The Effect of Co-Transforming Eucalyptus urophylla Catechol-O-methyltransferase and Caffeoyl-CoA O-methyltransferase on
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The Effect of Co-Transforming Eucalyptus urophylla Catechol-O-methyltransferase and Caffeoyl-CoA O-methyltransferase on the Biosynthesis of Lignin Monomers in Transgenic Tobacco Y. Xiaoa, J. Lia, H. Liua, Y. Zhanga, X. Zhanga, Z. Qina, and B. Chena,* a
Guangxi Key Laboratory of Superior Timber Trees Resource Cultivation, Guangxi Forestry Research Institute, Nanning, 530002 China *e-mail: [email protected] Received June 3, 2019; revised December 17, 2019; accepted January 30, 2020
Abstract—Here, the regulatory effects of co-transforming catechol-O-methyltransferase (COMT) and caffeoyl-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. Keywords: Nicotiana tabacum, Eucalyptus urophylla, co-transformation, lignin monomer synthesis, directional regulation, tobacco transformation DOI: 10.1134/S1021443720050180
INTRODUCTION Eucalyptus is a general term for plant species in Angophora, Corymbia and Eucalyptus genera of the Myrtaceae family, which originated in Australia. Since its introduction to south China in 1970, it has gradually become an important afforestation tree species in artificial timber forests [1]. Eucalyptus urophylla clone GLU4 has become the ultimate choice for pulpwood afforestation, because its pulping indicators, such as cellulose content and cellulose length, are significantly better than those of other Eucalyptus varieties. Recently, with the further development of Eucalyptus breeding, applying genetic engineering technology to improve wood quality and increase economic benefits Abbreviations: COMT—catechol-O-methyltransferase; CCoAOMT—caffeoyl-CoA O-methyltransferase; CCR—cinnamoyl-Coenzyme A reductase; F5H—ferulate-5 hydroxylase; G-lig
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