Abstract Among the potential non-food energy crops, the sugar-rich C4 grass sweet sorghum and the biomass-rich Miscanthus are increasingly considered as two leading candidates. Here, we outline the biological traits of these energy crops for large-scale production in China. We also review recent progress on understanding of plant cell wall composition and wall polymer features of both plant species from large populations that affect both biomass enzymatic digestibility and ethanol conversion rates under various pretreatment conditions. We finally propose genetic approaches to enhance biomass production, enzymatic digestibility and sugar-ethanol conversion efficiency of the energy crops.
This work was supported by grants from the Fundamental Research Funds for the Central Universities Project , China (2013QC042), the Fundamental Research Funds for the 111 Project of Ministry of Education of China (B08032), and the Starting Foundation for Changjiang Scholars Program of Ministry of Education of China (52204-14004).
Achyuthan K E, Achyuthan A M, Adams P D, Dirk S M, Harper J C, Simmons B A, Singh A K. 2010. Supramolecular self-assembled chaos: Polyphenolic lignin’s barrier to cost-effective lignocellulosic biofuels. Molecules, 15, 8641-8688.
Angelini L G, Ceccarini L, Nasso N, Bonari E. 2009. Comparison of Arundo donax L. and Miscanthus×giganteus in a long-term field experiment in Central Italy: Analysis of productive characteristics and energy balance. Biomass and Bioenergy, 33, 635-643.
Antonopoulou G, Gavala H N, Skiadas I V, Angelopoulos K, Lyberatos G. 2008. Biofuels generation from sweet sorghum: Fermentative hydrogen production and anaerobic digestion of the remaining biomass. Bioresource Technology, 99,110-119.
Arioli T, Peng L, Betzner A S, Burn J, Wittke W, Herth W, Camilleri C, Höfte H, Plazinski J, Birch R, Cork A, Glover J, Redmond J, Williamson R E. 1998. Molecular analysis of cellulose biosynthesis in Arabidopsis. Science, 279, 717-720.
Arruda P. 2011. Genetically modified sugarcane for bioenergy generation. Current Opinion in Biotechnology, 23, 1-8.
Byrt C, Grof C, Furbank R. 2011. C4 plants as biofuel feedstocks: Optimizing biomass production and feedstock quality from a lignocellulosic perspective. Journal of Integrative Plant Biology, 53, 120-135.
Cao W, Sun C, Liu R, Yin R, Wu X. 2012. Comparison of the effects of five pretreatment methods on enhancing the enzymatic digestibility and ethanol production from sweet sorghum bagasse. Bioresource Technology, 111, 215-221.
Chen L G, Xing L, Han L J. 2009. Renewable energy from agro-residues in China: Solid biofuels and biomass briquetting technology. Renewable and Sustainable Energy Reviews, 13, 2689-2695.
Chen P, Peng L. 2013. The diversity of lignocellulosic biomass resources and their evaluation for use as biofuels and chemicals. In: Sun J Z, Ding S Y, Peterson J D, eds., Biological Conversion of Biomass for Fuels and Chemicals: Exploration from Natural Biomass Utilization Systems. Royal Society of Chemistry, Oxfordshire. pp. 83-113.
Clifton-Brown J C, Stampfl P, Jones M B. 2004. Miscanthus biomass production for energy in Europe and its potential contribution to decreasing fossil fuel carbon emissions. Global Change Biology, 10, 509-518.
Cotton J, Burow G, Acosta-Martinez V, Moore-Kucera J. 2013. Biomass and cellulosic ethanol production of forage sorghum under limited water conditions. BioEnergy Research, 6, 711-718.
Dohleman F G, Long S P. 2009. More productive than maize in the midwest: How does Miscanthus do it? Plant Physiology, 150, 2104-2115.
Feng Y, Zou W, Li F, Zhang J, Zhang H, Xie G, Tu Y, Lu T, Peng L. 2013. Studies on biological characterization of rice brittle culm mutants and their biomass degradation efficiency. Journal of Agricultural Science and Technology, 15, 77-83.
Fry S C. 1988. The Growing Plant Cell Wall: Chemical and Metabolic Analysis. Longman, London. pp. 95-97.
Gao C, Zhai Y, Ding Y, Wu Q. 2010. Application of sweet sorghum for biodiesel production by heterotrophic microalga Chlorella protothecoides. Applied Energy, 87, 756-761.
Gao Z, Jayaraj J, Muthukrishnan S, Claflin L, Liang G H. 2005a. Efficient genetic transformation of sorghum using a visual screening marker. Genome Research, 48, 321-333.
Gao Z, Xie X, Ling Y, Muthukrishnan S, Liang G H. 2005b. Agrobacterium tumefaciens-mediated sorghum transformation using a mannose selection system. Plant Biotechnology, 3, 591-599.
Girio F M, Fonseca C, Carvalheiro F, Duarte L C, Marques S, Bogel-Lukasik R. 2010. Hemicelluloses for fuel ethanol: A review. Bioresource Technology, 101, 4775-4800.
Guo K, Zou W, Feng Y, Zhang M, Zhang J, Tu F, Xie G, Wang L, Wang Y, Senbastian K, Persson S, Peng L. 2014. An integrated genomic and metabolomic framework for cell wall biology in rice. BioMed Central Genomics, 15, 596-609.
Heaton E, Clifton-Brown J, Voigt T, Jones M, Long S. 2004. Miscanthus for renewable energy generation: European union experience and projections for illinois. Mitigation and Adaptation Strategies for Global Change, 9, 433-451.
Himmel M E, Ding S, Johoson D K, Adney W S, Nimlos M R, Brady J W, Foust T D. 2007. Biomass recalcitrance: Engineering plants and enzymes for biofuels production. Science, 315, 804-807.
Huang J, Xia T, Li A, Yu B, Li Q, Tu Y, Zhang W, Yi Z, Peng L. 2012. A rapid and consistent near infrared spectroscopic assay for biomass enzymatic digestibility upon various physical and chemical pretreatments in Miscanthus. Bioresource Technology, 121, 274-281.
Huang Y, Wei X, Zhou S, Liu M, Tu Y, Li A, Chen P, Wang Y, Zhang X, Tai H, Peng L, Xia T. 2015. Steam explosion distinctively enhances biomass enzymatic saccharification of cotton stalks by largely reducing cellulose polymerization degree in G. barbadense and G. hirsutum. Bioresource Technology, 181, 224-230.
Hwang O J, Cho M A, Han Y J, Kim Y M, Lim S H, Kim D S, Kim J I. 2014. Agrobacterium-mediated genetic transformation of Miscanthus sinensis. Plant Cell Tissue and Organ Culture, 117, 51-63.
Hyoung S K, Guirong Z, John A J, Jack M W. 2010. Miscanthus ×giganteus plant regeneration: Effect of callus types, ages and culture methods on regeneration. Global Change Biology Bioenergy, 2, 192-200.
Jakob K, Zhou F S, Paterson A H. 2009. Genetic improvement of C4 grasses as cellulosic biofuel feedstocks. In Vitro Cellular and Developmental Biology (Plant), 45, 291-305.
Jia J, Yu B, Wu L, Wang H, Wu Z, Li M, Huang P, Feng S, Chen P, Zheng Y, Peng L. 2014. Biomass enzymatic saccharification is determined by the non-KOH-extractable wall polymer features that predominately affect cellulose crystallinity in corn. PLOS ONE, 9, e108449.
Kokubo A, Sakurai N, Kuraishi S, Takeda K. 1991. Culm brittleness of barley (Hordeum vulgare L.) mutants is caused by smaller number of cellulose molecules in cell wall. Plant Physiology, 97, 509-514.
Laopaiboon L, Nuanpeng S, Srinophakun P, Klanrit P, Laopaiboon P. 2009. Ethanol production from sweet sorghum juice using very high gravity technology: Effects of carbon and nitrogen supplementations. Bioresource Technology, 100, 4176-4182.
Lewandowski I, Clifton-Brown J C, Scurlock J M O, Huisman W. 2000. Miscanthus: European experience with a novel energy crop. Biomass and Bioenergy, 19, 209-277.
Lewandowski I, Scurlock J, Lindvall E, Christou M. 2003. The development and current status of perennial rhizomatous grasses as energy crops in the USA and Europe. Biomass and Bioenergy, 25, 335-361.
Li F, Ren S, Zhang W, Xu Z, Xie G, Chen Y, Tu Y, Li Q, Zhou S, Li Y, Tu F, Liu L, Wang Y, Jiang J, Qin J, Li S, Li Q, Jing H, Zhou F, Gutterson N, et al. 2013. Arabinose substitution degree in xylan positively affects lignocellulose enzymatic digestibility after various NaOH/H2SO4 pretreatments in Miscanthus. Bioresource Technology, 130, 629-637.
Li F, Zhang M, Guo K, Hu Z, Zhang R, Feng Y, Yi X, Zou W, Wang L, Wu C, Tian J, Lu T, Xie G, Peng L. 2015. High-level hemicellulosic arabinose predominately affects lignocellulose crystallinity for genetically enhancing both plant lodging resistance and biomass enzymatic digestibility in rice mutants. Plant Biotechnology Journal, 13, 514-525.
Li J, Li S, Han B, Yu M, Li G, Jiang Y. 2013. A novel cost-effective technology to convert sucrose and homocelluloses in sweet sorghum stalks into ethanol. Biotechnology for Biofuels, 6, 174-185.
Li M, Feng S, Wu L, Li Y, Fan C, Zhang R, Zou W, Tu Y, Jing H, Li S, Peng L. 2014a. Sugar-rich sweet sorghum is distinctively affected by wall polymer features for biomass digestibility and ethanol fermentation in bagasse. Bioresource Technology, 167, 14-23.
Li M, Si S, Hao B, Zha Y, Wan C, Hong S, Kang Y, Jia J, Zhang J, Li M, Zhao C, Tu Y, Zhou S, Peng L. 2014b. Mild alkali-pretreatment effectively extracts guaiacyl-rich lignin for high lignocellulose digestibility coupled with largely diminishing yeast fermentation inhibitors in Miscanthus. Bioresource Technology, 169, 447-454.
Li S, Chan-Halbrendt C. 2009. Ethanol production in (the) People’s Republic of China: potential and technologies. Applied Energy, 86, 162-169.
Li X, Hou S, Su M, Yang M, Shen S, Jiang G, Qi D, Chen S, Liu G. 2010. Major energy plants and their potential for bioenergy development in China. Environmental Management, 46, 579-589.
Li Z, Zhao C, Zha Y, Wan C, Si S, Liu F, Zhang R, Li F, Yu B, Yi Z, Xu N, Peng L. 2014. The minor wall-networks between monolignols and interlinked-phenolics predominantly affect biomass enzymatic digestibility in Miscanthus. PLOS ONE, 9, e105115.
Liu L, Yu B, Huang P, Jia J, Zhao H, Peng J, Chen P, Peng L. 2013. Frequency of callus induction and plant regeneration among eight genotypes in Miscanthus sinensis species. Chinese Bulletin of Botany, 48, 192-198. (in Chinese)
Matsakas L, Rova U, Christakopoulos P. 2014. Evaluation of dried sweet sorghum stalks as raw material for methane production. BioMed Research International, 2014, 1-7.
NDRC (National Development and Reform Commission). 2007a. The Medium- and Long-term Development Plan for Renewable Energy in China. Beijing, China. (in Chinese)
NDRC (National Development and Reform Commission). 2007b. The 11th Five-Year Plan for the Energy Development Planning of China. Beijing, China. (in Chinese)
Pan X, Xie D, Yu R W, Saddler J N. 2008. The bioconversion of mountain pine beetle-killed lodgepole pine to fuel ethanol using the organosolv process. Biotechnology and Bioengineering, 1, 39-48.
Paterson A H, Bowers J E, Bruggmann R, Dubchak I, Grimwood J, Gundlach H, Haberer G, Hellsten U, Mitros T, Poliakov A, Schmutz J, Spannagl M, Tang H, Wang X, Wicker T, Bharti A K, Chapman J, Feltus F A, Gowik U, Grigoriev I V, et al. 2009. The sorghum bicolor genome and the diversification of grasses. Nature, 457, 551-556.
Pfeiffer T W, Bitzer M J, Toy J J, Pedersen J F. 2010. Heterosis in sweet sorghum and selection of a new sweet sorghum hybrid for use in syrup production in Appalachia. Crop Science, 50, 1788-1794.
Qazi H A, Paranjpe S, Bhargava S. 2012. Stem sugar accumulation in sweet sorghum - Activity and expression of sucrose metabolizing enzymes and sucrose transporters. Journal of Plant Physiology, 169, 605-613.
Ragauskas A J, Williams C K, Davison B H, Britovsek G, Cairney J, Eckert C A, Frederick Jr W J, Hallett J P, Leak D J, Liotta C L, Mielenz J R, Murphy R, Templer R, Tschaplinski T. 2006. The path forward for biofuels and biomaterials. Science, 311, 484-489.
Ratnavathi C, Suresh K, Vijay Kumar B, Pallavi M, Komala V, Seetharama N. 2010. Study on genotypic variation for ethanol production from sweet sorghum juice. Biomass and Bioenergy, 34, 947-952.
Reddy N, Yang Y. 2005. Biofibers from agricultural byproducts for industrial applications. Trends in Biotechnology, 23, 22-27.
Roberts C, Houx J, Fritschi F. 2011. Near-infrared analysis of sweet sorghum bagasse. Crop Science, 51, 2284-2288.
Sasaki K, Tsuge Y, Sasaki D, Teramura H, Wakai S, Kawaguchi H, Sazuka T, Ogino C, Kondo A. 2014. Increased ethanol production from sweet sorghum juice concentrated by a membrane separation process. Bioresource Technology, 169, 821-825.
Scheller H V, Ulvskov P. 2010. Hemicelluloses. The Annual Review of Plant Biology, 61, 263-289.
Shrawat A K, Lorz H. 2006. Agrobacterium-mediated transformation of cereals: A promising approach crossing barriers. Plant Biotechnology Journal, 4, 575-603.
Sipos B, Reczey J, Somorai Z, Kadar Z, Dienes D, Reczey K. 2009. Sweet sorghum as feedstock for ethanol production: Enzymatic hydrolysis of steam-pretreated bagasse. Applied Biochemistry and Biotechnology, 53, 151-162.
Si S, Chen Y, Fan C, Hu H, Li Y, Huang J, Liao H, Hao B, Li Q, Peng L, Tu Y. 2015. Lignin extraction distinctively enhances biomass enzymatic saccharification in hemicelluloses-rich Miscanthus species under various alkali and acid pretreatments. Bioresource Technology, 183, 248-254.
Slavov G, Allison G, Bosch M. 2013. Advances in the genetic dissection of plant cell walls: Tools and resources available in Miscanthus. Frontiers in Plant Science, 4, 217-237.
Sun H, Li Y, Feng S, Zou W, Guo K. 2013. Analysis of five rice 4-coumarate:coenzyme A ligase enzyme activity and stress response for potential roles in lignin and flavonoid biosynthesis in rice. Biochemical and Biophysical Research Communication, 430, 1151-1156.
Sun S L, Sun S N, Wen J, Zhang X, Peng F, Sun R. 2015. Assessment of integrated process based on hydrothermal and alkaline treatments for enzymatic saccharification of sweet sorghum stems. Bioresource Technology, 175, 473-479.
Wang B, Wang X, Feng H. 2010. Deconstructing recalcitrant Miscanthus with alkaline peroxide and electrolyzed water. Bioresource Technology, 101, 752-760.
Wang X, Tetsuya Y, Fan J, Yuki A, Yoichiro H, Hiroko S, Tadashi T, Akira K, Toshihiko Y. 2011. Establishment of an efficient in vitro culture and particle bombardment-mediated transformation systems in Miscanthus sinensis Anderss., a potential bioenergy crop. Global Change Biology Bioenergy, 3, 322-332.
Wang Y, Xu Z, Peng L. 2014. Research progress in the groove structures of plant cell walls and biomass utilizations. Scientia Sinica Vitae, 44, 766-774. (in Chinese)
Van der Weijde T, Alvim Kamei C L, Torres A F, Vermerris W, Dolstra O, Visser R G F, Trindade L M. 2013. The potential of C4 grasses for cellulosic biofuel production. Frontiers in Plant Science, 4, 107-124.
Wu L, Li M, Huang J, Zhang H, Zou W, Hu S, Li Y, Fan C, Zhang R, Jing H, Peng L, Feng S. 2015. A near infrared spectroscopic assay for stalk soluble sugars, bagasse enzymatic saccharification and wall polymers in sweet sorghum. Bioresource Technology, 177, 118-124.
Wu Z, Zhang M, Wang L, Tu Y, Zhang J, Xie G, Zou W, Li F, Guo K, Li Q, Gao C, Peng L. 2013. Biomass digestibility is predominantly affected by three factors of wall polymer features distinctive in wheat accessions and rice mutants. Biotechnol for Biofuels, 6, 183-196.
Xie G, Peng L. 2011. Genetic engineering of energy crops: A strategy for biofuel production in China. Journal of Integrative Plant Biology, 53, 143-150.
Xie G, Yang B, Xu Z, Li F, Guo K, Zhang M, Wang L, Zou W, Wang Y, Peng L. 2013. Global identification of multiple OsGH9 family members and their involvement in cellulose crystallinity. PLOS ONE, 8, e50171.
Xie T, Su P. 2012. Canopy and leaf photosynthetic characteristics and water use efficiency of sweet sorghum under drought stress. Russian Journal of Plant Physiology, 59, 224-234.
Xu N, Zhang W, Ren S, Liu F, Zhao C, Liao H, Xu Z, Huang J, Li Q, Tu Y, Yu B, Wang Y, Jiang J, Qin J, Peng L. 2012. Hemicelluloses negatively affect lignocellulose crystallinity for high biomass digestibility under NaOH and H2SO4 pretreatments in Miscanthus. Bitechnology for Biofuels, 5, 58-69.
Yan L Z, Zhang L, Wang S Q, Hu L. 2008. Potential yields of bioethanol from energy crops and their regional distribution in China. Transactions of the Chinese Society of Agricultural Engineering, 24, 213-216. (in Chinese)
Yang B, Dai Z, Ding S, Wyman C E. 2011. Enzymatic hydrolysis of cellulosic biomass. Biofuels, 2, 421-450.
Yu Y, Yi Z, Zhou G. 2014. Research progress and comprehensive utilization of Miscanthus. Chinese Bulletin of Life Sciences, 5, 474-480. (in Chinese)
Zegada-Lizarazu W, Monti A. 2012. Are we ready to cultivate sweet sorghum as a bioenergy feedstock? A review on field management practices. Biomass and Bioenergy, 40, 1-12.
Zhang L, Liu Z, Chen B, Hao D, Gao S, Jing H. 2012. Current status and application prospects of sweet sorghum breeding in China. Journal of China Agricultural University, 6, 76-82. (in Chinese)
Zhang W, Yi Z, Huang J, Li F, Hao B, Li M, Hong S, Lv Y, Su W, Ragauskas A, Hu F, Peng J, Peng L. 2013. Three lignocellulose features that distinctively affect biomass enzymatic digestibility under NaOH and H2SO4 pretreatments in Miscanthus. Bioresource Technology, 130, 30-37.
Zhang Y, Lynd L R. 2014. Toward an aggregated understanding of enzymatic hydrolysis of cellulose: Noncomplexed cellulase systems. Biotechnology and Bioengineering, 88, 797-824.
Zhao Z, Cai T, Tagliani L, Miller M, Wang N, Pang H, Rudert M, Schroeder S, Hondred D, Seltzer J, Pierce D. 2000. Agrobacterium-mediated sorghum transformation. Plant Molecular Biology, 44, 789-798.
Zheng L, He B, Sun L, Peng Y, Dong S, Liu T, Jiang S, Ramachandran S, Liu C, Jing H. 2011. Genome-wide patterns of genetic variation in sweet and grain sorghum (Sorghum bicolor). Genome Biology, 12, R114.
Zhou J, Li Q, Xiao L, Jiang J, Yi Z. 2012. Potential distribution of Miscanthus sinensis and M. floridulus in China. Chinese Journal of Plant Ecology, 36, 504-510. (in Chinese)
Zub H W, Brancourt H M. 2010. Agronomic and physiological performances of different species of Miscanthus, a major energy crop. A review. Agronomy for Sustainable Development, 30, 201-214.