Transgenic Plant as Bioreactors(Molecular Farming)

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Transgenic Plant as Bioreactors(Molecular Farming)

Plants can be used as cheap chemical factories that require only water, minerals, sun light and carbon dioxide to produce thousands of sophisticated chemical molecules with different structures. By transferring the right genes, plants can serve as bioreactors to modified or new compounds such as amino acids, proteins, vitamins, plastics, pharmaceuticals (peptides and proteins), drugs, enzymes for food industry and so on. The transgenic plants as bioreactors have some advantages such as the cost of production is low, there is an unlimited supply, safe and environmental friendly and there is no scare of spread of animal borne diseases.

Tobacco is the most preferred plant as a transgenic bioreactor because it can be easily transformed and engineered. Tobacco is an excellent biomass producer with about 40 tons of fresh leaf production as against e.g. rice with 4 tons. The seed production is very high (approx. one million seeds per plant) and it can be harvested several times in a year. Some of the uses of transgenic plants are:

Improvement of Nutrient quality

Transgenic crops with improved nutritional quality have already been produced by introducing genes involved in the metabolism of vitamins, minerals and amino acids. A transgenic Arabidopsis thaliana that can produce ten-fold higher vitamin E (alpha-tocopherol) than the native plant has been developed. The biochemical machinery to produce a compound close in structure to alpha-tocopherol is present in A. thaliana. A gene that can finally produce alpha-tocopherol is also present, but is not expressed. This dormant gene was activated by inserting a regulatory gene from a bacterium which resulted in an efficient production of vitamin E. Glycinin is a lysine-rich protein of soybean and the gene encoding glycinin has been introduced into rice and successfully expressed. The transgenic rice plants produced glycinin with high contents of lysine.

Using genetic engineering Prof Potrykus and Dr. Peter Beyer have developed rice which is enriched in pro-vitamin A by introducing three genes involved in the biosynthetic pathway for carotenoid, the precursor for vitamin A. The aim was to help millions of people who suffer from night blindness due to Vitamin A deficiency, especially whose staple diet is rice. The presence of beta-carotene in the rice gives a characteristic yellow/orange colour, hence this pro-vitamin A enriched rice is named as Golden Rice.

The genetic engineering is also being used to improve the taste of food e.g. a protein ‘monellin’ isolated from an African plant (Dioscorephyllum cumminsii) is about 100,000 sweeter than sucrose on molar basis. Monellin gene has been introduced into tomato and lettuce plants to improve their taste.

Improvement of seed protein quality

The nutritional quality of cereals and legumes has been improved by using biotechnological methods. Two genetic engineering approaches have been used to improve the seed protein quality. In the first case, a transgene (e.g. gene for protein containing sulphur rich amino acids) was introduced into pea plant (which is deficient in methionine and cysteine, but rich in lysine) under the control of seed-specific promoter. In the second approach, the endogenous genes are modified so as to increase the essential amino acids like lysine in the seed proteins of cereals. These transgenic routes have helped to improve the essential amino acids contents in the seed storage proteins of a number of crop plants. E.g. overproduction of lysine by de-regulation. The four essential amino acids namely lysine, methionine, threonine, and isoleucine are produced from a non-essential amino acid aspartic acid. The formation of lysine is regulated by feed back inhibition of the enzymes aspartokinase (AK) and dihydrodipicolinate synthase (DHDPS). The lysine feedback- insensitive genes encoding the enzymes AK and DHDPS have been respectively isolated from E. Coli and Cornynebacterium. After doing appropriate genetic manipulations, these genes were introduced into soybean and canola plants. The transgenic plants so produced had high quantities of lysine.

Diagnostic and therapeutic proteins

Experiments are going on to use transgenic plants in diagnostics for detecting human diseases and therapeutics for curing human and animal diseases. Several metabolites and compounds are already being produced in transgenic plants e.g. the monoclonal antibodies, blood plasma proteins, peptide hormones, cytokinins etc. The use of plants for commercial production of antibodies, referred to as plantbodies, is a novel approach in biotechnology. The first successful production of a functional antibody, namely a mouse immunoglobulin IgGI in plants, was reported in 1989. This was achieved by developing two transgenic tobacco plants-one synthesizing heavy chain gamma- chain and other light kappa- chain, and crossing them to generate progeny that can produce an assembled functional antibody. In 1992, C.J. Amtzen and co-workers expressed hepatitis B surface antigen in tobacco to produce immunologically active ingredients via genetic engineering of plants. Several other therapeutic proteins have also been produced like haemoglobin and erythropoietin in tobacco plants, lactoferrin in potato, trypsin inhivitor in maize etc. The first proteins/enzymes that were produced in transgenic plants (maize) are avidin and beta-glucuronidase and are used in diagnostic kits.

Edible vaccines

Crop plants offer cost-effective bioreactors to express antigens which can be used as edible vaccines. The approach is to isolate genes encoding antigenic proteins from the pathogens and then expressing them in plants. Such transgenic plants or their tissues producing antigens can be eaten for vaccination/immunization (edible vaccines). The expression of such antigenic proteins in crops like banana and tomato are useful for immunization of humans since banana and tomato fruits can be eaten raw.

Transgenic plants (tomato, potato) have been developed for expressing antigens derived from animal viruses e.g. rabies virus, herpes virus. In 1990, the first report of the production of edible vaccine (a surface protein from Streptococcus) in tobacco at 0.02% of total leaf protein level was published in the form of a patent application under the International Patent Cooperation Treaty (Mason and Arntzen,1995).The first clinical trials in humans, using a plant derived vaccine were conducted in 1997 and were met with limited success. This involved the ingestion of transgenic potatoes with a toxin of E. coli causing diarrhea.

The process of making of edible vaccines involves the incorporation of a plasmid carrying the antigen gene and an antibiotic resistance gene, into the bacterial cells e.g. Agrobacterium tumefaciens. The small pieces of potato leaves are exposed to an antibiotic which can kill the cells that lack the new genes. The surviving cells with altered genes multiply and form a callus. This callus is allowed to grow and subsequently transferred to soil to form a complete plant. In about a few weeks, the plants bear potatoes with antigen vaccines.

The bacteria E.coli, V. cholerae cause acute watery diarrhea by colonizing the small intestine and by producing toxins. Chloera toxin (CT) is very similar to E.Coli toxin. The CT has two subunits, A and B. Attempt was made to produce edible vaccine by expressing heat labile enterotoxin (CT-B) in tobacco and potato.

Another strategy adopted to produce a plant-based vaccine, is to infect the plants with recombinant virus carrying the desired antigen that is fused to viral coat protein. The infected plants are reported to produce the desired fusion protein in large amounts in a short duration. The technique involves either placing the gene downstream a subgenomic promoter, or fusing the gene with capsid protein that coats the virus.

Advantages of edible vaccines

The edible vaccines produced in transgenic plants will sole the storage problems, will ensure easy delivery system by feeding and will have low cost as compared to the recombinant vaccines produced by bacterial fermentation. Vaccinating people against dreadful diseases like cholera and hepatitis B, by feeding them banana, tomato, and vaccinating animals against important diseases will be an interesting development.

Biodegradable plastics

Polythenes and plastics are one of the major environmental hazards. Efforts are on to explore the possibility of using transgenic plants for biodegradable plastics. Transgenic plants can be used as factories to produce biodegradable plastics like polyhydroxy butyrate or PHB. Genetically engineered Arabidopisis plants can produce PHB globules exclusively in their chloroplasts without effecting plant growth and development. The large-scale production of PHB can easily be achieved in plants like Populus, where PHB can be extracted from leaves.

Molecular Breeding

The term molecular breeding is frequently used to represent the breeding methods that are coupled with genetic engineering techniques. Up till now, conventional breeding methods have been used to meet the food demands of the growing world population and the challenges of poverty and improved crop production and yields. However in the years to come, the development in the agriculture yields and techniques is going to be due to the use of molecular breeding programme. Linkage analysis which deals with the studies to correlate the link between the molecular marker and a desired trait is an important aspect of molecular breeding programme. In the past, linkage analysis was carried out by use of isoenzymes and the associated polymorphisms. Now a days, molecular markers are being used.

Molecular breeding involves breeding using molecular (nucleic acid) markers. A molecular marker is a DNA sequence in the genome which can be located and identified therefore molecular markers can be used to identify particular locations in the genome.

Due to mutations, insertions, deletions, etc. the base composition at a particular location may be different in different plants. These differences, termed polymorphisms, allow DNA markers to be mapped in a genetic linkage group. Generally, there are three types of markers used in screening/selection:

a) Morphological marker based on visible character (phenotypic expression) e.g. flower color, seed color, height, leaf shapes, etc. Morphological markers could be dominant or recessive. There are certain constraints in using these markers as the morphological markers are easily influenced by environmental factors and thus may not represent the desired genetic variation. Some of the visible markers have not much role to play in the plant breeding programme.

b) Biochemical marker: The proteins produced by gene expression are also used as markers in plant breeding programmes. The most commonly used are isozymes, the different molecular forms of the same enzyme. Each individual variety has its own isozyme variability (profiles) which can be detected by electrophoresis on starch gel.

c) Molecular marker based on DNA polymorphism detected by DNA probes or amplified products of PCR, e.g.Restriction fragment length polymorphism (RFLP), Randomly Amplified polymorphic DNA (RAPD), variable Number Tandom Repeats (VNTR), Microsatellites, etc. Plant breeders always prefer to detect the gene as molecular marker, although it is not always possible. Molecular markers provide a true representation of the genetic make up at the DNA level. They are consistent and free from environmental factors, and can be detected much before the development of plants occur. The advantage with a molecular marker is that a plant breeder can select a suitable marker for the desired trait which can be detected well in advance. A large number of markers can be generated as per the needs. The molecular markers to be used in plant breeding programme should have the following characteristics: (a) the marker should be closely linked with the desired trait, (b) the marker screening methods should be effective, efficient, reproducible and easy to carry out, (C) the entire analysis should be cost effective.

Molecular makers are of two types

(a) based on nucleic acid (DNA) hybridization- This involves the cloning of the DNA piece followed by the hybridization with the genomic DNA, which is later detected. The Restriction fragment length polymorphism (RFLP) was the very first technology employed for the detection of polymorphism, based on the DNA sequence differences. RFLP is mainly based on the altered restriction enzyme sites, as a result of mutations and recombinations of genomic DNA. The procedure involves the isolation of genomic DNA and it’s digestion by restriction enzymes. The fragments are separated by electrophoresis and finally hybridized by incubating with cloned and labeled probes.

(b) Molecular markers based on PCR amplification.
Polymerase chain reaction (PCR) is a novel technique for the amplification of selected regions of DNA. The most important advantage is that even a minute quantity of DNA can be amplified and the PCR- based molecular markers require only a small quantity of DNA to start with. Random amplified polymorphic DNA (RAPD) markers use PCR amplification where the DNA is isolated from the genome and is denatured. The template molecules are annealed with primers and amplified by PCR. The amplified products are separated on electrophoresis and identified. Based on the nucleotide alterations in the genome, the polymorphisms of amplified DNA sequences differ which can be identified as bends on gel electrophoresis. Amplified fragment length polymorphism (AFLP) is a novel technique involving a combination of RFLP and RAPD. AFLP is based on the principle of generation of DNA fragments using restriction enzymes and oligonucleotide adaptors (or linkers), and their amplification by PCR.

Microsatellites

Microsatellites are the tandemly repeated multiple copies of mono-, di-, tri-, and tetra nucleotide motifs. In some instances, there are unique flanking sequences present in the repeat sequences. Primers are designed for such flanking sequences to detect the sequence tagged microsatellites (STMS) which is done by PCR.

Commercial use of transgenic plants

The main goal of producing transgenic plants is to increase the productivity. In 1995-96, transgenic potato and cotton plants were used commercially for the first time in USA. By the year 1998-99, five other major transgenic crops cotton, maize, canola, soybean, and potato were introduced to the farmers. These accounted for about 75% of the total area planted by crops in USA. There are still a lot of concerns regarding the harmful environmental and hazardous health effects of transgenic plants. The major areas of public concern are- the development of resistance genes in insects, generation of a super weeds by mutation etc. Certain other legal and regulatory hurdles pertaining to commercial use of transgenic plants, needs to be addressed.

Bioethics in Plant genetic Engineering

There are issues and concerns regarding the use of transgenic crops and their effects on the health and the environment in general. The major concerns about GM crops and GM foods are:

a) Effect of GM crops on biodiversity and environment- As the GM crops are created artificially, there is no natural process of evolution in their development. Hence, there is a question of this affecting the biodiversity and overall effect on the environment.

b) The risk of transfer of transgene from GM crops to pathogenic microbes- Antibiotic marker genes are used to identify and select the modified cells. If GM food containing antibiotic resistance marker gene is consumed by animals and humans, there is a risk that the transgene will transfer from GM food to microflora of human and animals. This may lead to the gut microbes to become resistant to antibiotics.

c) The transfer of genes from animals into Gm crops for molecular farming may change the fundamental vegetable nature of plants.

d) The GM crops may bring about changes in evolutionary patterns. The plants adapt to the changing environment in the natural way by changing their genes and developing better races with superior traits which ultimately leads to the development of evolved races and varieties. What will be the evolutionary pattern of the GM crops? There are concerns about the effect of transgene flow from GM crops to other non-GM plants and the alteration of these non-GM crops.

e) There is a risk of transferring allergens (usually glycoproteins) from GM food to human and animals.

f) There is a risk of “gene pollution” i.e. transfer of transgene of GM crop through pollen grains to related plant species and development of super weeds.

g) There are also some religious issues related to the consumption of transgenic plants with animal genes introduced into them, especially, for some strict vegetarian people and some ethnic groups with certain food preferences and restrictions.

h) There is a need to study thoroughly as to how the genetically engineered plants will affect the ecological balance, once they are released in the environment.

Quality Traits in Genetically Modified Plants

1. Modified Flower Color
  • Researchers aimed to produce novel blue-violet pigments in commercially important flowers.
  • They addressed the natural limitation that many key ornamental flowers, such as carnations, roses, lilies, chrysanthemums, and gerberas, could not synthesize the blue pigment delphinidin.
  • To solve this, Scientists created genetically modified (GM) carnations, roses, and chrysanthemums with unique violet and mauve colors by introducing specific genes, most notably the flavonoid 3',5'-hydroxylase (F3'5'H) gene, from other plants.
  • Carnations: The “Moon” series carnations were engineered by introducing petuniaderived F3'5'H and DFR genes to enable delphinidin accumulation, producing stable blue to violet flower coloration.
  • Roses: The world’s first “blue” rose, Suntory blue rose APPLAUSE™, was created by introducing the F3'5'H gene from pansy into roses that naturally lack it, allowing delphinidin-based lavender–mauve pigmentation and commercial release in 2009.
  • Chrysanthemums: Blue-violet chrysanthemums were developed by introducing the F3'5'H gene from Canterbury bell along with the A3'5'GT gene from butterfly pea to enhance and stabilize blue anthocyanin pigmentation.
2. Delayed Fruit Ripening and Increased Shelf Life
  • The goal was to slow the ripening process and reduce spoilage to extend the marketable life of fruits.
  • Scientists suppressed the activity of key ripening-related genes in transgenic plants. They targeted genes encoding an enzyme for ethylene synthesis, a major ripening hormone, and genes for the enzyme polygalacturonase (PG), which breaks down cell walls (Prasanna et al., 2007).
  • This suppression was accomplished by inserting a truncated or anti-sense version of the target gene. The result was a delay in ripening initiation and a slowdown in fruit softening and rotting.
  • Cell Wall Degradation: Enzymes like polygalacturonase (PG) break down pectin, causing softening. Using antisense technology to reduce PG enzyme levels delays this softening.
  • RNA Interference (RNAi): This technique targets specific ripening-related mRNA, effectively "silencing" genes. Examples include targeting N-glycan-modifying enzymes (α-mannosidase) or ripening inhibitors (like MADS-box genes in bananas) to control ripening. RNAi targeting ACS or N-glycan enzymes resulted in delayed ripening, improved firmness, and up to 45 days of extended shelf life in tomatoes.
  • Transcription Factors: Modifying regulatory genes, such as MADS-box transcription factors in bananas, can control the onset of ripening. MaMADS genes (Musa MADS-box genes) are a specific family of transcription factors in banana (Musa spp.) that regulate crucial aspects of plant growth, particularly flower and fruit development, and fruit ripening,
  • Other Fruits: Similar genetic engineering efforts have targeted apples, melons, plums, and papayas.
3. Modification of Oil Composition

The objective was to create vegetable oils with improved heat stability and nutritional profiles. For example, oilseed rape and soybean were genetically modified to produce oil with a significantly higher oleic acid content (Kinney et al., 2002). The modification involved using a mutant FAD2 gene. In unmodified plants, the normal FAD2 gene encoded a desaturase enzyme that converted oleic acid into polyunsaturated fats. The mutant version prevented this conversion, leading to the accumulation of oleic acid. Consequently, the modified oil possessed greater heat stability and a lower polyunsaturated fat content compared to oil from conventional crops.

References

Kinney, A. J., Cahoon, E. B., & Hitz, W. D. (2002). Manipulating desaturase activities in transgenic crop plants. Biochemical Society Transactions, *30*(6), 1099–1103.

Prasanna, V., Prabha, T. N., & Tharanathan, R. N. (2007). Fruit ripening phenomena–an overview. Critical Reviews in Food Science and Nutrition, *47*(1), 1–19.

Virus resistance

Transgenic crop development has extensively targeted disease resistance, particularly against viruses, through pathogen-derived resistance in which expression of viral genes such as coat protein or replicase confers resistance to infection. In addition, transgenic strategies against fungal and bacterial pathogens employ genes encoding chitinases, glucanases, phytoalexin biosynthetic pathways, and resistance (R) genes to enhance plant defense responses.

Edible Vaccines
Plants as bioreactors for edible vaccine production

Plants can function as bioreactors for recombinant antigens suitable for oral delivery, provided the host supports high expression, scalability, and consumer acceptability (Patel et al., 2022). Human-targeted edible vaccines generally favor palatable edible tissues with stable antigen levels, whereas animal vaccines must integrate into routine feed (Tiwari et al., 2009). Major candidate platforms include staple and horticultural crops such as rice, maize, lettuce, tomato, potato, and banana (Gupta et al., 2022; Sahoo et al., 2020).

Potato

Potato was central in early edible vaccine development due to its transformability and its role in landmark animal and human studies (Tacket et al., 2004). It offers distribution advantages because tubers are widely handled and do not inherently require complex downstream bioprocessing (Gupta et al., 2022). A key limitation is that potatoes are typically consumed cooked, and heat can denature antigens, complicating efficacy unless stability strategies are used (Concha et al., 2017).

Tobacco

Tobacco is a high-biomass, high-expression platform used extensively in plant-based vaccine work, including hepatitis B antigens and other vaccine targets (Tacket, 2009). Seed-based expression can improve stability, storage, and handling relative to leaf-based production (Tiwari et al., 2009). Because tobacco is not a food crop and contains alkaloids, it is more suitable for PBV production with controlled delivery formats than for “edible” administration in routine diets (Patel et al., 2022).

Soybean

Soybean is attractive because protein-rich seeds can support higher antigen accumulation per unit mass, improving feasibility for oral dosing (Sahoo et al., 2020). Expression of enterotoxigenic E. coli toxin subunits in soybean seeds has been associated with strong antigen accumulation and measurable systemic antibody responses in animal models (Patel et al., 2022). Remaining challenges include dose standardization across seed lots and controlling variability in expression (Patel et al., 2022).

Banana

Banana is appealing because it can be eaten raw, is widely accepted, and grows in tropical regions where immunization access gaps are often greatest (Sahoo et al., 2020). Studies have demonstrated hepatitis B surface antigen expression in banana using multiple genetic constructs (Sahai et al., 2013). A major limitation is the long cultivation cycle, which slows scaling and rapid deployment (Aryamvally et al., 2017).

Maize

Maize enables large-scale agricultural production and can be integrated into human foods and animal feeds, supporting both public-health and veterinary use cases (Shah et al., 2022). Genetically modified maize has shown potential to elicit protective responses in animal models and has been explored for multiple targets. The central operational challenge is containment and segregation to prevent inadvertent entry into the food chain (Koul, 2022).

Rice

Rice is a globally important staple and supports seed-based antigen expression with favorable storage characteristics, making it a practical delivery concept for rice-dependent populations (Gupta et al., 2022). Transgenic rice platforms have been explored for both infectious disease targets (e.g., cholera antigens) and immune-modulating approaches (Nochi et al., 2009). Key constraints remain dosing consistency, regulatory containment, and demonstration of reliable protective efficacy (Patel et al., 2022).

Spinach

Spinach has been investigated as a platform for expressing vaccine candidates via plant viral vectors, including approaches involving TMV-based systems (Oszvald et al., 2007). Its attractiveness includes raw consumption and rapid cultivation compared with some fruit crops (Sussman, 2003). However, it remains a niche platform relative to staples, with ongoing constraints around consistent expression and dosing (Patel et al., 2022).

Lettuce

Lettuce is a strong candidate because it is commonly eaten raw and can support chloroplast-based expression strategies (Singh et al., 2023). It has been used to express enteric pathogen antigens and explored for SARS-CoV-2 spike expression in chloroplasts as an oral booster concept. Variability in biomass and antigen concentration across leaves and harvests must be addressed for clinical-grade dose control.

Production of edible vaccines

Edible vaccines typically express subunit antigens produced by inserting antigen-encoding genes into plants and optimizing expression using regulatory elements and codon considerations (Glick & Patten, 2022). Two strategies dominate: stable transformation (propagable lines enabling germplasm banking) and transient expression (often virus-vector based, faster and potentially higher-yield) (Day & Goldschmidt-Clermont, 2011). Success depends on sequence optimization and subcellular targeting to increase expression while preserving antigen structure and function (Khan et al., 2023).

Agrobacterium-mediated Gene Transfer

This method introduces transgenes into plants via Agrobacterium tumefaciens, followed by selection using marker systems and screening. It is widely used but can be relatively slow and may yield modest antigen expression depending on the species and construct (Patel et al., 2022). Early edible vaccine work relied heavily on this approach in model and crop systems.

Biolistic Method

Biolistics delivers DNA-coated particles into plant cells, enabling transformation across a broad range of species (Tripathi et al., 2024). It supports development of multiple vaccine targets, but requires specialized, costly equipment that can limit adoption. It is often used where Agrobacterium is less effective or where organelle transformation is targeted (Altindis et al., 2014).

Electroporation Method

Electroporation introduces DNA by transiently permeabilizing membranes using electrical pulses (Kim et al., 2024). In plants, the cell wall creates an additional barrier, often making this approach more technically demanding than other transformation systems. Consequently, it is less commonly used as the primary route for edible vaccine pipelines (Patel et al., 2022).

Chloroplast Transformation

Chloroplast engineering integrates foreign genes via homologous recombination, enabling high expression, reduced gene silencing, and improved containment in many crop contexts (Sahoo et al., 2020). It offers site-specific insertion and high protein accumulation, typically using biolistics or related delivery methods (Saleem et al., 2024). Vector design and marker choice are critical for identifying transformants and meeting biosafety requirements.

Role of Adjuvants

Adjuvants amplify immune responses and are particularly important for oral vaccines where antigens face degradation and tolerance risks.

Role of Promoters

Promoters regulate the strength and tissue specificity of antigen expression, determining whether edible vaccines can reach practical oral doses (Khan et al., 2023). Constitutive promoters (e.g., CaMV35S) can drive broad expression but may be inefficient for edible dosing and can burden non-target tissues. Tissue- and seed-specific promoters can increase antigen accumulation and storage stability, supporting feasible delivery formats (Khalid et al., 2022).

Regulatory and Ethical Aspects

Edible vaccines face regulatory ambiguity regarding classification (food vs drug vs agricultural product) and require strict containment because they are GMOs intended for consumption. Oversight generally demands segregated cultivation, storage, and processing to prevent food-chain contamination and to meet clinical and GMP-aligned requirements. Public acceptance remains a parallel challenge, reinforcing the need for transparency and education (Singh et al., 2023).

Clinical Trial

Early phase human studies—particularly potato-based trials for enterotoxigenic E. coli LT-B and Norwalk virus antigens—demonstrated that orally delivered plant-expressed antigens can stimulate immune responses with acceptable short-term safety (Pogrebnyak et al., 2005). These trials also highlighted variability in antigen expression across tissues, leading to inconsistent dosing and heterogeneous immune outcomes. Despite broader progress in plant-made biologics, edible vaccines have not yet achieved routine human program approval (Tregoning, 2020).

References
  1. Day, A., & Goldschmidt-Clermont, M. (2011). The chloroplast transformation toolbox: Selectable markers and marker removal. Plant Biotechnology Journal, 9, 540–553. https://doi.org/10.1111/j.1467-7652.2011.00604.x
  2. Oszvald, M., Kang, T.-J., Tomoskozi, S., Jenes, B., Kim, T.-G., Cha, Y.-S., Tamas, L., & Yang, M.-S. (2008). Expression of cholera toxin B subunit in transgenic rice endosperm. Molecular Biotechnology, 40, 261–268. https://doi.org/10.1007/s12033-008-9070
  3. Glick, B. R., & Patten, C. L. (2022). Molecular biotechnology: Principles and applications of recombinant DNA (5th ed.). John Wiley & Sons.
  4. Gupta, P., Andankar, I., Gunasekaran, B., Easwaran, N., & Muthukaliannan, G. K. (2022). Genetically modified potato and rice based edible vaccines—An overview. Biocatalysis and Agricultural Biotechnology, 43, 102405.
  5. Khalid, F., Tahir, R., Ellahi, M., Amir, N., Rizvi, S. F. A., & Hasnain, A. (2022). Emerging trends of edible vaccine therapy for combating human diseases especially COVID-19: Pros, cons, and future challenges. Phytotherapy Research, 36, 2746–2766. https://doi.org/10.1002/ptr.7475
  6. Khan, A., Nasim, N., Pudhuvai, B., Koul, B., Upadhyay, S. K., Sethi, L., & Dey, N. (2023). Plant synthetic promoters: Advancement and prospective. Agriculture, 13, 298.
  7. Kim, E. Y. S., de Souza, E. M., & Müller-Santos, M. (2024). Optimisation of DNA electroporation protocols for different plant-associated bacteria. Journal of Microbiological Methods, 220, 106912.
  8. Patel, P., Patel, R., Patel, S., Patel, Y., Patel, M., & Trivedi, R. (2022). Edible vaccines: A nutritional substitute for traditional immunization. Pharmacognosy Reviews, 16, 16.
  9. Pogrebnyak, N., Golovkin, M., Andrianov, V., Spitsin, S., Smirnov, Y., Egolf, R., & Koprowski, H. (2005). Severe acute respiratory syndrome (SARS) S protein production in plants: Development of recombinant vaccine. Proceedings of the National Academy of Sciences of the United States of America, 102, 9062–9067.
  10. Sahoo, A., Mandal, A. K., Dwivedi, K., & Kumar, V. (2020). A cross talk between the immunization and edible vaccine: Current challenges and future prospects. Life Sciences, 261, 118343.
  11. Saleem, A., Saeed, M. A., Shah, N. A., Kaleem, I., Ahmed, H., & Khattak, S. H. (2024). Using plants as vaccines. In M. Z. Hashmi, A. Saeed, S. G. Musharraf, & W. Shuhong (Eds.), Recent advances in industrial biochemistry (pp. 49–76). Springer International Publishing. https://doi.org/10.1007/978-3-031-50989-6_4
  12. Singh, R., Lin, S., Nair, S. K., Shi, Y., & Daniell, H. (2023). Oral booster vaccine antigen— Expression of full-length native SARS-CoV-2 spike protein in lettuce chloroplasts. Plant Biotechnology Journal, 21, 887.
  13. Tregoning, J. S. (2020). First human efficacy study of a plant-derived influenza vaccine. The Lancet, 396, 1464–1465.
  14. Tripathi, A., Rathore, M., Shukla, S., Das, A., & Debnath, S. C. (2024). Agrobacterium and biolistic mediated genetic transformation of mungbean cultivar Samrat using embryogenic explant. Plant Cell, Tissue and Organ Culture, 157, 72.
Question Bank: Edible Vaccines & Plant-Based Vaccination
Section A: Multiple Choice Questions (MCQs)

  1. Edible vaccines primarily differ from conventional vaccines because they are:

    A. Live attenuated pathogens
    B. Administered via inhalation
    C. Produced and delivered through genetically modified edible plants
    D. Synthesized chemically in vitro

    Answer: C

  2. Which global event accelerated vaccine innovation and highlighted limitations in cold-chain–dependent immunization systems?

    A. Ebola outbreak
    B. SARS epidemic (2003)
    C. COVID-19 pandemic
    D. Zika virus outbreak

    Answer: C

  3. Which plant organelle is most advantageous for high-level antigen expression and transgene containment?

    A. Nucleus
    B. Mitochondria
    C. Endoplasmic reticulum
    D. Chloroplast

    Answer: D

  4. The first human clinical trial of an edible vaccine involved genetically modified:

    A. Rice
    B. Banana
    C. Potato
    D. Lettuce

    Answer: C

  5. Which mucosal adjuvant enhances antigen uptake by binding to GM1 ganglioside receptors on M cells?

    A. Alum
    B. CpG oligonucleotides
    C. Cholera toxin B subunit (CTB)
    D. Saponins

    Answer: C

  6. A major limitation of potato-based edible vaccines is:

    A. Low transformation efficiency
    B. Antigen degradation during cooking
    C. Poor tuber yield
    D. Lack of immune response

    Answer: B

  7. Which crop is most suitable for large-scale veterinary edible vaccine production?

    A. Spinach
    B. Lettuce
    C. Maize
    D. Carrot

    Answer: C

  8. Which promoter is commonly used for constitutive expression in transgenic plants?

    A. GluB-1
    B. E8
    C. CaMV 35S
    D. Patatin

    Answer: C

  9. Oral edible vaccines mainly stimulate which immune system?

    A. Innate immunity only
    B. Cellular immunity only
    C. Mucosal and systemic immunity
    D. Passive immunity

    Answer: C

  10. Which disease has been targeted using lettuce chloroplast-based expression of spike protein?

    A. Influenza
    B. Hepatitis B
    C. SARS-CoV-2
    D. HIV

    Answer: C

Section B: True / False Questions

  1. Edible vaccines always require purification before administration.

    Answer: False

  2. Chloroplast transformation reduces the risk of gene silencing compared to nuclear transformation.

    Answer: True

  3. Tobacco is an ideal edible vaccine crop because it is commonly eaten raw.

    Answer: False

  4. Maize-based vaccines pose regulatory concerns due to potential entry into the food chain.

    Answer: True

  5. Oral vaccines can induce secretory IgA production in mucosal tissues.

    Answer: True

Section C: Short Answer Questions (2–4 sentences)

  1. Define edible vaccines.

    Answer:
    Edible vaccines are subunit vaccines produced by genetically engineering edible plants to express antigenic proteins. When consumed orally, these antigens stimulate mucosal and systemic immune responses without the need for injections or cold-chain logistics.

  2. Why are edible vaccines particularly relevant for developing countries?

    Answer:
    They eliminate the need for refrigeration, trained medical personnel, and sterile injection equipment. This reduces cost, improves accessibility, and enhances vaccine coverage in resource-limited and remote regions.

  3. What role do M cells play in edible vaccine immunization?

    Answer:
    M cells transport antigens from the intestinal lumen to Peyer’s patches, enabling antigen presentation to immune cells. This initiates mucosal immune responses, particularly IgA production.

  4. Why are seed-specific promoters preferred in edible vaccine development?

    Answer:
    Seed-specific promoters enhance antigen accumulation in storage tissues, improve stability against degradation, and allow long-term storage without refrigeration.

  5. State two advantages of chloroplast transformation.

    Answer:
    It enables high-level antigen expression and reduces gene escape through maternal inheritance. It also minimizes transgene silencing and allows site-specific insertion.

  6. Why is antigen dosage a challenge in edible vaccines?

    Answer:
    Antigen concentration can vary between plants, tissues, and generations, making standardized dosing difficult. Individual consumption patterns further complicate dose control.

  7. Discuss one ethical concern related to edible vaccines.

    Answer:
    Accidental consumption of vaccine-containing crops by non-target populations raises ethical and safety concerns. Strict containment and labeling are therefore required.

  8. Why is rice considered a promising platform for pediatric edible vaccines?

    Answer:
    Rice is widely consumed, easily stored, and commonly used in infant foods. Seed-based expression allows stable antigen storage and consistent delivery.

  9. How do nanoparticles improve edible vaccine efficacy?

    Answer:
    Nanoparticles protect antigens from gastrointestinal degradation, enhance uptake by antigen-presenting cells, and act as adjuvants to strengthen immune responses.

  10. A rural community lacks refrigeration and trained healthcare workers. Which vaccine strategy is most suitable and why?

    Answer:
    Edible vaccines are most suitable because they can be orally administered, stored at ambient temperatures, and distributed without medical infrastructure.

  11. A potato-based vaccine shows reduced immunogenicity after cooking. What strategies could address this?

    Answer:
    Using raw-consumable crops, chloroplast expression, encapsulation strategies, or heat-stable antigen variants can mitigate antigen degradation.

  12. A regulator is concerned about GMO contamination of the food supply. What containment strategies should be recommended?

    Answer:
    Cultivation in controlled greenhouses, physical isolation, separate storage and processing facilities, and use of chloroplast transformation can reduce risk.

Section F: Essay-Type Questions

  1. Critically evaluate the advantages and limitations of edible vaccines compared to conventional vaccines.

    Edible vaccines offer major advantages in cost and distribution. Plant-based systems (e.g., hepatitis B antigen in transgenic potato; cholera toxin B in rice) eliminate fermentation infrastructure and reduce cold-chain dependence, improving access in low-resource settings. Oral delivery induces strong mucosal immunity (IgA) in addition to systemic IgG, which is advantageous against enteric pathogens like cholera and rotavirus.

    However, limitations remain significant. Dosage control is challenging due to variability in antigen expression between plants and batches, unlike precisely standardized injectable vaccines. Gastric degradation and inconsistent antigen release may reduce immunogenicity. Regulatory approval for plant-made pharmaceuticals remains complex due to biosafety and GMO containment concerns. Public acceptance is also uncertain, particularly for genetically modified edible crops.

    In contrast, conventional vaccines provide controlled dosing, established manufacturing standards, and predictable efficacy, but require cold-chain logistics and trained personnel. Thus, edible vaccines are promising for global health equity but require further standardization and regulatory harmonization.

  2. Describe the mechanism of action of edible vaccines from ingestion to immune response.

    Edible vaccines deliver antigenic proteins expressed in transgenic plant tissues (e.g., potato expressing hepatitis B surface antigen or lettuce expressing cholera toxin B subunit). After ingestion, plant cell walls provide bio-encapsulation, protecting the antigen from gastric degradation. In the intestine, digestive enzymes and gut microbiota release the antigen.

    Antigens are taken up by specialized M cells (microfold cells) in Peyer’s patches of the gut-associated lymphoid tissue (GALT). These cells transport antigens to underlying antigen-presenting cells (APCs), such as dendritic cells, which process and present them via MHC molecules to T helper cells.

    Activated T cells stimulate B cells to differentiate into plasma cells producing mucosal IgA antibodies, crucial for protection at mucosal surfaces, and systemic IgG antibodies for broader immunity. For example, transgenic rice expressing cholera toxin B induces strong IgA responses. Memory B and T cells are generated, providing long-term immunological protection against future pathogen exposure.

  3. Discuss the future prospects of edible vaccines in the post-COVID-19 era.

    The COVID-19 pandemic accelerated innovation in alternative vaccine platforms, including plant-based and edible systems. Plant-derived virus-like particles (VLPs), such as the SARS-CoV-2 VLP vaccine produced in Nicotiana benthamiana (e.g., Medicago’s Covifenz), demonstrated that plants can rapidly generate immunogenic, scalable vaccines. Similar VLP approaches are being explored for influenza and norovirus.

    Chloroplast engineering enables high antigen accumulation and maternal inheritance, reducing transgene spread; for example, chloroplast-expressed cholera toxin B subunit in lettuce and tobacco has shown promising mucosal immune responses. Edible vaccines for hepatitis B (transgenic potato) and rabies (spinach, tomato) have also reached preclinical or early clinical evaluation.

    Nanoparticle-based oral boosters and bioencapsulation within plant cell walls enhance antigen stability and gut-associated lymphoid tissue (GALT) targeting. Post-COVID regulatory evolution around plant-made pharmaceuticals supports faster approvals. Importantly, localized plant cultivation could improve vaccine access in low-income regions, promoting global health equity, though dosage standardization and large-scale clinical validation remain essential.