Effect of betanin synthesis on photosynthesis and tyrosine metabolism in transgenic carrot.

BACKGROUND: Betalain is a natural pigment with important nutritional value and broad application prospects. Previously, we produced betanin biosynthesis transgenic carrots via expressing optimized genes CYP76AD1S, cDOPA5GTS and DODA1S. Betanin can accumulate throughout the whole transgenic carrots. But the effects of betanin accumulation on the metabolism of transgenic plants and whether it produces unexpected effects are still unclear. RESULTS: The accumulation of betanin in leaves can significantly improve its antioxidant capacity and induce a decrease of chlorophyll content. Transcriptome and metabolomics analysis showed that 14.0% of genes and 33.1% of metabolites were significantly different, and metabolic pathways related to photosynthesis and tyrosine metabolism were markedly altered. Combined analysis showed that phenylpropane biosynthesis pathway significantly enriched the differentially expressed genes and significantly altered metabolites. CONCLUSIONS: Results showed that the metabolic status was significantly altered between transgenic and non-transgenic carrots, especially the photosynthesis and tyrosine metabolism. The extra consumption of tyrosine and accumulation of betanin might be the leading causes.

Genetic engineering of complex feed enzymes into barley seed for direct utilization in animal feedstuff.

Currently, feed enzymes are primarily obtained through fermentation of fungi, bacteria, and other microorganisms. Although the manufacturing technology for feed enzymes has evolved rapidly, the activities of these enzymes decline during the granulating process and the cost of application has increased over time. An alternative approach is the use of genetically modified plants containing complex feed enzymes for direct utilization in animal feedstuff. We co-expressed three commonly used feed enzymes (phytase, ß-glucanase, and xylanase) in barley seeds using the Agrobacterium-mediated transformation method and generated a new barley germplasm. The results showed that these enzymes were stable and had no effect on the development of the seeds. Supplementation of the basal diet of laying hens with only 8% of enzyme-containing seeds decreased the quantities of indigestible carbohydrates, improved the availability of phosphorus, and reduced the impact of animal production on the environment to an extent similar to directly adding exogenous enzymes to the feed. Feeding enzyme-containing seeds to layers significantly increased the strength of the eggshell and the weight of the eggs by 10.0%-11.3% and 5.6%-7.7% respectively. The intestinal microbiota obtained from layers fed with enzyme-containing seeds was altered compared to controls and was dominated by Alispes and Rikenella. Therefore, the transgenic barley seeds produced in this study can be used as an ideal feedstuff for use in animal feed.

Metabolic engineering of Escherichia coli for 2,4-dinitrotoluene degradation.

2,4-Dinitrotoluene (2,4-DNT) as a common industrial waste has been massively discharged into the environment with industrial wastewater. Due to its refractory degradation, high toxicity, and bioaccumulation, 2,4-DNT pollution has become increasingly serious. Compared with the currently available physical and chemical methods, in situ bioremediation is considered as an economical and environmentally friendly approach to remove toxic compounds from contaminated environment. In this study, we relocated a complete degradation pathway of 2,4-DNT into Escherichia coli to degrade 2,4-DNT completely. Eight genes from Burkholderia sp. strain were re-synthesized by PCR-based two-step DNA synthesis method and introduced into E. coli. Degradation experiments revealed that the transformant was able to degrade 2,4-DNT completely in 12 h when the 2,4-DNT concentration reached 3 mM. The organic acids in the tricarboxylic acid cycle were detected to prove the degradation of 2,4-DNT through the artificial degradation pathway. The results proved that 2,4-DNT could be completely degraded by the engineered bacteria. In this study, the complete degradation pathway of 2,4-DNT was constructed in E. coli for the first time using synthetic biology techniques. This research provides theoretical and experimental bases for the actual treatment of 2,4-DNT, and lays a technical foundation for the bioremediation of organic pollutants.

Construction of complete degradation pathway for nitrobenzene in Escherichia coli.

Nitrobenzene is widely present in industrial wastewater and soil. Biodegradation has become an ideal method to remediate organic pollutants due to its low cost, high efficiency, and absence of secondary pollution. In the present study, 10 exogenous genes that can completely degrade nitrobenzene were introduced into Escherichia coli, and their successful expression in the strain was verified by fluorescence quantitative polymerase chain reaction and proteomic analysis. The results of the degradation experiment showed that the engineered strain could completely degrade 4 mM nitrobenzene within 8 h. The formation of intermediate metabolites was detected, and the final metabolites entered the E. coli tricarboxylic acid cycle smoothly. This process was discovered by isotope tracing method. Results indicated the integrality of the degradation pathway and the complete degradation of nitrobenzene. Finally, further experiments were conducted in soil to verify its degradation ability and showed that the engineered strain could also degrade 1 mM nitrobenzene within 10 h. In this study, engineered bacteria that can completely degrade nitrobenzene have been constructed successfully. The construction of remediation-engineered bacteria by synthetic biology laid the foundation for the industrial application of biological degradation of organic pollutants.

Phytoremediation of multiple persistent pollutants co-contaminated soil by HhSSB transformed plant.

The high toxicity of persistent pollutants limits the phytoremediation of pollutants-contaminated soil. In this study, heterologous expressing Halorhodospira halophila single-stranded DNA binding protein gene (HhSSB) improves tolerance to 2,4,6-trinitrotoluene (TNT), 2,4,6-trichlorophenol (2,4,6-TCP), and thiocyanate (SCN-) in A. thaliana and tall fescue (Festuca arundinacea). The HhSSB transformed Arabidopsis, and tall fescue also exhibited enhanced phytoremediation of TNT, 2,4,6-TCP, and SCN- separately contaminated soil and co-contaminated soil compared to control plants. TNT assay was selected to explore the mechanism of how HhSSB enhances the phytoremediation of persistent pollutants. Our result indicates that HhSSB enhances the phytoremediation of TNT by enhancing the transformation of TNT in Arabidopsis. Moreover, transcriptomics and comet analysis revealed that HhSSB improves TNT tolerance through three pathways: strengthening the defense system, enhancing the ROS scavenging system, and reducing DNA damage. These results presented here would be particularly useful for further studies in the remediation of soil contaminated by organic and inorganic pollutants.

Enhanced phytoremediation of TNT and cobalt co-contaminated soil by AfSSB transformed plant.

2,4,6-trinitrotoluene (TNT) and cobalt (Co) contaminants have posed a severe environmental problem in many countries. Phytoremediation is an environmentally friendly technology for the remediation of these contaminants. However, the toxicity of TNT and cobalt limit the efficacy of phytoremediation application. The present research showed that expressing the Acidithiobacillus ferrooxidans single-strand DNA-binding protein gene (AfSSB) can improve the tolerance of Arabidopsis and tall fescue to TNT and cobalt. Compared to control plants, the AfSSB transformed Arabidopsis and tall fescue exhibited enhanced phytoremediation of TNT and cobalt separately contaminated soil and co-contaminated soil. The comet analysis revealed that the AfSSB transformed Arabidopsis suffer reduced DNA damage than control plants under TNT or cobalt exposure. In addition, the proteomic analysis revealed that AfSSB improves TNT and cobalt tolerance by strengthening the reactive superoxide (ROS) scavenging system and the detoxification system. Results presented here serve as strong theoretical support for the phytoremediation potential of organic and metal pollutants mediated by single-strand DNA-binding protein genes. SUMMARIZES: This is the first report that AfSSB enhances phytoremediation of 2,4,6-trinitrotoluene and cobalt separately contaminated and co-contaminated soil.

Metabolic engineering of rice endosperm for betanin biosynthesis.

Betanin has been widely used as an additive for many centuries, and its use has increased because of its market application as an additive, high free radical scavenging activity, and safety, health-promoting properties. The main source of betanin is red beet, but many factors notably affect the yield of betanin from red beets. Betanin is not produced in cereal grains. Thus, developing biofortified crops with betanin is another alternative to health-promoting food additives. Here, rice endosperm was bioengineered for betanin biosynthesis by introducing three synthetic genes (meloS, BvDODA1S, and BvCYP76AD1S). The overexpression of these genes driven by rice endosperm-specific promoter established the betanin biosynthetic pathways in the endosperm, resulting in new types of germplasm - 'Betanin Rice' (BR). The BR grains were enriched with betanin and had relatively high antioxidant activity. Our results proved that betanin can be biosynthesized de novo in rice endosperm by introducing three genes in the committed betanin biosynthetic pathway. The betanin-fortified rice in this study can be used as a functional grain to promote health and as a raw material to process dietary supplements.

Transgenic Arabidopsis Plants Expressing Grape Glutathione S-Transferase Gene (VvGSTF13) Show Enhanced Tolerance to Abiotic Stress.

Although glutathione S-transferase (GST, EC 2.5.1.18) is thought to play important roles in abiotic stress, limited information is available regarding the function of its gene in grapes. In this study, a GST gene from grape, VvGSTF13, was cloned and functionally characterized. Transgenic Arabidopsis plants containing this gene were normal in terms of growth and maturity compared with control plants but had enhanced resistance to salt, drought, and methyl viologen stress. The increased tolerance of the transgenic plants correlated with changes in activities of antioxidative enzymes. Our results indicate that the gene from grape plays a positive role in improving tolerance to salinity, drought, and methyl viologen stresses in Arabidopsis.

Over-expression of AtGSTU19 provides tolerance to salt, drought and methyl viologen stresses in Arabidopsis.

The plant-specific tau class of glutathione S-transferases (GSTs) is often highly stress-inducible and expressed in a tissue-specific manner, thereby suggesting its important protective roles. Although activities associated with the binding and transport of reactive metabolites have been proposed, little is known about the regulatory functions of GSTs. Expression of AtGSTU19 is induced by several stimuli, but the function of this GST remains unknown. In this study, we demonstrated that transgenic over-expressing (OE) plants showed enhanced tolerance to different abiotic stresses and increased percentage of seed germination and cotyledon emergence. Transgenic plants exhibited an increased level of proline and activities of antioxidant enzymes, along with decreased malonyldialdehyde level under stress conditions. Real-time polymerase chain reaction (PCR) analyses revealed that the expression levels of several stress-regulated genes were altered in AtGSTU19 OE plants. These results indicate that AtGSTU19 plays an important role in tolerance to salt/drought/methyl viologen stress in Arabidopsis.

Enhancement of naphthalene tolerance in transgenic Arabidopsis plants overexpressing the ferredoxin-like protein (ADI1) from rice.

KEY MESSAGE: The ADI1 Arabidopsis plants enhanced tolerance and degradation efficiency to naphthalene and had great potential for phytoremediation of naphthalene in the plant material before composting or harvesting and removal. Naphthalene is a global environmental concern, because this substance is assumed to contribute considerably to human cancer risk. Cleaning up naphthalene contamination in the environment is crucial. Phytoremediation is an efficient technology to clean up contaminants. However, no gene that can efficiently degrade exogenous recalcitrant naphthalene in plants has yet been discovered. Ferredoxin (Fd) is a key player of biological electron transfer reaction in the PAH degradation process. The biochemical pathway for bacterial degradation of naphthalene has been well investigated. In this study, a rice gene, ADI1, which codes for a putative photosynthetic-type Fd, has been transformed into Arabidopsis thaliana. The transgenic Arabidopsis plants enhanced tolerance and degradation efficiency of naphthalene. Compared with wild-type plants, transgenic plants assimilated naphthalene from the culture media faster and removed more of this substance. When taken together, our findings suggest that breeding plants with overexpressed ADI1 gene is an effective strategy to degrade naphthalene in the environment.

Phytoremediation potential of Arabidopsis with reference to acrylamide and microarray analysis of acrylamide-response genes.

Acrylamide (ACR) is a widely used industrial chemical. However, it is a dangerous compound because it showed neurotoxic effects in humans and act as reproductive toxicant and carcinogen in many animal species. In the environment, acrylamide has high soil mobility and may travel via groundwater. Phytoremediation is an effective method to remove the environmental pollutants, but the mechanism of plant response to acrylamide remains unknown. With the purpose of assessing remediation potentials of plants for acrylamide, we have examined acrylamide uptake by the model plant Arabidopsis grown on contaminated substrates with high performance liquid chromatography (HPLC) analysis. The result revealed that acrylamide could be absorbed and degraded by Arabidopsis. Further microarray analysis showed that 527 transcripts were up-regulated within 2-days under acrylamide exposure condition. We have found many potential acrylamide-induced genes playing a major role in plant metabolism and phytoremediation.

Phytoremediation of phenanthrene by transgenic plants transformed with a naphthalene dioxygenase system from Pseudomonas.

Genes from microbes for degrading polycyclic aromatic hydrocarbons (PAHs) are seldom used to improve the ability of plants to remediate the pollution because the initiation of the microbial degradation of PAHs is catalyzed by a multienzyme system. In this study, for the first time, we have successfully transferred the complex naphthalene dioxygenase system of Pseudomonas into Arabidopsis and rice, the model dicot and monocot plant. As in bacteria, all four genes of the naphthalene dioxygenase system can be simultaneously expressed and assembled to an active enzyme in transgenic plants. The naphthalene dioxygenase system can develop the capacity of plants to tolerate a high concentration of phenanthrene and metabolize phenanthrene in vivo. As a result, transgenic plants showed improved uptake of phenanthrene from the environment over wild-type plants. In addition, phenanthrene concentrations in shoots and roots of transgenic plants were generally lower than that of wild type plants. Transgenic plants with a naphthalene dioxygenase system bring the promise of an efficient and environmental-friendly technology for cleaning up PAHs contaminated soil and water.

Gene expression profiles of Arabidopsis under the stress of methyl viologen: a microarray analysis.

Methyl viologen (MV) is the main ingredient of Paraquat. It is little known about how plants respond to this compound. To understand the mode of MV action and molecular mechanism of plant response, we performed experiments of microarray on Arabidopsis. In MV treated seedling, approximately 6% genes were altered at mRNA levels, including 818 genes increased, whereas 1,440 genes decreased. Studies of these genes expression patterns provided some new information on the reaction process of plant after the treatment with MV. These included signaling molecules for MV response and reactive oxygen species formation, enzymes required for secondary metabolism and, cell wall maintenance and strategy of photostasis balance. The expression kinetics of the genes induced by MV will provides useful information for the abiotic stress defense mechanism in plants.

Expression, purification, and characterization of recombinant mangrove glutamine synthetase.

To expand our knowledge about the relationship of nitrogen use efficiency and glutamine synthetase (GS) activity in the mangrove plant, a cytosolic GS gene from Avicennia marina has been heterologously expressed in and purified from Escherichia coli. Synthesis of the mangrove GS enzyme in E. coli was demonstrated by functional genetic complementation of a GS deficient mutant. The subunit molecular mass of GSI was ~40 kDa. Optimal conditions for biosynthetic activity were found to be 35 °C at pH 7.5. The Mg(2+)-dependent biosynthetic activity was strongly inhibited by Ni(2+), Zn(2+), and Al(3+), whereas was enhanced by Co(2+). The apparent K m values of AmGLN1 for the substrates in the biosynthetic assay were 3.15 mM for glutamate, and 2.54 mM for ATP, 2.80 mM for NH4 (+) respectively. The low affinity kinetics of AmGLN1 apparently participates in glutamine synthesis under the ammonium excess conditions.

Heterologous expression and characterization of laccase 2 from Coprinopsis cinerea capable of decolourizing different recalcitrant dyes.

The gene (CcLcc2) encoding laccase from the basidiomycete Coprinopsis cinerea Okayama-7 #130 was synthesized by polymerase chain reaction-based two-step DNA synthesis, and heterologously expressed in Pichia pastoris. The recombinant protein was purified by ammonium sulphate precipitation and nickel nitrilotriacetic acid chromatography. The molecular mass of CcLcc2 was estimated to be 54 kDa by denaturing polyacrylamide gel electrophoresis. The optimum pH and temperature for laccase catalysis for the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonate) (ABTS) were 2.6 and 45 °C, respectively. The Km values of the enzyme towards the substrates ABTS, 2,6-dimethoxyphenol (2,6-DMP) and guaiacol were 0.93, 1.02 and 28.07 mmol·L-1, respectively. The decolourization of methyl orange, crystal violet and malachite green, commonly used in the textile industry, was assessed. The decolourization percentage of crystal violet and malachite green was 80% after 4 h of reaction, and that of methyl orange was 50% at 4 h. These results show that the CcLcc2 has enormous potential for the decolourization of highly stable triphenylmethane dyes.

The complete degradation of 1,2-dichloroethane in Escherichia coli by metabolic engineering.

1,2-Dichloroethane (1,2-DCA), a widely utilized chemical intermediate and organic solvent in industry, frequently enters the environment due to accidental leaks and mishandling during application processes. Thus, the in-situ remediation of contaminated sites has become increasingly urgent. However, traditional remediation methods are inefficient and costly, while bioremediation presents a green, efficient, and non-secondary polluting alternative. In this study, an engineered strain capable of completely degrading 1,2-DCA was constructed. We introduced six exogenous genes of the 1,2-DCA degradation pathway into E. coli and confirmed their normal transcription and efficient expression in this engineered strain through qRT-PCR and proteomics. The degradation experiments showed that the strain completely degraded 2 mM 1,2-DCA within 12 h. Furthermore, the results of isotope tracing verified that the final degradation product, malic acid, entered the tricarboxylic acid cycle (TCA) of E. coli and was ultimately fully metabolized. Also, morphological changes in the engineered strain and control strain exposed to 1,2-DCA were observed under SEM, and the results revealed that the engineered strain is more tolerant to 1,2-DCA than the control strain. In conclusion, this study paved a new way for humanity to deal with the increasingly complex environmental challenges.

Mutation by DNA shuffling of 5-enolpyruvylshikimate-3-phosphate synthase from Malus domestica for improved glyphosate resistance.

A new 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene from Malus domestica (MdEPSPS) was cloned and characterized by rapid amplification of cDNA ends to identify an EPSPS gene appropriate for the development of transgenic glyphosate-tolerant plants. However, wild-type MdEPSPS is not suitable for the development of transgenic glyphosate-tolerant plants because of its poor glyphosate resistance. Thus, we performed DNA shuffling on MdEPSPS, and one highly glyphosate-resistant mutant with mutations in eight amino acids (N63D, N86S, T101A, A187T, D230G, H317R, Y399R and C413A.) was identified after five rounds of DNA shuffling and screening. Among the eight amino acid substitutions on this mutant, only two residue changes (T101A and A187T) were identified by site-directed mutagenesis as essential and additive in altering glyphosate resistance, which was further confirmed by kinetic analyses. The single-site A187T mutation has also never been previously reported as an important residue for glyphosate resistance. Furthermore, transgenic rice was used to confirm the potential of MdEPSPS mutant in developing glyphosate-resistant crops.

Phytoremediation of triphenylmethane dyes by overexpressing a Citrobacter sp. triphenylmethane reductase in transgenic Arabidopsis.

Triphenylmethane dyes are extensively utilized in textile industries, medicinal products, biological stains, and food processing industries, etc. They are generally considered as xenobiotic compounds, which are very recalcitrant to biodegradation. The widespread persistence of such compounds has generated concerns with regard to remediation of them because of their potential carcinogenicity, teratogenicity, and mutagenicity. In this study, we present a system of phytoremediation by Arabidopsis plants developed on the basis of overexpression of triphenylmethane reductase (TMR) from the Citrobacter sp. The morphology and growth of TMR transgenic Arabidopsis plants showed significantly enhanced tolerances to crystal violet (CV) and malachite green (MG). Further, HPLC and HPLC-MS analyses of samples before and after dye decolorization in culture media revealed that TMR transgenic plants exhibited strikingly higher capabilities of removing CV from their media and high efficiencies of converting CV to non-toxic leucocrystal violet (LCV). This work indicates that microbial degradative gene may be transgenically exploited in plants for bioremediation of triphenylmethane dyes in the environment.