Foreign gene products can be enhanced by introduction into low storage protein mutants

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.

Influence on Accumulation Levels and Subcellular Localization of Prolamins by Fusion with the Functional Peptide in Transgenic Rice Seeds

To exploit the rice seed-based oral vaccine against Sjögren's syndrome, altered peptide ligand of N-terminal 1 (N1-APL7) from its M3 muscarinic acetylcholine receptor (M3R) autoantigen was expressed as fusion protein with the representative four types of rice prolamins (16 kDa, 14 kDa, 13 kDa, and 10 kDa prolamins) under the control of the individual native prolamin promoter. The 10kD:N1-APL7 and 14kD:N1-APL7 accumulated at high levels (287 and 58 µg/grain), respectively, whereas production levels of the remaining ones were remarkably low. Co-expression of these fusion proteins did not enhance the accumulation level of N1-APL7 in an additive manner. Downregulation of endogenous seed storage proteins by RNAi-mediated suppression also did not lead to substantial elevation of the co-expressed prolamin:N1-APL7 products. When transgenic rice seeds were subjected to in vitro proteolysis with pepsin, the 10kD:N1-APL7 was digested more quickly than the endogenous 10 kDa prolamin and the 14kD:N1-APL7 deposited in PB-Is. This difference could be explained by the finding that the 10kD:N1-APL7 was unexpectedly localized in the PB-IIs containing glutelins. These results indicated that not only accumulation level but also subcellular localization of inherent prolamins were highly influenced by the liked N1-APL7 peptide.

Co-expression of four penaeidins in transgenic rice seeds: an alternative strategy for substitute antibiotic agricultural products

The co-expression of multiple antimicrobial peptides (AMPs) in genetically modified (GM) crops can give plants a broader antibacterial spectrum and lower the pathogen risk of drug resistance. Therefore, four penaeidins (shrimp-derived AMPs) were fused and encoded in an artificial gene (PEN1234), driven by the seed-specific promoter Pzein, with the aim of co-expression in seeds of transgenic rice. The resistant rice plants, acquired via Agrobacterium-mediated transformation and glufosinate screening, were identified by PCR and the modified disk-diffusion method, and eight GM lines with high AMP content in the seeds were obtained. Among them, the PenOs017 line had the largest penaeidin content, at approximately 251-300 μg/g in seeds and 15-47 μg/g in roots and leaves. The AMPs in the seeds kept their antibacterial properties even after the seed had been boiled in hot water and could significantly inhibit the growth of methicillin-resistant Staphylococcus aureus, and AMPs in the leaves could effectively inhibit Xanthomonas oryzae pv. Oryzae. The results indicate that PenOs017 seeds containing AMPs are an ideal raw-material candidate for antibiotic-free food and feed, and may require fewer petrochemical fungicides or bactericides for disease control during cultivation than conventional rice.

Targeted genome editing of plants and plant cells for biomanufacturing

Plants have provided humans with useful products since antiquity, but in the last 30 years they have also been developed as production platforms for small molecules and recombinant proteins. This initially niche area has blossomed with the growth of the global bioeconomy, and now includes chemical building blocks, polymers and renewable energy. All these applications can be described as “plant molecular farming” (PMF). Despite its potential to increase the sustainability of biologics manufacturing, PMF has yet to be embraced broadly by industry. This reflects a combination of regulatory uncertainty, limited information on process cost structures, and the absence of trained staff and suitable manufacturing capacity. However, the limited adaptation of plants and plant cells to the requirements of industry-scale manufacturing is an equally important hurdle. For example, the targeted genetic manipulation of yeast has been common practice since the 1980s, whereas reliable site-directed mutagenesis in most plants has only become available with the advent of CRISPR/Cas9 and similar genome editing technologies since around 2010. Here we summarize the applications of new genetic engineering technologies to improve plants as biomanufacturing platforms. We start by identifying current bottlenecks in manufacturing, then illustrate the progress that has already been made and discuss the potential for improvement at the molecular, cellular and organism levels. We discuss the effects of metabolic optimization, adaptation of the endomembrane system, modified glycosylation profiles, programmable growth and senescence, protease inactivation, and the expression of enzymes that promote biodegradation. We outline strategies to achieve these modifications by targeted gene modification, considering case-by-case examples of individual improvements and the combined modifications needed to generate a new general-purpose “chassis” for PMF.

Improvement of production yield and extraction efficacy of recombinant protein by high endosperm-specific expression along with simultaneous suppression of major seed storage proteins

Human transforming growth factor-β1 (hTGF-β1)　was produced in transgenic rice seeds. To boost its production yield and to extract it simply, it was expressed under the control of seed-specific promoters along with the simultaneous suppression of endogenous seed storage proteins　(SSPs)　through RNA interference (RNAi). When driven by the 26 kDa α-globulin endosperm-specific promoter, it accumulated up to the markedly high level of 452 μg/grain. However, exchange with other seed-specific promoters such as 18 kDa oleosin and AGPase promoters resulted in remarkable reduction to the levels of 62 and 48 μg/grain, respectively, even though endogenous SSPs were reduced to the similar level. These production levels were almost similar to those (42 and 108 μg/grain) produced by the glutelin GluB-1 endosperm-specific promoter and the maize ubiquitin constitutive promoter without reduction of SSPs, respectively. When extracted from these transgenic rice seeds with reduced SSPs with various buffers, it could be solubilized with denaturant solution, which was in remarkable contrast with those without depressed SSPs which required further supplementation of reducing agent for extraction. This difference was associated with the fact that it was mainly deposited to ER-derived structures though self-aggregation or interaction with remaining prolamin via intermolecular disulfide bonds.

Modulation of Barley (Hordeum vulgare L.) Grain Protein Sink-Source Relations Towards Human Epidermal Growth Factor Instead of B-hordein Storage Protein

Seeds have evolutionarily developed to store protein without immediately degrading it and constitute ideal tissues for recombinant protein storage. Unfortunately, the production of recombinant protein in seeds is compromised by low yield as compared to other heterologous expression systems. In order to improve the yield of the human epidermal growth factor (EGF) in barley, protein sink-source relations in the developing grain were modulated towards EGF instead of the barley storage protein. The EGF gene, under the control of a B-hordein and a seed-specific oat globulin promoter, was introduced by crossing EGF lines into the Risø 56 mutant deficient in B-hordein storage protein synthesis. Offspring plants were analysed for EGF and Hordein expression and for expression of the unfolded protein response (UPR) genes PDI and CRT to monitor changes in ER stress levels. EGF content was increased significantly in the mature grain of homozygous offspring and PDI and CRT gene expressions were upregulated. We demonstrate, for the first time in barley, that replacement of an abundant seed storage protein with a specific heterologous protein driven by the promoter of the removed gene can accelerate the production of a specific heterologous protein in barley grains.

Knock-in at GluA1 locus improves recombinant human serum albumin expression in rice grain

Improving recombinant protein expression is a perpetual goal for molecular pharming. However, over-transcription of recombinant protein induces ER stress, and causes protein degradation. Here, we describe a knock-in approach to integrate a human serum albumin expression cassette into the locus of the rice storage protein GluA1 by site-specific integration via the nonhomologous end joining (NHEJ) pathway. The expression level of OsrHSA in the knock-in (KI) lines was much higher than that of the random integration (RI) lines. ER stress in KI line endosperm cells was not significantly altered even after massive OsrHSA accumulation in rice endosperm cell. Instead, ER stress induced by high OsrHSA expression was alleviated in the KI line via the inositol-requiring enzyme 1 (IRE1)-mediated/OsbZIP50 pathway. Furthermore, improvement of OsrHSA expression in KI lines is likely due to reduction of contents of glutelin and globulin in rice endosperm cell. These results provide insight into an approach to improving recombinant protein accumulation by alleviating ER stress and protein trafficking.

A Plant-Produced Recombinant Fusion Protein-Based Newcastle Disease Subunit Vaccine and Rapid Differential Diagnosis Platform

Newcastle disease (ND) is a highly contagious avian disease, causing considerable economic losses to the poultry industry. To obtain a safe, inexpensive, and effective ND vaccine to meet the international trade requirements of differentiating infected from vaccinated animals (DIVA), here we report the production of Oryza sativa recombinant fusion (F) protein in stably transformed transgenic rice seeds via agroinfiltration. The F protein expression level was enhanced 3.6-fold with a genetic background in low glutelin. Inoculation of plant-produced F antigen into Specific Pathogen Free (SPF) chickens markedly elicited neutralizing antibody responses against homologous and heterologous ND virus strains. Two doses of 4.5 μg fully protected chickens from a lethal ND challenge without any clinical symptoms. The mean weight gain of F protein-immunized chickens within 15 days after challenge was significantly higher than that of traditional whole virus vaccine-immunized chickens, thereby obtaining higher economic benefits. Moreover, the sera from the chickens vaccinated with the plant-produced F vaccine did not show reactivity in an immunochromatographic strip targeting the haemagglutinin-neuraminidase protein (HN) protein, and DIVA could be achieved within 10 minutes. Our results demonstrate that the plant-derived F vaccine along with immunochromatographic strips could be useful in the implementation of an NDV eradication program.

Transgenic rice seeds expressing altered peptide ligands against the M3 muscarinic acetylcholine receptor suppress experimental sialadenitis-like Sjögren's syndrome

Objective: We previously reported that Rag1^-/- mice inoculated with splenocytes from M3 muscarinic acetylcholine receptor (M3R) knockout mice immunized with an M3R peptide mixture developed sialadenitis-like Sjögren's syndrome (M3R-induced sialadenitis [MIS]). We also found that intravenous administration of altered peptide ligand (APL) of N-terminal 1 (N1), which is one of the T-cell epitopes of M3R, suppressed MIS. In this study, we aimed to evaluate the suppressive ability and its mechanisms of rice seeds expressing N1-APL7 against MIS.Methods: Rice seeds expressing N1 and N1-APL7 were orally administered to MIS mice for 2 weeks. The changes in saliva flow and sialadenitis (salivary gland inflammation) were analyzed. The M3R-specific T-cell response in the spleen and the expression of regulatory molecules in the cervical lymph nodes and mesenteric lymph nodes were also analyzed.Results: Oral administration of N1-APL7-expressing rice seeds significantly recovered reduction in saliva flow and suppressed sialadenitis when compared with treatment with nontransgenic rice seeds and N1 rice seeds. IFNγ production from M3R-reactive T cells tended to decline in the N1-APL7 rice-treated group as compared with those in the other groups. In the N1-APL7 rice-treated group, the mRNA expression levels of Foxp3 in the cervical-lymph-node CD4⁺ T cells were higher than those in the other groups.Conclusion: Oral administration of N1-APL7-expressing rice suppressed MIS via suppression of M3R-specific IFNγ and IL-17 production and via enhancement of regulatory molecule expression.Key messagesWe generated N1-peptide- or N1-APL7-expressing rice seeds. Oral administration of N1-APL7-expressing rice seeds significantly recovered the reduction of saliva flow and suppressed sialadenitis via the suppression of M3R specific IFNγ and IL-17 production and via enhancement of regulatory T (Treg) cells.

CRISPR/Cas9 editing of three CRUCIFERIN C homoeologues alters the seed protein profile in Camelina sativa

BACKGROUND

The oilseed Camelina sativa is grown for a range of applications, including for biofuel, biolubricants, and as a source of omega-3 fatty acids for the aquaculture feed industry. The seed meal co-product is used as a source of protein for animal feed; however, the low value of the meal hinders profitability and more widespread application of camelina. The nutritional quality of the seed meal is largely determined by the abundance of specific seed storage proteins and their amino acid composition. Manipulation of seed storage proteins has been shown to be an effective means for either adjustment of nutritional content of seeds or for enhancing accumulation of high-value recombinant proteins in seeds.

RESULTS

CRISPR/Cas9 gene editing technology was used to generate deletions in the first exon of the three homoeologous genes encoding the seed storage protein CRUCIFERIN C (CsCRUC), creating an identical premature stop-codon in each and resulting in a CsCRUC knockout line. The mutant alleles were detected by applying a droplet digital PCR drop-off assay. The quantitative nature of this technique is particularly valuable when applied to polyploid species because it can accurately determine the number of mutated alleles in a gene family. Loss of CRUC protein did not alter total seed protein content; however, the abundance of other cruciferin isoforms and other seed storage proteins was altered. Consequently, seed amino acid content was significantly changed with an increase in the proportion of alanine, cysteine and proline, and decrease of isoleucine, tyrosine and valine. CsCRUC knockout seeds did not have changed total oil content, but the fatty acid profile was significantly altered with increased relative abundance of all saturated fatty acids.

CONCLUSIONS

This study demonstrates the plasticity of the camelina seed proteome and establishes a CRUC-devoid line, providing a framework for modifying camelina seed protein composition. The results also illustrate a possible link between the composition of the seed proteome and fatty acid profile.

Specific region affects the difference in accumulation levels between apple food allergen Mal d 1 and birch pollen allergen Bet v 1 which are expressed in vegetative tissues of transgenic rice

Specific domain of the Mal d 1 was identified to be mainly involved in higher accumulation level in vegetative tissues of transgenic rice than the Bet v 1. Apple food allergen Mal d 1 and birch pollen allergen Bet v 1 belong to the same pathogen related protein 10 (PR10) family. When green fluorescent protein (GFP) fused to either of these allergens was expressed as a secretory protein in transgenic rice by ligating an N terminal signal peptide and a C terminal KDEL ER retention signal under the control of the maize ubiquitin constitutive promoter, the GFP:Mald1 highly accumulated in various tissues, whereas accumulation level of the GFP:Betv1 was remarkably reduced in vegetative tissues except for seed. Analysis by RT-PCR exhibited that there was little difference in their transcript levels, indicating the involvement of post-transcriptional regulation. To investigate the cause of such difference in accumulation levels, deletion analysis of the Mal d 1 and domain swapping between them were carried out in transgenic rice. The results showed that the region between positions 41-90 in the Mal d 1 is predominantly implicated in higher level accumulation in vegetative tissues as well as seed as compared with the Bet v 1. The GFP:Mald1 was localized in oligomeric form within ER lumen or ER-derived particles in vegetative tissues, whereas in seed mainly deposited into novel huge ER-derived protein bodies with the size of 5-10 µm in aleurone cells.

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.

An overview on the strategies to exploit rice endosperm as production platform for biopharmaceuticals

Cereal seed has been utilized as production platform for high-value biopharmaceutical proteins. Especially, protein bodies (PBs) in seeds are not only natural specialized storage organs of seed storage proteins (SSPs), but also suitable intracellular deposition compartment for recombinant proteins. When various recombinant proteins were produced as secretory proteins by attaching N terminal ER signal peptide and C terminal KDEL endoplasmic reticulum (ER) retention signal or as fusion proteins with SSPs, high amounts of recombinant proteins can be predominantly accumulated in the PBs. Recombinant proteins bioencapsulated in PBs exhibit high resistance to digestive enzymes in gastrointestinal tract than other intracellular compartments and are highly stable at ambient temperature, thus allowing oral administration of PBs containing recombinant proteins as oral drugs or functional nutrients in cost-effective minimum processed formulation. In this review, we would like to address key factors determining accumulation levels of recombinant proteins in PBs. Understanding of bottle neck parts and improvement of specific deposition to PBs result in much higher levels of production of high quality recombinant proteins.

Deposition mode of transforming growth factor-β expressed in transgenic rice seed

Mouse TGF-β highly accumulated by expressing as a secretory homodimeric protein in transgenic rice endosperm. It was tightly deposited in ER-derived PBs by interaction with cysteine-rich prolamins. TGF-β is one of the key players involved in the induction and maintenance of mucosal immune tolerance to dietary proteins through the induction of regulatory T cells. In order to utilize rice-based TGF-β as a tool to promote oral immune tolerance induction, high production of TGF-β is essentially required. When the codon-optimized mTGF-β was expressed as a secretory protein by ligating an N-terminal signal peptide and C-terminal KDEL ER retention signal under the control of the endosperm-specific rice storage protein glutelin GluB-1 promoter, accumulation level was low in stable transgenic rice seeds. Then, to increase the accumulation level of mTGF-β, it was expressed as fusion proteins by inserting into the C terminus of acidic subunit of glutelin GluA and the variable region of 26 kDa globulin. When fused with the glutelin, it could accumulate well as visible bands by CBB staining gel, but not for the 26 kDa globulin. Unexpectedly, expression of homodimeric mTGF-β linked by a 6×Gly1×Ser linker as secretory protein resulted in higher level of accumulation. This expression level was further enhanced by reduction of some endogenous prolamins by RNA interference. The monomeric and dimeric mTGF-βs were deposited in ER-derived PBs containing prolamins. When highly produced in rice seed, it is notable that most of ER-derived PBs were distorted and granulated. Step-wise extraction of storage proteins from rice seeds suggested that the mTGF-β strongly interacted with cysteine-rich prolamins via disulfide bonds. This result was also supported by the finding that reducing agent was absolutely required for mTGF-β extraction.

Proteome rebalancing in transgenic Camelina occurs within the enlarged proteome induced by β-carotene accumulation and storage protein suppression

Oilseed crops are global commodities for their oil and protein seed content. We have engineered the oilseed Camelina sativa to exhibit increased protein content with a slight decrease in oil content. The introduction of a phytoene synthase gene with an RNAi cassette directed to suppress the storage protein 2S albumin resulted in seeds with an 11-24 % elevation in overall protein. The phytoene synthase cassette alone produced enhanced β-carotene content of an average 275 ± 6.10 μg/g dry seed and an overall altered seed composition of 11 % less protein and comparable nontransgenic amounts of both oil and carbohydrates. Stacking an RNAi to suppress the major 2S storage protein resulted in seeds that contain elevated protein and slight decrease in oil and carbohydrate amounts showing that Camelina rebalances its proteome within an enlarged protein content genotype. In both β-carotene enhanced seeds with/without RNAi2S suppression, the seed size was noticeably enlarged compared to nontransgenic counterpart seeds. Metabolic analysis of maturing seeds indicate that the enhanced β-carotene trait had the larger effect than the RNAi2S suppression on the seed metabolome. The use of a GRAS (generally regarded as safe) β-carotene as a visual marker in a floral dip transformation system, such as Camelina, might eliminate the need for costly regulatory and controversial antibiotic resistance markers. β-carotene enhanced RNAi2S suppressed Camelina seeds could be further developed as a rapid heterologous protein production platform in a nonfood crop leveraging its enlarged protein content and visual marker.

Inter-laboratory optimization of protein extraction, separation, and fluorescent detection of endogenous rice allergens

In rice, several allergens have been identified such as the non-specific lipid transfer protein-1, the α-amylase/trypsin-inhibitors, the α-globulin, the 33 kDa glyoxalase I (Gly I), the 52-63 kDa globulin, and the granule-bound starch synthetase. The goal of the present study was to define optimal rice extraction and detection methods that would allow a sensitive and reproducible measure of several classes of known rice allergens. In a three-laboratory ring-trial experiment, several protein extraction methods were first compared and analyzed by 1D multiplexed SDS-PAGE. In a second phase, an inter-laboratory validation of 2D-DIGE analysis was conducted in five independent laboratories, focusing on three rice allergens (52 kDa globulin, 33 kDa glyoxalase I, and 14-16 kDa α-amylase/trypsin inhibitor family members). The results of the present study indicate that a combination of 1D multiplexed SDS-PAGE and 2D-DIGE methods would be recommended to quantify the various rice allergens.

Cereal cystatins delay sprouting and nutrient loss in tubers of potato, Solanum tuberosum

BACKGROUND

Recent studies have reported agronomically useful ectopic effects for recombinant protease inhibitors expressed in leaves of transgenic plants, including improved tolerance to abiotic stress conditions and partial resistance to necrotrophic pathogens. Here we assessed the effects of these proteins on the post-dormancy sprouting of storage organs, using as a model potato tubers expressing cysteine protease inhibitors of the cystatin protein superfamily.

RESULTS

Sprout emergence and distribution, soluble proteins, starch and soluble sugars were monitored in tubers of cereal cystatin-expressing clones stored for several months at 4 °C. Cystatin expression had a strong repressing effect on sprout growth, associated with an apparent loss of apical dominance and an increased number of small buds at the skin surface. Soluble protein content remained high for up to 48 weeks in cystatin-expressing tubers compared to control (untransformed) tubers, likely explained by a significant stabilization of the major storage protein patatin, decreased hydrolysis of the endogenous protease inhibitor multicystatin and low cystatin-sensitive cysteine protease activity in tuber tissue. Starch content decreased after several months in cystatin-expressing tubers but remained higher than in control tubers, unlike sucrose showing a slower accumulation in the transgenics. Plantlet emergence, storage protein processing and height of growing plants showed similar time-course patterns for control and transgenic tubers, except for a systematic delay of 2 or 3 d in the latter group likely due to limited sprout size at sowing.

CONCLUSIONS

Our data point overall to the onset of metabolic interference effects for cereal cystatins in sprouting potato tubers. They suggest, in practice, the potential of endogenous cysteine proteases as relevant targets for the development of potato varieties with longer storage capabilities.

Rice seed for delivery of vaccines to gut mucosal immune tissues

Gut-associated lymphoid tissue (GALT) is the biggest lymphoid organ in the body. It plays a role in robust immune responses against invading pathogens while maintaining immune tolerance against nonpathogenic antigens such as foods. Oral vaccination can induce mucosal and systemic antigen-specific immune reactions and has several advantages including ease of administration, no requirement for purification and ease of scale-up of antigen. Thus far, taking advantage of these properties, various plant-based oral vaccines have been developed. Seeds provide a superior production platform over other plant tissues for oral vaccines; they offer a suitable delivery vehicle to GALT due to their high stability at room temperature, ample and stable deposition space, high expression level, and protection from digestive enzymes in gut. A rice seed production system for oral vaccines was established by combining stable deposition in protein bodies or protein storage vacuoles and enhanced endosperm-specific expression. Various types of rice-based oral vaccines for infectious and allergic diseases were generated. Efficacy of these rice-based vaccines was evaluated in animal models.

Effects of proteome rebalancing and sulfur nutrition on the accumulation of methionine rich δ-zein in transgenic soybeans

Expression of heterologous methionine-rich proteins to increase the overall sulfur amino acid content of soybean seeds has been only marginally successful, presumably due to low accumulation of transgenes in soybeans or due to gene silencing. Proteome rebalancing of seed proteins has been shown to promote the accumulation of foreign proteins. In this study, we have utilized RNAi technology to suppress the expression of the β-conglycinin, the abundant 7S seed storage proteins of soybean. Western blot and 2D-gel analysis revealed that β-conglycinin knockdown line (SAM) failed to accumulate the α', α, and β-subunits of β-conglycinin. The proteome rebalanced SAM retained the overall protein and oil content similar to that of wild-type soybean. We also generated transgenic soybean lines expressing methionine-rich 11 kDa δ-zein under the control of either the glycinin or β-conglycinin promoter. The introgression of the 11 kDa δ-zein into β-conglycinin knockdown line did not enhance the accumulation of the 11 kDa δ-zein. However, when the same plants were grown in sulfur-rich medium, we observed 3- to 16-fold increased accumulation of the 11 kDa δ-zein. Transmission electron microscopy observation revealed that seeds grown in sulfur-rich medium contained numerous endoplasmic reticulum derived protein bodies. Our findings suggest that sulfur availability, not proteome rebalancing, is needed for high-level accumulation of heterologous methionine-rich proteins in soybean seeds.

Stable accumulation of seed storage proteins containing vaccine peptides in transgenic soybean seeds

There has been a significant increase in the use of transgenic plants for the large-scale production of pharmaceuticals and industrial proteins. Here, we report the stable accumulation of seed storage proteins containing disease vaccine peptides in transgenic soybean seeds. To synthesize vaccine peptides in soybean seeds, we used seed storage proteins as a carrier and a soybean breeding line lacking major seed storage proteins as a host. Vaccine peptides were inserted into the flexible disordered regions in the A1aB1b subunit three-dimensional structure. The A1aB1b subunit containing vaccine peptides in the disordered regions were sorted to the protein storage vacuoles where vaccine peptides are partially cleaved by proteases. In contrast, the endoplasmic reticulum (ER)-retention type of the A1aB1b subunit containing vaccine peptides accumulated in compartments that originated from the ER as an intact pro-form. These results indicate that the ER may be an organelle suitable for the stable accumulation of bioactive peptides using seed storage proteins as carriers.

Suppression of collagen-induced arthritis by oral administration of transgenic rice seeds expressing altered peptide ligands of type II collagen

Rheumatoid arthritis (RA) is an autoimmune disease associated with the recognition of self proteins secluded in arthritic joints. We previously reported that altered peptide ligands (APLs) of type II collagen (CII256-271) suppress the development of collagen-induced arthritis (CIA). In this study, we generated transgenic rice expressing CII256-271 and APL6 contained in fusion proteins with the rice storage protein glutelin in the seed endosperm. These transgene products successfully and stably accumulated at high levels (7-24 mg/g seeds) in protein storage vacuoles (PB-II) of mature seeds. We examined the efficacy of these transgenic rice seeds by performing oral administration of the seeds to CIA model mice that had been immunized with CII. Treatment with APL6 transgenic rice for 14 days significantly inhibited the development of arthritis (based on clinical score) and delayed disease onset during the early phase of arthritis. These effects were mediated by the induction of IL-10 from CD4(+ ) CD25(-) T cells against CII antigen in splenocytes and inguinal lymph nodes (iLNs), and treatment of APL had no effect on the production of IFN-γ, IL-17, IL-2 or Foxp3(+) Treg cells. These findings suggest that abnormal immune suppressive mechanisms are involved in the therapeutic effect of rice-based oral vaccine expressing high levels of APLs of type II collagen on the autoimmune disease CIA, suggesting that the seed-based mucosal vaccine against CIA functions via a unique mechanism.

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.

Development of a novel transgenic rice with hypocholesterolemic activity via high-level accumulation of the α' subunit of soybean β-conglycinin

Soybean 7S globulin, known as β-conglycinin, has been shown to regulate human plasma cholesterol and triglyceride levels. Furthermore, the α' subunit of β-conglycinin has specifically been shown to possess low-density lipoprotein (LDL)-cholesterol-lowering activity. Therefore, accumulation of the α' subunit of β-conglycinin in rice seeds could lead to the production of new functional rice that could promote human health. Herein, we used the low-glutelin rice mutant 'Koshihikari' (var. a123) and suppressed its glutelins and prolamins, the major seed storage proteins of rice, by RNA interference. The accumulation levels of the α' subunit in the lines with suppressed glutelin and prolamin levels were >20 mg in 1 g of rice seeds, which is considerably higher than those in previous studies. Oral administration of the transgenic rice containing the α' subunit exhibited a hypocholesterolemic activity in rats; the serum total cholesterol and LDL cholesterol levels were significantly reduced when compared to those of the control rice (var. a123). The cholesterol-lowering action by transgenic rice accumulating the α' subunit induces a significant increase in fecal bile acid excretion and a tendency to increase in fecal cholesterol excretion. This is the first report that transgenic rice exhibits a hypocholesterolemic activity in rats in vivo by using the β-conglycinin α' subunit.

Transgenic rice endosperm as a bioreactor for molecular pharming

Plants provide a promising expression platform for producing recombinant proteins with several advantages in terms of high expression level, lower production cost, scalability, and safety and environment-friendly. Molecular pharming has been recognized as an emerging industry with strategic importance that could play an important role in economic development and healthcare in China. Here, this review represents the significant advances using transgenic rice endosperm as bioreactor to produce various therapeutic recombinant proteins in transgenic rice endosperm and large-scale production of OsrHSA, and discusses the challenges to develop molecular pharming as an emerging industry with strategic importance in China.

A strategy for targeting recombinant proteins to protein storage vacuoles by fusion to Brassica napus napin in napin-depleted seeds

Seeds are capable of accumulating high levels of seed storage proteins (SSP), as well as heterologous proteins under certain conditions. Arabidopsis thaliana was used to develop a strategy to deplete seeds of an endogenous SSP and then replenish them with the same protein fused to a heterologous protein. In several other studies, competition with endogenous SSP for space and metabolic resources was shown to affect the accumulation of recombinant proteins in seeds. We used RNAi to reduce the expression of the five napin genes and deplete the seeds of this SSP. Targeting a recombinant protein to a vacuole or structure within the seed where it can be protected from cytosolic proteases can also promote its accumulation. To achieve this, a synthetic Brassica napus napin gene (Bn napin) was designed that was both impervious to the A. thaliana napin (At napin) RNAi construct and permitted fusion to a heterologous protein, in this case green fluorescent protein (GFP). GFP was placed in several strategic locations within Bn napin with consideration to maintaining structure, processing sites and possible vacuolar targeting signals. In transgenic A. thaliana plants, GFP was strongly localized to the seed protein storage vacuole in all Bn napin fusion configurations tested, but not when expressed alone. This SSP depletion-replenishment strategy outlined here would be applicable to expression of recombinant proteins in industrial crops that generally have large repertoires of endogenous SSP genes.

Efficient recovery of recombinant proteins from cereal endosperm is affected by interaction with endogenous storage proteins

Cereal seeds are versatile platforms for the production of recombinant proteins because they provide a stable environment for protein accumulation. Endogenous seed storage proteins, however, include several prolamin-type polypeptides that aggregate and crosslink via intermolecular disulfide bridges, which could potentially interact with multimeric recombinant proteins such as antibodies, which assemble in the same manner. We investigated this possibility by sequentially extracting a human antibody expressed in maize endosperm, followed by precipitation in vitro with zein. We provide evidence that a significant proportion of the antibody pool interacts with zein and therefore cannot be extracted using non-reducing buffers. Immunolocalization experiments demonstrated that antibodies targeted for secretion were instead retained within zein bodies because of such covalent interactions. Our findings suggest that the production of soluble recombinant antibodies in maize could be enhanced by eliminating or minimizing interactions with endogenous storage proteins.

The use of rice seeds to produce human pharmaceuticals for oral therapy

Rice (Oryza sativa L.) is the major staple food consumed by half of the world's population. Rice seeds have gained recent attention as bioreactors for the production of human pharmaceuticals such as therapeutic proteins or peptides. Rice seed production platforms have many advantages over animal cell or microbe systems in terms of cost-effectiveness, scalability, safety, product stability and productivity. Rice seed-based human pharmaceuticals are expected to become innovative therapies as edible drugs. Therapeutic proteins can be sequestered within natural cellular compartments in rice seeds and protected from harsh gastrointestinal environments. This review presents the state-of-the-art on the construction of gene cassettes for accumulation of pharmaceutical proteins or peptides in rice seeds, the generation of transgenic rice plants, and challenges involved in the use of rice seeds to produce human pharmaceuticals.

A whole-genome analysis of a transgenic rice seed-based edible vaccine against cedar pollen allergy

Genetic modification (GM) by Agrobacterium-mediated transformation is a robust and widely employed method to confer new traits to crops. In this process, a transfer DNA is delivered into the host genome, but it is still unclear how the host genome is altered by this event at single-base resolution. To decipher genomic discrepancy between GM crops and their host, we conducted whole-genome sequencing of a transgenic rice line OSCR11. This rice line expresses a seed-based edible vaccine containing two major pollen allergens, Cry j 1 and Cry j 2, against Japanese cedar pollinosis. We revealed that genetic differences between OSCR11 and its host a123 were significantly less than those between a123 and its precedent cultivar Koshihikari. The pattern of nucleotide base substitution in OSCR11, relative to a123, was consistent with somaclonal variation. Mutations in OSCR11 probably occurred during the cell culture steps. In addition, strand-specific mRNA-Seq revealed similar transcriptomes of a123 and OSCR11, supporting genomic integrity between them.

Rice-based oral antibody fragment prophylaxis and therapy against rotavirus infection

Rotavirus-induced diarrhea is a life-threatening disease in immunocompromised individuals and in children in developing countries. We have developed a system for prophylaxis and therapy against rotavirus disease using transgenic rice expressing the neutralizing variable domain of a rotavirus-specific llama heavy-chain antibody fragment (MucoRice-ARP1). MucoRice-ARP1 was produced at high levels in rice seeds using an overexpression system and RNAi technology to suppress the production of major rice endogenous storage proteins. Orally administered MucoRice-ARP1 markedly decreased the viral load in immunocompetent and immunodeficient mice. The antibody retained in vitro neutralizing activity after long-term storage (>1 yr) and boiling and conferred protection in mice even after heat treatment at 94°C for 30 minutes. High-yield, water-soluble, and purification-free MucoRice-ARP1 thus forms the basis for orally administered prophylaxis and therapy against rotavirus infections.

High-level production of lactostatin, a hypocholesterolemic peptide, in transgenic rice using soybean A1aB1b as carrier

Hypercholesterolemia, a form of cardiovascular disease, is one of the leading causes of deaths worldwide. Lactostatin (Ile-Ile-Ala-Glu-Lys), derived from β-lactoglobulin in cow's milk, is a bioactive peptide with hypocholesterolemic activity higher than sitosterol, a known anti-hypercholesterolemic drug. Here, we successfully developed a transgenic rice accumulating a much higher level of lactostatin by inserting 29 IIAEK sequences into the structurally flexible (nonconserved) regions of soybean seed storage protein, A1aB1b, and introducing it into LGC-1 (low glutelin content mutant 1) as host variety. A1aB1b containing 29 lactostatins was expressed in the endosperm of rice seed cells by using seed specific promoters and sorted into novel compartments distinct from normal PB-I (ER-derived protein body) and PB-II (protein storage vacuoles). Transgenic rice seeds accumulated approximately 2 mg of lactostatins/g of dry seeds, which is relatively high compared with previous reports. Our findings suggest that the introduction of a high copy number of bioactive peptide into seed storage proteins as carrier is one of the effective means in producing higher amounts of bioactive peptides in rice.

Transgenic rice seeds accumulating recombinant hypoallergenic birch pollen allergen Bet v 1 generate giant protein bodies

A versatile hypoallergenic allergen derivative against multiple allergens is an ideal tolerogen for allergen-specific immunotherapy. Such a tolerogen should exhibit high efficacy, without side effects, when administered at high doses and should be applicable to several allergens. Tree pollen chimera 7 (TPC7), a hypoallergenic Bet v 1 tolerogen against birch pollen allergy, was previously selected by DNA shuffling of 14 types of Fagales tree pollen allergens. In this study, transgenic rice seed accumulating TPC7 was generated as an oral vaccine against birch pollen allergy by expressing this protein as a secretory protein using the N-terminal signal peptide and the C-terminal KDEL tag under the control of an endosperm-specific glutelin promoter. The highest level of TPC7 accumulation was approximately 207 µg grain(-1). Recombinant TPC7 is a glycoprotein with high mannose-type N-glycan, but without β1,2-xylose or α1,3-fucose, suggesting that TPC7 is retained in the endoplasmic reticulum (ER). TPC7 is deposited as a novel, giant spherical ER-derived protein body, >20 µm in diameter, which is referred to as the TPC7 body. Removal of the KDEL retention signal or mutation of a cysteine residue resulted in an alteration of TPC7 body morphology, and deletion of the signal peptide prevented the accumulation of TPC7 in rice seeds. Therefore, the novel TPC7 bodies may have formed aggregates within the ER lumen, primarily due to the intrinsic physicochemical properties of the protein.

Characterization of a cruciferin deficient mutant of Arabidopsis and its utility for overexpression of foreign proteins in plants

Plant seeds naturally accumulate storage reserves (proteins, carbohydrates, lipids) that are mobilized during germination to provide energy and raw materials to support early seedling growth. Seeds have been exploited as bioreactors for the production to foreign materials, but stable, high level expression has been elusive, in part due to the intrinsic bias for producing the natural reserves in their typical proportions. To identify mutants governing seed filling, we screened a population of mutagenized Arabidopsis plants for a mutant that failed to fill its seeds. Here we report the identification of ssp1, a recessive, viable mutant that accumulates approximately 15% less protein than wildtype seeds. Molecular analyses revealed that ssp1 is due to the introduction of a premature stop codon in CRU3, one of the major cruciferin genes. Unlike many other reserve mutants or transgenic lines in which seed storage protein levels are reduced by antisense/RNAi technologies, ssp1 exhibits low level compensation by other reserves, and represents a mutant background that might prove useful for high level expression of foreign proteins. To test this hypothesis, we used a bean phytohemagglutinin (PHA) gene as a reporter and compared PHA expression levels in single copy insertion lines in ssp1 vs. wildtype. These near isogenic lines allow reporter protein levels to be compared without the confounding and sometimes unknown influences of transgene copy number and position effects on gene expression. The ssp1 lines consistently accumulated more PHA than the backcrossed counterparts, with increases ranging from 12% to 126%. This proof of principle study suggests that similar strategies in crop plants may improve the yield of foreign proteins of agronomic and economic interest.

Increasing the production yield of recombinant protein in transgenic seeds by expanding the deposition space within the intracellular compartment

Seeds must maintain a constant level of nitrogen in order to germinate. When recombinant proteins are produced while endogenous seed protein expression is suppressed, the production levels of the foreign proteins increase to compensate for the decreased synthesis of endogenous proteins. Thus, exchanging the production of endogenous seed proteins for that of foreign proteins is a promising approach to increase the yield of foreign recombinant proteins. Providing a space for the deposition of recombinant protein in the intracellular compartment is critical, at this would lessen any competition in this region between the endogenous seed proteins and the introduced foreign protein. The production yields of several recombinant proteins have been greatly increased by this strategy.

ER stress response induced by the production of human IL-7 in rice endosperm cells

Rice seed has been used as a production platform for high value recombinant proteins. When mature human interleukin 7 (hIL-7) was expressed as a secretory protein in rice endosperm by ligating the N terminal glutelin signal peptide and the C terminal KDEL endoplasmic reticulum (ER) retention signal to the hIL-7 cytokine to improve production yield, this protein accumulated at levels visible by Coomassie Brilliant Blue staining. However, the production of this protein led not only to a severe reduction of endogenous seed storage proteins but also to a deterioration in grain quality. The appearance of aberrant grain phenotypes (such as floury and shrunken) was attributed to ER stress induced by the retention of highly aggregated unfolded hIL-7 in the ER lumen, and the expression levels of chaperones such as BiPs and PDIs were enhanced in parallel with the increase in hIL-7 levels. The activation of this ER stress response was shown to be mainly mediated by the OsIRE1-OsbZIP50 signal cascade, based on the appearance of unconventional splicing of OsbZIP50 mRNA and the induction of OsBiP4&5. Interestingly, the ER stress response could be induced by lower concentrations of hIL-7 versus other types of cytokines such as IL-1b, IL-4, IL-10, and IL-18. Furthermore, several ubiquitin 26S proteasome-related genes implicated in ER-associated degradation were upregulated by hIL-7 production. These results suggest that severe detrimental effects on grain properties were caused by proteo-toxicity induced by unfolded hIL-7 aggregates in the ER, resulting in the triggering of ER stress.

Oral immunotherapy with transgenic rice seed containing destructed Japanese cedar pollen allergens, Cry j 1 and Cry j 2, against Japanese cedar pollinosis

Transgenic rice accumulating the modified major Japanese cedar pollen allergens, Cryptomeria japonica 1 (Cry j 1) and Cryptomeria japonica 2 (Cry j 2), which were deconstructed by fragmentation and shuffling, respectively, in the edible part of the seed was generated by transformation of a good-tasting rice variety, 'Koshihikari'. These modified cedar pollen antigens were deposited in ER-derived protein bodies (PB-I), which are suitable for delivery to the mucosal immune system in gut-associated lymphoid tissue when orally administered because antigens bioencapsulated in PB-I are resistant against hydrolysis by intestinal enzymes and harsh environments. Mice fed transgenic seeds daily for three weeks and then challenged with crude cedar pollen allergen showed marked suppression of allergen-specific CD4(+) T-cell proliferation, IgE and IgG levels compared with mice fed nontransgenic rice seeds. As clinical symptoms of pollinosis, sneezing frequency and infiltration of inflammatory cells such as eosinophils and neutrophils were also significantly reduced in the nasal tissue. These results imply that oral administration of transgenic rice seeds containing the structurally disrupted Cry j 1 and Cry j 2 antigens, serving as universal antigens, is a promising approach for specific immunoprophylaxis against Japanese cedar pollinosis.

Recombinant protein yield in rice seed is enhanced by specific suppression of endogenous seed proteins at the same deposit site

Human IL-10 (hIL-10) is a therapeutic treatment candidate for inflammatory allergy and autoimmune diseases. Rice seed-produced IL-10 can be effectively delivered directly to gut-associated lymphoreticular tissue (GALT) via bio-encapsulation. Previously, the codon-optimized hIL-10 gene was expressed in transgenic rice with the signal peptide and endoplasmic reticulum (ER) retention signal (KDEL) at its 5' and 3' ends, respectively, under the control of the endosperm-specific glutelin GluB-1 promoter. The resulting purified hIL-10 was biologically active. In this study, the yield of hIL-10 in transgenic rice seed was improved. This protein accumulated at the intended deposition sites, which had been made vacant through the selective reduction, via RNA interference, of the endogenous seed storage proteins prolamins or glutelins. Upon suppression of prolamins that were sequestered into ER-derived protein bodies (PB-I), hIL-10 accumulation increased approximately 3-fold as compared to rice seed with no such suppression and reached 219 μg/grain. In contrast, reducing the majority of the glutelins stored in protein-storage vacuoles (PB-II) did not significantly affect the accumulation of hIL-10. Considering that hIL-10 is synthesized in the ER lumen and subsequently buds off in ER-derived granules called IL-10 granules in a manner similar to PB-Is, these results indicate that increases in the available deposition space for the desired recombinant proteins may be crucial for improvements in yield. Furthermore, efficient dimeric intermolecular formation of hIL-10 by inhibiting interaction with Cys-rich prolamins also contributed to the enhanced formation of IL-10 bodies. Higher yield of hIL-10 produced in rice seeds is expected to have broad application in the future.

Reduction of 13 kD prolamins increases recombinant protein yield and recovery rate in rice endosperm

RNA silencing inducible sequence (RSIS) causes post-transcriptional gene silencing (PTGS) of 5' or 3' flanking sequence-containing genes by inhibiting proper transcriptional termination. Exploiting this nature, 13 kD Pro-less, in which major seed storage protein (SSP) 13 kD prolamins are reduced, has been generated. In 13 kD Pro-less, other SSPs, such as glutelins, are increased as a compensation effect to maintain amino acid pool. 7Crp is the seven-linked epitope peptide derived from major cedar pollen allergens Cry j 1 and Cry j 2. When 7Crp is expressed in 13 kD Pro-less endosperm, accumulation level of 7Crp increased. Furthermore, recovery rate of 7Crp without reducing reagent increased. These findings indicate that 13 kD Pro-less endosperm provides a good production platform for recombinant proteins.

Expression of hypoallergenic Der f 2 derivatives with altered intramolecular disulphide bonds induces the formation of novel ER-derived protein bodies in transgenic rice seeds

House dust mites (HDM) are the most common source of indoor allergens and are associated with allergic diseases worldwide. To benefit allergic patients, safer and non-invasive mucosal routes of oral administration are considered to be the best alternative to conventional allergen-specific immunotherapy. In this study, transgenic rice was developed expressing derivatives of the major HDM allergen Der f 2 with reduced Der f 2-specific IgE reactivity by disrupting intramolecular disulphide bonds in Der f 2. These derivatives were produced specifically as secretory proteins in the endosperm tissue of seeds under the control of the endosperm-specific glutelin GluB-1 promoter. Notably, modified Der f 2 derivatives aggregated in the endoplasmic reticulum (ER) lumen and were deposited in a unique protein body (PB)-like structure tentatively called the Der f 2 body. Der f 2 bodies were characterized by their intracellular localization and physico-chemical properties, and were distinct from ER-derived PBs (PB-Is) and protein storage vacuoles (PB-IIs). Unlike ER-derived organelles such as PB-Is, Der f 2 bodies were rapidly digested in simulated gastric fluid in a manner similar to that of PB-IIs. Oral administration in mice of transgenic rice seeds containing Der f 2 derivatives encapsulated in Der f 2 bodies suppressed Der f 2-specific IgE and IgG production compared with that in mice fed non-transgenic rice seeds, and the effect was dependent on the type of Der f 2 derivative expressed. These results suggest that engineered hypoallergenic Der f 2 derivatives expressed in the rice seed endosperm could serve as a basis for the development of viable strategies for the oral delivery of vaccines against HDM allergy.

Production of human growth hormone in transgenic rice seeds: co-introduction of RNA interference cassette for suppressing the gene expression of endogenous storage proteins

Rice seeds are potentially useful hosts for the production of pharmaceutical proteins. However, low yields of recombinant proteins have been observed in many cases because recombinant proteins compete with endogenous storage proteins. Therefore, we attempt to suppress endogenous seed storage proteins by RNA interference (RNAi) to develop rice seeds as a more efficient protein expression system. In this study, human growth hormone (hGH) was expressed in transgenic rice seeds using an endosperm-specific promoter from a 10 kDa rice prolamin gene. In addition, an RNAi cassette for reduction of endogenous storage protein expressions was inserted into the hGH expression construct. Using this system, the expression levels of 13 kDa prolamin and glutelin were effectively suppressed and hGH polypeptides accumulated to 470 μg/g dry weight at the maximum level in transgenic rice seeds. These results suggest that the suppression of endogenous protein gene expression by RNAi could be of great utility for increasing transgene products.

Recent advances in soybean transformation and their application to molecular breeding and genomic analysis

Herbicide-resistant transgenic soybean plants hold a leading market share in the USA and other countries, but soybean has been regarded as recalcitrant to transformation for many years. The cumulative and, at times, exponential advances in genetic manipulation have made possible further choices for soybean transformation. The most widely and routinely used transformation systems are cotyledonary node-Agrobacterium-mediated transformation and somatic embryo-particle-bombardment-mediated transformation. These ready systems enable us to improve seed qualities and agronomic characteristics by transgenic approaches. In addition, with the accumulation of soybean genomic resources, convenient or promising approaches will be requisite for the determination and use of gene function in soybean. In this article, we describe recent advances in and problems of soybean transformation, and survey the current transgenic approaches for applied and basic research in Japan.

The hypocholesterolemic activity of transgenic rice seed accumulating lactostatin, a bioactive peptide derived from bovine milk β-lactoglobulin

Lactostatin is a novel pentapeptide (IIAEK) derived from bovine milk β-lactoglobulin with greater hypocholesterolemic activity than β-sitosterol, the drug commonly used to treat hypercholesterolemia. We developed transgenic rice expressing lactostatin as a fusion protein with seed storage protein (SSP) glutelins under the control of three different endosperm-specific promoters. Lactostatin accumulated in transgenic rice seed at approximately 1.6 mg/g seeds (dry seeds) without any apparent influence on seed traits such as endogenous SSP expression levels or alterations in the intracellular structures of endosperm cells. Short-term (three day) oral administration of the glutelin fraction containing lactostatin (namely three times of 300 mg/kg body weight/day) extracted from transgenic rice seeds resulted in hypocholesterolemic activity in rats; namely, the serum low-density-lipoprotein (LDL) cholesterol level was significantly reduced accompanied by a significant increase in beneficial serum high-density-lipoprotein (HDL) cholesterol.

Tubers from potato lines expressing a tomato Kunitz protease inhibitor are substantially equivalent to parental and transgenic controls

Recombinant protease inhibitors represent useful tools for the development of insect-resistant transgenic crops, but questions have been raised in recent years about the impact of these proteins on endogenous proteases and chemical composition of derived food products. In this study, we performed a detailed compositional analysis of tubers from potato lines expressing the broad-spectrum inhibitor of Ser and Asp proteases, tomato cathepsin D inhibitor (SlCDI), to detect possible unintended effects on tuber composition. A compositional analysis of key nutrients and toxic chemicals was carried out with tubers of SlCDI-expressing and control (comparator) lines, followed by a two-dimensional gel electrophoresis (2-DE) proteomic profiling of total and allergenic proteins to detect eventual effects at the proteome level. No significant differences were observed among control and SlCDI-expressing lines for most chemicals assayed, in line with the very low abundance of SlCDI in tubers. Likewise, proteins detected after 2-DE showed no quantitative variation among the lines, except for a few proteins in some control and test lines, independent of slcdi transgene expression. Components of the patatin storage protein complex and Kunitz protease inhibitors immunodetected after 2-DE showed unaltered deposition patterns in SlCDI-expressing lines, clearly suggesting a null impact of slcdi on the intrinsic allergenic potential of potato tubers. These data suggest, overall, a null impact of slcdi expression on tuber composition and substantial equivalence between comparator and SlCDI-expressing tubers despite reported effects on leaf protein catabolism. They also illustrate the usefulness of proteomics as a tool to assess the authenticity of foods derived from novel-generation transgenic plants.

Proteomic analysis of rice endosperm cells in response to expression of hGM-CSF

The accumulation of significant levels of transgenic products in plant cells is required not only for crop improvement, but also for molecular pharming. However, knowledge about the fate of transgenic products and endogenous proteins in grain cells is lacking. Here, we utilized a quantitative mass spectrometry-based proteomic approach for comparative analysis of expression profiles of transgenic rice endosperm cells in response to expression of a recombinant pharmaceutical protein, human granulocyte-macrophage colony stimulation factor (hGM-CSF). This study provided the first available evidence concerning the fate of exogenous and endogenous proteins in grain cells. Among 1883 identified proteins with a false positive rate of 5%, 103 displayed significant changes (p-value < 0.05) between the transgenic and the wild-type endosperm cells. Notably, endogenous storage proteins and most carbohydrate metabolism-related proteins were down-regulated, while 26S proteasome-related proteins and chaperones were up-regulated in the transgenic rice endosperm. Furthermore, it was observed that expression of hGM-CSF induced endoplasmic reticulum stress and activated the ubiquitin/26S-proteasome pathway, which led to ubiquitination of this foreign gene product in the transgenic rice endosperm.