Plant Physiol, May 2001, Vol. 126, pp. 145-155

Simultaneous Down-Regulation of Caffeic/5-Hydroxy Ferulic Acid-O-Methyltransferase I and Cinnamoyl-Coenzyme A Reductase in the Progeny from a Cross between Tobacco Lines Homozygous for Each Transgene. Consequences for Plant Development and Lignin Synthesis¹

Institut de Biologie Moléculaire des Plantes du Centre National de la Recherche Scientifique, Université Louis Pasteur, 67084 Strasbourg cedex, France (G.P., M.L.); Pôle de Biotechnologies Végétales, Centre National de la Recherche Scientifique-Université Paul Sabatier, 31326 Castanet-Tolosan, France (M.C., A.B.); Laboratoire de Chimie Biologique, Institut National Agronomique, 78850 Thiverval-Grignon, France (C.L., B.P.); and Centre de Recherche sur les Macromolécules Végétales du Centre National de la Recherche Scientifique, 38041 Grenoble cedex 9, France (K.R., J.-P.J.)

Inhibition of specific lignin biosynthetic steps by antisense strategy has previously been shown to alter lignin content and/or structure. In this work, homozygous tobacco (Nicotiana tabacum) lines transformed with cinnamoyl-coenzyme A reductase (CCR) or caffeic acid/5-hydroxy ferulic acid-O-methyltransferase I (COMT I) antisense sequences have been crossed and enzyme activities, lignin synthesis, and cell wall structure of the progeny have been analyzed. In single transformed parents, CCR inhibition did not affect COMT I expression, whereas marked increases in CCR activity were observed in COMT I antisense plants, suggesting potential cross talk between some genes of the pathway. In the progeny, both CCR and COMT I activities were shown to be markedly decreased due to the simultaneous repression of the two genes. In these double transformants, the lignin profiles were dependent on the relative extent of down-regulation of each individual enzyme. For the siblings issued from a strongly repressed antisense CCR parent, the lignin patterns mimicked the patterns obtained in single transformants with a reduced CCR activity. In contrast, the specific lignin profile of COMT I repression could not be detected in double transformed siblings. By transmission electron microscopy some cell wall loosening was detected in the antisense CCR parent but not in the antisense COMT I parent. In double transformants, immunolabeling of non-condensed guaiacyl-syringyl units was weaker and revealed changes in epitope distribution that specifically affected vessels. Our results more widely highlight the impact of culture conditions on phenotypes and gene expression of transformed plants.