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Different routes for conifer- and sinapaldehyde and higher saccharification upon deficiency in the dehydrogenase CAD1

(2017) PLANT PHYSIOLOGY. 175(3). p.1018-1039
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Biotechnology for a sustainable economy (Bio-Economy)
Abstract
In the search for renewable energy sources, genetic engineering is a promising strategy to improve plant cell wall composition for biofuel and bioproducts generation. Lignin is a major factor determining saccharification efficiency and, therefore, is a prime target to engineer. Here, lignin content and composition were modified in poplar (Populus tremula 3 Populus alba) by specifically down-regulating CINNAMYL ALCOHOL DEHYDROGENASE1 (CAD1) by a hairpin-RNA-mediated silencing approach, which resulted in only 5% residual CAD1 transcript abundance. These transgenic lines showed no biomass penalty despite a 10% reduction in Klason lignin content and severe shifts in lignin composition. Nuclear magnetic resonance spectroscopy and thioacidolysis revealed a strong increase (up to 20-fold) in sinapaldehyde incorporation into lignin, whereas coniferaldehyde was not increased markedly. Accordingly, ultra-high-performance liquid chromatography-mass spectrometry-based phenolic profiling revealed a more than 24,000-fold accumulation of a newly identified compound made from 8-8 coupling of two sinapaldehyde radicals. However, no additional cinnamaldehyde coupling products could be detected in the CAD1-deficient poplars. Instead, the transgenic lines accumulated a range of hydroxycinnamate-derived metabolites, of which the most prominent accumulation (over 8,500-fold) was observed for a compound that was identified by purification and nuclear magnetic resonance as syringyl lactic acid hexoside. Our data suggest that, upon down-regulation of CAD1, coniferaldehyde is converted into ferulic acid and derivatives, whereas sinapaldehyde is either oxidatively coupled into S'(8-8) S' and lignin or converted to sinapic acid and derivatives. The most prominent sink of the increased flux to hydroxycinnamates is syringyl lactic acid hexoside. Furthermore, low-extent saccharification assays, under different pretreatment conditions, showed strongly increased glucose (up to +81%) and xylose (up to +153%) release, suggesting that down-regulating CAD1 is a promising strategy for improving lignocellulosic biomass for the sugar platform industry.
Keywords
CINNAMYL-ALCOHOL-DEHYDROGENASE, O-METHYLTRANSFERASE ACTIVITY, LIGNIN, BIOSYNTHETIC-PATHWAY, CAFFEOYL SHIKIMATE ESTERASE, STATE 2D NMR, DOWN-REGULATION, MONOLIGNOL BIOSYNTHESIS, ARABIDOPSIS-THALIANA, TRANSGENIC POPLAR, GENE-EXPRESSION

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Citation

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Chicago
Van Acker, Rebecca, Annabelle Déjardin, Sandrien Desmet, Lennart Hoengenaert, Ruben Vanholme, Kris Morreel, Françoise Laurans, et al. 2017. “Different Routes for Conifer- and Sinapaldehyde and Higher Saccharification Upon Deficiency in the Dehydrogenase CAD1.” Plant Physiology 175 (3): 1018–1039.
APA
Van Acker, Rebecca, Déjardin, A., Desmet, S., Hoengenaert, L., Vanholme, R., Morreel, K., Laurans, F., et al. (2017). Different routes for conifer- and sinapaldehyde and higher saccharification upon deficiency in the dehydrogenase CAD1. PLANT PHYSIOLOGY, 175(3), 1018–1039.
Vancouver
1.
Van Acker R, Déjardin A, Desmet S, Hoengenaert L, Vanholme R, Morreel K, et al. Different routes for conifer- and sinapaldehyde and higher saccharification upon deficiency in the dehydrogenase CAD1. PLANT PHYSIOLOGY. 2017;175(3):1018–39.
MLA
Van Acker, Rebecca, Annabelle Déjardin, Sandrien Desmet, et al. “Different Routes for Conifer- and Sinapaldehyde and Higher Saccharification Upon Deficiency in the Dehydrogenase CAD1.” PLANT PHYSIOLOGY 175.3 (2017): 1018–1039. Print.
@article{8540297,
  abstract     = {In the search for renewable energy sources, genetic engineering is a promising strategy to improve plant cell wall composition for biofuel and bioproducts generation. Lignin is a major factor determining saccharification efficiency and, therefore, is a prime target to engineer. Here, lignin content and composition were modified in poplar (Populus tremula 3 Populus alba) by specifically down-regulating CINNAMYL ALCOHOL DEHYDROGENASE1 (CAD1) by a hairpin-RNA-mediated silencing approach, which resulted in only 5\% residual CAD1 transcript abundance. These transgenic lines showed no biomass penalty despite a 10\% reduction in Klason lignin content and severe shifts in lignin composition. Nuclear magnetic resonance spectroscopy and thioacidolysis revealed a strong increase (up to 20-fold) in sinapaldehyde incorporation into lignin, whereas coniferaldehyde was not increased markedly. Accordingly, ultra-high-performance liquid chromatography-mass spectrometry-based phenolic profiling revealed a more than 24,000-fold accumulation of a newly identified compound made from 8-8 coupling of two sinapaldehyde radicals. However, no additional cinnamaldehyde coupling products could be detected in the CAD1-deficient poplars. Instead, the transgenic lines accumulated a range of hydroxycinnamate-derived metabolites, of which the most prominent accumulation (over 8,500-fold) was observed for a compound that was identified by purification and nuclear magnetic resonance as syringyl lactic acid hexoside. Our data suggest that, upon down-regulation of CAD1, coniferaldehyde is converted into ferulic acid and derivatives, whereas sinapaldehyde is either oxidatively coupled into S'(8-8) S' and lignin or converted to sinapic acid and derivatives. The most prominent sink of the increased flux to hydroxycinnamates is syringyl lactic acid hexoside. Furthermore, low-extent saccharification assays, under different pretreatment conditions, showed strongly increased glucose (up to +81\%) and xylose (up to +153\%) release, suggesting that down-regulating CAD1 is a promising strategy for improving lignocellulosic biomass for the sugar platform industry.},
  author       = {Van Acker, Rebecca and D{\'e}jardin, Annabelle and Desmet, Sandrien and Hoengenaert, Lennart and Vanholme, Ruben and Morreel, Kris and Laurans, Fran\c{c}oise and Kim, Hoon and Santoro, Nicholas and Foster, Cliff and Goeminne, Geert and L{\'e}g{\'e}e, Fr{\'e}d{\'e}ric and Lapierre, Catherine and Pilate, Gilles and Ralph, John and Boerjan, Wout},
  issn         = {0032-0889},
  journal      = {PLANT PHYSIOLOGY},
  language     = {eng},
  number       = {3},
  pages        = {1018--1039},
  title        = {Different routes for conifer- and sinapaldehyde and higher saccharification upon deficiency in the dehydrogenase CAD1},
  url          = {http://dx.doi.org/10.1104/pp.17.00834},
  volume       = {175},
  year         = {2017},
}

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