Very bright orange fluorescent plants: endoplasmic reticulum targeting of orange fluorescent proteins as visual reporters in transgenic plants

The putative transporter MtUMAMIT14 participates in nodule formation in Medicago truncatula

Transport systems are crucial in many plant processes, including plant-microbe interactions. Nodule formation and function in legumes involve the expression and regulation of multiple transport proteins, and many are still uncharacterized, particularly for nitrogen transport. Amino acids originating from the nitrogen-fixing process are an essential form of nitrogen for legumes. This work evaluates the role of MtN21 (henceforth MtUMAMIT14), a putative transport system from the MtN21/EamA-like/UMAMIT family, in nodule formation and nitrogen fixation in Medicago truncatula. To dissect this transporter's role, we assessed the expression of MtUMAMIT14 using GUS staining, localized the corresponding protein in M. truncatula root and tobacco leaf cells, and investigated two independent MtUMAMIT14 mutant lines. Our results indicate that MtUMAMIT14 is localized in endosomal structures and is expressed in both the infection zone and interzone of nodules. Comparison of mutant and wild-type M. truncatula indicates MtUMAMIT14, the expression of which is dependent on the presence of NIN, DNF1, and DNF2, plays a role in nodule formation and nitrogen-fixation. While the function of the transporter is still unclear, our results connect root nodule nitrogen fixation in legumes with the UMAMIT family.

Construction of an easily detectable transgenic Synechococcus elongatus PCC 7942 against White Spot Syndrome Virus using vp28 and mOrange Gene and its metabolism in shrimp

White spot syndrome is an epidemic disease caused by the highly contagious and lethal white spot syndrome virus (WSSV), resulting in huge economic losses to the global aquaculture industry. VP28 is the main structural protein in the capsule of WSSV and is important in the early stage of infection. Under an excitation wavelength of 548 nm, the mOrange fluorescent protein releases a 562 nm emission wavelength, which is different from the autofluorescence of cyanobacteria. Therefore, using this characteristic combined with the receptor system of Synechococcus elongatus PCC 7942, we constructed transgenic S. elongatus to express the recombinant protein VP28-mOrange. In addition, PCR and western blotting were used to confirm the stable expression of the target gene in cyanobacteria. Using mOrange tracer features, we explored the recombinant protein VP28-mOrange in the metabolic cycle of young Litopenaeus Vannamei after feeding. After the young shrimp had stopped consuming transgenic cyanobacteria, the 24 to 33 h fluorescence signal in the intestine was very weak, and almost disappeared after 36 h. We explored the protective effect of transgenic vp28-mOrange S. elongatus within 48 h of being ingested by L. vannamei and set WSSV challenges at 2, 12, 24, and 48 h post-immunization. However, the survival rate of L. vannamei decreased as the time of the WSSV challenge increased. The survival rate on the seventh day was 81%, 52%, 45.5%, and 33.3% for shrimps challenged for 2, 12, 24, and 48 h, respectively. Enzyme activity can also support this conjecture, the enzyme activity indexes of the experimental groups were significantly reduced compared to positive and wild-type controls. Therefore, this immune agent functioned as a preventive agent. Compared with the traditional method, this method was easy to detect and can visualize the digestion of transgenic cyanobacteria in the Litopenaeus vannamei intestine.

Efficient fluorescence-based localization technique for real-time tracking endophytes route in host-plants colonization

Bacterial isolates that enhance plant growth and suppress plant pathogens growth are essential tools for reducing pesticide applications in plant production systems. The objectives of this study were to develop a reliable fluorescence-based technique for labeling bacterial isolates selected as biological control agents (BCAs) to allow their direct tracking in the host-plant interactions, understand the BCA localization within their host plants, and the route of plant colonization. Objectives were achieved by developing competent BCAs transformed with two plasmids, pBSU101 and pANIC-10A, containing reporter genes eGFP and pporRFP, respectively. Our results revealed that the plasmid-mediated transformation efficiencies of antibiotic-resistant competent BCAs identified as PSL, IMC8, and PS were up 84%. Fluorescent BCA-tagged reporter genes were associated with roots and hypocotyls but not with leaves or stems and were confirmed by fluoresence microscopy and PCR analyses in colonized Arabidopsis and sorghum. This fluorescence-based technique's high resolution and reproducibility make it a platform-independent system that allows tracking of BCAs spatially within plant tissues, enabling assessment of the movement and niches of BCAs within colonized plants. Steps for producing and transforming competent fluorescent BCAs, as well as the inoculation of plants with transformed BCAs, localization, and confirmation of fluorescent BCAs through fluorescence imaging and PCR, are provided in this manuscript. This study features host-plant interactions and subsequently biological and physiological mechanisms implicated in these interactions. The maximum time to complete all the steps of this protocol is approximately 3 months.

KIN3 impacts arbuscular mycorrhizal symbiosis and promotes fungal colonisation in Medicago truncatula

Arbuscular mycorrhizal fungi help their host plant in the acquisition of nutrients, and this association is itself impacted by soil nutrient levels. High phosphorus levels inhibit the symbiosis, whereas high nitrogen levels enhance it. The genetic mechanisms regulating the symbiosis in response to soil nutrients are poorly understood. Here, we characterised the symbiotic phenotypes in four Medicago truncatula Tnt1-insertion mutants affected in arbuscular mycorrhizal colonisation. We located their Tnt1 insertions and identified alleles for two genes known to be involved in mycorrhization, RAM1 and KIN3. We compared the effects of the kin3-2 and ram1-4 mutations on gene expression, revealing that the two genes alter the expression of overlapping but not identical gene sets, suggesting that RAM1 acts upstream of KIN3. Additionally, KIN3 appears to be involved in the suppression of plant defences in response to the fungal symbiont. KIN3 is located on the endoplasmic reticulum of arbuscule-containing cortical cells, and kin3-2 mutants plants hosted significantly fewer arbuscules than the wild type. KIN3 plays an essential role in the symbiotic response to soil nitrogen levels, as, contrary to wild-type plants, the kin3-2 mutant did not exhibit increased root colonisation under high nitrogen.

A New Plant Expression System for Producing Pharmaceutical Proteins

In the past decade, interest in the production of recombinant pharmaceutical proteins in plants has tremendously progressed because plants do not harbor mammalian viruses, are economically competitive, easily scalable, and capable of carrying out complex post-translational modifications required for recombinant pharmaceutical proteins. Mucuna bracteata is an essential perennial cover crop species widely planted as an underground cover in oil palm and rubber plantations. As a legume, they have high biomass, thrive in its habitat, and can fix nitrogen. Thus, M. bracteata is a cost-efficient crop that shows ideal characteristics as a platform for mass production of recombinant protein. In this study, we established a new platform for the transient production of a recombinant protein in M. bracteata via vacuum-assisted agro-infiltration. Five-week-old M. bracteata plants were vacuum infiltrated with Agrobacterium tumefaciens harboring a plasmid that encodes for an anti-toxoplasma immunoglobulin (IgG) under different parameters, including trifoliate leaf positional effects, days to harvest post-infiltration, and the Agrobacterium strain used. Our results showed that vacuum infiltration of M. bracteata plant with A. tumefaciens strain GV3101 produced the highest concentration of heterologous protein in its bottom trifoliate leaf at 2 days post-infiltration. The purified anti-toxoplasma IgG was then analyzed using Western blot and ELISA. It was demonstrated that, while structural heterogeneity existed in the purified anti-toxoplasma IgG from M. bracteata, its transient expression level was two-fold higher than the model platform, Nicotiana benthamiana. This study has laid the foundation towards establishing M. bracteata as a potential platform for the production of recombinant pharmaceutical protein.

Robust and Reproducible Agrobacterium-Mediated Transformation System of the C4 Genetic Model Species Setaria viridis

Setaria viridis (green foxtail) has been identified as a potential experimental model system to genetically and molecularly characterise the C4 monocotyledonous grasses due to its small physical size, short generation time and prolific seed production, together with a sequenced and annotated genome. Setaria viridis is the wild ancestor of the cropping species, foxtail millet (Setaria italica), with both Setaria species sharing a close evolutionary relationship with the agronomically important species, maize, sorghum, and sugarcane, as well as the bioenergy feedstocks, switchgrass, and Miscanthus. However, an efficient and reproducible transformation protocol is required to further advance the use of S. viridis to study the molecular genetics of C4 monocotyledonous grasses. An efficient and reproducible protocol was established for Agrobacterium tumefaciens-mediated transformation of S. viridis (Accession A10) regenerable callus material derived from mature seeds, a protocol that returned an average transformation efficiency of 6.3%. The efficiency of this protocol was the result of the: (i) use of mature embryo derived callus material; (ii) age of the seed used to induce callus formation; (iii) composition of the callus induction media, including the addition of the ethylene inhibitor, silver nitrate; (iv) use of a co-cultivation approach, and; (v) concentration of the selective agent. Our protocol furthers the use of S. viridis as an experimental model system to study the molecular genetics of C4 monocotyledonous grasses for the potential future development of improved C4 cropping species.

Embryogenic cell suspensions for high-capacity genetic transformation and regeneration of switchgrass (Panicum virgatum L.)

BACKGROUND

Switchgrass (Panicum virgatum L.), a North American prairie grassland species, is a potential lignocellulosic biofuel feedstock owing to its wide adaptability and biomass production. Production and genetic manipulation of switchgrass should be useful to improve its biomass composition and production for bioenergy applications. The goal of this project was to develop a high-throughput stable switchgrass transformation method using Agrobacterium tumefaciens with subsequent plant regeneration.

RESULTS

Regenerable embryogenic cell suspension cultures were established from friable type II callus-derived inflorescences using two genotypes selected from the synthetic switchgrass variety 'Performer' tissue culture lines 32 and 605. The cell suspension cultures were composed of a heterogeneous fine mixture culture of single cells and aggregates. Agrobacterium tumefaciens strain GV3101 was optimum to transfer into cells the pANIC-10A vector with a hygromycin-selectable marker gene and a pporRFP orange fluorescent protein marker gene at an 85% transformation efficiency. Liquid cultures gave rise to embryogenic callus and then shoots, of which up to 94% formed roots. The resulting transgenic plants were phenotypically indistinguishable from the non-transgenic parent lines.

CONCLUSION

The new cell suspension-based protocol enables high-throughput Agrobacterium-mediated transformation and regeneration of switchgrass in which plants are recovered within 6-7 months from culture establishment.

Transgene stacking in potato using the GAANTRY system

OBJECTIVE

GAANTRY (Gene Assembly in Agrobacterium by Nucleic acid Transfer using Recombinase technologY) is a flexible and effective system for stably stacking multiple genes within an Agrobacterium virulence plasmid Transfer-DNA (T-DNA). We examined the ability of the GAANTRY Agrobacterium rhizogenes ArPORT1 '10-stack' strain to generate transgenic potato plants.

RESULTS

The 28.5 kilobase 10-stack T-DNA, was introduced into Lenape potato plants with a 32% transformation efficiency. Molecular and phenotypic characterization confirmed that six of the seven tested independent transgenic lines carried the entire desired construct, demonstrating that the GAANTRY 10-stack strain can be used can be used in a tissue culture-based callus transformation method to efficiently generate transgenic potato plants. Analysis using droplet digital PCR showed that most of the characterized events carry one or two copies of the 10-stack transgenes and that 'backbone' DNA from outside of the T-DNA was absent in the transgenic plants. These results demonstrate that the GAANTRY system efficiently generates high quality transgenic potato plants with a large construct of stacked transgenes.

Production of functional human interleukin 37 using plants

KEY MESSAGE

We demonstrate for the first time that a fully bioactive human IL-37, a newly discovered cytokine acting as a fundamental inhibitor of innate immunity, can be recombinantly produced in plant cells. Interleukin 37 (IL-37), a newly discovered member of the interleukin (IL)-1 family of cytokines, plays a pivotal role in limiting innate inflammation and suppressing acquired immune responses, thus holding high potential for treating a wide array of human inflammatory and autoimmune disorders. In this study, we have developed transgenic plants as a novel expression platform for production of human IL-37 (IL-37). Plant transformation vectors synthesizing various forms of the b isoform of IL-37, including an unprocessed full-length precursor form (proIL-37b), a mature form (matIL-37b) and an IL-37 fusion protein in which IL-37b was fused to soybean agglutinin (SBA-IL-37b), have been constructed and introduced into tobacco plants. The expression of all forms of IL-37b was driven by a strong constitutive 35S promoter. Transgenic tobacco plants were generated with each of these constructs. Depending on the form of IL-37b being produced, the expression level of proIL-37b reached approximately 1% of TSP, while matIL-37b expression was substantially lower (0.01% TSP). Fusion to SBA substantially increased the expression of matIL-37b, with the expression level of fusion protein accounting for 1% of TSP. Functional analysis using a cell-based in vitro assay showed that plant-made matIL-37b and proIL-37b are both biologically active, but plant-made matIL-37b exhibited significantly greater biological activity than proIL-37b. These results demonstrate that plants have great potential of being a green bioreactor for low-cost, large-scale production of biologically active IL-37.

Generation of brilliant green fluorescent petunia plants by using a new and potent fluorescent protein transgene

The application of fluorescent proteins in ornamental plants has lagged behind despite the recent development of powerful genetic tools. Although we previously generated transgenic torenia plants expressing green fluorescent protein from marine plankton (CpYGFP), in which bright fluorescence was easily visible at the whole plant level, the maximum excitation of this protein within the visible light spectrum required the use of a coloured emission filter to eliminate exciting light. Here, to overcome this limitation, we generated transgenic petunia plants expressing eYGFPuv, a CpYGFP derivative exhibiting bright fluorescence under invisible ultraviolet (UV) light excitation, with a novel combination of transcriptional terminator plus translational enhancer. As expected, all transgenic plants exhibited brilliant green fluorescence easily visible to the naked eye without an emission filter. In addition, fluorescence expressed in transgenic petunia flowers was stable during long-term vegetative propagation. Finally, we visually and quantitatively confirmed that transgenic petunia flowers resist to long-term exposure of UV without any damages such as fluorescence decay and withering. Thus, our whole-plant fluorescence imaging tool, that does not require high sensitive imaging equipment or special imaging conditions for observation, might be useful not only for basic plant research but also for ornamental purposes as a novel flower property.

A versatile and robust Agrobacterium-based gene stacking system generates high-quality transgenic Arabidopsis plants

Biotechnology provides a means for the rapid genetic improvement of plants. Although single genes have been important in engineering herbicide and pest tolerance traits in crops, future improvements of complex traits like yield and nutritional quality will likely require the introduction of multiple genes. This research reports a system (GAANTRY; Gene Assembly in Agrobacterium by Nucleic acid Transfer using Recombinase technologY) for the flexible, in vivo stacking of multiple genes within an Agrobacterium virulence plasmid Transfer-DNA (T-DNA). The GAANTRY system utilizes in vivo transient expression of unidirectional site-specific recombinases and an alternating selection scheme to sequentially assemble multiple genes into a single transformation construct. To demonstrate GAANTRY's capabilities, 10 cargo sequences were sequentially stacked together to produce a 28.5-kbp T-DNA, which was used to generate hundreds of transgenic events. Approximately 90% of the events identified using a dual antibiotic selection screen exhibited all of the introduced traits. A total of 68% of the tested lines carried a single copy of the selection marker transgene located near the T-DNA left border, and only 8% contained sequence from outside the T-DNA. The GAANTRY system can be modified to easily accommodate any method of DNA assembly and generate high-quality transgenic plants, making it a powerful, yet simple to use tool for plant genetic engineering.

Reducing biomass recalcitrance by heterologous expression of a bacterial peroxidase in tobacco (Nicotiana benthamiana)

Commercial scale production of biofuels from lignocellulosic feed stocks has been hampered by the resistance of plant cell walls to enzymatic conversion, primarily owing to lignin. This study investigated whether DypB, the lignin-degrading peroxidase from Rodococcus jostii, depolymerizes lignin and reduces recalcitrance in transgenic tobacco (Nicotiana benthamiana). The protein was targeted to the cytosol or the ER using ER-targeting and retention signal peptides. For each construct, five independent transgenic lines were characterized phenotypically and genotypically. Our findings reveal that expression of DypB in the cytosol and ER does not affect plant development. ER-targeting increased protein accumulation, and extracts from transgenic leaves showed higher activity on classic peroxidase substrates than the control. Intriguingly, in situ DypB activation and subsequent saccharification released nearly 200% more fermentable sugars from transgenic lines than controls, which were not explained by variation in initial structural and non-structural carbohydrates and lignin content. Pyrolysis-GC-MS analysis showed more reduction in the level of lignin associated pyrolysates in the transgenic lines than the control primarily when the enzyme is activated prior to pyrolysis, consistent with increased lignin degradation and improved saccharification. The findings reveal for the first time that accumulation and in situ activation of a peroxidase improves biomass digestibility.

The TcEG1 beetle (Tribolium castaneum) cellulase produced in transgenic switchgrass is active at alkaline pH and auto-hydrolyzes biomass for increased cellobiose release

BACKGROUND

Genetically engineered biofuel crops, such as switchgrass (Panicum virgatum L.), that produce their own cell wall-digesting cellulase enzymes would reduce costs of cellulosic biofuel production. To date, non-bioenergy plant models have been used in nearly all studies assessing the synthesis and activity of plant-produced fungal and bacterial cellulases. One potential source for cellulolytic enzyme genes is herbivorous insects adapted to digest plant cell walls. Here we examine the potential of transgenic switchgrass-produced TcEG1 cellulase from Tribolium castaneum (red flour beetle). This enzyme, when overproduced in Escherichia coli and Saccharomyces cerevisiae, efficiently digests cellulose at optima of 50 °C and pH 12.0.

RESULTS

TcEG1 that was produced in green transgenic switchgrass tissue had a range of endoglucanase activity of 0.16-0.05 units (µM glucose release/min/mg) at 50 °C and pH 12.0. TcEG1 activity from air-dried leaves was unchanged from that from green tissue, but when tissue was dried in a desiccant oven (46 °C), specific enzyme activity decreased by 60%. When transgenic biomass was "dropped-in" into an alkaline buffer (pH 12.0) and allowed to incubate at 50 °C, cellobiose release was increased up to 77% over non-transgenic biomass. Saccharification was increased in one transgenic event by 28%, which had a concurrent decrease in lignin content of 9%. Histological analysis revealed an increase in cell wall thickness with no change to cell area or perimeter. Transgenic plants produced more, albeit narrower, tillers with equivalent dry biomass as the control.

CONCLUSIONS

This work describes the first study in which an insect cellulase has been produced in transgenic plants; in this case, the dedicated bioenergy crop switchgrass. Switchgrass overexpressing the TcEG1 gene appeared to be morphologically similar to its non-transgenic control and produced equivalent dry biomass. Therefore, we propose TcEG1 transgenics could be bred with other transgenic germplasm (e.g., low-lignin lines) to yield new switchgrass with synergistically reduced recalcitrance to biofuel production. In addition, transgenes for other cell wall degrading enzymes may be stacked with TcEG1 in switchgrass to yield complementary cell wall digestion features and complete auto-hydrolysis.

Development of a rapid, low-cost protoplast transfection system for switchgrass (Panicum virgatum L.)

A switchgrass protoplast system was developed, achieving a cost reduction of ~1000-fold, a threefold increase in transformation efficiency, and a fourfold reduction in required DNA quantity compared to previous methods. In recent years, there has been a resurgence in the use of protoplast systems for rapid screening of gene silencing and genome-editing targets for siRNA, miRNA, and CRISPR technologies. In the case of switchgrass (Panicum virgatum L.), to achieve economic feasibility for biofuel production, it is necessary to develop plants with decreased cell wall recalcitrance to reduce processing costs. To achieve this goal, transgenic plants have been generated with altered cell wall chemistry; however, with limited success owing to the complexity of cell walls. Because of the considerable cost, time, and effort required to screen transgenic plants, a protoplast system that can provide data at an early stage has potential to eliminate low performing candidate genes/targets prior to the creation of transgenic plants. Despite the advantages of protoplast systems, protoplast isolation in switchgrass has proven costly, requiring expensive lab-grade enzymes and high DNA quantities. In this paper, we describe a low-cost protoplast isolation system using a mesophyll culture approach and a cell suspension culture. Results from this work show a cost reduction of ~1000-fold compared to previous methods of protoplast isolation in switchgrass, with a cost of $0.003 (USD) per reaction for mesophyll protoplasts and $0.018 for axenic cell culture-derived protoplasts. Further, the efficiency of protoplast transformation was optimized threefold over previous methods, despite a fourfold reduction in DNA quantity. The methods developed in this work remove the cost barrier previously limiting high-throughput screening of genome-editing and gene silencing targets in switchgrass, paving the way for more efficient development of transgenic plants.

Downregulation of a UDP-Arabinomutase Gene in Switchgrass (Panicum virgatum L.) Results in Increased Cell Wall Lignin While Reducing Arabinose-Glycans

Background: Switchgrass (Panicum virgatum L.) is a C₄ perennial prairie grass and a dedicated feedstock for lignocellulosic biofuels. Saccharification and biofuel yields are inhibited by the plant cell wall's natural recalcitrance against enzymatic degradation. Plant hemicellulose polysaccharides such as arabinoxylans structurally support and cross-link other cell wall polymers. Grasses predominately have Type II cell walls that are abundant in arabinoxylan, which comprise nearly 25% of aboveground biomass. A primary component of arabinoxylan synthesis is uridine diphosphate (UDP) linked to arabinofuranose (Araf). A family of UDP-arabinopyranose mutase (UAM)/reversible glycosylated polypeptides catalyze the interconversion between UDP-arabinopyranose (UDP-Arap) and UDP-Araf. Results: The expression of a switchgrass arabinoxylan biosynthesis pathway gene, PvUAM1, was decreased via RNAi to investigate its role in cell wall recalcitrance in the feedstock. PvUAM1 encodes a switchgrass homolog of UDP-arabinose mutase, which converts UDP-Arap to UDP-Araf. Southern blot analysis revealed each transgenic line contained between one to at least seven T-DNA insertions, resulting in some cases, a 95% reduction of native PvUAM1 transcript in stem internodes. Transgenic plants had increased pigmentation in vascular tissues at nodes, but were otherwise similar in morphology to the non-transgenic control. Cell wall-associated arabinose was decreased in leaves and stems by over 50%, but there was an increase in cellulose. In addition, there was a commensurate change in arabinose side chain extension. Cell wall lignin composition was altered with a concurrent increase in lignin content and transcript abundance of lignin biosynthetic genes in mature tillers. Enzymatic saccharification efficiency was unchanged in the transgenic plants relative to the control. Conclusion: Plants with attenuated PvUAM1 transcript had increased cellulose and lignin in cell walls. A decrease in cell wall-associated arabinose was expected, which was likely caused by fewer Araf residues in the arabinoxylan. The decrease in arabinoxylan may cause a compensation response to maintain cell wall integrity by increasing cellulose and lignin biosynthesis. In cases in which increased lignin is desired, e.g., feedstocks for carbon fiber production, downregulated UAM1 coupled with altered expression of other arabinoxylan biosynthesis genes might result in even higher production of lignin in biomass.

A double built-in containment strategy for production of recombinant proteins in transgenic rice

Using transgenic rice as a bioreactor for mass production of pharmaceutical proteins could potentially reduce the cost of production significantly. However, a major concern over the bioreactor transgenic rice is the risk of its unintended spreading into environment and into food or feed supplies. Here we report a mitigating method to prevent unwanted transgenic rice spreading by a double built-in containment strategy, which sets a selectively termination method and a visual tag technology in the T-DNA for transformation. We created transgenic rice with an inserted T-DNA that harbors a human proinsulin gene fused with the far-red fluorescent protein gene mKate_S158A, an RNAi cassette suppressing the expression of the rice bentazon detoxification enzyme CYP81A6, and an EPSPS gene as the selection marker for transformation. Herbicide spray tests indicated that such transgenic rice plants can be killed selectively by a spray of bentazon at regular field application dosage for rice weed control. Moreover, the transgenic rice seeds were bright red in color due to the fused far-red fluorescent protein, and could be easily visualized under daylight by naked eyes. Thus, the transgenic rice plants reported in this study could be selectively killed by a commonly used herbicide during their growth stage, and their seeds may be detected visually during processing and consumption after harvest. This double built-in containment strategy may greatly enhance the confinement of the transgenic rice.

Computational discovery of soybean promoter cis-regulatory elements for the construction of soybean cyst nematode-inducible synthetic promoters

Computational methods offer great hope but limited accuracy in the prediction of functional cis-regulatory elements; improvements are needed to enable synthetic promoter design. We applied an ensemble strategy for de novo soybean cyst nematode (SCN)-inducible motif discovery among promoters of 18 co-expressed soybean genes that were selected from six reported microarray studies involving a compatible soybean-SCN interaction. A total of 116 overlapping motif regions (OMRs) were discovered bioinformatically that were identified by at least four out of seven bioinformatic tools. Using synthetic promoters, the inducibility of each OMR or motif itself was evaluated by co-localization of gain of function of an orange fluorescent protein reporter and the presence of SCN in transgenic soybean hairy roots. Among 16 OMRs detected from two experimentally confirmed SCN-inducible promoters, 11 OMRs (i.e. 68.75%) were experimentally confirmed to be SCN-inducible, leading to the discovery of 23 core motifs of 5- to 7-bp length, of which 14 are novel in plants. We found that a combination of the three best tools (i.e. SCOPE, W-AlignACE and Weeder) could detect all 23 core motifs. Thus, this strategy is a high-throughput approach for de novo motif discovery in soybean and offers great potential for novel motif discovery and synthetic promoter engineering for any plant and trait in crop biotechnology.

The performance of pathogenic bacterial phytosensing transgenic tobacco in the field

Phytosensors are useful for rapid-on-the-plant detection of contaminants and agents that cause plant stress. Previously, we produced a series of plant pathogen-inducible synthetic promoters fused to an orange fluorescent protein (OFP) reporter gene and transformed them into tobacco and Arabidopsis thaliana plants; in these transgenic lines, an OFP signal is expressed commensurate with the presence of plant pathogens. We report here the results of 2 years of field experiments using a subset of these bacterial phytosensing tobacco plants. Time-course analysis of field-grown phytosensors showed that a subset of plants responded predictably to treatments with Pseudomonas phytopathogens. There was a twofold induction in the OFP fluorescence driven by two distinct salicylic acid-responsive synthetic promoters, 4 × PR1 and 4 × SARE. Most notably, transgenic plants containing 4 × PR1 displayed the earliest and highest OFP induction at 48 and 72 h postinoculation (h p.i.) upon inoculation with two phytopathogens Pseudomonas syringae pv. tomato and P. syringae pv. tabaci, respectively. These results demonstrate transgenic tobacco harbouring a synthetic inducible promoter-driven OFP could be used to facilitate monitoring and early-warning reporting of phytopathogen infections in agricultural fields.

Synthetic TAL effectors for targeted enhancement of transgene expression in plants

Transcription activator-like effectors (TALEs), secreted by the pathogenic bacteria Xanthomonas, specifically activate expression of targeted genes in plants. Here, we designed synthetic TALEs that bind to the flanking regions of the TATA-box motif on the CaMV 35S promoter for the purpose of understanding the engineerable 'hot-spots' for increasing transgene expression. We demonstrated that transient expression of de novo-engineered TALEs using agroinfiltration could significantly increase reporter gene expression in stable transgenic tobacco expressing the orange fluorescent protein reporter gene pporRFP under the control of synthetic inducible, minimal or full-length 35S promoters. Moreover, the additive effects of a combination of two different synthetic TALEs could significantly enhance the activation effects of TALEs on reporter gene expression more than when each TALE was used individually. We also studied the effects of the C-terminal domain and the activation domain of synthetic TALEs, as well as the best 'hot-spots' on the 35S promoter on targeted transgene activation. Furthermore, TALE activation of the Arabidopsis MYB transcription factor AtPAP1 (PRODUCTION OF ANTHOCYANIN PIGMENT 1) in stable transgenic tobacco gave rise to a dark purple colour on infiltrated leaves when driven by four copies of cis-regulatory elements of pathogenesis-related gene (PR1) with enhancer motifs B and A1 from the 35S promoter. These results provide novel insights into the potential applications of synthetic TALEs for targeted gene activation of transgenes in plants.

Flow cytometry and sorting in Arabidopsis

Flow cytometry, and the accompanying technology of cell sorting, represents an established and valuable experimental platform for the analysis of cellular populations. Applications involving higher plants, which started to emerge around 30 years ago, are now widely employed both to provide unique information regarding fundamental questions in basic and applied bioscience and to advance agricultural productivity in practical ways. Further developments of this platform are being actively pursued, promising additional advances in our understanding of the interactions of cells within the complex tissues and organs. Higher plants offer unique challenges in terms of flow cytometric analysis, first since their organs and tissues are, almost without exception, three-dimensional assemblies of different cell types and second that their individual cells are generally larger than those of mammals. This chapter focuses on the use of flow cytometry and cell sorting with the model species Arabidopsis thaliana, in particular addressing (1) fluorescence in vivo labeling of specific cell types, (2) fluorescence-activated sorting of protoplasts and nuclei, and (3) transcriptome analyses using sorted protoplasts and nuclei.

Single-molecule detection and tracking in plants

Combining optical properties with a limited choice of fluorophores turns single-molecule imaging in plants into a challenging task. This explains why the technique, despite its success in the field of animal cell biology, is far from being routinely applied in plant cell research. The same challenges, however, also apply to the application of single-molecule microscopy to any intact tissue or multicellular 3D cell culture. As recent and upcoming progress in fluorescence microscopy will permit single-molecule detection in the context of multicellular systems, plant tissue imaging will experience a huge benefit from this progress. In this review, we address every step of a single-molecule experiment, highlight the critical aspects of each and elaborate on optimizations and developments required for improvements. We relate each step to recent achievements, which have so far been conducted exclusively on the root epidermis of Arabidopsis thaliana seedlings with inclined illumination and show examples of single-molecule measurements using different cells or illumination schemes.

Overexpression of a soybean salicylic acid methyltransferase gene confers resistance to soybean cyst nematode

Salicylic acid plays a critical role in activating plant defence responses after pathogen attack. Salicylic acid methyltransferase (SAMT) modulates the level of salicylic acid by converting salicylic acid to methyl salicylate. Here, we report that a SAMT gene from soybean (GmSAMT1) plays a role in soybean defence against soybean cyst nematode (Heterodera glycines Ichinohe, SCN). GmSAMT1 was identified as a candidate SCN defence-related gene in our previous analysis of soybean defence against SCN using GeneChip microarray experiments. The current study started with the isolation of the full-length cDNAs of GmSAMT1 from a SCN-resistant soybean line and from a SCN-susceptible soybean line. The two cDNAs encode proteins of identical sequences. The GmSAMT1 cDNA was expressed in Escherichia coli. Using in vitro enzyme assays, E. coli-expressed GmSAMT1 was confirmed to function as salicylic acid methyltransferase. The apparent Km value of GmSAMT1 for salicylic acid was approximately 46 μM. To determine the role of GmSAMT1 in soybean defence against SCN, transgenic hairy roots overexpressing GmSAMT1 were produced and tested for SCN resistance. Overexpression of GmSAMT1 in SCN-susceptible backgrounds significantly reduced the development of SCN, indicating that overexpression of GmSAMT1 in the transgenic hairy root system could confer resistance to SCN. Overexpression of GmSAMT1 in transgenic hairy roots was also found to affect the expression of selected genes involved in salicylic acid biosynthesis and salicylic acid signal transduction.

Stable transformation of ferns using spores as targets: Pteris vittata and Ceratopteris thalictroides

Ferns (Pteridophyta) are very important members of the plant kingdom that lag behind other taxa with regards to our understanding of their genetics, genomics, and molecular biology. We report here, to our knowledge, the first instance of stable transformation of fern with recovery of transgenic sporophytes. Spores of the arsenic hyperaccumulating fern Pteris vittata and tetraploid 'C-fern Express' (Ceratopteris thalictroides) were stably transformed by Agrobacterium tumefaciens with constructs containing the P. vittata actin promoter driving a GUSPlus reporter gene. Reporter gene expression assays were performed on multiple tissues and growth stages of gametophytes and sporophytes. Southern-blot analysis confirmed stable transgene integration in recovered sporophytes and also confirmed that no plasmid from A. tumefaciens was present in the sporophyte tissues. We recovered seven independent transformants of P. vittata and four independent C. thalictroides transgenics. Inheritance analyses using β-glucuronidase (GUS) histochemical staining revealed that the GUS transgene was stably expressed in second generation C. thalictroides sporophytic tissues. In an independent experiment, the gusA gene that was driven by the 2× Cauliflower mosaic virus 35S promoter was bombarded into P. vittata spores using biolistics, in which putatively stable transgenic gametophytes were recovered. Transformation procedures required no tissue culture or selectable marker genes. However, we did attempt to use hygromycin selection, which was ineffective for recovering transgenic ferns. This simple stable transformation method should help facilitate functional genomics studies in ferns.

An orange fluorescent protein tagging system for real-time pollen tracking

BACKGROUND

Monitoring gene flow could be important for future transgenic crops, such as those producing plant-made-pharmaceuticals (PMPs) in open field production. A Nicotiana hybrid (Nicotiana. tabacum × Nicotiana glauca) shows limited male fertility and could be used as a bioconfined PMP platform. Effective assessment of gene flow from these plants is augmented with methods that utilize fluorescent proteins for transgenic pollen identification.

RESULTS

We report the generation of a pollen tagging system utilizing an orange fluorescent protein to monitor pollen flow and as a visual assessment of transgene zygosity of the parent plant. This system was created to generate a tagged Nicotiana hybrid that could be used for the incidence of gene flow. Nicotiana tabacum 'TN 90' and Nicotiana glauca were successfully transformed via Agrobacterium tumefaciens to express the orange fluorescent protein gene, tdTomato-ER, in pollen and a green fluorescent protein gene, mgfp5-er, was expressed in vegetative structures of the plant. Hybrids were created that utilized the fluorescent proteins as a research tool for monitoring pollen movement and gene flow. Manual greenhouse crosses were used to assess hybrid sexual compatibility with N. tabacum, resulting in seed formation from hybrid pollination in 2% of crosses, which yielded non-viable seed. Pollen transfer to the hybrid formed seed in 19% of crosses and 10 out of 12 viable progeny showed GFP expression.

CONCLUSION

The orange fluorescent protein is visible when expressed in the pollen of N. glauca, N. tabacum, and the Nicotiana hybrid, although hybrid pollen did not appear as bright as the parent lines. The hybrid plants, which show limited ability to outcross, could provide bioconfinement with the benefit of detectable pollen using this system. Fluorescent protein-tagging could be a valuable tool for breeding and in vivo ecological monitoring.

Smaller, faster, brighter: advances in optical imaging of living plant cells

The advent of fluorescent proteins and access to modern imaging technologies have dramatically accelerated the pace of discovery in plant cell biology. Remarkable new insights into such diverse areas as plant pathogenesis, cytoskeletal dynamics, sugar transport, cell wall synthesis, secretory control, and hormone signaling have come from careful examination of living cells using advanced optical probes. New technologies, both commercially available and on the horizon, promise a continued march toward more quantitative methods for imaging and for extending the optical exploration of biological structure and activity to molecular scales. In this review, we lay out fundamental issues in imaging plant specimens and look ahead to several technological innovations in molecular tools, instrumentation, imaging methods, and specimen handling that show promise for shaping the coming era of plant cell biology.

Bacterial pathogen phytosensing in transgenic tobacco and Arabidopsis plants

Plants are subject to attack by a wide range of phytopathogens. Current pathogen detection methods and technologies are largely constrained to those occurring post-symptomatically. Recent efforts were made to generate plant sentinels (phytosensors) that can be used for sensing and reporting pathogen contamination in crops. Engineered phytosensors indicating the presence of plant pathogens as early-warning sentinels potentially have tremendous utility as wide-area detectors. We previously showed that synthetic promoters containing pathogen and/or defence signalling inducible cis-acting regulatory elements (RE) fused to a fluorescent protein (FP) reporter could detect phytopathogenic bacteria in a transient phytosensing system. Here, we further advanced this phytosensing system by developing stable transgenic tobacco and Arabidopsis plants containing candidate constructs. The inducibility of each synthetic promoter was examined in response to biotic (bacterial pathogens) or chemical (plant signal molecules salicylic acid, ethylene and methyl jasmonate) treatments using stably transgenic plants. The treated plants were visualized using epifluorescence microscopy and quantified using spectrofluorometry for FP synthesis upon induction. Time-course analyses of FP synthesis showed that both transgenic tobacco and Arabidopsis plants were capable to respond in predictable ways to pathogen and chemical treatments. These results provide insights into the potential applications of transgenic plants as phytosensors and the implementation of emerging technologies for monitoring plant disease outbreaks in agricultural fields.

A never ending race for new and improved fluorescent proteins

Bioluminescent and fluorescent proteins are now used as tools for research in all organisms. There has been massive progress over the past 15 years in creating a palette of fluorescent proteins with a wide spectrum of specific properties. One of the big challenges is to decide which variant may be best for a certain application. A recent article by Mann et al. in BMC Biotechnology describes a new orange fluorescent protein in plants.