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The aim of this study was to determine how the mulberry (<i>Morus notabilis</i>) polyphenol oxidase 1 gene (<i>MnPPO1</i>) is regulated during plant stress responses by exploring the interaction between its promoter region and regulatory transcription factors. First, we analyzed the <i>cis</i>-acting elements in the <i>MnPPO1</i> promoter. Then, we used the <i>MnPPO1</i> promoter region [(1268 bp, including an MYB3R-binding <i>cis</i>-element (MSA)] as a probe to capture proteins in DNA pull-down assays. These analyses revealed that the MYB3R1 transcription factor in <i>M. notabilis</i> (encoded by <i>MnMYB3R1</i>) binds to the <i>MnPPO1</i> promoter region. We further explored the interaction between the <i>MnPPO1</i> promoter and MYB3R1 with the dual luciferase reporter, yeast one-hybrid, and chromatin immunoprecipitation assays. These analyses verified that MnMYB3R1 binds to the MSA in the <i>MnPPO1</i> promoter region. The overexpression of <i>MnMYB3R1</i> in tobacco upregulated the expression of the tobacco <i>PPO</i> gene. This observation as well as the quantitative real-time PCR results implied that <i>MnMYB3R1</i> and <i>PPO</i> are involved in the abscisic acid-responsive stress response pathway.