Cloning, expression and immunological characterization of Ory s 1, the major allergen of rice pollen

Molecular features of grass allergens and development of biotechnological approaches for allergy prevention

Allergic diseases are characterized by elevated allergen-specific IgE and excessive inflammatory cell responses. Among the reported plant allergens, grass pollen and grain allergens, derived from agriculturally important members of the Poaceae family such as rice, wheat and barley, are the most dominant and difficult to prevent. Although many allergen homologs have been predicted from species such as wheat and timothy grass, fundamental aspects such as the evolution and function of plant pollen allergens remain largely unclear. With the development of genetic engineering and genomics, more primary sequences, functions and structures of plant allergens have been uncovered, and molecular component-based allergen-specific immunotherapies are being developed. In this review, we aim to provide an update on (i) the distribution and importance of pollen and grain allergens of the Poaceae family, (ii) the origin and evolution, and functional aspects of plant pollen allergens, (iii) developments of allergen-specific immunotherapy for pollen allergy using biotechnology and (iv) development of less allergenic plants using gene engineering techniques. We also discuss future trends in revealing fundamental aspects of grass pollen allergens and possible biotechnological approaches to reduce the amount of pollen allergens in grasses.

Evaluation of rice promoters conferring pollen-specific expression in a heterologous system, Arabidopsis

Promoters can direct gene expression specifically to targeted tissues or cells. Effective with both crop species and model plant systems, these tools can help researchers overcome the practical obstacles associated with transgenic protocols. Here, we identified promoters that allow one to target the manipulation of gene expression during pollen development. Utilizing published transcriptomic databases for rice, we investigated the promoter activity of selected genes in Arabidopsis. From various microarray datasets, including those for anthers and pollen grains at different developmental stages, we selected nine candidate genes that showed high levels of expression in the late stages of rice pollen development. We named these Oryza sativa late pollen-specific genes. Their promoter regions contained various cis-acting elements that could be responsible for anther-/pollen-specific expression. Promoter::GUS-GFP reporters were constructed and introduced into Arabidopsis plants. Histochemical GUS staining revealed that six of the nine rice promoters conferred strong GUS expression that was restricted to the anthers in Arabidopsis. Further analysis showed that although the GUS signals were not detected at the unicellular stage, they strengthened in the bicellular or tricellular stages, peaking at the mature pollen stage. This paralleled their transcriptomic profiles in rice. Based on our results, we proposed that these six rice promoters, which are active in the late stages of pollen formation in the dicot Arabidopsis, can aid molecular breeders in generating new varieties of a monocot plant, rice.

Allergenic potential of rice-pollen proteins: expression, immuno-cross reactivity and IgE-binding

Pollen proteins from several grass species have been identified and characterized as causative allergens in grass pollinosis. In contrast, allergenic potential of pollen proteins from rice, which belongs to the same Poaceae family, has not well been investigated, despite that a few clinical cases have been reported on rice-pollen allergy. In this study, to characterize expression and allergenic potential of pollen proteins from rice (Oryza sativa, ssp. japonica), rice putative proteins for β-expansin (EXP), a Ca(2+)-binding protein (CBP)/polcalcin, extensin (EXT), profilin (PRF) and polygalacturonase (PGA) retrieved from a rice complete cDNA database were prepared as recombinant proteins, and the antibodies to these recombinant proteins were obtained. Immuno-blotting and immuno-histological analyses showed that rice putative EXP, EXT and PGA were expressed abundantly in anther tissue and pollen granules and immuno-cross reactive with pollen proteins from timothy grass. ELISA and immuno-dot blotting analyses using serum specimens from allergic patients showed that majority of the specimens was positive in the IgE-binding to EXP and EXT, but weakly to PGA and almost negative to PRF. EXP and EXT were suggested to be potentially allergenic in the rice-pollen allergy as well as the grass pollinosis.

Rice-induced anaphylaxis: IgE-mediated allergy against a 56-kDa glycoprotein

BACKGROUND

Although rice (Oryza sativa) is one of the most common cereals produced and consumed around the world, there have been only a few reports on immediate hypersensitivity reactions after ingestion of rice. Few clinical studies on rice allergy in Asia have been reported concerning rhinitis, asthma and atopic dermatitis. In this case study, we identify allergens presumably responsible for anaphylaxis after ingestion of rice in a German patient.

METHODS

Prick-to-prick tests, determination of specific IgE and the basophil activation test (BAT) were performed to confirm IgE-mediated allergy. IgE reactivity was further analyzed by immunoblotting of protein extracts from cooked commercial rice products. Rice allergens were purified, subjected to N-terminal sequencing and characterized by IgE binding and IgE inhibition assays using additional sera from 8 subjects with sensitization to rice and/or a history of hypersensitivity symptoms after rice ingestion.

RESULTS

Prick-to-prick tests were positive to raw and cooked rice (basmati rice and long-grain rice) and preparations of different rice extracts. Specific IgE against rice (f9) was 1.87 kU(A)/l. The BAT showed specific IgE-mediated activation of basophils after stimulation with rice extracts. Four IgE-reactive rice proteins with an apparent molecular weight of 49, 52, 56 and 98 kDa were identified. Interestingly, only binding to the 56-kDa glycoprotein was at least partially independent from cross-reactive carbohydrate determinants (CCD), whereas IgE binding to the other rice proteins was completely inhibited by pre-incubation with the CCD MUXF derived from bromelain.

CONCLUSIONS

Yet unidentified high-molecular-weight allergens from rice seeds, predominantly a 56-kDa glycoprotein, seem to be responsible for anaphylaxis after consumption of rice in a German patient.

Agrobacterium-mediated transformation of Australian rice varieties and promoter analysis of major pollen allergen gene, Ory s 1

A simple protocol for Agrobacterium-mediated transformation of Australian rice using mature embryos is described. Transgenic plants of two commercial genotypes of Australian rice, Amaroo and Millin, were produced. Transgenic plants were obtained by applying selection pressure to callus and to the regenerated shoots. Exclusion of the selective agent (hygromycin) during plant regeneration was found to be critical for recovery of transgenic plants from these commercial varieties. Transgenic plants were produced after 3 months. The developed system was also used to study spatial and temporal expression of a rice pollen-specific gene, Ory s 1. Expression of pOry s 1::uidA in transgenic rice demonstrated GUS expression in mature pollen, hence indicating potential use of this promoter to direct pollen-specific gene expression. Further Ory s 1 5' deletion study indicated that the pollen-specificity element may reside within -405 bp to the start of the transcription, while the region upstream of -405 contained a cis-acting regulatory element(s) responsible for quantitative expression of this gene.

A genome-wide survey of imprinted genes in rice seeds reveals imprinting primarily occurs in the endosperm

Genomic imprinting causes the expression of an allele depending on its parental origin. In plants, most imprinted genes have been identified in Arabidopsis endosperm, a transient structure consumed by the embryo during seed formation. We identified imprinted genes in rice seed where both the endosperm and embryo are present at seed maturity. RNA was extracted from embryos and endosperm of seeds obtained from reciprocal crosses between two subspecies Nipponbare (Japonica rice) and 93-11 (Indica rice). Sequenced reads from cDNA libraries were aligned to their respective parental genomes using single-nucleotide polymorphisms (SNPs). Reads across SNPs enabled derivation of parental expression bias ratios. A continuum of parental expression bias states was observed. Statistical analyses indicated 262 candidate imprinted loci in the endosperm and three in the embryo (168 genic and 97 non-genic). Fifty-six of the 67 loci investigated were confirmed to be imprinted in the seed. Imprinted loci are not clustered in the rice genome as found in mammals. All of these imprinted loci were expressed in the endosperm, and one of these was also imprinted in the embryo, confirming that in both rice and Arabidopsis imprinted expression is primarily confined to the endosperm. Some rice imprinted genes were also expressed in vegetative tissues, indicating that they have additional roles in plant growth. Comparison of candidate imprinted genes found in rice with imprinted candidate loci obtained from genome-wide surveys of imprinted genes in Arabidopsis to date shows a low degree of conservation, suggesting that imprinting has evolved independently in eudicots and monocots.

The expression of maternal or paternal alleles in either a preferentially or exclusively uniparental manner, termed imprinting, is prevalent in the transient endosperm of seeds in the model plant Arabidopsis. Cereals form seeds where both the embryo and endosperm are present at seed maturity. They are an important world food source. To date, very few imprinted genes have been identified in cereal seeds. How parental gene expression biases contribute to rice seed development has not yet been studied in detail. The deep resolution of transcript sequencing platforms was used to identify loci expressed in a parentally biased manner in the embryo and endosperm of Indica and Japonica rice at a genome-wide level. We identified 262 candidate imprinted loci expressed in the endosperm, experimentally verified 56 of these, and found novel features pertaining to their expression. Only one gene was found to be imprinted in the rice embryo. Imprinting in Arabidopsis and rice seeds is confined primarily to the endosperm, but the identified loci do not share extensive sequence conservation. Imprinting thus appears to have evolved independently in these plant species.

A case of occupational rhinitis caused by rice powder in the grain industry

Rice is the major staple food in a large part of the world, especially in Asia. Hypersensitivity reactions to rice are rare. Moreover, cases of occupational allergies induced by inhalation of rice powder are uncommon. We report a 31-year-old male with work-related rhinitis and conjunctivitis symptoms caused by occupational exposure to rice powder in the grain industry. He showed positive responses to rice extracts on a skin prick test, and a high level of serum specific IgE to rice was detected by ELISA. Occupational rhinitis was confirmed by a nasal provocation test with rice extracts. An IgE ELISA inhibition test showed cross-creativity between rice and various grass pollen extracts. These findings suggest that the inhalation of rice powder can induce IgE-mediated occupational rhino-conjunctivitis, which may be derived from cross-reactivity to major grass pollens.

Class B beta-expansins are needed for pollen separation and stigma penetration

Group 1 grass pollen allergens comprise a distinctive clade within the beta-expansin family of cell wall-loosening proteins and are divided by sequence divergence into two phylogenetically separable classes (A and B). They have been proposed to loosen the walls of the stigma and style. Supporting this idea, we recently showed that a transposon insertion in one of the maize group-1 allergen genes reduces the ability of pollen to effect fertilization under conditions of pollen competition. In this work, we provide additional information on the phenotype of this mutant, showing that pollen deficient in beta-expansin gene expression tended to form large aggregates, leading to poor pollen dispersal on anther dehiscence, and that emerging pollen tubes had difficulties entering the silk. In addition, a silencing construct was created to reduce expression of all the class B genes with results that are consistent with those seen with the transposon insertional line, including reduced transgene transmission through the pollen. Our results provide a more detailed understanding of the role of group 1 allergens (pollen beta-expansins) in maize pollen development, pollen dispersal, pollen tube penetration into the style, and pollen tube growth through the transmitting tract.

Transcriptome-based examination of putative pollen allergens of rice (Oryza sativa ssp. japonica)

Pollen allergens are among the most abundantly transcribed and translated products in the life history of plants, and particularly grasses. To identify different pollen allergens in rice, putative allergens were identified in the rice genome and their expression characterized using the Affymetrix 57K rice GeneChip microarray. Among the most abundant pollen-specific candidate transcripts were Ory s 1 beta-expansin, Ory s 2, Ory s 7 EF hand, Ory s 11, Ory s 12 profilin A, Ory s 23, glycosyl hydrolase family 28 (polygalacturonase), and FAD binding proteins. Highly expressed pollen proteins are frequently present in multiple copy numbers, sometimes with mirror images located on nearby regions of the opposite DNA strand. Many of these are intronless and inserted as copies that retain nearly exact copies of their regulatory elements. Ory s 23 reflects low variability and high copy number, suggesting recent gene amplification. Some copies contain pseudogenes, which may reflect their origin through activity of retrotransposition; some putative allergenic sequences bear fusion products with repeat sequences of transposable elements (LTRs). The abundance of nearby repetitive sequences, activation of transposable elements, and high production of mRNA transcripts appear to coincide in pollen and may contribute to a syndrome in which highly transcribed proteins may be copied and inserted with streamlined features for translation, including grouping and removal of introns.

Antigenic similarity among group 1 allergens from grasses and quantitation ELISA using monoclonal antibodies to Phl p 1

BACKGROUND

Group 1 allergens elicit a specific IgE response in about 90% of grass pollen-allergic patients. The aim of this work was to study the antigenic similarity among group 1 allergens from different grasses and to develop a monoclonal antibody (MAb)-based quantitation ELISA.

METHODS

Twenty specific MAbs were produced from BALB/c mice immunized with natural Phl p 1. These MAbs were tested for specificity with thirteen different grass pollen extracts from the Poaceae family and in cross-inhibition experiments for the binding of Phl p 1. Purified group 1 allergens from Poeae grasses (Dactylis glomerata, Lolium perenne, Festuca pratensis and Poa pratensis) were tested for parallelism in quantitation ELISA.

RESULTS

Eighteen to nineteen anti-Phl p 1 MAbs recognized the homologous allergen in pollen extracts from grasses of the Poeae tribe. In contrast, only four MAbs recognized group 1 from Cynodon dactylon and Phragmites communis. Four groups of MAbs with different epitope specificity were identified. A grass group 1 quantitation ELISA was developed using a mix of three MAbs on the solid phase and a polyclonal rabbit antibody as the second antibody. The group 1 content could be measured in different batches of Phleum pratense as well as in pollen extracts from Poeae grasses, since they showed parallel dose-response curves.

CONCLUSIONS

MAbs produced in this work enabled us to show the high antigenic similarity between group 1 allergens from temperate grasses. The results prove the usefulness of the ELISA method developed for standardization of grass allergen products.

Recent proliferation and translocation of pollen group 1 allergen genes in the maize genome

The dominant allergenic components of grass pollen are known by immunologists as group 1 allergens. These constitute a set of closely related proteins from the beta-expansin family and have been shown to have cell wall-loosening activity. Group 1 allergens may facilitate the penetration of pollen tubes through the grass stigma and style. In maize (Zea mays), group 1 allergens are divided into two classes, A and B. We have identified 15 genes encoding group 1 allergens in maize, 11 genes in class A and four genes in class B, as well as seven pseudogenes. The genes in class A can be divided by sequence relatedness into two complexes, whereas the genes in class B constitute a single complex. Most of the genes identified are represented in pollen-specific expressed sequence tag libraries and are under purifying selection, despite the presence of multiple copies that are nearly identical. Group 1 allergen genes are clustered in at least six different genomic locations. The single class B location and one of the class A locations show synteny with the rice (Oryza sativa) regions where orthologous genes are found. Both classes are expressed at high levels in mature pollen but at low levels in immature flowers. The set of genes encoding maize group 1 allergens is more complex than originally anticipated. If this situation is common in grasses, it may account for the large number of protein variants, or group 1 isoallergens, identified previously in turf grass pollen by immunologists.

Gain of structure and IgE epitopes by eukaryotic expression of the major Timothy grass pollen allergen, Phl p 1

Approximately 400 million allergic patients are sensitized against group 1 grass pollen allergens, a family of highly cross-reactive allergens present in all grass species. We report the eukaryotic expression of the group 1 allergen from Timothy grass, Phl p 1, in baculovirus-infected insect cells. Domain elucidation by limited proteolysis and mass spectrometry of the purified recombinant glycoprotein indicates that the C-terminal 40% of Phl p 1, a major IgE-reactive segment, represents a stable domain. This domain also exhibits a significant sequence identity of 43% with the family of immunoglobulin domain-like group 2/3 grass pollen allergens. Circular dichroism analysis demonstrates that insect cell-expressed rPhl p 1 is a folded species with significant secondary structure. This material is well behaved and is adequate for the growth of crystals that diffract to 2.9 A resolution. The importance of conformational epitopes for IgE recognition of Phl p 1 is demonstrated by the superior IgE recognition of insect-cell expressed Phl p 1 compared to Escherichia coli-expressed Phl p 1. Moreover, insect cell-expressed Phl p 1 induces potent histamine release and leads to strong up-regulation of CD203c in basophils from grass pollen allergic patients. Deglycosylated Phl p 1 frequently exhibits higher IgE binding capacity than the recombinant glycoprotein suggesting that rather the intact protein structure than carbohydrate moieties themselves are important for IgE recognition of Phl p 1. This study emphasizes the important contribution of conformational epitopes for the IgE recognition of respiratory allergens and provides a paradigmatic tool for the structural analysis of the IgE allergen interaction.

Antibody profiles and self-reported symptoms to pollen-related food allergens in grass pollen-allergic patients from northern Europe

BACKGROUND

Most studies on pollen-related food allergy have so far focused on the association of birch/weed pollen allergens and plant food allergy. The aim of this study was to elucidate the allergen spectrum among a group of grass pollen-allergic patients from northern Europe and to relate the results to clinical histories of pollen-related food allergy.

METHODS

Fifty-eight grass pollen-allergic patients answered a questionnaire regarding allergy to foods. Blood samples were taken to test IgE-reactivity to a large panel of pollen allergens and pollen- and nonpollen-related food allergens using crude allergen extracts and recombinant and native allergens.

RESULTS

Three different groups of grass pollen-allergic patients were identified according to their IgE antibody profile: a grass pollen group only (19%), a grass and tree pollen group (29%) and a grass, tree and compositae (pan-) pollen group (48%). No sensitization to Bet v 1 as well as almost no IgE to plant food was observed in the grass pollen group. In contrast, nearly all patients in the two tree-related groups had IgE to Bet v 1, which reflected the high frequency of adverse reactions to typical birch-related food in these groups. Only four patients belonging to the pan-pollen group displayed IgE to profilin Phl p 12/Bet v 2. Patients in the pan-pollen group reported significantly more symptoms to food allergens compared with patients in the two other groups. The most frequently reported symptom was the oral allergy syndrome.

CONCLUSIONS

Sensitization to grass pollen alone is rare among grass pollen-allergic patients from northern Europe. The majority of patients are in addition sensitized to birch (Bet v 1), which seems to be closely related to their pollen-derived food allergy. The study highlights the advantage of using well-defined allergen molecules for the diagnosis of cross-reactivity between pollen and food allergens.

Improving diagnostic tests for food allergy with recombinant allergens

Food allergy is one important manifestation of atopic allergy. Primary food allergy mainly affects young children (class I), whereas adults frequently develop food allergy as a consequence of an inhalant sensitization (class II). At present, the diagnostic instrument for proving class II food allergy is not satisfactory. Skin tests as well as serological tests are in general neither very specific nor highly sensitive because they depend on food extracts, which differ in their content of individual allergens, vary between manufacturers, and even between different batches. Since the presence of food allergen-specific IgE antibodies does not always correlate with clinical symptoms against the respective food, oral provocation tests (ideally double-blind placebo-controlled food challenges) have to be performed to validate serological diagnosis or skin tests. However, oral provocation tests are connected to several practical problems and include a specific risk for the allergic patient. Applying DNA technology, up to 40 food allergens have been produced in recombinant form, which implies standardized quality and unlimited quantity of the respective proteins. Hence, such molecules might be used to solve problems of clinical and molecular allergology in diagnosis, research, and therapy of class II food allergies. First experiments with recombinant food allergens in this respect appear very promising.

Carbohydrate moieties can induce mediator release: a detailed characterization of two major timothy grass pollen allergens

Specific IgE binding to carbohydrate moieties of glycosylated allergens has been known for years, but the importance of these structures for the elicitation of allergic reactions is still a matter of debate. Because of their conserved carbohydrate structures, especially N-glycans have always been prime candidates for IgE cross-reactivity between allergens from unrelated species. The aim of our study was to determine whether carbohydrate structures on glycoproteins can by themselves elucidate allergic reactions. We characterized in detail the carbohydrate moieties of the major allergens Phl p 1 and Phl p 13 of timothy grass pollen (Phleum pratense L.) by performing tryptic digests followed by HPLC, N-terminal sequencing, sugar analysis, MALDI-TOF- and ESI-ICRFT-MS. Phl p 1 contains one N-glycan with one of the two glycoforms MMXF3 and M0XF3 and a single furanosidic arabinose, which is bound to a hydroxyproline residue in direct vicinity to the N-glycan. This O-glycosylation is probably due to an arabinosylation consensus sequence found in the N-terminal part of Phl p 1 and other group 1 allergens, but displayed no IgE-reactivity. Thus, Phl p 1 is monovalent with respect to its IgE-binding carbohydrate epitopes and showed no mediator release. In contrast, the carbohydrate moiety of Phl p 13, which carries four of the same N-glycans (like Phl p 1), can cross-link IgE-receptors via carbohydrate chains and elicits IL-4 release from basophils.

The ACVD task force on canine atopic dermatitis (IV): environmental allergens

Numerous environmental allergens have been incriminated in the pathogenesis of canine atopic dermatitis (AD). These include dust and storage mite antigens, house dust, pollens from grasses, trees and weeds, mould spores, epidermal antigens, insect antigens, and miscellaneous antigens such as kapok. In this paper, we review the literature concerning the allergens that have been reported to contribute to canine AD. We conclude that attempts to identify the relevant canine antigens in the past have been plagued by a lack of standardisation of extracts and techniques, and the presence of false-positive and -negative reactions in allergy tests. Until these problems are rectified, it is unlikely that we will be able to provide a list of major and minor antigens for dogs. Hence, we recommend that future studies should be aimed at determining the major patterns of reactivity and cross-reactivity to specific protein allergens within antigenic extracts using electrophoresis and immunoblotting techniques. Once this information becomes available, it may be possible to use a selection of genetically engineered, highly pure antigens for both diagnostic and therapeutic purposes in canine allergy investigations. The use of such antigens will allow standardisation of canine allergy testing and immunotherapy so that the reliability and efficacy of these procedures can be objectively assessed.

B cell epitopes of the major timothy grass pollen allergen, phl p 1, revealed by gene fragmentation as candidates for immunotherapy

Group 1 grass pollen allergens are recognized by IgE antibodies of almost 40% of allergic individuals and therefore belong to the most important elicitors of Type I allergy worldwide. We have previously isolated the cDNA coding for the group 1 allergen from timothy grass, Phl p 1, and demonstrated that recombinant Phl p 1 contains most of the B cell as well as T cell epitopes of group 1 allergens from a variety of grass and corn species. Here we determine continuous B cell epitopes of Phl p 1 by gene fragmentation. IgE antibodies of grass pollen allergic patients identified five continuous epitope-containing areas that on an average bound 40% of Phl p 1-specific IgE antibodies and were stably recognized in the course of disease. In contrast to untreated patients, patients undergoing grass pollen immunotherapy started to mount IgG(4) antibodies to the recombinant IgE-defined fragments in the course of immunotherapy. The protective role of these IgG(4) antibodies is demonstrated by observations that 1) increases in rPhl p 1 fragment-specific IgG(4) were in parallel with decreases in Phl p 1-specific IgE, and 2) preincubation of rPhl p 1 with patients sera containing rPhl p 1 fragment-specific IgG(4) blocked histamine release from basophils of an untreated grass pollen allergic patient. We propose to use recombinant Phl p 1 fragments for active immunotherapy in order to induce protective IgG responses against IgE epitopes in grass pollen allergic patients. This concept may be applied for the development of allergy vaccines whenever the primary sequence or structure of an allergen is available.

Group I allergens of grass pollen as cell wall-loosening agents

Group I allergens are the major allergens of grass pollen, but their biological function is unknown. These proteins are shown here to be structurally related to expansins, which are able to induce extension (creep) of plant cell walls. Extracts of maize pollen possess potent expansin-like activity, as measured in wall extension and wall stress-relaxation assays. This activity is selective for grass cell walls and is, at least partly, due to the action of maize group I allergens. We propose that group I allergens facilitate invasion of the pollen tube into the maternal tissues by loosening the cell walls of the grass stigma and style. Additionally, the presence of related mRNAs in vegetative tissues of rice, Arabidopsis, and soybean implies that allergen homologs may function to loosen walls in growing vegetative tissues as well.