Plant Physiol, December 2002, Vol. 130, pp. 1675-1685

Down-Regulation of Caffeic Acid O-Methyltransferase in Maize Revisited Using a Transgenic Approach¹

Signaux et Messages Cellulaires chez les Végétaux, Unité Mixte de Recherche, Centre National de la Recherche Scientifique-Université Paul Sabatier 5546, Pôle de Biotechnologie Végétale, 24 Chemin de Borde Rouge, 31326 Castanet Tolosan, France (J.P., S.C., A.J., C.D., A.-M.B., D.G., M.P.); Génétique et Amélioration des Plantes, Institut National de la Recherche Agronomique, Domaine de Crouelle, 234 Avenue du Brezet, 63039 Clermont-Ferrand, France (I.N., M.B.); Unité de Génétique et d'Amélioration des Plantes Fourragères, Institut National de la Recherche Agronomique, Route de Saintes, 86600 Lusignan, France (Y.B.); Laboratoire de Chimie Biologique, Institut National Agronomique, F-78850 Thivernal-Grignon, France (I.M., C.L.); and Departament de Genetica Molecular, Institut de Biologia Molecular de Barcelona, Centre d'Investigació i Desenvolupament-Consejo Superior de Investigaciones Científicas, Jordi Girona, 18-08034 Barcelona, Spain (J.R., P.P.)

Transgenic maize (Zea mays) plants were generated with a construct harboring a maize caffeic acid O-methyltransferase (COMT) cDNA in the antisense (AS) orientation under the control of the maize Adh1 (alcohol dehydrogenase) promoter. Adh1-driven -glucuronidase expression was localized in vascular tissues and lignifying sclerenchyma, indicating its suitability in transgenic experiments aimed at modifying lignin content and composition. One line of AS plants, COMT-AS, displayed a significant reduction in COMT activity (15%-30% residual activity) and barely detectable amounts of COMT protein as determined by western-blot analysis. In this line, transgenes were shown to be stably integrated in the genome and transmitted to the progeny. Biochemical analysis of COMT-AS showed: (a) a strong decrease in Klason lignin content at the flowering stage, (b) a decrease in syringyl units, (c) a lower p-coumaric acid content, and (d) the occurrence of unusual 5-OH guaiacyl units. These results are reminiscent of some characteristics already observed for the maize bm3 (brown-midrib3) mutant, as well as for COMT down-regulated dicots. However, as compared with bm3, COMT down-regulation in the COMT-AS line is less severe in that it is restricted to sclerenchyma cells. To our knowledge, this is the first time that an AS strategy has been applied to modify lignin biosynthesis in a grass species.