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Table 1 Targeted genetic engineering of plant cell wall chemical constituents for improved industrial utility

From: Tailoring renewable materials via plant biotechnology

Cell wall compound Gene Type of modification Outcomes Plant References
Pectin PL1-27 OE Increased xylose (21%) and glucose (7%) yields Poplar [55]
RG-lyase6 OE Increased xylose (4%) and glucose (25%) yields Poplar [51]
PMEI2 OE Reduced proportion of egg box structures
Increased saccharification (40%) yields
Arabidopsis [58]
GAUT4 RNAi Reduced HG and RG-I content, calcium, borate, and ferulate cross-linking
Increased lignin migration and hemicellulose dissolution
Switchgrass and Poplar [60,61]
GAUT12 RNAi Increased glucose release, plant height, and stem radius Poplar [62]
Xyloglucan XEG2 (Aspergillus aculeatus) OE Increased stem height and cellulose content
Affected development of G-layers
Increased glucose (50%) yields
Increased cellulose conversion (60%)
Poplar [79, 81, 82, 95]
XTH4 and XTH9 KO (T-DNA insertion) Reduced XET activity
Altered xylem cell expansion and production, and secondary cell deposition
Increased carbohydrate production (15%)
Arabidopsis [84]
XET16-34 OE Stimulated cell expansion in vessel elements
Increased overall xyloglucan content
Poplar [83]
BGAL10 KO (T-DNA insertion) Reduced β-galactosidase activity against XyG
Altered XyG composition and plant growth
Arabidopsis [104]
Xylan ESK1 KO (T-DNA insertion and induced point mutation) Dwarf plants
Collapsed xylem vessels
Arabidopsis [106]
DARX1 KO (CRISPR/Cas9 mutation) Altered arabinoxylan conformation and cellulose microfibril orientation
Reduced mechanical stem strength and plant height
Rice [117]
GUX1 and GUX2 KO (T-DNA insertion) Weak stems
Increased glucose (30%) release
Increased xylose (700%) release
Increased ethanol yields
Arabidopsis [118, 119]
ARAF1 and ARAF2 OE Reduced arabinose (up to 25%) content
Increased glucose (up to 34%) release
Rice [126]
AT10 from Rice OE Reduced ferulic acid levels
Increased saccharification efficiency (40%)
Switchgrass [127]
Mannan CSLA2,3,7, and 9 KO (T-DNA insertion) CSLA 7 is essential for embryogenesis
CSLA 2,3,9 reduced glucomannan content without affecting plant growth
Arabidopsis [144]
MUCI10 KO (T-DNA insertion) Altered seed mucilage density and cellulose structure Arabidopsis [150]
Cellulose CesA1 and 9 KO (T-DNA insertion and point mutation) Reduced cellulose crystallinity (up to 34%)
Increased fermentable sugar release (up to 151%)
Reduced anisotropic growth
Arabidopsis [168, 171, 172]
CesA4, CesA7-A/B, and CesA8-A/B RNAi Reduced cellulose content and plant growth
Collapsed vessels and thinner fibre cell walls
Stems exhibited reduced mechanical strength
Poplar [173]
RIC1 OE Reduced cellulose crystallinity Arabidopsis [174]
Cel9A6 and KOR1 RNAi Collapsed xylem vessels
Reduced cellulose content and crystallinity
Reduced stem mechanical strength
Poplar [176, 177]
Cel9A6 OE Increased plant growth and fibre cell length
Caused male sterility
Arabidopsis [176]
Cel9A1/KOR1 OE Reduced cellulose crystallinity
Improved glucose yields
Arabidopsis [179]
GH9B1 and GH9B3 OE Reduced cellulose degree polymerization and crystallinity
Increased bioethanol yields
Rice [180]
SuSy OE Increased cellulose content (up to 6%) and crystallinity
Increased wood density
Poplar [185]
SUS3 OE Reduced cellulose crystallinity and xylose–arabinose proportions
Increased stress-induced callose accumulation
Rice [186]
Lignin 4CL RNAi Reduced lignin, changed lignin composition, growth impairments Poplar [215]
HCT RNAi Reduced lignin, changed lignin composition, growth impairments Poplar, alfalfa [216, 218, 219]
CCR RNAi Reduced lignin, changed lignin composition (incorporation of ferulic acid, increase in acetal bonds), growth impairments Poplar, maize [217, 260]
C4H RNAi Reduced lignin, changed lignin composition, growth impairments Alfalfa [218, 219]
C3′H RNAi Reduced lignin, changed lignin composition, growth impairments Alfalfa [218, 219]
PAL RNAi Reduced lignin content, but no growth impairments Poplar [216]
Ref8-1 med5a/med5b KO (Triple mutant T-DNA insertion) Restoration of growth of the ref8-1 (c3h), lignin almost completely composed of H units Arabidopsis [226]
HCHL OE Reduced lignin degree of polymerization, but no differences in biomass yield or lignin amount. Increased saccharification efficiency Arabidopsis [229]
CHS Natural mutant (C2-Idf) Reduced incorporation of tricin in the lignin, lignin was enriched in β–β and β-5 units Maize [232]
Sfe Transposon Mutant Reduced feruloylation, better forage digestibility Maize [237,238,241]
Gt61 Natural KO mutant (xax1) Reduced arabinosyl substitutions, increased processing efficiency, dwarfed Rice [124]
COMT KO and RNAi Incorporation of 5-hydroxyconiferyl alcohol, increase in benzodioxane structures in the lignin, but no lignin reductions. Increased saccharification efficiency Arabidopsis, Poplar [243, 244]
F5H OE Increased S units (around 90% of all lignin monomers), increased monomer yield after hydrogenolysis Poplar [40, 258]
FMT OE Incorporation of ester linkages in the lignin backbone, increased saccharification efficiency after alkaline pretreatment, increased pulping efficiency Poplar [216, 260]
PMT OE Incorporation of p-coumarate conjugates in the lignin, higher frequency of terminal units with free phenolic groups Arabidopsis, Poplar [263, 264]
DCS & CURS2 OE Incorporation of curcumin in the lignin, increased saccharifcation efficiency Arabidopsis [265]
Cα-dehydrogenase OE Appearance of chemical labile α-keto-β-ether units in the lignin Arabidopsis [266]
CAD RNAi and KO mutants Increased concentrations of aldehydeS, increased saccharification efficiency Pine, Arabidopsis, Medicago, Poplar [230, 243]
QsuB OE Reduced lignin concentrations Arabidopsis [282]
  1. OE overexpression, RNAi RNA interference, KO gene knockout, T-DNA transfer DNA