Ectopic expression of an antisense BpCCoAOMT gene from Betula platyphylla Suk. affects growth and development of tobacco due to lignin content reduction

摘要

Lignin is an aromatic polymer and macromolecular organic material and is one of the major components of plant cellular walls. It provides mechanical support for plants and protection against pathogen invasion. Caffeoyl-CoA O-methyltransferase (CCoAOMT) is recognized to be involved in phenylpropanoid metabolism and lignin synthesis, and plays an important role in precursor synthesis of G-lignin units. In this study, a gene encoding CCoAOMT (Genbank ID: AY860952) was isolated from birch (Betula platyphylla Suk.). The predicted BpCCoAOMT polypeptide had high affinity with CCoAOMT from other species. Real-time quantitative polymerase chain reaction (RT-qPCR) results revealed that BpCCoAOMT is most highly expressed in young stems. To study its function in vivo, antisense BpCCoAOMT complementary deoxyribonucleic acid (cDNA) was transformed into tobacco (SR-1) by the Agrobacterium tumefaciens-mediated method. The expression of NtCCoOAMT in antisense BpCCoAOMT transgenic tobacco was down-regulated and total lignin content of transgenic plants decreased by 39% compared to control plants. Maule reagent was used to distinguish lilac lignin and guaiac wood lignin in situ, which enables S-lignin to exhibit a specific red response. Results revealed that all transgenic tobacco plants were dark brown, while controls were dark red. This indicated that S-lignin content in the xylem was reduced. Compared to wild-type (WT) plants, transgenic tobacco plants had delayed flowering and some had slender stems, curling, and easy lodging. This indicates that the decrease in lignin content interferes with the normal growth of plants.