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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

The Wound-, Pathogen-, and Ultraviolet B-Responsive MYB134 Gene Encodes an R2R3 MYB Transcription Factor That Regulates Proanthocyanidin Synthesis in Poplar^1,[W],[OA]

Centre for Forest Biology and Department of Biology, University of Victoria, Victoria, British Columbia, Canada V8W 3N5 (R.D.M., L.T.T., C.P.C.); and Department of Cell and Systems Biology (M.B.P., M.M.C.) and Centre for the Analysis of Genome Evolution and Function (M.B.P., M.M.C.), University of Toronto, Toronto, Ontario, Canada M5S 3B2

In poplar (Populus spp.), the major defense phenolics produced in leaves are the flavonoid-derived proanthocyanidins (PAs) and the salicin-based phenolic glycosides. Transcriptional activation of PA biosynthetic genes leading to PA accumulation in leaves occurs following herbivore damage and mechanical wounding as well as infection by the fungal biotroph Melampsora medusae. In this study, we have identified a poplar R2R3 MYB transcription factor gene, MYB134, that exhibits close sequence similarity to the Arabidopsis (Arabidopsis thaliana) PA regulator TRANSPARENT TESTA2 and that is coinduced with PA biosynthetic genes following mechanical wounding, M. medusae infection, and exposure to elevated ultraviolet B light. Overexpression of MYB134 in poplar resulted in transcriptional activation of the full PA biosynthetic pathway and a significant plant-wide increase in PA levels, and electrophoretic mobility shift assays showed that recombinant MYB134 protein is able to bind to promoter regions of PA pathway genes. MYB134-overexpressing plants exhibited a concomitant reduction in phenolic glycoside concentrations and other minor alterations to levels of small phenylpropanoid metabolites. Our data provide insight into the regulatory mechanisms controlling stress-induced PA metabolism in poplar, and the identification of a regulator of stress-responsive PA biosynthesis constitutes a valuable tool for manipulating PA metabolism in poplar and investigating the biological functions of PAs in resistance to biotic and abiotic stresses.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: C. Peter Constabel (cpc{at}uvic.ca).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.139071

^* Corresponding author; e-mail cpc{at}uvic.ca.

Received March 27, 2009; accepted April 21, 2009; published April 24, 2009.