Expression of a bacterial 3‐dehydroshikimate dehydratase reduces lignin content and improves biomass saccharification efficiency

Abstract

SummaryLignin confers recalcitrance to plant biomass used as feedstocks in agro-processing industries or as source of renewable sugars for the production of bioproducts. The metabolic steps for the synthesis of lignin building blocks belong to the shikimate and phenylpropanoid pathways. Genetic engineering efforts to reduce lignin content typically employ gene knockout or gene silencing techniques to constitutively repress one of these metabolic pathways. Recently, new strategies have emerged offering better spatiotemporal control of lignin deposition, including the expression of enzymes that interfere with the normal process for cell wall lignification. In this study, we report that expression of a 3-dehydroshikimate dehydratase (QsuB from Corynebacterium glutamicum) reduces lignin deposition in Arabidopsis cell walls. QsuB was targeted to the plastids to convert 3-dehydroshikimate -an intermediate of the shikimate pathway -into protocatechuate. Compared to wild-type plants, lines expressing QsuB contain higher amounts of protocatechuate, p-coumarate, p-coumaraldehyde and p-coumaryl alcohol, and lower amounts of coniferaldehyde, coniferyl alcohol, sinapaldehyde and sinapyl alcohol. 2D-NMR spectroscopy and pyrolysis-gas chromatography/mass spectrometry (pyro-GC/MS) reveal an increase of p-hydroxyphenyl units and a reduction of guaiacyl units in the lignin of QsuB lines. Size-exclusion chromatography indicates a lower degree of lignin polymerization in the transgenic lines. Therefore, our data show that the expression of QsuB primarily affects the lignin biosynthetic pathway. Finally, biomass from these lines exhibits more than a twofold improvement in saccharification efficiency. We conclude that the expression of QsuB in plants, in combination with specific promoters, is a promising gain-of-function strategy for spatiotemporal reduction of lignin in plant biomass.

Structurally diverse dehydroshikimate dehydratase variants participate in microbial quinate catabolism

“…A related 'two-domain' DSD (40% sequence identity with P. putida QuiC1) known as QsuB has been identified in C. glutamicum where its gene is situated in an operon that is associated with quinate usage (Teramoto et al, 2009). Recently, expression of QsuB in the plant, Arabidopsis thaliana, has been shown to enhance biomass saccharification through an increase in protocatechuate production at the expense of lignin deposition (Eudes et al, 2015). Here, we investigate the biochemical and structural properties of the bacterial two-domain DSD.…”

Vessel-Specific Reintroduction of CINNAMOYL-COA REDUCTASE1 (CCR1) in Dwarfed ccr1 Mutants Restores Vessel and Xylary Fiber Integrity and Increases Biomass

“…saccharification; Weng et al, 2008;Pauly and Keegstra, 2010). Therefore, several efforts to reduce cell wall recalcitrance have focused on modifying the lignin content and/or composition (Goujon et al, 2003;Chen and Dixon, 2007;Leplé et al, 2007;Shadle et al, 2007;Jackson et al, 2008;Day et al, 2009;Voelker et al, 2010;Eudes et al, 2012Eudes et al, , 2015Eudes et al, , 2016Mansfield et al, 2012;Wilkerson et al, 2014;Mottiar et al, 2016).…”

Cell Wall Engineering by Heterologous Expression of Cell Wall-Degrading Enzymes for Better Conversion of Lignocellulosic Biomass into Biofuels

“…Alternatively, there is a novel and promising strategy that involve expression of specific proteins to alter lignin building blocks composition and make lignin polymer more prone to degradation [107,140,141]. For instance, expression of bacterial 3-dehydroshikimate dehydratase in combination with specific promoters in Arabidopsis reduced lignin content and improved saccharification efficiency [107].…”