Genetic Engineering of Energy Crops: A Strategy for Biofuel Production in China Free Access

Biomass utilization is increasingly considered as a practical way for sustainable energy supply and long‐term environment care around the world. In concerns with food security in China, starch or sugar‐based bioethanol and edible‐oil‐derived biodiesel are harshly restricted for large scale production. However, conversion of lignocellulosic residues from food crops is a potential alternative. Because of its recalcitrance, current biomass process is unacceptably expensive, but genetic breeding of energy crops is a promising solution. To meet the need, energy crops are defined with a high yield for both food and biofuel purposes. In this review, main grasses (rice, wheat, maize, sorghum and miscanthus) are evaluated for high biomass production, the principles are discussed on modification of plant cell walls that lead to efficient biomass degradation and conversion, and the related biotechnologies are proposed in terms of energy crop selection.     

Modifying plants for biofuel and biomaterial production

The productivity of plants as biofuel or biomaterial crops is established by both the yield of plant biomass per unit area of land and the efficiency of conversion of the biomass to biofuel. Higher yielding biofuel crops with increased conversion efficiencies allow production on a smaller land footprint minimizing competition with agriculture for food production and biodiversity conservation. Plants have traditionally been domesticated for food, fibre and feed applications. However, utilization for biofuels may require the breeding of novel phenotypes, or new species entirely. Genomics approaches support genetic selection strategies to deliver significant genetic improvement of plants as sources of biomass for biofuel manufacture. Genetic modification of plants provides a further range of options for improving the composition of biomass and for plant modifications to assist the fabrication of biofuels. The relative carbohydrate and lignin content influences the deconstruction of plant cell walls to biofuels. Key options for facilitating the deconstruction leading to higher monomeric sugar release from plants include increasing cellulose content, reducing cellulose crystallinity, and/or altering the amount or composition of noncellulosic polysaccharides or lignin. Modification of chemical linkages within and between these biomass components may improve the ease of deconstruction. Expression of enzymes in the plant may provide a cost‐effective option for biochemical conversion to biofuel.     

C_4 Plants as Biofuel Feedstocks: Optimising Biomass Production and Feedstock Quality from a Lignocellulosic Perspective

The main feedstocks for bioethanol are sugarcane (Saccharum officinarum) and maize (Zea mays),both of which are C4 grasses,highly efficient at converting solar energy into chemical energy,and both are food crops.As the systems for lignocellulosic bioethanol production become more efficient and cost effective,plant biomass from any source may be used as a feedstock for bioethanol production.Thus,a move away from using food plants to make fuel is possible,and sources of biomass such as wood from forestry and ...     

基因工程在能源植物改良中的应用

利用基因工程技术改良能源植物,对降低能源植物向生物燃料(生物乙醇、生物柴油)的转化成本、提高能源转化效率有着非常重要的意义。目前,基因工程技术已被广泛应用于提高植物总的生物产量、降低或改变植物木质素的含量与成分、在植物体中大量表达纤维素降解酶、提高油料植物的产油量以及改变植物油酯的组成成分等方面的研究。概述了利用基因工程技术在以上方面对能源植物进行改良已取得的进展,讨论了现存问题及未来的发展前景。     

Scientific challenges of bioethanol production in Brazil

Bioethanol (fuel alcohol) has been produced by industrial alcoholic fermentation processes in Brazil since the beginning of the twentieth century. Currently, 432 mills and distilleries crush about 625 million tons of sugarcane per crop, producing about 27 billion liters of ethanol and 38.7 million tons of sugar. The production of bioethanol from sugarcane represents a major large-scale technology capable of producing biofuel efficiently and economically, providing viable substitutes to gasoline. The combination of immobilization of CO₂ by sugarcane crops by photosynthesis into biomass together with alcoholic fermentation of this biomass has allowed production of a clean and high-quality liquid fuel that contains 93% of the original energy found in sugar. Over the last 30 years, several innovations have been introduced to Brazilian alcohol distilleries resulting in the improvement of plant efficiency and economic competitiveness. Currently, the main scientific challenges are to develop new technologies for bioethanol production from first and second generation feedstocks that exhibit positive energy balances and appropriately meet environmental sustainability criteria. This review focuses on these aspects and provides special emphasis on the selection of new yeast strains, genetic breeding, and recombinant DNA technology, as applied to bioethanol production processes.     

Genetic Engineering of Energy Crops: A Strategy for Biofuel Production in China

Biomass utilization is increasingly considered as a practical way for sustainable energy supply and long-term environment care around the world.In concerns with food security in China,starch or sugar-based bioethanol and edible-oil-derived biodiesel are harshly restricted for large scale production.However,conversion of lignocellulosic residues from food crops is a potential alternative.Because of its recalcitrance,current biomass process is unacceptably expensive,but genetic breeding of energy crops is a p...     

C4 plants as biofuel feedstocks: optimising biomass production and feedstock quality from a lignocellulosic perspective

The main feedstocks for bioethanol are sugarcane (Saccharum officinarum) and maize (Zea mays), both of which are C(4) grasses, highly efficient at converting solar energy into chemical energy, and both are food crops. As the systems for lignocellulosic bioethanol production become more efficient and cost effective, plant biomass from any source may be used as a feedstock for bioethanol production. Thus, a move away from using food plants to make fuel is possible, and sources of biomass such as wood from forestry and plant waste from cropping may be used. However, the bioethanol industry will need a continuous and reliable supply of biomass that can be produced at a low cost and with minimal use of water, fertilizer and arable land. As many C(4) plants have high light, water and nitrogen use efficiency, as compared with C(3) species, they are ideal as feedstock crops. We consider the productivity and resource use of a number of candidate plant species, and discuss biomass 'quality', that is, the composition of the plant cell wall.     

A review of biological delignification and detoxification methods for lignocellulosic bioethanol production

Future biorefineries will integrate biomass conversion processes to produce fuels, power, heat and value-added chemicals. Due to its low price and wide distribution, lignocellulosic biomass is expected to play an important role toward this goal. Regarding renewable biofuel production, bioethanol from lignocellulosic feedstocks is considered the most feasible option for fossil fuels replacement since these raw materials do not compete with food or feed crops. In the overall process, lignin, the natural barrier of the lignocellulosic biomass, represents an important limiting factor in biomass digestibility. In order to reduce the recalcitrant structure of lignocellulose, biological pretreatments have been promoted as sustainable and environmentally friendly alternatives to traditional physico-chemical technologies, which are expensive and pollute the environment. These approaches include the use of diverse white-rot fungi and/or ligninolytic enzymes, which disrupt lignin polymers and facilitate the bioconversion of the sugar fraction into ethanol. As there is still no suitable biological pretreatment technology ready to scale up in an industrial context, white-rot fungi and/or ligninolytic enzymes have also been proposed to overcome, in a separated or in situ biodetoxification step, the effect of the inhibitors produced by non-biological pretreatments. The present work reviews the latest studies regarding the application of different microorganisms or enzymes as useful and environmentally friendly delignification and detoxification technologies for lignocellulosic biofuel production. This review also points out the main challenges and possible ways to make these technologies a reality for the bioethanol industry.     

Improvement of biomass through lignin modification

Lignin, a major component of the cell wall of vascular plants, has long been recognized for its negative impact on forage quality, paper manufacturing, and, more recently, cellulosic biofuel production. Over the last two decades, genetic and biochemical analyses of brown midrib mutants of maize, sorghum and related grasses have advanced our understanding of the relationship between lignification and forage digestibility. This work has also inspired genetic engineering efforts aimed at generating crops with altered lignin, with the expectation that these strategies would enhance forage digestibility and/or pulping efficiency. The knowledge gained from these bioengineering efforts has greatly improved our understanding of the optimal lignin characteristics required for various applications of lignocellulosic materials while also contributing to our understanding of the lignin biosynthetic pathway. The recent upswing of interest in cellulosic biofuel production has become the new focus of lignin engineering. Populus trichocarpa and Brachypodium distachyon are emerging as model systems for energy crops. Lignin research on these systems, as well as on a variety of proposed energy crop species, is expected to shed new light on lignin biosynthesis and its regulation in energy crops, and lead to rational genetic engineering approaches to modify lignin for improved biofuel production.     

Role of transgenic plants in agriculture and biopharming

At present, environmental degradation and the consistently growing population are two main problems on the planet earth. Fulfilling the needs of this growing population is quite difficult from the limited arable land available on the globe. Although there are legal, social and political barriers to the utilization of biotechnology, advances in this field have substantially improved agriculture and human life to a great extent. One of the vital tools of biotechnology is genetic engineering (GE) which is used to modify plants, animals and microorganisms according to desired needs. In fact, genetic engineering facilitates the transfer of desired characteristics into other plants which is not possible through conventional plant breeding. A variety of crops have been engineered for enhanced resistance to a multitude of stresses such as herbicides, insecticides, viruses and a combination of biotic and abiotic stresses in different crops including rice, mustard, maize, potato, tomato, etc. Apart from the use of GE in agriculture, it is being extensively employed to modify the plants for enhanced production of vaccines, hormones, etc. Vaccines against certain diseases are certainly available in the market, but most of them are very costly. Developing countries cannot afford the disease control through such cost-intensive vaccines. Alternatively, efforts are being made to produce edible vaccines which are cheap and have many advantages over the commercialized vaccines. Transgenic plants generated for this purpose are capable of expressing recombinant proteins including viral and bacterial antigens and antibodies. Common food plants like banana, tomato, rice, carrot, etc. have been used to produce vaccines against certain diseases like hepatitis B, cholera, HIV, etc. Thus, the up- and down-regulation of desired genes which are used for the modification of plants have a marked role in the improvement of genetic crops. In this review, we have comprehensively discussed the role of genetic engineering in generating transgenic lines/cultivars of different crops with improved nutrient quality, biofuel production, enhanced production of vaccines and antibodies, increased resistance against insects, herbicides, diseases and abiotic stresses as well as the safety measures for their commercialization.     

Impact of protein concentrate coproducts on net land requirement for European biofuel production

A methodology is proposed for calculating the net land area requirement for European biofuels, accounting for the substitution impact of animal feed protein coproducts such as dried distillers grains and solubles (DDGS) and rape meal. For example, when bioethanol is produced from cereal grain starch, grain protein is preserved in the DDGS coproduct. Each tonne of wheat DDGS has the potential to replace 0.59 tonnes of soy meal and 0.39 tonnes of cereals in EU animal feed, and the land area required for soy and cereal feed production offsets much of the land requirement for wheat bioethanol feedstock. While the land area needed for bioethanol from feed wheat in North West Europe is 0.40 ha t^?1, the net requirement after accounting for coproducts is just 0.03ha t^?1 of bioethanol produced, 6% of the gross land requirement. Calculated in this way, the net land area required to produce biofuel from EU cereal, rapeseed and sugar beet crops is much lower than the gross land requirement, and from cereal and sugar beet crops is less than the land requirement of biofuel from oil palm and sugar cane.     

Global Potential of Rice Husk as a Renewable Feedstock for Ethanol Biofuel Production

The production of ethanol for the energy market has traditionally been from corn and sugar cane biomass. The use of such biomass as energy feedstocks has recently been criticised as ill-fated due to competitive threat against food supplies. At the same time, ethanol production from cellulosic biomass is becoming increasingly popular. In this paper, we analyse rice husk (RH) as a cellulosic feedstock for ethanol biofuel production on the ground of its abundance. The global potential production of bioethanol from RH is estimated herein and found to be in the order of 20.9 to 24.3 GL per annum, potentially satisfying around one fifth of the global ethanol biofuel demand for a 10% gasohol fuel blend. Furthermore, we show that this is especially advantageous for Asia, in particular, India and China, where economic growth and demand for energy are exploding.     

Industrial‐strength ecology: trade‐offs and opportunities in algal biofuel production

Microalgae represent one of the most promising groups of candidate organisms for replacing fossil fuels with contemporary primary production as a renewable source of energy. Algae can produce many times more biomass per unit area than terrestrial crop plants, easing the competing demands for land with food crops and native ecosystems. However, several aspects of algal biology present unique challenges to the industrial‐scale aquaculture of photosynthetic microorganisms. These include high susceptibility to invading aquatic consumers and weeds, as well as prodigious requirements for nutrients that may compete with the fertiliser demands of other crops. Most research on algal biofuel technologies approaches these problems from a cellular or genetic perspective, attempting either to engineer or select algal strains with particular traits. However, inherent functional trade‐offs may limit the capacity of genetic selection or synthetic biology to simultaneously optimise multiple functional traits for biofuel productivity and resilience. We argue that a community engineering approach that manages microalgal diversity, species composition and environmental conditions may lead to more robust and productive biofuel ecosystems. We review evidence for trade‐offs, challenges and opportunities in algal biofuel cultivation with a goal of guiding research towards intensifying bioenergy production using established principles of community and ecosystem ecology.     

QTL Mapping of Enzymatic Saccharification in Short Rotation Coppice Willow and Its Independence from Biomass Yield

Short rotation coppice (SRC) willows (Salix spp.) are fast-growing woody plants which can achieve high biomass yields over short growth cycles with low agrochemical inputs. Biomass from SRC willow is already used for heat and power, but its potential as a source of lignocellulose for liquid transport biofuels has still to be assessed. In bioethanol production from lignocellulose, enzymatic saccharification is used as an approach to release glucose from cellulose in the plant cell walls. In this study, 138 genotypes of a willow mapping population were used to examine variation in enzymatic glucose release from stem biomass to study relationships between this trait and biomass yield traits and to identify quantitative trait loci (QTL) associated with enzymatic saccharification yield. Significant natural variation was found in glucose yields from willow stem biomass. This trait was independent of biomass yield traits. Four enzyme-derived glucose QTL were mapped onto chromosomes V, X, XI, and XVI, indicating that enzymatic saccharification yields are under significant genetic influence. Our results show that SRC willow has strong potential as a source of bioethanol and that there may be opportunities to improve the breeding programs for willows for increasing enzymatic saccharification yields and biofuel production.     

Cost-effectiveness of bioethanol policies to reduce carbon dioxide emissions in Greece

Purpose

The aim of this study was to evaluate the cost-effectiveness of bioethanol as regards to its carbon dioxide emissions. The production of the raw material accounts for more than 50 % of the total cost as well as having a significant part of greenhouse gases emitted during the entire process. For this reason, special emphasis is given to a change in agricultural land usage influenced by the demand of biofuel. Therefore, we have estimated the extent of policy influence according to its bioethanol cost-effectiveness. A case study on bioethanol production in an ex-sugar factory in the region of Thessaly, Greece, illustrates the above ideas.

Methods

A partial equilibrium micro-economic model of regional supply in the arable farming system of Thessaly was coupled to industrial processing sub-models of bioethanol production from beets and grains. The maximisation of total welfare determines the most suitable crop mix for farmers as well as the lowest cost configurations for industry and, eventually, the minimal level of support by the government for biofuel activity to take off. The environmental performance is assessed under the life cycle assessment (LCA) framework following three interrelated phases: data inventory, data analysis and interpretation. The economic burden to society to support the activity divided by avoided CO₂ eq. emissions indicates the bioethanol cost-effectiveness, in other words, the cost of greenhouse gases emissions savings.

Results

The integrated agro-industry model has been parametrically run for a range of biofuel capacities. A change in direct land use results in lower emissions in the agricultural phase, since energy crops are a substitute for intensive cultivations, such as cotton and corn. A change in indirect land use moderates these estimations, as it takes in account imported food crops that are replaced by energy crops in the region. The savings in cost vary around 160 euros per ton of CO₂ eq. for the basic agricultural policy scenario. The current policy that supports cotton production by means of increased coupled area payment has increased up to 30 % the cost of greenhouse gas savings due to bioethanol production.

Conclusions

An integrated model, articulating the agricultural supply of biomass with ethanol processing, maximises the total surplus that is under constraints in order to determine the cost-effectiveness for different production levels. Results demonstrate that economic performances, as well as the environmental cost-effectiveness of bioethanol, are clearly affected by the parameters of agricultural policies. Therefore, bioenergy, environmental and economic performances, when based on LCA and the conceptual change in land usage, are context dependent. Agricultural policies for decoupling subsidies from production are in favour of cultivation in biomass for energy purposes.     

Molecular marker-assisted breeding options for maize improvement in Asia

Maize is one of the most important food and feed crops in Asia, and is a source of income for several million farmers. Despite impressive progress made in the last few decades through conventional breeding in the “Asia-7” (China, India, Indonesia, Nepal, Philippines, Thailand, and Vietnam), average maize yields remain low and the demand is expected to increasingly exceed the production in the coming years. Molecular marker-assisted breeding is accelerating yield gains in USA and elsewhere, and offers tremendous potential for enhancing the productivity and value of Asian maize germplasm. We discuss the importance of such efforts in meeting the growing demand for maize in Asia, and provide examples of the recent use of molecular markers with respect to (i) DNA fingerprinting and genetic diversity analysis of maize germplasm (inbreds and landraces/OPVs), (ii) QTL analysis of important biotic and abiotic stresses, and (iii) marker-assisted selection (MAS) for maize improvement. We also highlight the constraints faced by research institutions wishing to adopt the available and emerging molecular technologies, and conclude that innovative models for resource-pooling and intellectual-property-respecting partnerships will be required for enhancing the level and scope of molecular marker-assisted breeding for maize improvement in Asia. Scientists must ensure that the tools of molecular marker-assisted breeding are focused on developing commercially viable cultivars, improved to ameliorate the most important constraints to maize production in Asia.     

Foxtail millet: a model crop for genetic and genomic studies in bioenergy grasses

Foxtail millet is one of the oldest domesticated diploid C₄ Panicoid crops having a comparatively small genome size of approximately 515?Mb, short life cycle, and inbreeding nature. Its two species, Setaria italica (domesticated) and Setaria viridis (wild progenitor), have characteristics that classify them as excellent model systems to examine several aspects of architectural, evolutionary, and physiological importance in Panicoid grasses especially the biofuel crops such as switchgrass and napiergrass. Foxtail millet is a staple crop used extensively for food and fodder in parts of Asia and Africa. In its long history of cultivation, it has been adapted to arid and semi-arid areas of Asia, North Africa, South and North America. Foxtail millet has one of the largest collections of cultivated as well as wild-type germplasm rich with phenotypic variations and hence provides prospects for association mapping and allele-mining of elite and novel variants to be incorporated in crop improvement programs. Most of the foxtail millet accessions can be primarily abiotic stress tolerant particularly to drought and salinity, and therefore exploiting these agronomic traits can enhance its efficacy in marker-aided breeding as well as in genetic engineering for abiotic stress tolerance. In addition, the release of draft genome sequence of foxtail millet would be useful to the researchers worldwide in not only discerning the molecular basis of biomass production in biofuel crops and the methods to improve it, but also for the introgression of beneficial agronomically important characteristics in foxtail millet as well as in related Panicoid bioenergy grasses.     

Use of tropical maize for bioethanol production

Tropical maize is an alternative energy crop being considered as a feedstock for bioethanol production in the North Central and Midwest United States. Tropical maize is advantageous because it produces large amounts of soluble sugars in its stalks, creates a large amount of biomass, and requires lower inputs (e.g. nitrogen) than grain corn. Soluble sugars, including sucrose, glucose and fructose were extracted by pressing the stalks at dough stage (R4). The initial extracted syrup fermented faster than the control culture grown on a yeast extract/phosphate/sucrose medium. The syrup was subsequently concentrated 1.25–2.25 times, supplemented with urea, and fermented using Saccharomyces cerevisiae for up to 96 h. The final ethanol concentrations obtained were 8.1 % (v/v) to 15.6 % (v/v), equivalent to 90.3–92.2 % of the theoretical yields. However, fermentation productivity decreased with sugar concentration, suggesting that the yeast might be osmotically stressed at the increased sugar concentrations. These results provide in-depth information for utilizing tropical maize syrup for bioethanol production that will help in tropical maize breeding and development for use as another feedstock for the biofuel industry.     

Food and bioenergy: reviewing the potential of dual‐purpose wheat crops

Within the bioenergy debate, the ‘food vs. fuel’ controversy quickly replaced enthusiasm for biofuels derived from first‐generation feedstocks. Second‐generation biofuels offer an opportunity to produce fuels from dedicated energy crops, waste materials or coproducts such as cereal straw. Wheat represents one of the most widely grown arable crops around the world, with wheat straw, a potential source of biofuel feedstock. Wheat straw currently has limited economic value; hence, wheat cultivars have been bred for increased grain yield; however, with the development of second‐generation biofuel production, utilization of straw biomass provides the potential for ‘food and fuel’. Reviewing the evidence for the development of dual‐purpose wheat cultivars optimized for food grain and straw biomass production, we present a holistic assessment of a potential ideotype for a dual‐purpose cultivar (DPC). An ideal DPC would be characterized by high grain and straw yields, high straw digestibility (i.e. biofuel yield potential) and good lodging resistance. Considerable variation in these traits exists among current wheat cultivars, facilitating the selection of improved individual traits; however, increasing straw yield and digestibility could potentially have negative trade‐off impacts on grain yield and lodging resistance, reducing the feasibility of a single ideotype. Adoption of alternative management practices could potentially increase straw yield and digestibility, albeit these practices are also associated with potential trade‐offs among cultivar traits. Benefits from using DPCs include reduced logistics costs along the biofuel feedstock supply chain, but practical barriers to differential pricing for straw digestibility traits are likely to reduce the financial incentive to farmers for growing higher ‘biofuel‐quality’ straw cultivars. Further research is required to explore the relationships among the ideotype traits to quantify potential DPC benefits; this will help to determine whether stakeholders along the bioenergy feedstock supply chain will invest in the development of DPCs that provide food and fuel potential.     

Genetic modification of lignin biosynthesis for improved biofuel production

The energy in cellulosic biomass largely resides in plant cell walls. Cellulosic biomass is more difficult than starch to break down into sugars because of the presence of lignin and the complex structure of cell walls. Transgenic down-regulation of major lignin genes led to reduced lignin content, increased dry matter degradability, and improved accessibility of cellulases for cellulose degradation. This review provides background information on lignin biosynthesis and focuses on genetic manipulation of lignin genes in important monocot species as well as the dicot potential biofuel crop alfalfa. Reduction of lignin in biofuel crops by genetic engineering is likely one of the most effective ways of reducing costs associated with pretreatment and hydrolysis of cellulosic feedstocks, although some potential fitness issues should also be addressed.