TABLE 1.
List of C4 crops genes as candidates for exploiting biomass-related traits.
| Crop species | Gene/Enzyme manipulated | Description | Comments | References |
|
Cell cycle machinery
| ||||
| Tobacco | CycA3;3 | A-type cyclins | Antisense expression led the formation of defective embryo and impaired callus formation | Yu et al., 2003 |
| Tobacco | Arath-CYCD2 or Arath-CYCD3 | D-type cyclins (G1-specific cyclins) | OE transgenics exhibited increased cell number but not cell size with higher leaf initiation rates | Boucheron et al., 2005 |
| Maize | Samba1 and samba 3 | SAMBA | CRISPR/Cas9 mutant lines accelerated cell cycle, erect and shortened foliage upper top leaf length, ligule formation and internode elongation | Gong et al., 2021 |
|
| ||||
|
Hormone related genes
| ||||
| Arabidopsis | GA20ox | GA20-oxidase | OE produced 25% taller plants, accelerated shoot growth and early flowering | Coles et al., 1999 |
| Switchgrass | GA20ox | GA20-oxidase | OE lines showed 2 folds biomass increase due to more tillers, leaf size and elevated bioactive GAs | Do et al., 2016 |
| Sorghum | GA20ox1 | GA20-oxidase | Higher expression in bioenergy sorghum culms. Moreover, sweet sorghum had higher GA levels and biomass. | Wang et al., 2020 |
| Sugarcane | GAI | DELLA repressors | OE lines showing the stunted culm growth and development and modulation of shoot-to-root ratio in sugarcane | Garcia Tavares et al., 2018 |
| Maize | AUX1 | (AUX/LAX) Auxin influx facilitators | Mutant showed inflorescence development and root gravitropism | Huang et al., 2017 |
| Green foxtail | AUX1 | (AUX/LAX) | Mutants led to defective inflorescence, reduced plant height, increased panicle length and sparse panicle phenotype | Huang et al., 2017 |
| Maize | Aux/IAA | RUM1 (ROOTLESS WITH UNDETECTABLE MERISTEMS 1) | Mutant rum1 showed defective xylem organization and more lignin deposition in root cells | Zhang et al., 2015 |
| Maize | ARF5 | (MONOPTEROS) | Mutant showed root altered patterning of vascular cells differentiation, thick cell walls with higher lignin contents | Zhang et al., 2014 |
| Maize | D11 | Biosynthesis of BL | Higher expression in young ears and seeds, Improve seed quantity and quality. | Sun et al., 2021 |
| Maize | BRI1 | BRASSINOSTEROID INSENSITIVE 1 | Mutant displayed overall dwarf stature, shortened internodes, folded dark green leaves, decreased auricle formation and feminization of female flowers | Kir et al., 2015 |
|
| ||||
|
Cell wall biosynthesis related genes
| ||||
| Arabidopsis | xxt1 xxt2 | Xyloglucan transferase | Double mutant showed aberrant root hairs and modified mechanical properties | Cavalier et al., 2008 |
| Arabidopsis | TED6 and TED7 | Tracheary Element (TE) Differentiation-Related 6 and 7 | RNAi showed delay in TE differentiation, abnormality in SCW and cellulose synthesis | Endo et al., 2009 |
| Arabidopsis | LAC4 & LAC17 | Laccases | T-DNA insertion showed LAC17 effected the deposition of G lignin units in the interfascicular fiber. lac4-2 lac17 double mutant resulted in 40% reduced lignin. | Berthet et al., 2011 |
|
| ||||
| Plant species | Gene/Enzyme manipulated | Description | Comments | References |
|
| ||||
| Sugarcane | LAC | Laccases | Complementation in Arabidopsis lac17 (–19% lignin) mutant restored lignin content | Cesarino et al., 2013 |
| Sorghum | (bmr) bmr2, bmr6, and bmr12 | Brown midrib mutant | 2 years-based field study of EMS bmr mutants displayed decreased levels of lignin | Sattler et al., 2014 |
| Maize | (bm3) COMT | Brown-midrib-3, lacking caffeic acid O-methyltransferase (COMT) | Antisense (AS225), and bm3 maize plants resulted in disturbed cell wall assembly. | Guillaumie et al., 2008 |
| Sorghum | CslF6 | Cellulose synthase-like F6 (CslF6) Glucan biosynthesis | Chimeric cDNA construct modifies the fine structure of (1,3;1,4)-β-glucan polysaccharide chain | Dimitroff et al., 2016 |
|
| ||||
|
Transcription factors and MicroRNA
| ||||
| Switch grass | ERF001 | SHINE “SHINE/WAX INDUCER” (SHN/WIN) TF (AP2/ERF) superfamily | Increased biomass, and efficient saccharification process | Wuddineh et al., 2015 |
| Sugarcane | SHN1 | SHINE “SHINE/WAX INDUCER” (SHN/WIN) TF e factor (AP2/ERF) superfamily | OE results modified cell walls and increase in biomass by (91–340%), | Martins et al., 2018 |
| Maize | MYB46/83 | MYB (myeloblastosis) | Synthesis and thickening of cell wall | Zhong et al., 2011 |
| Switchgrass | R2R3-MYB | MYB (myeloblastosis) | OE lines showed an increased biomass up to ∼ 63% and reduced lignin content around 50% | Shen et al., 2012 |
| Maize | MYB31 and MYB42 | MYB (myeloblastosis) | Redirected phenylpropanoid and lignin biosynthesis in Arabidopsis, reduced S/G ratio (S, syringl units; G, guaiacyl units) | Sonbol et al., 2009; Vélez-Bermúdez et al., 2015 |
| Sorghum | Myb60 | Myeloblastosis (MYB) | Overexpressed lines displayed enhanced lignification in leaf midribs and increased phenolics | Scully et al., 2016 |
| Finger millet | bHLH57 | (BASIC HELIX-LOOP-HELIX) | Over-expressing depicted resistance to salinity stress with enhanced photosynthetic efficiency and increased biomass | Babitha et al., 2015 |
| Maize | Dof 1 | Zinc finger protein | Increased NUE in transgenic sorghum and wheat. Activation of carbon skeleton metabolism, i.e., PEPC activity | Peña et al., 2017 |
| Maize | miR156, AtSPL9, MIR172 | SQUAMOSA Promoter-Binding Protein-Like (SPL) miRNA | Delays reproductive phase leading the prolonged vegetative stage | Lauter et al., 2005; Chuck et al., 2007 |
| Switchgrass | GAUT4-KD, miRNA156-OE, MYB4-OE, COMT-KD and FPGS-KD). | Myeloblastosis (MYB) miRNA | Increased contents of carbohydrates by 12% and ethanol yields by 21% | Dumitrache et al., 2017 |