Rapid lignification occurring in the endocarp of dove tree results in the formation of a rigid and compact structure, which seriously hinders seed germination. A gene named DiCCoAOMT1, which encodes a hyperactive O-methyltransferase, was identified and thought to play a critical role in the process of endocarp lignification. In this study, the DiCCoAOMT1 gene was introduced into A. thaliana and poplar, respectively, to further verify its function. The lignin content was increased by 45% and 20% in the stems of transgenic A. thaliana and poplar lines, respectively. There was a positive correlation between the expression levels of DiCCoAOMT1 and lignin amount in transgenic lines. Furthermore, the shifts of lignin composition was indicated by the elevated S/G ratio in transgenic poplar lines. Lignin accumulation was promoted specifically in the phloem cells, and the cells in secondary xylem was thickened in transgenic plants. In addition, lengthened pods and elevated plant height, and elongated petioles and internodes were observed in transgenic A. thaliana and poplar lines, respectively. Taken together, our data indicated that an endocarp-specific DiCCoAOMT1 gene could effectively increase lignin accumulation and alter lignin composition in both herbs and woody plants, which provides new insights to understand the regulatory mechanism of lignin biosynthesis and the biological significance of lignification in specific tissues.