The Effect of Co-Transforming Eucalyptus urophylla Catechol-O-methyltransferase and Caffeoyl-CoA O-methyltransferase on the Biosynthesis of Lignin Monomers in Transgenic Tobacco

Abstract

Here, the regulatory effects of co-transforming catechol-O-methyltransferase (COMT) and ca-ffeoyl‑CoA O-methyltransferase (CCoAOMT) isolated from Eucalyptus urophylla S. T. Blake on the biosynthesis of lignin monomers were investigated using a tobacco as a model system. Tobacco (Nicotiana tabacum L.) plants were separately transformed with sense EuCOMT and full-length interfering RNA of EuCCoAOMT, and co-transformed with both EuCOMT and EuCCoAOMT respectively. The target genes’ expression levels, the lignin, lignin monomer and cellulose contents, and the anatomical structures of the stems in transgenic tobacco lines were determined. The expression of EuCOMT was detected, and a significant inhibition of tobacco’s native CCoAOMT expression was triggered by the full-length interfering RNA of EuCCoAOMT in transgenic tobacco plants. No significant differences were observed in stem diameter at both the 5th and 7th nodes among transgenic and wild type plants, nor in the xylem cell area or cell wall thickness at the 7th node of the stem. Compared with wild-type plants, the changes in the lignin and cellulose contents in transgenic plants were less than 10%. The G-lignin content of the co-transformed transgenic plants decreased by 57.38%, resulting in a 114.94% increase in the S/G ratio. Thus, the suppression of CCoAOMT’s expression substantially inhibited the synthesis of G-lignin, and the optimal directional regulatory effect on the S/G ratio was observed in plants co-regulated by EuCOMT and EuCCoAOMT.