Increasing Lignin Accumulation in Arabidopsis and Poplar by Overexpressing a CCoAOMT Gene from the Dove Tree (Davidia involucrata Baill.)

Rapid lignification and high lignin accumulation occur in the endocarps of the dove tree (Davidia involucrata) during a short developmental phase. Through transcriptome analysis, we identified a gene named DiCCoAOMT1 that plays a vital role in the rapid lignification process. The expression profile of the DiCCoAOMT1 gene was endocarp-specific, and its encoding product showed strong O-methyltransferase activity in vitro. Here, we overexpressed the DiCCoAOMT1 gene in both Arabidopsis and poplar (Populus tomentosa) to verify its function of lignin biosynthesis and accumulation. Increased plant height and lengthened pods arose in transgenic Arabidopsis lines, while elongated petioles were observed in transgenic poplar lines. Moreover, the stems exhibited enlarged xylem area, reduced pith area, and more compact cell architecture in both transgenic Arabidopsis and poplar lines. The lignin content was elevated by 26% and 20% on average in the stems of transgenic Arabidopsis and poplar lines, respectively. Furthermore, the lignin composition was altered in the transgenic lines indicated by the elevated S/G ratio. Taken together, we proposed that overexpressing the DiCCoAOMT1 gene can effectively increase lignin biosynthesis and change lignin monomer composition in both herb and woody plants. The endocarp-specific expression pattern of the DiCCoAOMT1 gene is assumed to be a key point to form the highly lignified structure in a short period, thus causing the long-period dormancy of Davidia seeds.