Expression and molecular characterization of ZmMYB-IF35 and related R2R3-MYB transcription factors

R2R3-MYB transcription factors play many important roles in higher plants including the regulation of secondary metabolism, the control of cell shape, and in the response to various stress conditions. In spite of their large number and significance, very few of these genes have been functionally characterized in monocots. Here, we describe the characterization of ZmMYB-IF35 from maize. Using GAL4 fusion constructs, we show that ZmMYB-IF35 possesses the ability to bind DNA in a sequence specific manner and activate transcription in yeast. We also show that ZmMYB-IF35 is capable of binding to the a1 promoter in planta, but it is not sufficient for activation of a1 transcription. Interestingly, a chimeric protein consisting of the MYB domain from ZmMYB-IF35 and the non-MYB C-terminal region of PI, a closely related R2R3-MYB protein, activated transcription from the a1 promoter in planta, suggesting that regions outside the conserved R2R3-MYB domain contribute to regulatory specificity. In situ hybridization experiments demonstrate that ZmMYB-IF35 expresses primarily in epidermal and vascular cells, while its rice ortholog, OsMYB-IF, displays a broad expression pattern in aerial parts of the plant. Together, our results provide novel insights on the participation of ZmMYB-IF35 and related genes in the regulation of secondary metabolic pathways in the grasses.