Physiological and Molecular Plant Pathology 70 (2007) 38–48 Engineering flax with increased flavonoid content and thus Fusarium resistance Katarzyna Lorenc-Kuku"a a , Magdalena Wro´bel-Kwiatkowska a,b , Micha" Starzycki c , Jan Szopa a,d,Ã a Faculty of Biotechnology, Wroclaw University, Przybyszewskiego 63/77, 51-148 Wroclaw, Poland b Madex S.J., Kos´cieleczki 10A, 82-210 Malbork, Poland c Research Division, Plant Breeding and Acclimatization Institute IHAR, Strzeszynska 36, 60-479 Poznan, Poland d Departament of Plant Physiology and Biotechnology, University of Szczecin, Waska 13, 71-415 Szczecin, Poland Accepted 29 May 2007 Abstract Flavonoids are a group of secondary plant metabolites important for plant growth and development, and thus the regulation of their biosynthesis is of special interest. We used a transgenic approach for flavonoid content manipulation. The multigene construct contained the cDNAs for chalcone synthase (CHS), and chalcone isomerase (CHI) and dihydroflavonol reductase (DFR) were prepared. Following flax plants transformation, the levels of the products of the enzyme overproduction were assessed in leaves and seeds. The simultaneous expression of genes resulted in a significant increase in the levels of flavanones, flavones, flavonols and anthocyanins, suggesting those three overproducing enzymes efficiently control the flavonoid route of the phenylpropanoid pathway. The increase in the flavonoid content in the transgenic flax plants might be the reason for observed, enhanced antioxidant capacity of those plants. The increased antioxidative properties of transgenic plants lead to improved resistance to Fusarium, the main pathogen of flax. The changes in phenylpropanoids accumulation in transgenic plants affect cell wall carbohydrate content. Immunochemical studies revealed significant increase in carbohydrates, constituents of pectin and hemicellulose. Since pectins contribute to flax stem retting, the compounds increase might affect fibre production. An increase in pectin and hemicellulose content leads to enhanced disease resistance of those plants. r 2007 Elsevier Ltd. All rights reserved. Keywords: Flax; Flavonoids; Antioxidant capacity; Fusarium; Linum usitatissimum L 1. Introduction Plant phenylpropanoids are a broad and diverse group of low molecular weight secondary metabolites that include flavonoids, phenolic acids, phenols, lignans and tannins. To date, over 9000 flavonoids have been identified and this number is still increasing [1]. The pathway is initiated by the deamination of phenylalanine to cinnamic acid, and the following reactions lead to the formation of hydroxycin- namoyl CoA thioester, which is then the substrate for the branch pathways of flavonoid, lignin monomer, coumarin and simple ester (e.g. chlorogenic acid) synthesis [2]. Flavonoids constitute a class of phenylpropanoid; this metabolic route starts with the synthesis of chalcone in a reaction controlled by chalcone synthase (CHS), goes via flavanone and flavonol (the products of chalcone isomerase (CHI) action) and flavan (the product of dihydroflavonol reductase (DFR) activity) and ends with the synthesis of anthocyanidin and proanthocyanidin. The great diversity of these compounds results also from combinatorial ARTICLE IN PRESS www.elsevier.com/locate/pmpp 0885-5765/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.pmpp.2007.05.005 Abbreviations: CHS, chalcone synthase; CHI, chalcone isomerase; DFR, dihydroflavonol reductase; IC 50 , the antioxidant potential; AAPH, 2, 2 0 -azobis (2-amidinopropane) dihydrochloride; HGA, homo- galacturonan; RG-I, rhamnogalacturonan I Ã Corresponding author. Faculty of Biotechnology, Wroclaw Univer- sity, Przybyszewskiego 63/77, 51-148 Wroclaw, Poland. Tel.: +48 71 3756202; fax: +48 71 3252930. E-mail address: szopa@ibmb.uni.wroc.pl (J. Szopa).