Plant Science 145 (1999) 51–65 Review Lignin genetic engineering revisited Jacqueline Grima-Pettenati *, Deborah Goffner UMR CNRS /UPS 5546, Po ˆle de Biotechnologie Ve ´ge ´tale, 24 Chemin de Borde Rouge, BP 17, Auzeille, 31 326 Castanet Tolosan, France Received 6 January 1999; received in revised form 24 March 1999; accepted 26 March 1999 Abstract In the last decade our understanding of lignin biosynthesis has rapidly progressed. In many cases, the genetic manipulation of genes encoding enzymes of the conventional lignin pathway has generated unexpected results which have led the scientific community to re-evaluate lignin biosynthesis. The analysis of transgenics and mutants have demonstrated that genetically modified lignins may possess significant advantages over and above traditional raw materials currently used in the pulp and paper industry. In order to further ‘fine-tune’ lignin profiles in economically important plant species in a rational manner, new biotechnological strategies including the genetic manipulation of more than one gene simultaneously, and the use of xylem-specific promoters must be employed. The identification of novel target genes by molecular and genetic approaches will also be instrumental in opening up new avenues of lignin research in the future. © 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Lignins; Cell wall; Genetic engineering; Phenylpropanoid metabolism; Transcription factors; Mutants www.elsevier.com/locate/plantsci 1. Introduction The cell wall has a major impact on the utiliza- tion of plants by mankind, and has therefore become a major target for genetic engineering. A growing number of biotechnological strategies are being developed to alter cell wall properties in order to improve the yield and quality of commer- cially useful wall-derived products (for review, see Ref. [1]). In this review we will focus on the genetic engineering of lignins, major secondary cell wall components. These aromatic polymers result from the oxidative polymerization of three hy- droxycinnamyl alcohols commonly referred to as monolignols (p -coumaryl, coniferyl, sinapyl alco- hols), that give rise to hydroxyphenyl (H), guaia- cyl (G) and syringyl (S) residues of lignin, respectively (Fig. 1). The occurrence of lignins coincided with the appearance of the vascular system of tra- cheophytes and has undoubtedly been a decisive factor in the successful land colonization by plants. Deposited in certain specialized cells in- cluding xylem tracheary elements and phloem fibers, they cause dramatic variations in cell wall properties, providing increased strength and water impermeability. In addition, lignins can be synthe- sized in response to various environmental factors such as mechanical stress or pathogen attack [2]. Trees synthesize large amounts of lignins needed for structural support and long distance water transport. In woody species, lignins account for 15–36% of the dry weight of wood, this amount being highly species-dependant. They represent the second most abundant organic constituent on earth after cellulose. The lignin content of woody species is an impor- tant trait for the pulp and paper industry. Indeed, lignins which are closely associated with cellulose are usually removed from cellulose by harsh chem- * Corresponding author. Tel. +33-5-62193513; fax: +33-5- 62193502. E-mail address: grima@cict.fr (J. Grima-Pettenati) 0168-9452/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved. PII:S0168-9452(99)00051-5