MODIFICATION OF LIGNIN BIOSYNTHESIS IN TRANSGENIC NICOTIANA THROUGH EXPRESSION OF AN ANTISENSE O-METHYLTRANSFERASE GENE FROM POPULUS

An aspen lignin-specific O-methyltransferase (bi-OMT; S-adenosyl-L-met hionine: caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase, E C 2.1.1.68) antisense sequence in the form of a synthetic gene contain ing the cauliflower mosaic virus 35S gene sequences for enhancer eleme nts, promoter and terminator was stably integrated into the tobacco ge nome and inherited in transgenic plants with a normal phenotype. Leave s and stems of the transgenes expressed the antisense RNA and the endo genous tobacco bi-OMT mRNA was suppressed in the stems. Bi-OMT activit y of stems was decreased by an average of 29% in the four transgenic p lants analyzed. Chemical analysis of woody tissue of stems for lignin building units indicated a reduced content of syringyl units in most o f the transgenic plants, which corresponds well with the reduced activ ity of bi-OMT. Transgenic plants with a suppressed level of syringyl u nits and a level of guaiacyl units similar to control plants were pres umed to have lignins of distinctly different structure than control pl ants. We concluded that regulation of the level of bi-OMT expression b y an antisense mechanism could be a useful tool for genetically engine ering plants with modified lignin without altering normal growth and d evelopment.