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.

A thermostable 5-enolpyruvylshikimate-3-phosphate synthase from Thermotoga maritima enhances glyphosate tolerance in Escherichia coli and transgenic Arabidopsis.

5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) overexpression, attempting to provide excess EPSPS to combine with glyphosate, is one way to improve glyphosate resistance of plants. The EPSPS in extremophiles which is selected by nature to withstand the evolutionary pressure may possess some potential-specific biological functions. In this study, we reported the cloning, expression and enzymatic characterization of a novel Class II EPSPS AroAT. maritima from Thermotoga maritima MSB8. The enzyme showed low sequence identities with other EPSPSs, and was one of the most thermostable EPSPSs so far, which showed the optimum enzyme activity at 80 °C. The enzyme maintains the activity below 50 °C and in a wide range of pH 4.0-10, which indicated its stability under rough environment, especially in tropical regions and alkaline soil. Excellent Ki/Km value of AroAT. maritima suggested that the enzyme showed powerful competitive binding capacity of PEP over glyphosate and high glyphosate tolerance. Furthermore, aroAT. maritima gene was transformed into Arabidopsis thaliana. The transgenic lines were resistant to 15 mM glyphosate, which proved the application value in the cultivation of glyphosate-tolerant plants.

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.

Dietary safety assessment of genetically modified rice EH rich in ß-carotene.

This 90-day study aimed to assess the dietary safety of transgenic rice EH which is rich in ß-carotene. Two experimental groups of Sprague-Dawley rats were fed diets containing 45% rice flour of Zhonghua 11 rice and transgenic rice EH rich in ß-carotene, respectively. The reference group was fed a diet containing standard feed nutrition. During the trial period, each rat was weighed and the food intake was recorded twice a week. Their behaviors were observed daily. In the end, blood samples were obtained from all anesthetized rats to measure the hematologic and serum chemistry indicators. Growth performance, anatomy and pathology of all organs in each group were analyzed. Although a few parameters were found to be statistically significantly different across groups, they were within the normal reference range for this breed and age of rats. Therefore, the changes were not considered to be diet related. The results revealed that the transgenic rice EH rich in ß-carotene was as nutritious as Zhonghua 11 rice and showed a lack of biologically meaningful unintended effects.

Isolation and characterization of a novel L-glutamate oxidase with strict substrate specificity from Streptomyces diastatochromogenes.

OBJECTIVES: To find an L-glutamate oxidase (LGox), to be used for the quantitative analysis of L-glutamic acid, an lgox gene encoding LGox from Streptomyces diastatochromogenes was isolated, cloned and characterized. RESULTS: The gene had an ORF of 1974 bp encoding a protein of 657 amino acid residues. In comparison to the LGox precursor, the proteinase K-treated enzyme exhibited improved affinity to substrate and with a K m of 0.15 mM and V max of 62 µmol min-1 mg-1. The 50% thermal inactivation temperature of the proteinase K treated enzyme was increased from 50 to 70 °C. The enzyme exhibited strict specificity for L-glutamate. CONCLUSIONS: LGox treated by proteinase K exhibited strict specificity for L-glutamate, good thermostability and high substrate affinity.

Genome-Wide Identification and Analysis of the MYB Transcription Factor Superfamily in Solanum lycopersicum.

MYB proteins constitute one of the largest transcription factor families in the plant kingdom, members of which perform a variety of functions in plant biological processes. However, there are only very limited reports on the characterization of MYB transcription factors in tomato (Solanum lycopersicum). In our study, a total of 127 MYB genes have been identified in the tomato genome. A complete overview of these MYB genes is presented, including the phylogeny, gene structures, protein motifs, chromosome locations and expression patterns. The 127 SlMYB proteins could be classified into 18 subgroups based on domain similarity and phylogenetic topology. Phylogenetic analysis of SlMYBs along with MYBs from Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) indicated 14 subfamilies. Conserved motifs outside the MYB domain may reflect their functional conservation. The identified tomato MYB genes were distributed on 12 chromosomes at various densities but mainly in chromosomes 6 and 10 (12.6% and 11.8%, respectively). Genome-wide segmental and tandem duplications were also found, which may contribute to the expansion of SlMYB genes. RNA-sequencing and microarray data revealed tissue-specific and stress-responsive expression patterns of SlMYB genes. The expression profiles of SlMYB genes in response to salicylic acid (SA) and jasmonic acid methyl ester (MeJA) were also investigated by real-time PCR. Moreover, ethylene-responsive element-binding factor-associated amphiphilic repression (EAR) motifs were found in 24 SlMYB proteins. Collectively, our comprehensive analysis of SlMYB genes will facilitate future functional studies of the tomato MYB gene family and probably other Solanaceae plants.

AtMYB12 regulates flavonoids accumulation and abiotic stress tolerance in transgenic Arabidopsis thaliana.

In plants, transcriptional regulation is the most important tool for modulating flavonoid biosynthesis. The AtMYB12 gene from Arabidopsis thaliana has been shown to regulate the expression of key enzyme genes involved in flavonoid biosynthesis, leading to the increased accumulation of flavonoids. In this study, the codon-optimized AtMYB12 gene was chemically synthesized. Subcellular localization analysis in onion epidermal cells indicated that AtMYB12 was localized to the nucleus. Its overexpression significantly increased accumulation of flavonoids and enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of AtMYB12 resulted in the up-regulation of genes involved in flavonoid biosynthesis, abscisic acid (ABA) biosynthesis, proline biosynthesis, stress responses and ROS scavenging under salt and drought stresses. Further analyses under salt and drought stresses showed significant increases of ABA, proline content, superoxide dismutase (SOD) and peroxidase (POD) activities, as well as significant reduction of H2O2 and malonaldehyde (MDA) content. The results demonstrate the explicit role of AtMYB12 in conferring salt and drought tolerance by increasing the levels of flavonoids and ABA in transgenic Arabidopsis. The AtMYB12 gene has the potential to be used to enhance tolerance to abiotic stresses in plants.

The Antirrhinum AmDEL gene enhances flavonoids accumulation and salt and drought tolerance in transgenic Arabidopsis.

MAIN CONCLUSION: A basic helix-loop-helix (bHLH) transcription factor gene from Antirrhinum, AmDEL , increases flavonoids accumulation and enhances salt and drought tolerance via up-regulating flavonoid biosynthesis, proline biosynthesis and ROS scavenging genes in transgenic Arabidopsis. In plants, transcriptional regulation is the most important tools for increasing flavonoid biosynthesis. The AmDEL gene, as a basic helix-loop-helix transcription factor gene from Antirrhinum, has been shown to increase flavonoids accumulation in tomato. However, its role in tolerance to abiotic stresses has not yet been investigated. In this study, the codon-optimized AmDEL gene was chemically synthesized. Subcellular localization analysis in onion epidermal cells indicated that AmDEL protein was localized to the nucleus. Expression analysis in yeast showed that the full length of AmDEL exhibited transcriptional activation. Overexpression of AmDEL significantly increased flavonoids accumulation and enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR analysis showed that overexpression of AmDEL resulted in the up-regulation of genes involved in flavonoid biosynthesis, proline biosynthesis and ROS scavenging under salt and drought stresses. Meanwhile, Western blot and enzymatic analyses showed that the activities of phenylalanine ammonia lyase, chalcone isomerase, dihydroflavonol reductase, pyrroline-5-carboxylate synthase, superoxide dismutase and peroxidase were also increased. Further components analyses indicated that the significant increase of proline and relative water content and the significant reduction of H2O2 and malonaldehyde content were observed under salt and drought stresses. In addition, the rates of electrolyte leakage and water loss were reduced in transgenic plants. These findings imply functions of AmDEL in accumulation of flavonoids and tolerance to salt and drought stresses. The AmDEL gene has the potential to be used to increase the content of valuable flavonoids and improve tolerance to abiotic stresses in plants.

A novel Cys2/His2 zinc finger protein gene from sweetpotato, IbZFP1, is involved in salt and drought tolerance in transgenic Arabidopsis.

MAIN CONCLUSION: IbZFP1, encoding a Cys 2/His 2 zinc finger protein gene from sweetpotato, enhances salt and drought tolerance in transgenic Arabidopsis by regulating ABA signaling pathway, proline biosynthesis, stress responses and ROS scavenging. In plants, Cys2/His2 zinc finger proteins play important roles in regulating the growth and development or responses to abiotic stresses. In this study, a novel Cys2/His2 zinc finger protein gene, named IbZFP1, was isolated from drought-tolerant sweetpotato [Ipomoea batatas (L.) Lam.] line Xu55-2. Subcellular localization analysis in onion epidermal cells indicated that IbZFP1 was localized to the nucleus. Expression analysis in yeast showed that the full length of IbZFP1 exhibited transcriptional activation. Expression of IbZFP1 was induced by NaCl, polyethylene glycol and abscisic acid (ABA). Overexpression of IbZFP1 significantly enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of IbZFP1 up-regulated the genes involved in ABA signaling pathway, proline biosynthesis, stress responses, and ROS scavenging under salt and drought stresses. Meanwhile, Western blot and enzymatic analyses showed that the activities of 9-cis-epoxycarotenoid dioxygenase, pyrroline-5-carboxylate synthase, superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase were also increased. Further component analyses indicated that the significant increase of ABA, proline, soluble sugar and total chlorophyll content and the significant reduction of H2O2 and malonaldehyde content were observed under salt and drought stresses. In addition, the rates of electrolyte leakage and water loss were reduced in transgenic plants. The overall results demonstrate the explicit role of IbZFP1 in conferring salt and drought tolerance in transgenic Arabidopsis plants. The IbZFP1 gene has the potential to be used to enhance the tolerance to abiotic stresses in plants.

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.

Heterologous expression and characterisation of a laccase from Colletotrichum lagenarium and decolourisation of different synthetic dyes.

Laccases have received considerable attention in recent decades because of their ability to oxidise a large spectrum of phenolic and non-phenolic organic substrates and highly recalcitrant environmental pollutants. In this research, a laccase gene from Colletotrichum lagenarium was chemically synthesised using yeast bias codons and expressed in Pichia pastoris. The molecular mass of the recombinant laccase was estimated to be 64.6 kDa by SDS-PAGE, and the enzyme exhibited maximum activity at pH 3.6-4.0 but more stability in buffer with higher pH (>pH 3.6). The optimal reaction temperature of the enzyme was 40 °C, beyond which stability significantly decreased. By using 2,2'-azino-bis-(3-ethylbenzothiazoline)-6-sulphonate (ABTS) as a substrate, K m and V max values of 0.34 mM and 7.11 mM min(-1) mg(-1), respectively, were obtained. Using ABTS as a mediator, the laccase could oxidise hydroquinone to p-benzoquinone and decolourise the synthetic dyes malachite green, crystal violet and orange G. These results indicated that the laccase could be used to treat industrial effluents containing artificial dyes.

Overexpression of D-amino acid oxidase from Bradyrhizobium japonicum, enhances resistance to glyphosate in Arabidopsis thaliana.

KEY MESSAGE: The glyphosate resistance in Escherichia coli and Arabidopsis was due to D-amino acid oxidase expression. Transgenic glyphosate-resistant crops have a high percentage in the total area devoted to transgenic crops worldwide. D-amino acid oxidase (DAAO) can metabolize glyphosate by oxidative cleavage of the carbon-nitrogen bond on the carboxyl side and yield aminomethyl phosphonic acid and glyoxylate, which are less toxic to plants than glyphosate. To date, reports on the use of DAAO to enhance glyphosate resistance in plants are lacking. In this paper, we report synthesis, and codon usage optimization for plant expression, of the DAAO gene by successive polymerase chain reaction from Bradyrhizobium japonicum. To confirm the glyphosate resistance of the DAAO gene, the recombinant plasmid pYPX251 (GenBank Accession No: AY178046) harboring the wild-type DAAO gene was transformed into DH5α. The positive transformants grew well both on solid and in liquid M9 medium containing 200 mM glyphosate. The optimized DAAO gene was transformed into Arabidopsis and 9 days after application of 10 mM glyphosate, the 4-week-old wild-type plants all died; by contrast, transgenic plants could grow normally. The proline content and peroxidase activity showed that glyphosate could induce proline accumulation and produce reactive oxygen species.