Biochemical safety evaluation of transgenic rice seeds expressing T cell epitopes of Japanese cedar pollen allergens

Generation of major glutelin-deficient (GluA, GluB, and GluC) semi-dwarf Koshihikari rice line

KEY MESSAGE

We generated a new Koshihikari rice line with a drastically reduced content of glutelin proteins and higher lodging resistance by using new and conventional plant breeding techniques. Using CRISPR/Cas9-mediated genome editing, we generated mutant rice with drastically decreased contents of major glutelins. A Koshihikari rice mutant line, a123, lacking four glutelins (GluA1, GluA2, GluB4, and GluB5) was used as a host, and another five major glutelin genes (GluA3, GluB1a, GluB1b, GluB2, and GluC) were knocked out through two iterations of Agrobacterium-mediated transformation. Mutant seeds were deficient in the GluA family, GluB family, and GluC, and the line obtained was named GluABC KO. Glutelin content was much lower in GluABC KO than in the existing low-glutelin rice mutant LGC-1. A null segregant of GluABC KO was selected using new-generation sequencing and backcrossing, and the sd-1 allele for the semi-dwarf trait was introduced to increase lodging resistance.

Oral intake of rice overexpressing ubiquitin ligase inhibitory pentapeptide prevents atrophy in denervated skeletal muscle

We previously reported that intramuscular injections of ubiquitin ligase CBLB inhibitory pentapeptide (Cblin; Asp-Gly-pTyr-Met-Pro) restored lost muscle mass caused by sciatic denervation. Here, we detected Cblin on the basolateral side of Caco-2 cells after being placed on the apical side, and found that cytochalasin D, a tight junction opener, enhanced Cblin transport. Orally administered Cblin was found in rat plasma, indicating that intact Cblin was absorbed in vitro and in vivo. Furthermore, transgenic Cblin peptide-enriched rice (CbR) prevented the denervation-induced loss of muscle mass and the upregulation of muscle atrophy-related ubiquitin ligases in mice. These findings indicated that CbR could serve as an alternative treatment for muscle atrophy.

An overview of tolerogenic immunotherapies based on plant-made antigens

INTRODUCTION

Over the last two decades, genetically engineered plants became attractive and mature platforms for producing vaccines and other relevant biopharmaceuticals. Autoimmune and inflammatory disorders demand the availability of accessible treatments, and one alternative therapy is based on therapeutic vaccines able to downregulate immune responses that favor pathology progression.

AREAS COVERED

The current status of plant-made tolerogenic vaccines is presented with emphasis on the candidates under evaluation in test animals. Nowadays, this concept has been assessed in models of food and pollen allergies, autoimmune diabetes, asthma, arthritis, and prevention of blocking antibodies induction against a biopharmaceutical used in replacement therapies.

EXPERT OPINION

According to the current evidence generated at the preclinical level, plant-made tolerogenic therapies are a promise to treat several immune-related conditions, and the beginning of clinical trials is envisaged for the next decade. Advantages and limitations for this technology are discussed.

Transgene-independent heredity of RdDM-mediated transcriptional gene silencing of endogenous genes in rice

To induce transcriptional gene silencing (TGS) of endogenous genes of rice (Oryza sativa L.), we expressed double-strand RNA of each promoter region and thus induced RNA-directed DNA methylation (RdDM). We targeted constitutively expressed genes encoding calnexin (CNX), protein disulphide isomerase (PDIL1-1) and luminal binding protein (BiP1); an endoplasmic reticulum stress-inducible gene (OsbZIP50); and genes with seed-specific expression encoding α-globulin (Glb-1) and glutelin-B4 (GluB4). TGS of four genes was obtained with high efficiency (CNX, 66.7% of regenerated plants; OsBiP1, 67.4%; OsbZIP50, 63.4%; GluB4, 66.1%), whereas the efficiency was lower for PDIL1-1 (33.3%) and Glb-1 TGS lines (10.5%). The heredity of TGS, methylation levels of promoter regions and specificity of silencing of the target gene were investigated in some of the TGS lines. In progeny of CNX and OsbZIP50 TGS lines, suppression of the target genes was preserved (except in the endosperm) even after the removal of trigger genes (T-DNA) by segregation. TGS of CNX was reverted by demethylation treatment, and a significant difference in CG and CHG methylation levels in the -1 to -250 bp region of the CNX promoter was detected between the TGS and revertant lines, suggesting that TGS is closely related to the methylation levels of promoter. TGS exhibited specific suppression towards the target gene compared with post-transcriptional gene silencing when GluB4 gene from glutelin multigene family was targeted. Based on these results, future perspectives and problems to be solved in the application of RdDM to new plant breeding techniques in rice are discussed.

Compensatory rebalancing of rice prolamins by production of recombinant prolamin/bioactive peptide fusion proteins within ER-derived protein bodies

Bioactive peptide was produced by fusion to rice prolamins in transgenic rice seeds. Their accumulation levels were affected by their deposition sites and by compensatory rebalancing between prolamins within PB-Is. Peptide immunotherapy using analogue peptide ligands (APLs) is one of promising treatments against autoimmune diseases. Use of seed storage protein as a fusion carrier is reasonable strategy for production of such small size bioactive peptides. In this study, to examine the efficacy of various rice prolamins deposited in ER-derived protein bodies (PB-Is), the APL12 from the Glucose-6-phosphate isomerase (GPI325-339) was expressed by fusion to four types of representative prolamins under the control of the individual native promoters. When the 14 and 16 kDa Cys-rich prolamins, which were localized in middle layer of PB-Is, were used for production of the APL12, they highly accumulated in transgenic rice seeds (~ 200 µg/grain). By contrast, fusion to the 10 and 13 kDa prolamins, which were localized in the core and outermost layer of PB-Is, resulted in lower levels of accumulation (~ 40 µg/grain). These results suggest that accumulation levels were highly affected by their deposition sites. Next, when different prolamin/APL12 fusion proteins were co-expressed to increase accumulation levels, they could not be increased so much as their expected additive levels. High accumulation of one type prolamin/APL12 led to reduction of other type(s) prolamin/APL12 to maintain the limited amounts of prolamins that can be deposited in PB-Is. Moreover, suppression of endogenous seed proteins by RNA interference also did not significantly enhance the accumulation levels of prolamin/APL12. These findings suggest that there may be compensatory rebalancing mechanism that controls the accumulation levels of prolamins deposited within PB-Is.

Production of BP178, a derivative of the synthetic antibacterial peptide BP100, in the rice seed endosperm

BACKGROUND

BP178 peptide is a synthetic BP100-magainin derivative possessing strong inhibitory activity against plant pathogenic bacteria, offering a great potential for future applications in plant protection and other fields. Here we report the production and recovery of a bioactive BP178 peptide using rice seeds as biofactories.

RESULTS

A synthetic gene encoding the BP178 peptide was prepared and introduced in rice plants. The gene was efficiently expressed in transgenic rice under the control of an endosperm-specific promoter. Among the three endosperm-specific rice promoters (Glutelin B1, Glutelin B4 or Globulin 1), best results were obtained when using the Globulin 1 promoter. The BP178 peptide accumulated in the seed endosperm and was easily recovered from rice seeds using a simple procedure with a yield of 21 μg/g. The transgene was stably inherited for at least three generations, and peptide accumulation remained stable during long term storage of transgenic seeds. The purified peptide showed in vitro activity against the bacterial plant pathogen Dickeya sp., the causal agent of the dark brown sheath rot of rice. Seedlings of transgenic events showed enhanced resistance to the fungal pathogen Fusarium verticillioides, supporting that the in planta produced peptide was biologically active.

CONCLUSIONS

The strategy developed in this work for the sustainable production of BP178 peptide using rice seeds as biofactories represents a promising system for future production of peptides for plant protection and possibly in other fields.

The next generation of antimicrobial peptides (AMPs) as molecular therapeutic tools for the treatment of diseases with social and economic impacts

Anti-infective drugs have had a key role in the contemporary world, contributing to dramatically decrease mortality rates caused by infectious diseases worldwide. Antimicrobial peptides (AMPs) are multifunctional effectors of the innate immune system of mucosal surfaces and present antimicrobial activity against a range of pathogenic viruses, bacteria, and fungi. However, the discovery and development of new antibacterial drugs is a crucial step to overcome the great challenge posed by the emergence of antibiotic resistance. In this review, we outline recent advances in the development of novel AMPs with improved antimicrobial activities that were achieved through characteristic structural design. In addition, we describe recent progress made to overcome some of the major limitations that have hindered peptide biosynthesis.

Concentrated protein body product derived from rice endosperm as an oral tolerogen for allergen-specific immunotherapy--a new mucosal vaccine formulation against Japanese cedar pollen allergy

The endoplasmic reticulum-derived type-I protein body (PB-I) from rice endosperm cells is an ideal candidate formulation for the oral delivery of bioencapsulated peptides as tolerogens for allergen-specific immunotherapy. In the present study, PBs containing the deconstructed Japanese cedar pollen allergens Cryptomeria japonica 1 (Cry j 1) and Cry j 2 were concentrated by treatment with thermostable α-amylase at 90°C to remove the starch from milled rice powder, which resulted in a 12.5-fold reduction of dry weight compared to the starting material. The modified Cry j 1 and Cry j 2 antigens in this concentrated PB product were more resistant to enzymatic digestion than those in the milled seed powder despite the absence of intact cell wall and starch, and remained stable for at least 10 months at room temperature without detectable loss or degradation. The high resistance of these allergens could be attributed to changes in protein physicochemical properties induced by the high temperature concentration process, as suggested by the decreased solubility of the antigens and seed proteins in PBs in step-wise-extraction experiments. Confocal microscopy showed that the morphology of antigen-containing PB-Is was preserved in the concentrated PB product. The concentrated PB product induced specific immune tolerance against Cry j 1 and Cry j 2 in mice when orally administered, supporting its potential use as a novel oral tolerogen formulation.

Insect-protected event DAS-81419-2 soybean (Glycine max L.) grown in the United States and Brazil is compositionally equivalent to nontransgenic soybean

The transgenic soybean event DAS-81419-2 contains genes that encode the Cry1F, Cry1Ac, and PAT proteins. Cry1F and Cry1Ac provide protection against key lepidopteran insect pests, while PAT confers tolerance to the herbicide glufosinate. To satisfy regulatory requirements for the safety evaluation of transgenic crops, studies were conducted in the United States and Brazil to evaluate the nutrient and antinutrient composition of event DAS-81419-2 soybean. On the basis of the results of these studies, event DAS-81419-2 soybean is compositionally equivalent to nontransgenic soybean. This conclusion concurs with numerous other published studies in soybean and other crops where compositional equivalence between the transgenic crop and its nontransgenic comparator has been demonstrated.

Generation of transgenic rice with reduced content of major and novel high molecular weight allergens

BACKGROUND

Rice seed proteins contain antigens that provoke allergic responses in some individuals with food allergy, particularly in those with cereal allergy, and these antigens can elicit clinical symptoms such as eczema and dermatitis. We previously generated transgenic rice with reduced accumulation of the three major allergens, which dramatically reduced the level of IgE binding from patients' sera. However, the transgenic rice still possesses allergenic reactivity. Recently, two globulin-like proteins were identified as candidates of novel high molecular weight (HMW) IgE-binding proteins that cause rice allergy.

RESULTS

We identified a glucosidase family encoded by four genes as novel HMW rice allergens based on IgE antibody reactivity from individuals with allergy to rice. To further reduce allergenicity, we generated transgenic rice with reduced accumulation of these HMW allergens. We crossed the rice with reduced HMW allergens and with reduced major allergens, and all major and HMW allergens were substantially reduced in the progeny of the crossed rice. Allergen suppression did not significantly alter accumulation patterns of seed storage proteins and protein folding enzymes. The sera of a portion of patients showed low IgE-binding to the crossed line, suggesting that the crossed line is effective for a portion of patients who are allergic to proteins other than major allergens.

CONCLUSIONS

The transgenic rice with reduced levels of all major and HMW allergens is thought to be an option for a portion of allergy patients with hypersensitive responses to various kinds of rice allergens.

RNA silencing is induced by the expression of foreign recombinant products in transgenic rice

RNA silencing plays important roles in the regulation of gene expression in eukaryotes. We previously reported that RNA silencing of a linked endogenous gene and a transgene in transgenic rice seeds can be induced by the expression of foreign recombinant mGLP-1, which acts as a silencing-inducible sequence through RNA interference. In this study, we found that the induction of RNA silencing by foreign transgenes is not restricted to mGLP-1 but is observed in many other genes as a relatively general phenomenon, as several foreign genes were involved in inducing RNA silencing in the same manner as mGLP-1 in transgenic rice. We detected 21-24-nt siRNAs using both sense and antisense probes specific to the silenced genes in both the leaves and endosperm of transgenic rice plants. Moreover, read-through transcripts were consistently observed in silenced transgenic rice plants. Taken together, these results suggest that proper transcription termination was prevented in these plants, and the highly divergent 3'-end transcripts served as templates for double-stranded RNA synthesis, resulting in the degradation of the target genes via siRNA.

Novel transgenic rice-based vaccines

Oral vaccination can induce both systemic and mucosal antigen-specific immune responses. To control rampant mucosal infectious diseases, the development of new effective oral vaccines is needed. Plant-based vaccines are new candidates for oral vaccines, and have some advantages over the traditional vaccines in cost, safety, and scalability. Rice seeds are attractive for vaccine production because of their stability and resistance to digestion in the stomach. The efficacy of some rice-based vaccines for infectious, autoimmune, and other diseases has been already demonstrated in animal models. We reported the efficacy in mice, safety, and stability of a rice-based cholera toxin B subunit vaccine called MucoRice-CTB. To advance MucoRice-CTB for use in humans, we also examined its efficacy and safety in primates. The potential of transgenic rice production as a new mucosal vaccine delivery system is reviewed from the perspective of future development of effective oral vaccines.

GLUTELIN PRECURSOR ACCUMULATION3 encodes a regulator of post-Golgi vesicular traffic essential for vacuolar protein sorting in rice endosperm

In seed plants, a major pathway for sorting of storage proteins to the protein storage vacuole (PSV) depends on the Golgi-derived dense vesicles (DVs). However, the molecular mechanisms regulating the directional trafficking of DVs to PSVs remain largely elusive. Here, we report the functional characterization of the rice (Oryza sativa) glutelin precursor accumulation3 (gpa3) mutant, which exhibits a floury endosperm phenotype and accumulates excess proglutelins in dry seeds. Cytological and immunocytochemistry studies revealed that in the gpa3 mutant, numerous proglutelin-containing DVs are misrouted to the plasma membrane and, via membrane fusion, release their contents into the apoplast to form a new structure named the paramural body. Positional cloning of GPA3 revealed that it encodes a plant-specific kelch-repeat protein that is localized to the trans-Golgi networks, DVs, and PSVs in the developing endosperm. In vitro and in vivo experiments verified that GPA3 directly interacts with the rice Rab5a-guanine exchange factor VPS9a and forms a regulatory complex with Rab5a via VPS9a. Furthermore, our genetic data support the notion that GPA3 acts synergistically with Rab5a and VPS9a to regulate DV-mediated post-Golgi traffic in rice. Our findings provide insights into the molecular mechanisms regulating the plant-specific PSV pathway and expand our knowledge of vesicular trafficking in eukaryotes.

Unintended compositional changes in genetically modified (GM) crops: 20 years of research

The compositional equivalency between genetically modified (GM) crops and nontransgenic comparators has been a fundamental component of human health safety assessment for 20 years. During this time, a large amount of information has been amassed on the compositional changes that accompany both the transgenesis process and traditional breeding methods; additionally, the genetic mechanisms behind these changes have been elucidated. After two decades, scientists are encouraged to objectively assess this body of literature and determine if sufficient scientific uncertainty still exists to continue the general requirement for these studies to support the safety assessment of transgenic crops. It is concluded that suspect unintended compositional effects that could be caused by genetic modification have not materialized on the basis of this substantial literature. Hence, compositional equivalence studies uniquely required for GM crops may no longer be justified on the basis of scientific uncertainty.

Oral immunotherapy for allergic diseases using transgenic rice seeds: current state and future prospects

Allergen-specific immunotherapy (IT) has been shown to provide clinical benefit for patients with allergic diseases. At present, subcutaneous and sublingual ITs are mainly authorized for clinical treatment. Oral administration of allergens seems to be the easiest way to achieve IT, though it has yet to be translated to the clinical setting, mainly due to the requirement of a large amount of allergens. Plants, especially rice seeds, have recently been recognized as superior allergen carriers for oral administration, because of their high productivity, stability and safety. Therefore, in order to establish clinically applicable oral IT, we have been developing transgenic rice seeds (Tg rice), in which major epitopes of cedar pollen allergens or house-dust mites (HDM) are expressed. The efficacy of this orally administered Tg rice was confirmed in murine models of allergic rhinitis and bronchial asthma. In the safety study of the Tg rice, no adverse effects on cynomolgus macaques were observed. In this review, we summarized the current state and future prospects of allergen-specific IT, focusing particularly on oral IT with allergen-expressing Tg rice.

Secretory type of recombinant thioredoxin h induces ER stress in endosperm cells of transgenic rice

Thioredoxin h (TRX h) functions as a reducing protein and is present in all organisms. As a new approach for inducing the endoplasmic reticulum (ER) stress, TRX h (OsTRX23) was expressed as a secretory protein using the endosperm-specific glutelin GluB-1 promoter and a signal peptide. In transgenic rice seeds, the majority of the recombinant TRX h accumulated in the ER but some was also localized to the protein body IIs (PB-IIs). The rice grain quality was dependent on the TRX h accumulation level. Increased TRX h expression resulted in aberrant phenotypes, such as chalky and shriveled features, lower seed weight and lower seed protein content. Furthermore, the accumulation of some seed storage proteins (SSPs) was significantly suppressed and the morphology of the protein bodies (PB-Is and PB-IIs) changed according to the level of TRX h. SSPs, such as 13kDa prolamin and GluA, were specifically modified via the reducing action of TRX h. These changes led to the activation of the ER stress response, which was accompanied by the expression of several chaperone proteins. Specifically, the ER stress markers BiP4 and BiP5 were significantly up-regulated by an increase in the level of TRX h. These results suggest that changes in the conformation of certain SSPs via the action of recombinant TRX h lead to an induced ER stress response in transgenic rice seeds.

Public attitudes to the promotion of genomic crop studies in Japan: correlations between genomic literacy, trust, and favourable attitude

This study aimed to assess public attitudes in Japan to the promotion of genomic selection in crop studies and to examine associated factors. We analysed data from a nationwide opinion survey. A total of 4,000 people were selected from the Japanese general population by a stratified two-phase sampling method, and 2,171 people participated by post; this survey asked about the pros and cons of crop-related genomic studies promotion, examined people's scientific literacy in genomics, and investigated factors thought to be related to genomic literacy and attitude. The relationships were examined using logistic regression models stratified by gender. Survey results showed that 50.0% of respondents approved of the promotion of crop-related genomic studies, while 6.7% disapproved. No correlation was found between literacy and attitude towards promotion. Trust in experts, belief in science, an interest in genomic studies and willingness to purchase new products correlated with a positive attitude towards crop-related genomic studies.

Metabolic profiling based on LC/MS to evaluate unintended effects of transgenic rice with cry1Ac and sck genes

As a primary characteristic of substantial equivalence, the evaluation of unintended effects of genetically modified plants has been evolving into an important field of research. In this study, a metabolic profiling method for rice seeds was developed using rapid resolution liquid chromatography/quadrupole time-of-flight mass spectrometry. The analytical properties of the method, including the linearity, reproducibility, intra-day precision and inter-day precision, were investigated and were found to be satisfactory. The method was then applied to investigate the differences between transgenic rice and its native counterparts, in addition to the differences found between native rice with different sowing dates or locations. Global metabolic phenotype differences were visualized, and metabolites from different discriminated groups were discovered using multivariate data analysis. The results indicated that environmental factors played a greater role than gene modification for most metabolites, including tryptophan, 9,10,13-trihydroxyoctadec-11-enoic acid, and lysophosphatidylethanolamine 16:0. The concentrations of phytosphingosine, palmitic acid, 5-hydroxy-2-octadenoic acid and three other unidentified metabolites varied slightly due to gene modification.

Detection of specific DNA from crude extracts of rice seed grains using matrix-assisted laser desorption ionization time-of-flight mass spectrometry

To rapidly detect specific genes, crude extracts prepared from rice seed grains were used as templates for PCR, the PCR products were digested with restriction enzymes or urasil-DNA glycosylase, and then matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) was used to detect amplified DNA. It was possible to amplify small DNA fragments (50-60bp), but not large ones (>200bp), using crude extracts as the PCR template. This method can be completed within 1h, including extractions, and is well suited to automation for high-throughput analyses.

Reducing rice seed storage protein accumulation leads to changes in nutrient quality and storage organelle formation

Rice (Oryza sativa) seed storage proteins (SSPs) are synthesized and deposited in storage organelles in the endosperm during seed maturation as a nitrogen source for germinating seedlings. We have generated glutelin, globulin, and prolamin knockdown lines and have examined their effects on seed quality. A reduction of one or a few SSP(s) was compensated for by increases in other SSPs at both the mRNA and protein levels. Especially, reduction of glutelins or sulfur-rich 10-kD prolamin levels was preferentially compensated by sulfur-poor or other sulfur-rich prolamins, respectively, indicating that sulfur-containing amino acids are involved in regulating SSP composition. Furthermore, a reduction in the levels of 13-kD prolamin resulted in enhancement of the total lysine content by 56% when compared with the wild type. This observation can be mainly accounted for by the increase in lysine-rich proteins. Although reducing the level of glutelins slightly decreased protein storage vacuoles (PSVs), the simultaneous reduction of glutelin and globulin levels altered the inner structure of PSVs, implicating globulin in framing PSV formation. Knock down of 13-kD prolamins not only reduced the size of endoplasmic reticulum-derived protein bodies (PBs) but also altered the rugged peripheral structure. In contrast, PBs became slightly smaller or unchanged by severe suppression of 10- or 16-kD prolamins, respectively, indicating that individual prolamins have distinct functions in the formation of PBs. Extreme increases or decreases in sulfur-poor prolamins resulted in the production of small PBs, suggesting that the ratio of individual prolamins is crucial for proper aggregation and folding of prolamins.

Vaccine production in plant systems--an aid to the control of viral diseases in domestic animals: a review

Plants have been identified as promising expression systems for the commercial production of vaccines because of the possibility of introducing exogenous genes into them, which permits the development of a new generation of biological products called edible vaccines. The advantages of oral vaccines of this new type are that they induce mucosal, humoral, cellular and protective immunity, they are cheaper, easier to store, distribute and administer, they do not require cold chain management, and some species can be stored for long periods of time without any spoilage and may be administered as purified proteins. Owing to these benefits, plant-produced vaccines represent a valuable option for animal health. The aim of this paper is to present a review of plant-produced vaccines against viruses affecting domestic animals. Some aspects of the feasibility of their use and the immune response elicited by such vaccines are also discussed, as the balance between tolerance and immunogenicity is a major concern for the use of plant-based vaccines.

Analysis of ER stress in developing rice endosperm accumulating beta-amyloid peptide

The common neurodegenerative disorder known as Alzheimer's disease is characterized by cerebral neuritic plaques of amyloid beta (Abeta) peptide. Plaque formation is related to the highly aggregative property of this peptide, because it polymerizes to form insoluble plaques or fibrils causing neurotoxicity. Here, we expressed Abeta peptide as a new causing agent to endoplasmic reticulum (ER) stress to study ER stress occurred in plant. When the dimer of Abeta(1-42) peptide was expressed in maturing seed under the control of the 2.3-kb glutelin GluB-1 promoter containing its signal peptide, a maximum of about 8 mug peptide per grain accumulated and was deposited at the periphery of distorted ER-derived PB-I protein bodies. Synthesis of Abeta peptide in the ER lumen severely inhibited the synthesis and deposition of seed storage proteins, resulting in the generation of many small and abnormally appearing PB bodies. This ultrastructural change was accounted for by ER stress leading to the accumulation of aggregated Abeta peptide in the ER lumen and a coordinated increase in ER-resident molecular chaperones such as BiPs and PDIs in Abeta-expressing plants. Microarray analysis also confirmed that expression of several BiPs, PDIs and OsbZIP60 containing putative transmembrane domains was affected by the ER stress response. Abeta-expressing transgenic rice kernels exhibited an opaque and shrunken phenotype. When grain phenotype and expression levels were compared among transgenic rice grains expressing several different recombinant peptides, such detrimental effects on grain phenotype were correlated with the expressed peptide causing ER stress rather than expression levels.

Rice seed ER-derived protein body as an efficient delivery vehicle for oral tolerogenic peptides

Mucosal delivery of peptide/protein therapeutics via the oral route is a desirable strategy in human immunotherapy. A key step for enhancing the bioavailability of orally administered therapeutics is to protect them from enzymatic digestion in the gastrointestinal tract. Here, we generated transgenic rice seeds accumulating allergen-derived T cell epitopes, a model tolerogen for the control of pollen allergy, in either ER-derived protein body-I (PB-I) or protein storage vacuole protein body-II (PB-II). Compared with PB-II-localized or chemically synthesized forms, PB-I-localized T cell epitopes showed higher resistance to enzymatic digestion in simulated gastric fluid. Moreover, the dose of T cell epitope required for suppression of allergen-specific IgE in mice was about 20-fold lower when fed in PB-I localized form than when unprotected. These findings demonstrate the potential of bioencapsulation in PB-I for broad applications as a viable strategy to achieve efficient mucosal delivery of oral peptide/protein therapeutics.

The mucosal immune response to plant-derived vaccines

Transgenic plants present enormous potential as one of the most cost-effective and safe systems for large-scale production of proteins for industrial, pharmaceutical, veterinary and agricultural uses. Heat-stable plant-derived vaccines that are administered orally could in effect enhance vaccine coverage in children and infants, particularly in developing countries. Here we discuss the current status of plant-derived vaccines and their potential to champion the battle against infectious diseases in the least developed countries.

Compensation and interaction between RISBZ1 and RPBF during grain filling in rice

The rice (Oryza sativa L.) basic leucine Zipper factor RISBZ1 and rice prolamin box binding factor (RPBF) are transcriptional activators of rice seed storage protein (SSP) genes in vivo. To ascertain the functions of these trans-activators in seed development, knock-down (KD) transgenic rice plants were generated in which the accumulation of RISBZ1 and RPBF was reduced in an endosperm-specific manner by co-suppression (KD-RISBZ1 and KD-RPBF). The accumulation of most SSPs changed little between individual KD mutants and wild-type plants, whereas a double KD mutant (KD-RISBZ1/KD-RPBF) resulted in a significant reduction of most SSP gene expression and accumulation. The reduction of both trans-activators also caused a greater reduction in seed starch accumulation than individual KD mutants. Storage lipids were accumulated at reduced levels in KD-RISBZ1 and KD-RISBZ1/KD-RPBF seeds. KD-RPBF and KD-RISBZ1/KD-RPBF seeds exhibited multi-layered aleurone cells. Gene expression of DEFECTIVE KERNEL1 (OsDEK1), CRINKLY4 (OsCR4) and SUPERNUMERARY ALEURONE LAYER 1 (OsSAL1) rice homologues was decreased in the KD mutants, suggesting that these genes are regulated by RISBZ1 and RPBF. These phenotypes suggest that combinatorial interactions between RISBZ1 and RPBF play an essential role during grain filling. The functional redundancy and compensation between RISBZ1 and RPBF possibly account for weak effects on the SSP levels in single KD mutants, and help maintain various processes during seed development in rice. Physical interaction between RISBZ1 and RPBF may ensure that these processes are carried out properly.

26-Week oral safety study in macaques for transgenic rice containing major human T-cell epitope peptides from Japanese cedar pollen allergens

A study of repeated oral administration of transgenic rice containing a hybrid peptide of major human T-cell epitopes (7Crp) from Japanese cedar pollen allergens was carried out in cynomolgus macaques over 26 weeks. The monkeys were divided into three groups, each comprising three males and three females, administered a high dose of transgenic rice, a low dose of transgenic rice, or a high dose of the parental rice strain. The transgenic rice 7crp#10 and the parental nontransgenic control were polished, steamed, mashed, and prepared in water at 40% (w/v). Monkeys were orally administered a high or low dose of transgenic rice or the nontransgenic control by gavage every day. No adverse effects on general behavior or body weight of animals were observed during the study. Analysis of blood from monkeys administered for 26 weeks showed that, with few exceptions, there were no significant differences in hematological or biochemical values between them. Additionally, neither pathological symptoms nor histopathological abnormalities were observed. Thus, it was concluded that oral administration of transgenic rice containing T-cell epitopes from Japanese cedar pollen allergens has no adverse effects.

Production of recombinant allergens in plants

A large percentage of allergenic proteins are of plant origin. Hence, plant-based expression systems are considered ideal for the recombinant production of certain allergens. First attempts to establish production of plant-derived allergens in plants focused on transient expression in Nicotiana benthamiana infected with recombinant viral vectors. Accordingly, allergens from birch and mugwort pollen, as well as from apple have been expressed in plants. Production of house dust mite allergens has been achieved by Agrobacterium-mediated transformation of tobacco plants. Beside the use of plants as production systems, other approaches have focused on the development of edible vaccines expressing allergens or epitopes thereof, which bypasses the need of allergen purification. The potential of this approach has been convincingly demonstrated for transgenic rice seeds expressing seven dominant human T cell epitopes derived from Japanese cedar pollen allergens. Parallel to efforts in developing recombinant-based diagnostic and therapeutic reagents, different gene-silencing approaches have been used to decrease the expression of allergenic proteins in allergen sources. In this way hypoallergenic ryegrass, soybean, rice, apple, and tomato were developed.

Characterization of a new rice glutelin gene GluD-1 expressed in the starchy endosperm

A new glutelin gene, designated GluD-1, has been discovered by comparing the seed storage proteins from 48 japonica and indica rice cultivars on SDS-PAGE gels. Evidence that GluD-1 is a member of the glutelin family was provided by Western blots using anti-glutelin antiserum and by mapping the gene to the chromosomal glutelin gene cluster. The limited GluD-1 size polymorphism among the rice varieties is due to amino acid substitutions rather than to post-transcriptional modification. GluD-1 is maximally expressed in the starchy endosperm starting at 5 d after flowering (DAF) and increasing through 30 DAF, a major difference from the other glutelins which are primarily expressed in the subaleurone from 10-16 DAF. Only about 0.2 kb of the GluD-1 promoter was sufficient to confer inner starchy endosperm-specific expression. The 0.2 kb truncated GluD-1 promoter contains a bifactorial endosperm box consisting of a truncated GCN4 motif (TGA(G/C)TCA) and AAAG Prolamin box (P box), and ACGT and AACA motifs as cis-regulatory elements. Gel retardation assays and trans-activation experiments indicated that the truncated GCN4 and P box are specifically recognized by RISBZ1 b-ZIP and RPBF Dof activators in vitro, respectively, and are synergistically transactivated, indicating that combinatorial interactions of these motifs are involved in essential endosperm-specific regulation. Furthermore, deviation from the cognate GCN4 motif alters tissue-specific expression in the inner starchy endosperm to include other endosperm tissues.

Development of transgenic rice seed accumulating a major Japanese cedar pollen allergen (Cry j 1) structurally disrupted for oral immunotherapy

Rice seed-based edible vaccines expressing T-cell epitope peptides derived from Japanese cedar major pollen allergens have been used to successfully suppress allergen-specific Th2-mediated immunoglobulin E (IgE) responses in mouse experiments. In order to further expand the application of seed-based allergen-specific immunotherapy for controlling Japanese cedar pollinosis, we generated transgenic rice plants that specifically express recombinant Cry j 1 allergens in seeds. Cry j 1 allergens give low specific IgE-binding activity but contain all of the T-cell epitopes. The allergens were expressed directly or as a protein fusion with the major rice storage protein glutelin. Fusion proteins expressed under the control of the strong rice endosperm-specific GluB-1 promoter accumulated in rice endosperm tissue up to 15% of total seed protein. The fusion proteins aggregated with cysteine-rich prolamin and were deposited in endoplasmic reticulum-derived protein body I. The production of transgenic rice expressing structurally disrupted Cry j 1 peptides with low IgE binding activity but spanning the entire Cry j1 region can be used as a universal, safe and effective tolerogen for rice seed-based oral immunotherapy for cedar pollen allergy in humans and other mammals.