Leple JC, Dauwe R, Morreel K, Storme V, Lapierre C, Pollet B, Naumann A, Kang KY, Kim H, Ruel K, Lefebvre A, Joseleau JP, Grima-Pettenati J, De Rycke R, Andersson-Gunnerås S, Erban A, Fehrle I, Petit-Conil M, Kopka J, Polle A, Messens E, Sundberg B, Mansfield SD, Ralph J, Pilate G, Boerjan W.
Downregulation of cinnamoyl-coenzyme A reductase in poplar: multiple-level phenotyping reveals effects on cell wall polymer metabolism and structure
The Plant Cell: 2007 19:3669-3691

Cinnamoyl-CoA reductase (CCR) catalyzes the penultimate stepin monolignol biosynthesis. We show that downregulation of CCRin transgenic poplar (Populus tremula x Populus alba) was associatedwith up to 50% reduced lignin content and an orange-brown, oftenpatchy, coloration of the outer xylem. Thioacidolysis, nuclearmagnetic resonance (NMR), immunocytochemistry of lignin epitopes,and oligolignol profiling indicated that lignin was relativelymore reduced in syringyl than in guaiacyl units. The cohesionof the walls was affected, particularly at sites that are generallyricher in syringyl units in wild-type poplar. Ferulic acid wasincorporated into the lignin via ether bonds, as evidenced independentlyby thioacidolysis and by NMR. A synthetic lignin incorporatingferulic acid had a red-brown coloration, suggesting that thexylem coloration was due to the presence of ferulic acid duringlignification. Elevated ferulic acid levels were also observedin the form of esters. Transcript and metabolite profiling wereused as comprehensive phenotyping tools to investigate how CCRdownregulation impacted metabolism and the biosynthesis of othercell wall polymers. Both methods suggested reduced biosynthesisand increased breakdown or remodeling of noncellulosic cellwall polymers, which was further supported by Fourier transforminfrared spectroscopy and wet chemistry analysis. The reducedlevels of lignin and hemicellulose were associated with an increasedproportion of cellulose. Furthermore, the transcript and metaboliteprofiling data pointed toward a stress response induced by thealtered cell wall structure. Finally, chemical pulping of woodderived from 5-year-old, field-grown transgenic lines revealedimproved pulping characteristics, but growth was affected inall transgenic lines tested.

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