Plant-based material, protein and biodegradable plastic

Sustainable Bioplastic Made from Biomass DNA and Ionomers

Plastics play important roles in modern life and currently the development of plastic recycling is highly demanding and challenging. To relieve this dilemma, one option is to develop new sustainable bioplastics that are compatible with the environment over the whole material life cycle. We report a sustainable bioplastic made from natural DNA and biomass-derived ionomers, termed as DNA plastics. The sustainability involves all aspects of the production, use, and end-of-life options of DNA plastics: (1) the raw materials are derived from biorenewable resources; (2) the water-processable strategy is environmentally friendly, not involving high-energy consumption, the use of organic solvents, and the production of byproducts; (3) recyclable and nondestructive use is achieved to significantly prolong the service lifetime of the plastics; and (4) the disposal of waste plastics follows two green routes including the recycling of waste plastics and enzyme-triggered controllable degradation under mild conditions. Besides, DNA plastics can be "aqua-welded" to form arbitrary designed products such as a plastic cup. This work provides a solution to transform biobased hydrogel to bioplastic and demonstrates the closed-loop recycling of DNA plastics, which will advance the development of sustainable materials.

Heterologous production of hyaluronic acid in Nicotiana tabacum hairy roots expressing a human hyaluronan synthase 2

Hyaluronic acid (HA), a unique polysaccharide with excellent Physico-chemical properties, is broadly used in pharmaceutical, biomedical, and cosmetic fields. It is widely present in all vertebrates, certain bacterial strains, and even viruses while it is not found in plants, fungi, and insects. HA is naturally synthesized by a class of integral membrane proteins called Hyaluronic acid synthase (HAS). Thus far, industrial production of HA is carried out based on either extraction from animal sources or large-scale microbial fermentation. The major drawbacks to using these systems are contamination with pathogens and microbial toxins. Recently, the production of HA through recombinant systems has received considerable attention. Plants are eco-friendly ideal expression systems for biopharmaceuticals production. In this study, the optimized human hyaluronic acid synthase2 (hHAS2) sequence was transformed into Nicotiana tabacum using Agrobacterium rhizogenes. The highest rhHAS2 concentration of 65.72 ng/kg (wet weight) in transgenic tobacco hairy roots was measured by the human HAS2 ELISA kit. The HA production in the transgenic hairy roots was verified by scanning electron microscope (SEM) and quantified by the HA ELISA kit. The DPPH radical scavenging activity of HA with the highest concentration of 0.56 g/kg (wet weight) showed a maximum activity of 46%. Gel Permeation Chromatography (GPC) analyses revealed the high molecular weight HA (HMW-HA) with about > 0.8 MDa.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.

Properties of Engineered and Fabricated Silks

Silk is a protein-based material which is predominantly produced by insects and spiders. Hundreds of millions of years of evolution have enabled these animals to utilize different, highly adapted silk types in a broad variety of applications. Silk occurs in several morphologies, such as sticky glue or in the shape of fibers and can, depending on the application by the respective animal, dissipate a high mechanical energy, resist heat and radiation, maintain functionality when submerged in water and withstand microbial settling. Hence, it's unsurprising that silk piqued human interest a long time ago, which catalyzed the domestication of silkworms for the production of silk to be used in textiles. Recently, scientific progress has enabled the development of analytic tools to gain profound insights into the characteristics of silk proteins. Based on these investigations, the biotechnological production of artificial and engineered silk has been accomplished, which allows the production of a sufficient amount of silk materials for several industrial applications. This chapter provides a review on the biotechnological production of various silk proteins from different species, as well as on the processing techniques to fabricate application-oriented material morphologies.

Recombinant Technology in the Development of Materials and Systems for Soft-Tissue Repair

The field of biomedicine is constantly investing significant research efforts in order to gain a more in-depth understanding of the mechanisms that govern the function of body compartments and to develop creative solutions for the repair and regeneration of damaged tissues. The main overall goal is to develop relatively simple systems that are able to mimic naturally occurring constructs and can therefore be used in regenerative medicine. Recombinant technology, which is widely used to obtain new tailored synthetic genes that express polymeric protein-based structures, now offers a broad range of advantages for that purpose by permitting the tuning of biological and mechanical properties depending on the intended application while simultaneously ensuring adequate biocompatibility and biodegradability of the scaffold formed by the polymers. This Progress Report is focused on recombinant protein-based materials that resemble naturally occurring proteins of interest for use in soft tissue repair. An overview of recombinant biomaterials derived from elastin, silk, collagen and resilin is given, along with a description of their characteristics and suggested applications. Current endeavors in this field are continuously providing more-improved materials in comparison with conventional ones. As such, a great effort is being made to put these materials through clinical trials in order to favor their future use.

Highly stretchable thermoset fibers and nonwovens using thiol-ene photopolymerization

In this report, we describe the preparation and characterization of a new class of thermoset fibers with high elongation and elastic recovery. Integrating UV-activated thiol-ene photopolymerization and electrospinning, we demonstrate an environmentally friendly single step approach to convert small monomeric precursor molecules into highly elastic fibers and nonwoven mats. The fibers were derived by in situ photopolymerization of a trifunctional vinyl ether monomer and a tetrafunctional thiol. Although thermosets often offer good chemical and thermal stability, these fibers also have a high average elongation at break of 62%. The elastomeric nature of these vinyl-ether based fibers can be partly attributed to their subambient Tg and partly to the cross-link density, monomer structure, and resulting network homogeneity. Nonwoven mats of these fibers were also stretchable and exhibited a much higher elongation at break of about 85%. These thermoset stretchable fibers could have potential applications as textile, biomedical, hot chemical filtration, and composite materials.

Transglutamination allows production and characterization of native-sized ELPylated spider silk proteins from transgenic plants

In the last two decades it was shown that plants have a great potential for production of specific heterologous proteins. But high cost and inefficient downstream processing are a main technical bottleneck for the broader use of plant-based production technology especially for protein-based products, for technical use as fibres or biodegradable plastics and also for medical applications. High-performance fibres from recombinant spider silks are, therefore, a prominent example. Spiders developed rather different silk materials that are based on proteins. These spider silks show excellent properties in terms of elasticity and toughness. Natural spider silk proteins have a very high molecular weight, and it is precisely this property which is thought to give them their strength. Transgenic plants were generated to produce ELPylated recombinant spider silk derivatives. These fusion proteins were purified by Inverse Transition Cycling (ITC) and enzymatically multimerized with transglutaminase in vitro. Layers produced by casting monomers and multimers were characterized using atomic force microscopy (AFM) and AFM-based nanoindentation. The layered multimers formed by mixing lysine- and glutamine-tagged monomers were associated with the highest elastic penetration modulus.

Recombinant DNA production of spider silk proteins

Spider dragline silk is considered to be the toughest biopolymer on Earth due to an extraordinary combination of strength and elasticity. Moreover, silks are biocompatible and biodegradable protein-based materials. Recent advances in genetic engineering make it possible to produce recombinant silks in heterologous hosts, opening up opportunities for large-scale production of recombinant silks for various biomedical and material science applications. We review the current strategies to produce recombinant spider silks.

Recombinant production of spider silk proteins

Natural spider silk fibers combine extraordinary properties such as stability and flexibility which results in a toughness superseding that of all other fiber materials. As the spider's aggressive territorial behavior renders their farming not feasible, the biotechnological production of spider silk proteins (spidroins) is essential in order to investigate and employ them for applications. In order to accomplish this task, two approaches have been tested: firstly, the expression of partial cDNAs, and secondly, the expression of synthetic genes in several host organisms, including bacteria, yeast, plants, insect cells, mammalian cells, and transgenic animals. The experienced problems include genetic instability, limitations of the translational and transcriptional machinery, and low solubility of the produced proteins. Here, an overview of attempts to recombinantly produce spidroins will be given, and advantages and disadvantages of the different approaches and host organisms will be discussed.

Stable plastid transformation for high-level recombinant protein expression: promises and challenges

Plants are a promising expression system for the production of recombinant proteins. However, low protein productivity remains a major obstacle that limits extensive commercialization of whole plant and plant cell bioproduction platform. Plastid genetic engineering offers several advantages, including high levels of transgenic expression, transgenic containment via maternal inheritance, and multigene expression in a single transformation event. In recent years, the development of optimized expression strategies has given a huge boost to the exploitation of plastids in molecular farming. The driving forces behind the high expression level of plastid bioreactors include codon optimization, promoters and UTRs, genotypic modifications, endogenous enhancer and regulatory elements, posttranslational modification, and proteolysis. Exciting progress of the high expression level has been made with the plastid-based production of two particularly important classes of pharmaceuticals: vaccine antigens, therapeutic proteins, and antibiotics and enzymes. Approaches to overcome and solve the associated challenges of this culture system that include low transformation frequencies, the formation of inclusion bodies, and purification of recombinant proteins will also be discussed.

Plastid genetic engineering in Solanaceae

Plastid genetic engineering has come of age, becoming today an attractive alternative approach for the expression of foreign genes, as it offers several advantages over nuclear transformants. Significant progress has been made in plastid genetic engineering in tobacco and other Solanaceae plants, through the use of improved regeneration procedures and transformation vectors with efficient promoters and untranslated regions. Many genes encoding for industrially important proteins and vaccines, as well as genes conferring important agronomic traits, have been stably integrated and expressed in the plastid genome. Despite these advances, it remains a challenge to achieve marked levels of plastid transgene expression in non-green tissues. In this review, we summarize the basic requirements of plastid genetic engineering and discuss the current status, limitations, and the potential of plastid transformation for expanding future studies relating to Solanaceae plants.

Environment-Friendly Cottonseed Protein Bioplastics: Preparation and Properties

A novel class of environmentally friendly protein-based bioplastics—cottonseed protein plastic sheets (CP-sheets)—were prepared by compression molding in the presence of cottonseed flour as main raw material, aldehydes as crosslink agent and glycerol as plasticizer. FTIR, TGA, tensile tests and water uptake measurements were applied to characterize the structure, thermal stability, mechanical properties and water absorption of the CP-sheets. It was found that the crosslinked CP-sheets (CP-FA, CP-GX and CP-GA) showed higher thermal stability and tensile properties, less water uptake than the CP-sheet withou crosslinking treatment (CP-0CL). The CP-sheets with good thermal, mechanical and hydrophobic properties are emerging and promising bioplastics for potential applications in food packaging as well as flower planting.

Construction of PHB and PHBV multiple-gene vectors driven by an oil palm leaf-specific promoter

One of the targets in oil palm genetic engineering programme is the production of polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) in the oil palm leaf tissues. Production of PHB requires the use of phbA (beta-ketothiolase type A), phbB (acetoacetyl-CoA reductase) and phbC (PHB synthase) genes of Ralstonia eutropha, whereas bktB (beta-ketothiolase type B), phbB, phbC genes of R. eutropha and tdcB (threonine dehydratase) gene of Escherichia coli were used for PHBV production. Each of these genes was fused with a transit peptide (Tp) of oil palm acyl-carrier-protein (ACP) gene, driven by an oil palm leaf-specific promoter (LSP1) to genetically engineer the PHB/PHBV pathway to the plastids of the leaf tissues. In total, four transformation vectors, designated pLSP15 (PHB) and pLSP20 (PHBV), and pLSP13 (PHB) and pLSP23 (PHBV), were constructed for transformation in Arabidopsis thaliana and oil palm, respectively. The phosphinothricin acetyltransferase gene (bar) driven by CaMV35S promoter in pLSP15 and pLSP20, and ubiquitin promoter in pLSP13 and pLSP23 were used as the plant selectable markers. Matrix attachment region of tobacco (RB7MAR) was also included in the vectors to stabilize the transgene expression and to minimize silencing due to positional effect. Restriction digestion, PCR amplification and/or sequencing were carried out to ensure sequence integrity and orientation.

Plants as bioreactors: Recent developments and emerging opportunities

In recent years, the use of plants as bioreactors has emerged as an exciting area of research and significant advances have created new opportunities. The driving forces behind the rapid growth of plant bioreactors include low production cost, product safety and easy scale up. As the yield and concentration of a product is crucial for commercial viability, several strategies have been developed to boost up protein expression in transgenic plants. Augmenting tissue-specific transcription, elevating transcript stability, tissue-specific targeting, translation optimization and sub-cellular accumulation are some of the strategies employed. Various kinds of products that are currently being produced in plants include vaccine antigens, medical diagnostics proteins, industrial and pharmaceutical proteins, nutritional supplements like minerals, vitamins, carbohydrates and biopolymers. A large number of plant-derived recombinant proteins have reached advanced clinical trials. A few of these products have already been introduced in the market.

Dispersal of viable row-crop seeds of commercial agriculture by farmland birds: implication for genetically modified crops

To address some concerns about the expansion of genetically engineered pharmaceutical and industrial crops to outdoor plantings and potential impacts on the human food supply, we determined whether commercial agriculture seeds of maize or corn Zea mays L., barley Hordeum vulgare L., safflower Carthamus tinctorius L. and rice Oryza sativa L. are digested or pass viably through the digestive tract, or are transported externally, by captive mallard ducks Anas platyrhynchos L., ring-necked pheasants Phasianus colchicus L., red-winged blackbirds Agelaius phoeniceus (L.) and rock pigeons Columba livia Gmelin (with the exception of whole maize seeds which were too large to feed to the blackbirds). These crop seeds, whether free-fed or force-fed, did not pass through the digestive tract of these bird species. The birds nonetheless did retain viable seeds in the esophagus/crop and gizzard for several hours. For example, after foraging for 6 h, mallards had retained an average of 228 +/- 112 barley seeds and pheasants 192 +/- 78 in the esophagus/crop, and their germination rates were 93 and 50%, respectively. Birds externally transported seeds away from the feeding location, but in only four instances were seeds found attached to their muddy feet or legs and in no case to feathers. Risk of such crop seeds germinating, establishing and reproducing off site after transport by a bird (externally or internally) or movement of a carcass by a predator, will depend greatly on the crop and bird species, location, environmental conditions (including soil characteristics), timing, and seed condition.

High levels of stable phytase accumulate in the culture medium of transgenic Medicago truncatula cell suspension cultures

The use of plants for production of recombinant proteins is becoming widely accepted. More recently, plant cell cultures have been proposed as valuable systems for producing a wide range of biologically active proteins. Such systems provide certain advantages over whole plants, but yields are still considered a limitation. In this study we established a Medicago truncatula cell suspension line expressing phytase from Aspergillus niger. Phytase is an N-glycosylated enzyme that breaks down indigestible phytate, resulting in an increased availability of phosphorus and other minerals in monogastric animals and reduced levels of phosphorus output in their manure. Various production systems have previously been used to express heterologous phytase, including several plant species. In this work, remarkable amounts of enzymatically active recombinant phytase were produced and secreted into the culture medium. Recombinant phytase accumulated to at least 25 mg/L and remained stable along the growth curve, and an enriched fraction with high enzymatic activity was easily obtained. We therefore propose M. truncatula cell suspension cultures as a potential system for the production of recombinant proteins. Most importantly, we have shown that, contrary to general belief, it is possible to achieve high levels of a functional recombinant protein in plant cell culture systems.

Production of renewable polymers from crop plants

Plants produce a range of biopolymers for purposes such as maintenance of structural integrity, carbon storage, and defense against pathogens and desiccation. Several of these natural polymers are used by humans as food and materials, and increasingly as an energy carrier. In this review, we focus on plant biopolymers that are used as materials in bulk applications, such as plastics and elastomers, in the context of depleting resources and climate change, and consider technical and scientific bottlenecks in the production of novel or improved materials in transgenic or alternative crop plants. The biopolymers discussed are natural rubber and several polymers that are not naturally produced in plants, such as polyhydroxyalkanoates, fibrous proteins and poly-amino acids. In addition, monomers or precursors for the chemical synthesis of biopolymers, such as 4-hydroxybenzoate, itaconic acid, fructose and sorbitol, are discussed briefly.

Engineering plant oils as high-value industrial feedstocks for biorefining: the need for underpinning cell biology research

Plant oils represent renewable sources of long-chain hydrocarbons that can be used as both fuel and chemical feedstocks, and genetic engineering offers an opportunity to create further high-value specialty oils for specific industrial uses. While many genes have been identified for the production of industrially important fatty acids, expression of these genes in transgenic plants has routinely resulted in a low accumulation of the desired fatty acids, indicating that significantly more knowledge of seed oil production is required before any future rational engineering designs are attempted. Here, we provide an overview of the cellular features of fatty acid desaturases, the so-called diverged desaturases, and diacylglycerol acyltransferases, three sets of enzymes that play a central role in determining the types and amounts of fatty acids that are present in seed oil, and as such, the final application and value of the oil. Recent studies of the intracellular trafficking, assembly and regulation of these enzymes have provided new insights to the mechanisms of storage oil production, and suggest that the compartmentalization of enzyme activities within specific regions or subdomains of the ER may be essential for both the synthesis of novel fatty acid structures and the channeling of these important fatty acids into seed storage oils.

High expression of transgene protein in Spirodela

The monocot family Lemnaceae (duckweed) is composed of small, edible, aquatic plants. Spirodela oligorrhiza SP is a duckweed with a biomass doubling time of about 2 days under controlled, axenic conditions. Stably transformed Spirodela plants were obtained following co-cultivation of regenerative calli with Agrobacterium tumefaciens. GFP activity was successfully monitored in different subcellular compartments of the plant and correlated with different targeting sequences. Transgenic lines were followed for a period of at least 18 months and more than 180 vegetative doublings (generations). The lines are stable in morphology, growth rate, transgene expression, and activity as measured by DNA-DNA and immunoblot hybridizations, fluorescence activity measurements, and antibiotic resistance. The level of transgene expression is a function of leader sequences rather than transgene copy number. A stable, transgenic, GFP expression level >25% of total soluble protein is demonstrated for the S. oligorrhiza system, making it among the higher expressing systems for nuclear transformation in a higher plant.

Prospects for biopolymer production in plants

It is likely that during this century polymers based on renewable materials will gradually replace industrial polymers based on petrochemicals. This chapter gives an overview of the current status of research on plant biopolymers that are used as a material in non-food applications. We cover technical and scientific bottlenecks in the production of novel or improved materials, and the potential of using transgenic or alternative crops in overcoming these bottlenecks. Four classes of biopolymers will be discussed: starch, proteins, natural rubber, and poly-beta-hydroxyalkanoates. Renewable polymers produced by chemical polymerization of monomers derived from sugars, vegetable oil, or proteins, are not considered here.

Biotechnological Production of Spider-Silk Proteins Enables New Applications

The outstanding mechanical properties of spider silks have motivated many researchers to establish biotechnological production techniques which are necessary to provide sufficient amounts of silk proteins for industrial applications. Based on recent developments in genetic engineering, two strategies for the recombinant production of spider-silk proteins have been established which are discussed in detail. Further, protein-design strategies are described, enabling the combination of silk properties with additional biological, chemical, or technical features. We highlight the potential of engineered and recombinantly-produced spider-silk proteins to provide the basis for a new generation of biomaterials.

Functional expression of a biologically active fragment of soluble gp130 as an ELP-fusion protein in transgenic plants: purification via inverse transition cycling

In murine models of Crohn's disease, rheumatoid arthritis and colon cancer, IL-6 (interleukin-6) signalling via the sIL-6R (soluble IL-6 receptor; termed IL-6 trans-signalling) has been shown to promote the pathology associated with these conditions. These detrimental activities can, however, be selectively blocked by soluble forms of the gp130 (glycoprotein 130) receptor. Although sgp130 (soluble gp130) therefore represents a viable therapeutic modality for the treatment of these conditions, the mass manufacture of such biologics is often expensive. The advent of molecular farming has, however, provided an extremely cost-effective strategy for the engineering of recombinant proteins. Here, we describe the expression and production of a biologically active sgp130 variant that is expressed in transgenic tobacco plants as an ELP (elastin-like peptide)-fusion protein (mini-gp130-ELP). Mini-gp130-ELP consists of the first three domains of gp130 (Ig-like domain and cytokine binding module) fused to 100 repeats of ELP. Expression of mini-gp130-ELP did not affect the growth rate or morphology of the transgenic plants, and purification was achieved using inverse transition cycling. This approach led to an overall yield of 141 microg of purified protein per g of fresh leaf weight. The purified mini-gp130-ELP specifically inhibited sIL-6R-mediated trans-signalling as measured by binding to the IL-6-sIL-6R complex and through its ability to block sIL-6R-mediated activation of STAT3 (signal transducer and activator of transcription 3) phosphorylation and proliferation in human hepatoma cells and murine pre-B-cells. Consequently, the present study validates the potential application of molecular farming in transgenic tobacco plants as a strategy for the expression and purification of therapeutically advantageous biologics such as sgp130.

Polymers from plants to develop biodegradable plastics

Katrin Neumann et al. have recently shown that transgenic tobacco and potato plants can accumulate high levels of cyanophycin, a possible source for poly-aspartate. This work opens the way to the future production of biodegradable plastics using a plant-based production system. Several problems need to be overcome first, such as growth retardation as a result of cyanophycin accumulating in the cytosol, and a co-production system needs to be developed for economical reasons.