examined on Haemonchus contortus and Trichostrongylus colubriformis by the in vitro larval exsheathment inhibition assay. Ellagitannins were found to be promising natural anthelmintics as they showed direct inhibition on larval exsheathment for both nematode species. In general, ellagitannins were more efficient at inhibiting the exsheathment of H. contortus larvae than those of T. colubriformis. The efficiency of inhibition increased as the degree of oligomerization or the molecular weight of the ellagitannin increased. Otherwise, we found no other structural features of ellagitannins that significantly affected the anthelmintic activity on the third-stage infective larvae. The effective concentrations were physiologically relevant and should be achievable in the gastrointestinal tract also in in vivo conditions.

Main conclusion The polyphenol profiles of 18 cell cultures from 12 plant species were screened. The detected polyphenol fingerprints were diverse and differed from polyphenol profiles typically found in corresponding plant species. Cell cultures originating from 12 different plant species growing or grown in the Nordic countries were screened for their ability to synthesize polyphenols to assess their suitability for future studies and applications. The focus was on plant families Rosaceae and Ericaceae. On average, the Rosaceae cultures were the most efficient to produce hydrolysable tannins and the Ericaceae cultures were the most efficient to produce proanthocyanidins. This is in line with the general trend of polyphenols found in Rosaceae and Ericaceae leaves and fruits, even though several individual cell cultures differed from natural plants in their polyphenolic composition. Overall, several of the studied cell cultures exhibited capability in producing a large variety of polyphenols, including tannins with a high molecular weight, thus also showing promise for further studies concerning, for example, the accumulation of specific polyphenols or biosynthesis of polyphenols in the cell cultures.

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Berries of common sea-buckthorn (Hippophaë rhamnoides L.) are well-known and used for their bioactive components, and while there is a considerable amount of research on the leaves as well, their ellagitannins (ETs) have not been a prominent focus of research. We identified and quantified ten major hydrophilic polyphenols, all ETs, in H. rhamnoides leaves and compared their abundance between 58 plant individuals. Of these compounds, hippophaenin C was characterized as a new ellagitannin by various spectrometric methods. The total concentrations of ETs ranged from 42.5 mg g dry weight (DW) to 109.1 mg g DW between individual plants. Among the ETs, hippophaenin C, stachyurin, and casuarinin were on average the most abundant compounds. Sexes did not differ significantly, while cultivars showed variation in some ETs. These results suggest that H. rhamnoides leaves could be a potential and rich source of several ETs.