Molecular phenotyping of lignin-modified tobacco reveals associated changes in cell-wall metabolism, primary metabolism, stress metabolism and photorespiration
Lignin is an important component of secondarily thickened cell walls. Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) are two key enzymes that catalyse the penultimate and last steps in the biosynthesis of the monolignols. Downregulation of CCR in tobacco (Nicotiana tabacum) has been shown to reduce lignin content, whereas lignin in tobacco downregulated for CAD incorporates more aldehydes. We show that altering the expression of either or both genes in tobacco has far-reaching consequences on the transcriptome and metabolome. cDNA-amplified fragment length polymorphism-based transcript profiling, combined with HPLC and GC–MS-based metabolite profiling, revealed differential transcripts and metabolites within monolignol biosynthesis, as well as a substantial network of interactions between monolignol and other metabolic pathways. In general, in all transgenic lines, the phenylpropanoid biosynthetic pathway was downregulated, whereas starch mobilization was upregulated. CCR-downregulated lines were characterized by changes at the level of detoxification and carbohydrate metabolism, whereas the molecular phenotype of CAD-downregulated tobacco was enriched in transcript of light- and cell-wall-related genes. In addition, the transcript and metabolite data suggested photo-oxidative stress and increased photorespiration, mainly in the CCR-downregulated lines. These predicted effects on the photosynthetic apparatus were subsequently confirmed physiologically by fluorescence and gas-exchange measurements. Our data provide a molecular picture of a plant’s response to altered monolignol biosynthesis.
Document Type: Research Article
Affiliations: 1: Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium, 2: Department of Biochemistry, Physiology and Microbiology, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium, 3: US Dairy Forage Research Center, USDA–Agricultural Research Service and Department of Biological Systems Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706-1108, USA, 4: Max-Planck Institute of Molecular Plant Physiology, Cooperative Research Group, Am Mühlenberg 1, 14476 Golm, Germany 5: University of Dundee, Plant Research Unit at the Scottish Research Institute, Invergowrie, Dundee DD2 5DA, UK
Publication date: October 1, 2007