Suppression of CINNAMOYL-CoA REDUCTASE increases the level of monolignol ferulates incorporated into maize lignins

Abstract

BackgroundThe cell wall polymer lignin provides structural support and rigidity to plant cell walls, and therefore to the plant body. However, the recalcitrance associated with lignin impedes the extraction of polysaccharides from the cell wall to make plant-based biofuels and biomaterials. The cell wall digestibility can be improved by introducing labile ester bonds into the lignin backbone that can be easily broken under mild base treatment at room temperature. The FERULOYL-CoA MONOLIGNOL TRANSFERASE (FMT) enzyme, which may be naturally found in many plants, uses feruloyl-CoA and monolignols to synthesize the ester-linked monolignol ferulate conjugates. A mutation in the first lignin-specific biosynthetic enzyme, CINNAMOYL-CoA REDUCTASE (CCR), results in an increase in the intracellular pool of feruloyl-CoA.ResultsMaize (Zea mays) has a native putative FMT enzyme, and its ccr mutants produce an increased pool of feruloyl-CoA that can be used for conversion to monolignol ferulate conjugates. The decreased lignin content and monomers did not, however, impact the plant growth or biomass. The increase in monolignol conjugates correlated with an improvement in the digestibility of maize stem rind tissue.ConclusionsTogether, increased monolignol ferulates and improved digestibility in ccr1 mutant plants suggests that they may be superior biofuel crops.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0793-1) contains supplementary material, which is available to authorized users.

Downregulation of p‐COUMAROYL ESTER 3‐HYDROXYLASE in rice leads to altered cell wall structures and improves biomass saccharification

“…The lignin content was evaluated by the Klason lignin assay (Hatfield et al ., ) as well as the thioglycolic acid assay (Suzuki et al ., ). In addition, we performed thioacidolysis (Lapierre et al ., ; Yamamura et al ., ) and derivatization followed by reductive cleavage (DFRC) methods (Lu and Ralph, , ; Ralph and Lu, ; Smith et al ., ). Thioacidolysis quantifies H‐, G‐ and S‐type monomeric degradation products (H thio , G thio and S thio ) released via cleavage of both γ‐free and (most of the) γ‐acylated β– O –4 substructures in the lignin polymers, and their relative abundances reflect the overall aromatic composition of β– O –4‐linked H/G/S lignin units (Figure ).…”

“…() as described in Materials and Methods S1. Klason lignin assay (Hatfield et al ., ), thioglycolic acid lignin assay (Suzuki et al ., ), thioacidolysis (Yamamura et al ., ; Yue et al ., ), DFRC (Smith et al ., ; Regner et al ., ), DFRC‐Pr (Karlen et al ., ), determination of cell‐wall‐bound p CA and FA content (Yamamura et al ., ), and amorphous and crystalline neutral sugar composition analysis (Lam et al ., ) were performed largely according to literature methods and as further described in Materials and Methods S1. Analytical parameters and multiple reaction monitoring (MRM) parameters used for DFRC analysis are shown in Tables S6 and S7.…”

“…The lignin content was evaluated by the Klason lignin assay (Hatfield et al, 1994) as well as the thioglycolic acid assay (Suzuki et al, 2009). In addition, we performed thioacidolysis (Lapierre et al, 1986;Yamamura et al, 2012) and derivatization followed by reductive cleavage (DFRC) methods Ralph, 1997, 1999;Ralph and Lu, 1998;Smith et al, 2017). Ralph, 1997, 1999;Smith et al, 2017), along with its modification, DFRC-Pr (Ralph and Lu, 1998;Karlen et al, 2017), cleaves b-O-4 ether bonds without disrupting any c-ester linkages present and consequently releases quantifiable amounts of acylated degradation products (H DFRC-pCA , G DFRC-Ac , H DFRC-FA , G DFRC-pCA , G DFRC-Ac , G DFRC-FA , S DFRC-pCA , S DFRC-Ac and S DFRC-FA ) from c-acylated units along with non-acylated products (H DFRC-OH , G DFRC-OH and S DFRC-OH ) from c-OH units ( Figure 3).…”

“…In addition, we performed thioacidolysis (Lapierre et al, 1986;Yamamura et al, 2012) and derivatization followed by reductive cleavage (DFRC) methods Ralph, 1997, 1999;Ralph and Lu, 1998;Smith et al, 2017). Ralph, 1997, 1999;Smith et al, 2017), along with its modification, DFRC-Pr (Ralph and Lu, 1998;Karlen et al, 2017), cleaves b-O-4 ether bonds without disrupting any c-ester linkages present and consequently releases quantifiable amounts of acylated degradation products (H DFRC-pCA , G DFRC-Ac , H DFRC-FA , G DFRC-pCA , G DFRC-Ac , G DFRC-FA , S DFRC-pCA , S DFRC-Ac and S DFRC-FA ) from c-acylated units along with non-acylated products (H DFRC-OH , G DFRC-OH and S DFRC-OH ) from c-OH units ( Figure 3). We also quantified wall-bound pCA and FA via saponification (Yamamura et al, 2011;Petrik et al, 2014) as well as cell wall polysaccharide units via a combination of trifluoroacetic acid (TFA) and sulfuric acid-catalyzed hydrolysis (Chen et al, 2012;Lam et al, 2017).…”

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

“…ms1-1 and ap3-1) also produce more axillary branches (Hensel et al, 1994;Wuest et al, 2016). Moreover, field-grown ccr1 maize (Zea mays) mutants, which also suffered from reduced seed weights, produced significantly more stem biomass when compared with wild-type maize plants (Smith et al, 2017a). The underlying signal leading to an increased biomass in seed-compromised plants remains largely unknown.…”