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 | ||
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 | |
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 | ||
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 | |
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 | ||
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 | ||
CCR | RNAi | Reduced lignin, changed lignin composition (incorporation of ferulic acid, increase in acetal bonds), growth impairments | Poplar, maize | ||
C4H | RNAi | Reduced lignin, changed lignin composition, growth impairments | Alfalfa | ||
C3′H | RNAi | Reduced lignin, changed lignin composition, growth impairments | Alfalfa | ||
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 | ||
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 | ||
F5H | OE | Increased S units (around 90% of all lignin monomers), increased monomer yield after hydrogenolysis | Poplar | ||
FMT | OE | Incorporation of ester linkages in the lignin backbone, increased saccharification efficiency after alkaline pretreatment, increased pulping efficiency | Poplar | ||
PMT | OE | Incorporation of p-coumarate conjugates in the lignin, higher frequency of terminal units with free phenolic groups | Arabidopsis, Poplar | ||
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 | ||
QsuB | OE | Reduced lignin concentrations | Arabidopsis | [282] |