Transient Expression Systems in Plants: Potentialities and Constraints

Expression of mastitis causing fibrinogen binding protein of gram positive bacteria in genetically engineered switchgrass and antibodies production in mice

The current study is the first comprehensive report on the expression of fibrinogen binding protein (FIB) antigen in the genetically engineered switchgrass. Mammary tissue inflammation is one of the major infectious diseases caused by Staphylococcus aureus in the dairy animals. The aim of the present study is to develop an efficient and economical bioengineered immunogen for controlling mastitis in developing countries. Plant parts are served as bio-factories to produce antigens against infectious diseases. In this research, mastitis antigenic target (FIB) of S. aureus was expressed in switchgrass via Ag-nanoparticle mediated nuclear gene transformation to ease oral delivery of FIB antigen. FIB gene was cloned in expression vector through TOPO and Gateway cloning method. Transformation and integration of transgene was confirmed through PCR. The maximum concentration of total soluble fraction of FIB was calculated, and total soluble protein accumulated up to 0.5%. The recombinant FIB protein was purified and extract was prepared. FIB protein induced humoral immune response in mice and immunized orally. To administration oral immunogens against mastitis, FIB from S. aureus was commercially synthesized and PCR purified, the purified FIB gene was cloned into expression vector. Ag-NPs were encapsulated with pFIB and used as nanocarrier to target delivery of gene in forage grass. Forage seeds were successfully transformed through nuclear delivery and presence of transgene was confirmed through polymerase chain reaction. Transgenic lines of forage grass expressing FIB antigen is successfully developed. The transgenic lines expressing FIB gene were used for mouse study and in-vivo trials showed that switchgrass as transgenic immunogen developed antibodies in blood of animals upon orally delivering the FIB antigen. The expression of mastitis antigen in edible plants could contribute significantly to the development of cost effective and orally administered antigen-based subunit immunogen against dairy mastitis.

Advancements in plant transformation: from traditional methods to cutting-edge techniques and emerging model species

The ability to efficiently genetically modify plant species is crucial, driving the need for innovative technologies in plant biotechnology. Existing plant genetic transformation systems include Agrobacterium-mediated transformation, biolistics, protoplast-based methods, and nanoparticle techniques. Despite these diverse methods, many species exhibit resistance to transformation, limiting the applicability of most published methods to specific species or genotypes. Tissue culture remains a significant barrier for most species, although other barriers exist. These include the infection and regeneration stages in Agrobacterium, cell death and genomic instability in biolistics, the creation and regeneration of protoplasts for protoplast-based methods, and the difficulty of achieving stable transformation with nanoparticles. To develop species-independent transformation methods, it is essential to address these transformation bottlenecks. This review examines recent advancements in plant biotechnology, highlighting both new and existing techniques that have improved the success rates of plant transformations. Additionally, several newly emerged plant model systems that have benefited from these technological advancements are also discussed.

Establishment of a Rapid and Effective Agrobacterium-Mediated Genetic Transformation System of Oxalis triangularis 'Purpurea'

Oxalis triangularis 'Purpurea' has significant ornamental value in landscaping. There is a critical necessity to elucidate the gene functions of O. triangularis 'Purpurea' and dissect the molecular mechanisms governing key ornamental traits. However, a reliable genetic transformation method remains elusive. In this study, our investigation revealed that various transformation parameters, including recipient material (petioles), pre-culture time (2-5 days), acetosyringone (AS) concentration (100-400 μM), Agrobacterium concentrations (OD600 = 0.4-1.0), infection time (5-20 min), and co-culture time (2-5 days), significantly impacted the stable genetic transformation in O. triangular 'Purpurea'. Notably, the highest genetic transformation rate was achieved from the leaf discs pre-cultured for 3 days, treated with 200 μM AS infected with Agrobacterium for 11 min at OD600 of 0.6, and subsequently co-cultured for 3 days. This treatment resulted in a genetic transformation efficiency of 9.88%, and it only took 79 days to produce transgenic plants. Our transformation protocol offers advantages of speed, efficiency, and simplicity, which will greatly facilitate genetic transformation for O. triangular 'Purpurea' and gene function studies.

Subcellular compartmentalization in the biosynthesis and engineering of plant natural products

Plant natural products (PNPs) are specialized metabolites with diverse bioactivities. They are extensively used in the pharmaceutical, cosmeceutical and food industries. PNPs are synthesized in plant cells by enzymes that are distributed in different subcellular compartments with unique microenvironments, such as ions, co-factors and substrates. Plant metabolic engineering is an emerging and promising approach for the sustainable production of PNPs, for which the knowledge of the subcellular compartmentalization of their biosynthesis is instrumental. In this review we describe the state of the art on the role of subcellular compartments in the biosynthesis of major types of PNPs, including terpenoids, phenylpropanoids, alkaloids and glucosinolates, and highlight the efforts to target biosynthetic pathways to subcellular compartments in plants. In addition, we will discuss the challenges and strategies in the field of plant synthetic biology and subcellular engineering. We expect that newly developed methods and tools, together with the knowledge gained from the microbial chassis, will greatly advance plant metabolic engineering.

Advancements and challenges in bamboo breeding for sustainable development

Bamboo is a highly renewable biomass resource with outstanding ecological, economic and social benefits. However, its lengthy vegetative growth stage and uncertain flowering period have hindered the application of traditional breeding methods. In recent years, significant progress has been made in bamboo breeding. While technical advances in bamboo breeding have been impressive, it is essential to also consider the broader implications we can learn from bamboo's extraordinary features for sustainable development. This review provides an overview of the current status of bamboo breeding technology, including a detailed history of bamboo breeding divided into four eras, a comprehensive map of bamboo germplasm gardens worldwide, with a focus on China, and a summary of available transgenic technologies for gene function verification and genetic improvement. As the demand for bamboo as a sustainable and renewable resource increases continuously, breeding objectives should be focused on enhancing yield, wood properties and adaptability to diverse environmental conditions. In particular, priority should be given to improving fiber length, internode length and wall thickness, as well as regulating lignin and cellulose content for papermaking, substitute for plastic and other applications. Furthermore, we highlight the challenges and opportunities for future research and development in bamboo breeding, including the application of omics technologies, artificial intelligence and the development of new breeding methods. Finally, by integrating the technical advances in bamboo breeding with a discussion of its broader implications for sustainable development, this review provides a comprehensive framework for the development of bamboo industry.

An Agrobacterium-Mediated Transient Expression Method for Functional Assay of Genes Promoting Disease in Monocots

Agrobacterium-mediated transient expression (AMTE) has been widely used for high-throughput assays of gene function in diverse plant species. However, its application in monocots is still limited due to low expression efficiency. Here, by using histochemical staining and a quantitative fluorescence assay of β-glucuronidase (GUS) gene expression, we investigated factors affecting the efficiency of AMTE on intact barley plants. We found prominent variation in GUS expression levels across diverse vectors commonly used for stable transformation and that the vector pCBEP produced the highest expression. Additionally, concurrent treatments of plants with one day of high humidity and two days of darkness following agro-infiltration also significantly increased GUS expression efficiency. We thus established an optimized method for efficient AMTE on barley and further demonstrated its efficiency on wheat and rice plants. We showed that this approach could produce enough proteins suitable for split-luciferase assays of protein-protein interactions on barley leaves. Moreover, we incorporated the AMTE protocol into the functional dissection of a complex biological process such as plant disease. Based on our previous research, we used the pCBEP vector to construct a full-length cDNA library of genes upregulated during the early stage of rice blast disease. A subsequent screen of the library by AMTE identified 15 candidate genes (out of ~2000 clones) promoting blast disease on barley plants. Four identified genes encode chloroplast-related proteins: OsNYC3, OsNUDX21, OsMRS2-9, and OsAk2. These genes were induced during rice blast disease; however, constitutive overexpression of these genes conferred enhanced disease susceptibility to Colletotrichum higginsianum in Arabidopsis. These observations highlight the power of the optimized AMTE approach on monocots as an effective tool for facilitating functional assays of genes mediating complex processes such as plant-microbe interactions.

The establishment of transient expression systems and their application for gene function analysis of flavonoid biosynthesis in Carthamus tinctorius L

BACKGROUND

Safflower (Carthamus tinctorius L.) is an important economic crop and a traditional medicinal material rich in flavonoids, which can alleviate cardiovascular and cerebrovascular pathologies. Thus, many candidate genes involved in safflower flavonoid biosynthesis have been cloned. However, owing to the lack of a homologous gene expression system, research on gene function is limited to model plants. Therefore, a gene function identification protocol for safflower must be established.

RESULTS

In the present study, using safflower callus as the experimental material, Agrobacterium and biolistic transient expression systems were established. In the Agrobacterium transient expression system, the highest transformation rate was obtained at the original Agrobacterium concentration of OD600 0.4, infiltration concentration of OD600 0.6, infection for 20 min, co-culture for 3 days, and acetosyringone concentration of 100 μmol·L-1. In the biolistic transient expression system, the highest transformation efficiency was observed at helium pressure of 1,350 psi, vacuum degree of -0.8 bar, flight distance of 6.5 cm, one round of bombardment, plasmid concentration of 3 μg·shot-1, and gold particle concentration of 100 μg·shot-1. Further, these two transient expression systems were used for the functional analysis of CtCHS1 as an example. After overexpression, relative CtCHS1 expression increased, particularly in Agrobacterium-transformed calli. Additionally, the contents of some flavonoids were altered; for instance, naringenin and genistein levels were significantly increased in Agrobacterium-transformed calli, whereas luteolin, luteolin-7-O-rutinoside, and apigenin derivative levels were significantly decreased in biolistic-transformed calli.

CONCLUSION

Using safflower callus as the experimental material, highly efficient Agrobacterium and biolistic transient expression systems were successfully established, and the utility of both systems for investigating gene function was demonstrated. The proposed safflower callus transient expression systems will be useful for further functional analyses of flavonoid biosynthetic genes in safflower.

Plant-Derived Human Vaccines: Recent Developments

The idea of producing vaccines in plants originated in the late 1980s. Initially, it was contemplated that this notion could facilitate the concept of edible vaccines, making them more cost effective and easily accessible. Initial studies on edible vaccines focussed on the use of a variety of different transgenic plant host species for the production of vaccine antigens. However, adequate expression levels of antigens, the difficulties predicted with administration of consistent doses, and regulatory rules required for growth of transgenic plants gave way to the development of vaccine candidates that could be purified and administered parenterally. The field has subsequently advanced with improved expression techniques including a shift from using transgenic to transient expression of antigens, refinement of purification protocols, a deeper understanding of the biological processes and a wealth of evidence of immunogenicity and efficacy of plant-produced vaccine candidates, all contributing to the successful practice of what is now known as biopharming or plant molecular farming. The establishment of this technology has resulted in the development of many different types of vaccine candidates including subunit vaccines and various different types of nanoparticle vaccines targeting a wide variety of bacterial and viral diseases. This has brought further acceptance of plants as a suitable platform for vaccine production and in this review, we discuss the most recent advances in the production of vaccines in plants for human use.

Further Characterization of MUAS35SCP and FUAS35SCP Recombinant Promoters and Their Implication in Translational Research

Recombinant promoters are of high value in translational research. Earlier, we developed two recombinant promoters, namely MUAS35SCP and FUAS35SCP, and their transcriptional activities were found to be stronger than that of the most widely used CaMV35S promoter in dicot plants. Presently, we are reporting constitutive expression of both GUS and GFP reporters under the control of these promoters in several monocots, including rice, wheat, and pearl millet. We observed that these promoters could express the reporter genes constitutively, and their expression abilities were almost equal to that of the CaMV35S² promoter. Plant-derived enriched PaDef (Persea americana var. drymifolia defensin) and NsDef2 (Nigella sativa L. defensin 2) antimicrobial peptides expressed under the control of these promoters arrest the growth of devastating phytopathogens like Pseudomonas syringae, Rhodococcus fascians, and Alternaria alternata. We observed that plant-derived NsDef2 and PaDef under control of these promoters showed approximately 80-90% inhibitory activity against Pseudomonas syringae. Hence, these promoters were constitutive and universal, as they can drive the expression of transgenes in both dicot and monocot plants. Alongside, these promoters could become a valuable tool for raising genetically modified plants with in-built resistance toward phytopathogens.

Strategies for High-Efficiency Mutation Using the CRISPR/Cas System

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated systems have revolutionized traditional gene-editing tools and are a significant tool for ameliorating gene defects. Characterized by high target specificity, extraordinary efficiency, and cost-effectiveness, CRISPR/Cas systems have displayed tremendous potential for genetic manipulation in almost any organism and cell type. Despite their numerous advantages, however, CRISPR/Cas systems have some inherent limitations, such as off-target effects, unsatisfactory efficiency of delivery, and unwanted adverse effects, thereby resulting in a desire to explore approaches to address these issues. Strategies for improving the efficiency of CRISPR/Cas-induced mutations, such as reducing off-target effects, improving the design and modification of sgRNA, optimizing the editing time and the temperature, choice of delivery system, and enrichment of sgRNA, are comprehensively described in this review. Additionally, several newly emerging approaches, including the use of Cas variants, anti-CRISPR proteins, and mutant enrichment, are discussed in detail. Furthermore, the authors provide a deep analysis of the current challenges in the utilization of CRISPR/Cas systems and the future applications of CRISPR/Cas systems in various scenarios. This review not only serves as a reference for improving the maturity of CRISPR/Cas systems but also supplies practical guidance for expanding the applicability of this technology.

Advances and Perspectives of Transgenic Technology and Biotechnological Application in Forest Trees

Transgenic technology is increasingly used in forest-tree breeding to overcome the disadvantages of traditional breeding methods, such as a long breeding cycle, complex cultivation environment, and complicated procedures. By introducing exogenous DNA, genes tightly related or contributed to ideal traits-including insect, disease, and herbicide resistance-were transferred into diverse forest trees, and genetically modified (GM) trees including poplars were cultivated. It is beneficial to develop new varieties of GM trees of high quality and promote the genetic improvement of forests. However, the low transformation efficiency has hampered the cultivation of GM trees and the identification of the molecular genetic mechanism in forest trees compared to annual herbaceous plants such as Oryza sativa. In this study, we reviewed advances in transgenic technology of forest trees, including the principles, advantages and disadvantages of diverse genetic transformation methods, and their application for trait improvement. The review provides insight into the establishment and improvement of genetic transformation systems for forest tree species. Challenges and perspectives pertaining to the genetic transformation of forest trees are also discussed.

Advantages of Heterotrophic Microalgae as a Host for Phytochemicals Production

Currently, most commercial recombinant technologies rely on host systems. However, each host has their own benefits and drawbacks, depending on the target products. Prokaryote host is lack of post-transcriptional and post-translational mechanisms, making them unsuitable for eukaryotic productions like phytochemicals. Even there are other eukaryote hosts (e.g., transgenic animals, mammalian cell, and transgenic plants), but those hosts have some limitations, such as low yield, high cost, time consuming, virus contamination, and so on. Thus, flexible platforms and efficient methods that can produced phytochemicals are required. The use of heterotrophic microalgae as a host system is interesting because it possibly overcome those obstacles. This paper presents a comprehensive review of heterotrophic microalgal expression host including advantages of heterotrophic microalgae as a host, genetic engineering of microalgae, genetic transformation of microalgae, microalgal engineering for phytochemicals production, challenges of microalgal hosts, key market trends, and future view. Finally, this review might be a directions of the alternative microalgae host for high-value phytochemicals production in the next few years.

Development of Plant-Produced Recombinant ACE2-Fc Fusion Protein as a Potential Therapeutic Agent Against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease (COVID-19) which has recently emerged as a potential threat to global public health. SARS-CoV-2 is the third known human coronavirus that has huge impact on the human population after SARS-CoV and MERS-CoV. Although some vaccines and therapeutic drugs are currently in clinical trials, none of them are approved for commercial use yet. As with SARS-CoV, SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) as the cell entry receptor to enter into the host cell. In this study, we have transiently produced human ACE2 fused with the Fc region of human IgG1 in Nicotiana benthamiana and the in vitro neutralization efficacy of the plant-produced ACE2-Fc fusion protein was assessed. The recombinant ACE2-Fc fusion protein was expressed in N. benthamiana at 100 μg/g leaf fresh weight on day 6 post-infiltration. The recombinant fusion protein showed potent binding to receptor binding domain (RBD) of SARS-CoV-2. Importantly, the plant-produced fusion protein exhibited potent anti-SARS-CoV-2 activity in vitro. Treatment with ACE2-Fc fusion protein after viral infection dramatically inhibit SARS-CoV-2 infectivity in Vero cells with an IC50 value of 0.84 μg/ml. Moreover, treatment with ACE2-Fc fusion protein at the pre-entry stage suppressed SARS-CoV-2 infection with an IC50 of 94.66 μg/ml. These findings put a spotlight on the plant-produced ACE2-Fc fusion protein as a potential therapeutic candidate against SARS-CoV-2.

Design, production and immunomodulatory potency of a novel allergen bioparticle

Allergen immunotherapy (AIT) is the only disease-modifying treatment with evidence for sustained efficacy. However, it is poorly developed compared to symptomatic drugs. The main reasons come from treatment duration implying monthly injections during 3 to 5 years or daily sublingual use, and the risk of allergic side-effects. To become a more attractive alternative to lifelong symptomatic drug use, improvements to AIT are needed. Among the most promising new immunotherapy strategies is the use of bioparticles for the presentation of target antigen to the immune system as they can elicit strong T cell and B cell immune responses. Virus-like particles (VLPs) are a specific class of bioparticles in which the structural and immunogenic constituents are from viral origin. However, VLPs are ill-suited for use in AIT as their antigenicity is linked to structure. Recently, synthetic biology has been used to produce artificial modular bioparticles, in which supramolecular assemblies are made of elements from heterogeneous biological sources promoting the design and use of in vivo-assembling enveloped bioparticles for viral and non-viral antigens presentation. We have used a coiled-coil hybrid assembly for the design of an enveloped bioparticle (eBP) that present trimers of the Der p 2 allergen at its surface, This bioparticle was produced as recombinant and in vivo assembled eBPs in plant. This allergen biotherapeutic was used to demonstrate i) the capacity of plants to produce synthetic supramolecular allergen bioparticles, and ii) the immunomodulatory potential of naturally-assembled allergen bioparticles. Our results show that allergens exposed on eBPs induced a very strong IgG response consisting predominantly of IgG2a in favor of the TH1 response. Finally, our results demonstrate that rDer p 2 present on the surface of BPs show a very limited potential to stimulate the basophil degranulation of patient allergic to this allergen which is predictive of a high safety potential.

Optimised production of an anti-fungal antibody in Solanaceae hairy roots to develop new formulations against Candida albicans

BACKGROUND

Infections caused by fungi are often refractory to conventional therapies and urgently require the development of novel options, such as immunotherapy. To produce therapeutic antibodies, a plant-based expression platform is an attractive biotechnological strategy compared to mammalian cell cultures. In addition to whole plants, hairy roots (HR) cultures can be used, representing an expression system easy to build up, with indefinite growth while handled under containment conditions.

RESULTS

In this study the production in HR of a recombinant antibody, proved to be a good candidate for human immunotherapy against fungal infections, is reported. Expression and secretion of this antibody, in an engineered single chain (scFvFc) format, by HR from Nicotiana benthamiana and Solanum lycopersicum have been evaluated with the aim of directly using the deriving extract or culture medium against pathogenic fungi. Although both Solanaceae HR showed good expression levels (up to 68 mg/kg), an optimization of rhizosecretion was only obtained for N. benthamiana HR. A preliminary assessment to explain this result highlighted the fact that not only the presence of proteases, but also the chemical characteristics of the growth medium, can influence antibody yield, with implications on recombinant protein production in HR. Finally, the antifungal activity of scFvFc 2G8 antibody produced in N. benthamiana HR was evaluated in Candida albicans growth inhibition assays, evidencing encouraging results.

CONCLUSIONS

Production of this anti-fungal antibody in HR of N. benthamiana and S. lycopersicum elucidated factors affecting pharming in this system and allowed to obtain promising ready-to-use immunotherapeutics against C. albicans.

Expression of Single Chain Variable Fragment (scFv) Molecules in Plants: A Comprehensive Update

Single chain variable fragments (scFvs) are generated by joining together the variable heavy and light chain of a monoclonal antibody (mAb) via a peptide linker. They offer some advantages over the parental mAb such as low molecular weight, heterologous production, multimeric form, and multivalency. The scFvs were produced against more than 50 antigens till date using 10 different plant species as the expression system. There were considerable improvements in the expression and purification strategies of scFv in the last 24 years. With the growing demand of scFv in therapeutic and diagnostic fields, its biosynthesis needs to be increased. The easiness in development, maintenance, and multiplication of transgenic plants make them an attractive expression platform for scFv production. The review intends to provide comprehensive information about the use of plant expression system to produce scFv. The developments, advantages, pitfalls, and possible prospects of improvement for the exploitation of plants in the industrial level are discussed.

Current state-of-the-art in the use of plants for the production of recombinant vaccines against infectious bursal disease virus

Infectious bursal disease is a widely spread threatening contagious viral infection of chickens that induces major damages to the Bursa of Fabricius and leads to severe immunosuppression in young birds causing significant economic losses for poultry farming. The etiological agent is the infectious bursal disease virus (IBDV), a non-enveloped virus belonging the family of Birnaviridae. At present, the treatment against the spread of this virus is represented by vaccination schedules mainly based on inactivated or live-attenuated viruses. However, these conventional vaccines present several drawbacks such as insufficient protection against very virulent strains and the impossibility to differentiate vaccinated animals from infected ones. To overcome these limitations, in the last years, several studies have explored the potentiality of recombinant subunit vaccines to provide an effective protection against IBDV infection. In this review, we will give an overview of these novel types of vaccines with special emphasis on current state-of-the-art in the use of plants as "biofactories" (plant molecular farming). In fact, plants have been thoroughly and successfully characterized as heterologous expression systems for the production of recombinant proteins for different applications showing several advantages compared with traditional expression systems (Escherichia coli, yeasts and insect cells) such as absence of animal pathogens in the production process, improved product quality and safety, reduction of manufacturing costs, and simplified scale-up.

Transient Expression of Human Cytochrome P450s 2D6 and 3A4 in Nicotiana benthamiana Provides a Possibility for Rapid Substrate Testing and Production of Novel Compounds

Employment of transient expression of foreign genes for bioconversion of pharmaceutically valuable low-molecular-weight compounds, including plant secondary metabolites, is an enticing trend still scantily explored in plant biotechnology. In the present work, an efficient protocol for rapid assessment of synthetic and plant-derived metabolites as potential substrates for human P450s (CYP2D6 and CYP3A4) via Agrobacterium-mediated transient expression in Nicotiana benthamiana is put forth. Animal P450s with broad substrate specificity are promising candidates for transformation of diverse metabolites. The efficiency of P450s in heterologous surroundings is not always satisfactory and depends on the availability of an associated electron-transfer enzyme. Plants represent an attractive assortment of prospective hosts for foreign P450s expression. The optimal composition of genetic blocks providing the highest transient expression efficiency is designed, an effective substrate administration scheme is validated, and biological activity of the investigated P450s against loratadine and several indole alkaloids with different molecular scaffold structures is tested. A novel indole alkaloid, 11-hydroxycorynanthine, is isolated from N. benthamiana plants transiently expressing CYP2D6 and supplemented with corynanthine, and its structure was elucidated. The proposed technique might be of value in realization of combinatorial biosynthesis concept comprising the junction of heterologous enzymes and substrates in different metabolic surroundings.

Re-assessment of biolistic transient expression: An efficient and robust method for protein localization studies in seedling-lethal mutant and juvenile plants

Knowledge on the subcellular localization of target proteins in a plant mutant background is important for revealing the function of the genes investigated. However, in Arabidopsis and rice, mutant lethality is one major barrier to such studies. Here we describe an optimized bombardment-mediated transient expression approach for studying subcellular protein localization in Arabidopsis seedling of lethal mutants. The whole experiment comprises four stages: cultivation and preparation of plants, coating gold particles with plasmid DNA, delivery of DNA into plants via bombardment, plant incubation and gene expression analysis which include localization and dynamics, co-localization comparison with reporter proteins and functional analysis. The entire process takes about 3-10 days from plant cultivation to protein detection. It has a high efficiency and the results are reproducible. Additionally, this protocol is applicable for the transient expression of chimeric fluorescent fusion proteins in juvenile rice seedlings and leaf sheaths, saving time dramatically in comparison of generating transgenic rice plant.

Co-expression of Multiple Chimeric Fluorescent Fusion Proteins in an Efficient Way in Plants

Information about the spatiotemporal subcellular localization(s) of a protein is critical to understand its physiological functions in cells. Fluorescent proteins and generation of fluorescent fusion proteins have been wildly used as an effective tool to directly visualize the protein localization and dynamics in cells. It is especially useful to compare them with well-known organelle markers after co-expression with the protein of interest. Nevertheless, classical approaches for protein co-expression in plants usually involve multiple independent expression plasmids, and therefore have drawbacks that include low co-expression efficiency, expression-level variation, and high time expenditure in genetic crossing and screening. In this study, we describe a robust and novel method for co-expression of multiple chimeric fluorescent proteins in plants. It overcomes the limitations of the conventional methods by using a single expression vector that is composed of multiple semi-independent expressing cassettes. Each protein expression cassette contains its own functional protein expression elements, and therefore it can be flexibly adjusted to meet diverse expression demand. Also, it is easy and convenient to perform the assembly and manipulation of DNA fragments in the expression plasmid by using an optimized one-step reaction without additional digestion and ligation steps. Furthermore, it is fully compatible with current fluorescent protein derived bio-imaging technologies and applications, such as FRET and BiFC. As a validation of the method, we employed this new system to co-express fluorescently fused vacuolar sorting receptor and secretory carrier membrane proteins. The results show that their perspective subcellular localizations are the same as in previous studies by both transient expression and genetic transformation in plants.

Detecting the interaction of peptide ligands with plant membrane receptors

The field of plant receptor biology has rapidly expanded in recent years, however the demonstration of direct interaction between receptor-ligand pairs remains a challenge. Click chemistry has revolutionized small molecule research but lacks popularity in plant research. Here we describe a method that tests for the direct physical interaction of a candidate receptor protein and a peptide ligand. This protocol describes the generation of the ligand probe, transient expression of a receptor protein, enrichment of membrane-bound receptors, photo-crosslinking and click chemistry-mediated reporter addition, and detection of the receptor-ligand complex. Copper-based click chemistry confers several advantages, including the versatility to use almost any azide-containing reporter molecule for detection or visualization of the complex and addition of the reporter molecule after receptor-ligand binding which reduces the need for bulky ligand modifications that could interfere with the interaction.

Once for All: A Novel Robust System for Co-expression of Multiple Chimeric Fluorescent Fusion Proteins in Plants

Chimeric fluorescent fusion proteins have been employed as a powerful tool to reveal the subcellular localizations and dynamics of proteins in living cells. Co-expression of a fluorescent fusion protein with well-known organelle markers in the same cell is especially useful in revealing its spatial and temporal functions of the protein in question. However, the conventional methods for co-expressing multiple fluorescent tagged proteins in plants have the drawbacks of low expression efficiency, variations in the expression level and time-consuming genetic crossing. Here, we have developed a novel robust system that allows for high-efficient co-expression of multiple chimeric fluorescent fusion proteins in plants in a time-saving fashion. This system takes advantage of employing a single expression vector which consists of multiple semi-independent expressing cassettes for the protein co-expression thereby overcoming the limitations of using multiple independent expressing plasmids. In addition, it is a highly manipulable DNA assembly system, in which modification and recombination of DNA molecules are easily achieved through an optimized one-step assembly reaction. By employing this effective system, we demonstrated that co-expression of two chimeric fluorescent fusion reporter proteins of vacuolar sorting receptor and secretory carrier membrane protein gave rise to their perspective subcellular localizations in plants via both transient expression and stable transformation. Thus, we believed that this technical advance represents a promising approach for multi-color-protein co-expression in plant cells.