Condensed tannins are wide-spread polyphenols with diverse ecological functions, including defense against herbivores and microbial pathogens. In poplar, condensed tannin synthesis is induced by a variety of biotic and abiotic stresses. The objective of this study was to determine the function of the R2R3 MYB transcription factor MYB115 in the regulation of condensed tannin synthesis. MYB115 was shown to be induced by wounding along with tannin biosynthetic genes and shows sequence similarity to characterized regulators of tannin synthesis in grape and persimmon suggesting that it functions in the regulation of condensed tannin synthesis. To analyze the function of MYB115, transgenic plants overexpressing MYB115 were generated and showed enhanced accumulation of condensed tannins and higher expression of flavonoid biosynthetic genes involved in condensed tannin biosynthesis compared to wild-type control plants. In promoter activation assays, MYB115 activated the promoter of a tannin-specific biosynthetic enzyme, anthocyanidin reductase. This suggests that MYB115 acts as a regulator of condensed tannin synthesis. MYB115 overexpressors showed additional changes to phenolic metabolism, including changes in levels of phenolic glycosides and hydroxycinnamic acids. These results indicate an important role of MYB115 in the regulation of the condensed tannin pathway in poplar. / Graduate / 0817 / 0307 / 0487 / frankla@uvic.ca