Regulation of Enzymes Involved in Lignin Biosynthesis: Induction of O-Methyltransferase mRNAs During the Hypersensitive Reaction of Tobacco to Tobacco Mosaic Virus. Estelle Jaeck. Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, 67000 Strasbourg, France. Bernard Dumas(1), Pierrette Geoffroy(1), Noëlle Favet(1), Dirk Inzé(2), Marc Van Montagu(2), Bernard Fritig(1), and Michel Legrand(1). (1)Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, 67000 Strasbourg, France; (2)Laboratorium voor Genetica, Rijksuniversiteit Gent, K. Ledeganckstraat 35, B9000 Gent, Belgium.. MPMI 5:294-300. Accepted 13 March 1992. Copyright 1992 The American Phytopathological Society.

The mRNAs encoding orthodiphenol-O-methyltransferases (OMTs; EC 2.1.1.6), which are involved in the biosynthesis of lignin precursors, are highly induced in tobacco leaves during the hypersensitive reaction to tobacco mosaic virus (TMV). OMT messengers were fractionated on a sucrose gradient and translated in vitro. Protein A-Sepharose columns adsorbed with specific antisera raised against purified OMTs were used to select translation products, and the translatable activity of OMT mRNA was measured at different stages of infection. Oligonucleotides derived from peptide sequences of purified OMT I were used to prime polymerase chain reactions; total RNA was used as template to allow the isolation of an OMT I clone. RNA blots, hybridized with the OMT I probe, revealed a unique messenger of 1.7 kb. The kinetics of accumulation of OMT I mRNAs during the hypersensitive reaction to TMV parallels the kinetics of translation and suggests that an increase in mRNA controls the increase in the rate of enzyme synthesis. In healthy plants, RNA blot hybridization showed that the steady-state level of OMT I mRNA is very high in vascular tissue compared to the level measured in leaves.