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Structure and Biosynthesis of Lignin
Published in Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel, Hemicelluloses and Lignin in Biorefineries, 2017
Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel
These reactions are mediated by A phenylalanine ammonia-lyase (PAL)Three different cytochrome P450-dependent monooxygenases: cinnamate 4-hydroxylase (C4H), p-coumarate 3-hydroxylase (C3H), and ferulate 5-hydroxylase (F5H)Two methyltransferases: caffeoyl-CoA O-methyltransferase (CCoAOMT; CoA, coenzyme A) and caffeic acid O-methyltransferase (COMT)Two oxidoreductases: cinnamoyl-CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD)1
Metabolic Engineering for Liquid Biofuels Generations from Lignocellulosic Biomass
Published in Arindam Kuila, Sustainable Biofuel and Biomass, 2019
Lignin biosynthetic pathway and its enzymes are well characterized. Lignin reduction remains a challenging task. This problem stems from a lack of specificity in traditional lignin-reduction methods, which usually compromise plant growth or impair the plant defense system. Emerging strategies like genome bioediting and transgene regulation provide new options to achieve controlled lignin manipulations in targeted plant tissues when applies in conjunction with tissue-type-specific or cell-type-specific promoters. It will finally give the opportunity to design crops with optimized lignin composition and distribution while retaining all other traits related to the phenylpropanoid pathway. This new trend for lignin engineering focuses on the redirection of carbon flux to the production of related phenolic compounds and on the replacement of monolignols with novel lignin monomers to improve biophysical and chemical properties of lignins such as recalcitrance or industrial use. Concerning lignin decomposition, downregulation of caffeic acid O-methyltransferase or COMB (EC 2.1.1.68) and cinnamoyl-CoA reductase or CCR (EC1.2.1.44) enzymes in switch grass trigger moderate lignin reduction, along with a decrease in the syringyl and guaiacyl units (S/G) ratio. This results in an increase in lignin decomposition (Fu et al., 2011). Another possible way to lower lignin content is by blocking the free parahydroxyl groups in monolignols responsible for the creation of lignin subunits via oxidative coupling (notably 4-O-methylation of monolignols). This shows no detrimental effect on transport across the membrane or on growth and development of the plant (Zhang et al., 2012).
Right on target: using plants and microbes to remediate explosives
Published in International Journal of Phytoremediation, 2019
Elizabeth L. Rylott, Neil C. Bruce
The fate of UGT and GST-catalyzed TNT conjugates is still to be determined. In Arabidopsis, glutathionylated xenobiotics can be compartmentalized to the vacuole by MRP2, an ATP-binding cassette transporter belonging to the multidrug resistance-associated protein (MRP) family. MRP2 is upregulated in TNT-fed Arabidopsis (Gandia-Herrero et al. 2008), but compartmentation and the ultimate fate of TNT conjugates are still to be elucidated. Towards this, subcellular fractionation studies on bean (Phaseolus vulgaris) fed 14C TNT found over half of the label in the lignin fraction (Sens et al. 1998, 1999). Tobacco (Nicotiana tabacum) cell suspension cultures fed TNT, accumulate more mono and diglycoside conjugates of 2‐ and 4‐HADNT than are found in whole‐plant cultures (Vila et al. 2005), possibly because of the lack of a significant lignin sink for incorporation of these conjugates. In agreement with this finding, a gene expression study in Arabidopsis roots treated with TNT identified upregulation of lignin biosynthesis genes (including phenyl ammonium lyase, cinnamate 4‐hydroxylase, 4‐coumarate CoA ligase, hydroxycinnamoyltransferase, cinnamoyl‐CoA reductase, caffeic acid O‐methyltransferase and cinnamyl alcohol dehydrogenase; Ekman et al. 2003). Thus is it plausible that TNT conjugates are incorporated, through non-enzymatic free radical polymerization and self-assembly, into root cell wall lignin? Subsequent metabolism is likely to occur during natural composting of dead plant material, with mineralization of any re-released TNT-intermediates by fungal lignolytic activities, as described above (Rylott and Bruce 2009; Rylott, Lorenz, et al. 2011).