Downregulation of cinnamoyl-coenzyme A reductase in poplar: multiple-level phenotyping reveals effects on cell wall polymer metabolism and structure.
Cinnamoyl-CoA reductase (CCR) catalyzes the penultimate step in monolignol biosynthesis. We show that downregulation of CCR in transgenic poplar (Populus tremula x Populus alba) was associated with up to 50% reduced lignin content and an orange-brown, often patchy, coloration of the outer xylem. Thioacidolysis, nuclear magnetic resonance (NMR), immunocytochemistry of lignin epitopes, and oligolignol profiling indicated that lignin was relatively more reduced in syringyl than in guaiacyl units. The cohesion of the walls was affected, particularly at sites that are generally richer in syringyl units in wild-type poplar. Ferulic acid was incorporated into the lignin via ether bonds, as evidenced independently by thioacidolysis and by NMR. A synthetic lignin incorporating ferulic acid had a red-brown coloration, suggesting that the xylem coloration was due to the presence of ferulic acid during lignification. Elevated ferulic acid levels were also observed in the form of esters. Transcript and metabolite profiling were used as comprehensive phenotyping tools to investigate how CCR downregulation impacted metabolism and the biosynthesis of other cell wall polymers. Both methods suggested reduced biosynthesis and increased breakdown or remodeling of noncellulosic cell wall polymers, which was further supported by Fourier transform infrared spectroscopy and wet chemistry analysis. The reduced levels of lignin and hemicellulose were associated with an increased proportion of cellulose. Furthermore, the transcript and metabolite profiling data pointed toward a stress response induced by the altered cell wall structure. Finally, chemical pulping of wood derived from 5-year-old, field-grown transgenic lines revealed improved pulping characteristics, but growth was affected in all transgenic lines tested.
Leplé
Jean-Charles
JC
Department of Plant Systems Biology, Flanders Institute for Biotechnology, 9052 Gent, Belgium.
Dauwe
Rebecca
R
Morreel
Kris
K
Storme
Véronique
V
Lapierre
Catherine
C
Pollet
Brigitte
B
Naumann
Annette
A
Kang
Kyu-Young
KY
Kim
Hoon
H
Ruel
Katia
K
Lefèbvre
Andrée
A
Joseleau
Jean-Paul
JP
Grima-Pettenati
Jacqueline
J
De Rycke
Riet
R
Andersson-Gunnerås
Sara
S
Erban
Alexander
A
Fehrle
Ines
I
Petit-Conil
Michel
M
Kopka
Joachim
J
Polle
Andrea
A
Messens
Eric
E
Sundberg
Björn
B
Mansfield
Shawn D
SD
Ralph
John
J
Pilate
Gilles
G
Boerjan
Wout
W
D000445:Aldehyde Oxidoreductases / Q000235:genetics*; D002241:Carbohydrates; D002473:Cell Wall / Q000737:chemistry* / Q000648:ultrastructure; D002851:Chromatography, High Pressure Liquid; D015536:Down-Regulation / Q000235:genetics*; D005453:Fluorescence; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D007150:Immunohistochemistry; D008031:Lignin / Q000737:chemistry* / Q000378:metabolism*; D010636:Phenols / Q000032:analysis; D010641:Phenotype; D030821:Plants, Genetically Modified; D032107:Populus / Q000166:cytology / Q000201:enzymology* / Q000235:genetics* / Q000648:ultrastructure; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D052584:Xylem / Q000166:cytology / Q000254:growth & development / Q000648:ultrastructure
D002241:Carbohydrates; D010636:Phenols; D008031:Lignin; D000445:Aldehyde Oxidoreductases; C019904:cinnamoyl CoA reductase