title: Molecular phenotyping of lignin-modified tobacco reveals associated changes in cell-wall metabolism, primary metabolism, stress metabolism and photorespiration.
abstract: 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.
authors.affiliation: Department of Plant Systems Biology, Flanders Institute for Biotechnology, Technologiepark 927, 9052 Gent, Belgium.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Dauwe
authors.forename: Kris
authors.initials: K
authors.lastname: Morreel
authors.forename: Geert
authors.initials: G
authors.lastname: Goeminne
authors.forename: Birgit
authors.initials: B
authors.lastname: Gielen
authors.forename: Antje
authors.initials: A
authors.lastname: Rohde
authors.forename: Jos
authors.initials: J
authors.lastname: Van Beeumen
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Alain-Michel
authors.initials: AM
authors.lastname: Boudet
authors.forename: Joachim
authors.initials: J
authors.lastname: Kopka
authors.forename: Soizic F
authors.initials: SF
authors.lastname: Rochange
authors.forename: Claire
authors.initials: C
authors.lastname: Halpin
authors.forename: Eric
authors.initials: E
authors.lastname: Messens
authors.forename: Wout
authors.initials: W
authors.lastname: Boerjan
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism; D054458:Amplified Fragment Length Polymorphism Analysis; D019069:Cell Respiration; D002473:Cell Wall / Q000378:metabolism*; D002734:Chlorophyll; D016207:Cytokines; D018076:DNA, Complementary; D018744:DNA, Plant; D005453:Fluorescence; D020869:Gene Expression Profiling; D047908:Intracellular Signaling Peptides and Proteins; D008031:Lignin / Q000378:metabolism*; D010101:Oxygen Consumption; D010641:Phenotype; D010777:Photochemistry; D010788:Photosynthesis; D011134:Polysaccharides / Q000378:metabolism; D013213:Starch / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D016207:Cytokines; D018076:DNA, Complementary; D018744:DNA, Plant; C504459:FILIP1L protein, human; D047908:Intracellular Signaling Peptides and Proteins; D011134:Polysaccharides; D002734:Chlorophyll; C007916:hemicellulose; D013213:Starch; D008031:Lignin; D000429:Alcohol Oxidoreductases; C018656:cinnamyl alcohol dehydrogenase; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase