Canadian Forest Service Publications

MYB115 and MYB134 transcription factors regulate proanthocyanidin synthesis and structure. 2017. James, A.M.; Ma, D.; Mellway, R.; Gesell, A.; Yoshida, K.; Walker, V.; Tran, L.; Stewart, D.; Reichelt, M.; Suvanto, J.; Salminen, J.-P.; Gershenzon, J.; Séguin, A.; Constabel, C.P. Plant Physiol. 174: 154-171.

Year: 2017

Issued by: Laurentian Forestry Centre

Catalog ID: 38307

Language: English

Availability: PDF (request by e-mail)

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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 3',5'-hydroxylases and cytochrome b5. Overall, this work provides new insight into the complexity of the gene regulatory network for proanthocyanidin synthesis in poplar.

Plain Language Summary

This study provides new information about the complexity of the regulatory network of genes involved in the synthesis of condensed tannins (proanthocyanidins) in poplar.

The accumulation of condensed tannins in different parts of the tree is regulated by an ensemble of transcription factors that control certain genes involved in this metabolic pathway. These tannins fulfill a variety of ecological functions; for example, they increase resistance to herbivorous insects and play a role in nutrient cycling and litter decomposition. In this study, the researchers identified a second transcription factor, which is a main regulator of the synthetic pathway for condensed tannins.

Due to recent advances in genomics, it is now possible to study all the genetic characteristics of a living organism and to understand how they function.