Genetic and environmental factors affecting allergen-related gene expression in apple fruit (Malus domestica L. Borkh)

New Mass Spectrometric Approach to Quantify the Major Isoallergens of the Apple Allergen Mal d 1

Patients who suffer from birch pollinosis often develop adverse reactions to the consumption of fresh apples due to the structural similarity of the allergens Bet v 1 and Mal d 1 from birch and apples, respectively. A different allergenic potential for Mal d 1 isoallergens is postulated, but approaches to quantify the Mal d 1 isoallergen-specific are missing. Therefore, a bottom-up proteomics approach was developed to quantify Mal d 1 by stable isotope dilution and microHPLC-QTOF analyses. Marker peptides for individual isoallergens (Mal d 1.01-Mal d 1.03 and Mal d 1.06), combinations thereof (Mal d 1.01 + 1.02, Mal d 1.02 + 1.06, and Mal d 1.04 + 1.05), and two global marker peptides, comprising Mal d 1.01 + 1.02 + 1.04 + 1.05 and Mal d 1.03 + 1.06 + 1.07 + 1.08 + 1.09, were identified. By the use of an extraction standard (r-Mal d 1_mut), an optimized protocol for extraction and tryptic digestion of apple proteins was developed, and the variety-specific extraction efficiency was monitored for the flesh and peel of apples. The Mal d 1 contents in flesh and peel of five commercial apple breeds and four apple varieties from orchard meadows were quantified isoallergen-specific.

Apple allergy: Causes and factors influencing fruits allergenic properties-Review

BACKGROUND

Apple tree fruits (Malus × domestica Borkh.) are a rich source of nutrients and nutraceuticals and are recommended as a part of the healthy, staple diet. However, apples could be also the cause of allergies including severe reactions. Allergies to fruits like apples are predominantly associated with pollinosis. In North and Central Europe, sensitisation to apples is caused mainly by cross-reactive birch pollen aeroallergen, whereas in the Mediterranean area of Europe, apple allergy is mostly associated with allergies to peach. The allergenicity of apples differ across cultivars but only a few varieties were studied. Some factors changing apples allergenicity were identified, including unmodifiable and potentially modifiable factors for example cultivation method, ripening stage and storage conditions.

AIM

This review presents current knowledge about the molecular basis of apple allergenicity and factors influencing its level.

CONCLUSIONS

Selecting cultivars with low potential of allergenicity, removing apple peel and heat treatment could reduce the risk of severe allergy reaction incidence and presumably can be used in birch pollen immunotherapy.

Selenium biofortification of different varieties of apples (Malus domestica) - Influence on protein content and the allergenic proteins Mal d 1 and Mal d 3

As allergy towards apples is widespread, the evaluation of various cultivation and postharvest influences on the allergenic potential is of great importance. Therefore, the analysis of the Mal d 1 content was the focus of this study, originally dealing with investigating the influence of a selenium biofortification on apple quality. The Mal d 1 content of apples was in most cases reduced when the fruits were biofortified with selenium. Apple variety and climatic conditions were identified as further influencing factors for the Mal d 1 content of the fruits. The separate analysis of the peel and the fruit flesh showed that the content of Mal d 1 in the fruit flesh was significantly lower in the biofortified samples than in the controls. In conclusion, the results indicate that the selenium biofortification of apples and biochemical mechanism behind can reduce the allergenic potential regarding the content of Mal d 1.

Relationship between Phenolic Compounds, Antioxidant Properties, and the Allergenic Protein Mal d 1 in Different Selenium-Biofortified Apple Cultivars (Malus domestica)

Notable parts of the population in Europe suffer from allergies towards apples. To address this health problem, the analysis of the interactions of relevant allergens with other substances such as phenolic compounds is of particular importance. The aim of this study was to evaluate the correlations between the total phenolic content (TPC), polyphenol oxidase (PPO) activity, antioxidant activity (AOA), and the phenolic compound profile and the content of the allergenic protein Mal d 1 in six apple cultivars. It was found that the PPO activity and the content of individual phenolic compounds had an influence on the Mal d 1 content. With regard to the important constituents, flavan-3-ols and phenolic acids, it was found that apples with a higher content of chlorogenic acid and a low content of procyanidin trimers and/or epicatechin had a lower allergenic potential. This is probably based on the reaction of phenolic compounds (when oxidized by the endogenous PPO) with proteins, thus being able to change the conformation of the (allergenic) proteins, which further corresponds to a loss of antibody recognition. When apples were additionally biofortified with selenium, the composition of the apples, with regard to TPC, phenolic profile, AOA, and PPO, was significantly affected. Consequently, this innovative agronomic practice seems to be promising for reducing the allergenic potential of apples.

Molecular and Immunological Identification of Low Allergenic Fruits among Old and New Apple Varieties

About 50–70% of patients allergic to birch pollen suffer from sensitization after apple ingestion. Apple allergenicity was established in only few varieties. Studies were performed on apple fruits of 21 traditional and nine modern varieties organically, intensively, or integratively produced. The aim of the study was to assess whether the factors like cultivation method, maturity stage, genotype, or type of tissue place an impact on the allergenic potential of apples. To answer these questions, we used semiquantitative real-time PCR, ELISA, and immunoblotting. Apple allergen genes present divergent expression across apple cultivars. Expression of the Mal d 1.06A correlates with the Mal d 1 level and is affected by the cultivation method and maturity of the fruit. The content of the main allergen Mal d 1 varied widely across cultivars. Interestingly, in our study, the Gala variety presented a low Mal d 1 concentration regardless of the cultivation method. Based on the Mal d 1.06A expression, the Mal d 1 protein content, and the immunoreactivity assay, the Kandil Sinap, Kosztela, Rumianka from Alma-Ata, Kantówka Gdańska, Reinette Coulon, and Gala cultivars emerged as potentially hypoallergenic apple cultivars. Our study allowed distinguishing between potentially low, medium, and highly allergenic varieties.

Tiered approach for the identification of Mal d 1 reduced, well tolerated apple genotypes

A rising proportion of the world population suffers from food-related allergies, including incompatibilities to apples. Although several allergenic proteins have been found in apples, the most important proteins that cause allergic reactions to apples in Central-Northern Europe, and North America are the Mal d 1 proteins, which are homologues of the birch pollen allergen Bet v 1. As the demand for hypoallergenic fruits is constantly increasing, we selected apple genotypes with a low total content of Mal d 1 by enzyme-linked immunosorbent assay analysis from segregating populations and tested the tolerability of these fruits through a human provocation study. This tiered approach, which exploited the natural diversity of apples, led to the identification of fruits, which were tolerated by allergic patients. In addition, we found a significant correlation (coefficient >0.76) between the total Mal d 1 content and flavan-3-ol amount and show that the isoform composition of the Mal d 1 proteins, which was determined by LC-MS/MS has a decisive effect on the tolerability of apple genotypes. The approach presented can be applied to other types of fruit and to other allergenic proteins. Therefore, the strategy can be used to reduce the allergen content of other plant foods, thereby improving food safety for allergy subjects.

Significant Reduction of the Expression of Peach ( Prunus persica L. Batsch) Allergen-Encoding Genes by Fruit Bagging with Opaque Paper

Freshly consumed peaches ( Prunus persica L. Batsch) can cause allergic reactions in the worldwide population because of the presence of four classes of allergens (Pru p 1, Pru p 2, Pru p 3, and Pru p 4). Fruit bagging has been widely practiced in peach cultivation to improve fruit quality; however, its effect on the expression of peach allergen-encoding genes remains unknown. In this study, the influence of fruit bagging with opaque paper bags on the major peach allergen-encoding genes, including Pru p 1.01, Pru p 1.06B, Pru p 2.01B, Pru p 2.02, Pru p 3.01, Pru p 4.01, and Pru p 4.02, were measured by means of real-time PCR. A significant reduction in transcript accumulation was observed for all of the selected genes in the epicarps of the bagged peach fruits, whereas slight increases were observed in the mesocarps for these genes, with the two exceptions of Pru p 2.02 and Pru p 3.01. For most of these genes, much higher transcripts were determined in the epicarps than in the mesocarps. Taken together, a significant reduction in the transcription rate of the allergen-encoding genes in the whole peach fruit was achieved by shading with opaque paper bags. According to these data, modifications in growing practices of peach may help to obtain fruits with lower levels of allergens and thus contribute to reducing potential allergenic risks in consumers.

Allergen immunotherapy for birch-apple syndrome: what do we know?

Apple allergy is common in patients allergic to birch pollen, and this is defined as ‘birch-apple syndrome’. Allergens responsible for cross-reactivity belong to the pathogenesis-related-10 family, and high homology in the amino acid sequences of the major allergens Bet v 1 from birch and Mal d 1 from apple has been demonstrated. Here we review the literature on the treatment of birch-apple syndrome by allergen immunotherapy. The only allergen immunotherapy method available thus far is based on the administration of birch-pollen extracts, through the subcutaneous or sublingual route, to induce tolerance to Bet v1 and to the homologous allergen Mal d 1. However, the studies performed thus far show modest efficacy, and thus other methods of immunotherapy should be investigated.

Old Apple (Malus domestica L. Borkh) Varieties with Hypoallergenic Properties: An Integrated Approach for Studying Apple Allergenicity

Freshly consumed apples (Malus domestica L. Borkh) can cause allergic reactions because of the presence of four classes of allergens. Knowledge of the genetic factors affecting the allergenic potential of apples would provide important information for the selection of hypoallergenic genotypes, which can be combined with the adoption of new agronomical practices to produce fruits with a reduced amount of allergens. In the present research, a multiple analytical approach was adopted to characterize the allergenic potential of 24 apple varieties released at different ages (pre- and post-green revolution). A specific workflow was set up including protein quantification by means of polyclonal antibodies, immunological analyses with sera of allergic subjects, enzymatic assays, clinical assessments on allergic patients, and gene expression assays on fruit samples. Taken as a whole, the results indicate that most of the less allergenic genotypes were found among those deriving from selection processes carried out prior to the so-called "green revolution".

Development and Application of a Multiplex Real-Time PCR Assay as an Indicator of Potential Allergenicity in Citrus Fruits

The effects of tissue type, harvest maturity, and genetic factors on the expression of genes that related to citrus fruit allergies remain poorly understood. In the present study, a multiplex real-time PCR assay was developed to monitor the expression of citrus allergen genes individually with the advantages of much fewer sample requirements and simultaneously multiple target genes detection. Gene specific primer pairs and Taqman probes of three citrus allergen genes Cit s 1.01, Cit s 2.01, and Cit s 3.01 and the house-keeping gene β-actin were designed based on gene sequence differences. The PCR results showed that differential expression patterns were found during the ripening process. The expression levels of Cit s 3.01 were much higher than those of Cit s 1.01 and Cit s 2.01 in both peel and pulp tissues among 10 citrus cultivars. Data suggested that Kao Phuang Pummelo could be safely consumed with a potential low risk in allergenicity. Considering that assessing allergenicity is one of the tests in food safety, this assay might also facilitate the breeding and production of "allergy-friendly" citrus fruits.

Targeted proteomics: Current status and future perspectives for quantification of food allergens

Allergen levels in fresh and processed foods can vary dynamically. As different sources of foods can cause different types of allergic reactions, the food industry and regulatory bodies urgently require reliable detection and absolute quantitation methods for allergen detection in complex food products to effectively safeguard the food-allergic population. Recent advances of targeted proteomic technologies namely multiple-reaction monitoring (MRM) mass spectrometry (MS) coupled with isotope-labeled internal standard, also known as AQUA peptides offers absolute quantitation of food allergens even at 10ppb level in a multiplex fashion. However, development of successful AQUA-MRM assay relies on a number of pre and post MS criteria. In this review, we briefly describe how allergen levels could potentially change in plant and animal based foods, necessitating the development of a high throughput multiplexed allergen quantification methodology for successful AQUA-MRM assay. We also propose some future strategies that could provide better management of food allergy.

BIOLOGICAL SIGNIFICANCE

Given the rapid increases of food allergenicity, it has become imperative to know absolute allergen levels in foods. This essential information could be the most effective means of protecting humans suffering from allergies. In this review, we emphasize the significance of the absolute quantitation of food allergens using AQUA-MRM approach and discuss the likely critical steps for successful assay development.

First successful reduction of clinical allergenicity of food by genetic modification: Mal d 1-silenced apples cause fewer allergy symptoms than the wild-type cultivar

BACKGROUND

Genetic modification of allergenic foods such as apple has the potential to reduce their clinical allergenicity, but this has never been studied by oral challenges in allergic individuals.

METHODS

We performed oral food challenges in 21 apple-allergic individuals with Elstar apples which had undergone gene silencing of the major allergen of apple, Mal d 1, by RNA interference. Downregulation of Mal d 1 gene expression in the apples was verified by qRT-PCR. Clinical responses to the genetically modified apples were compared to those seen with the wild-type Elstar using a visual analogue scale (VAS).

RESULTS

Gene silencing produced two genetically modified apple lines expressing Mal d 1.02 and other Mal d 1 gene mRNA levels which were extensively downregulated, that is only 0.1-16.4% (e-DR1) and 0.2-9.9% (e-DR2) of those of the wild-type Elstar, respectively. Challenges with these downregulated apple lines produced significantly less intense maximal symptoms to the first dose (Vmax1) than with Elstar (Vmax1 Elstar 3.0 mm vs 0.0 mm for e-DR1, P = 0.017 and 0.0 mm for e-DR2, P = 0.043), as well as significantly less intense mean symptoms per dose (meanV/d) than with Elstar (meanV/d Elstar 2.2 mm vs 0.2 mm for e-DR1, P = 0.017 and 0.0 mm for e-DR2, P = 0.043). Only one subject (5%) remained symptom-free when challenged with the Elstar apple, whereas 43% did so with e-DR1 and 63% with e-DR2.

CONCLUSION

These data show that mRNA silencing of Mal d 1 results in a marked reduction of Mal d 1 gene expression in the fruit and reduction of symptoms when these apples are ingested by allergic subjects. Approximately half of the subjects developed no symptoms whatsoever, and virtually all subjects wished to consume the apple again in the future.

Impact of sulfur and vitamin C on the allergenicity of Mal d 2 from apple (Malus domestica)

Mal d 2 is a minor allergen from apple which shows a high conformational stability due to its eight conserved disulfide bridges. Chemical reduction of disulfide bridges and linearization of Mal d 2 lead to enhanced IgE reactivity in vitro and indicate a higher potential for allergenicity. Since food preservatives such as sulfur and vitamin C are reducing and denaturing agents, their influence on Mal d 2 allergenicity was verified by simulated food processing conditions. The immunoreactivity of purified Mal d 2 was investigated after different treatments in vitro and in vivo using IgG/IgE Western blotting, mediator-releasing cell assay, and skin prick and oral smear tests. The conformational changes of Mal d 2 upon addition of 1% and 5% vitamin C were also monitored by attenuated total reflectance Fourier transform infrared spectroscopy. The results show no positive skin and oral smear test reactivity to native, heated, or vitamin C-treated purified Mal d 2. Furthermore, the results confirm that sulfur in combination with heat treatment can influence the structural integrity and thus the allergenicity of Mal d 2, while vitamin C is too weak as a reducing agent to change allergenicity.

Effects of long-term storage on Mal d 1 content of four apple cultivars with initial low Mal d 1 content

BACKGROUND

Up to 6.6% of adults and 11.5% of children aged between 0 and 6 years are reporting a perceived fruit allergy. In the last group 8.5% perceived reactions against apple. To keep allergic reactions as low as possible and to make apple consumption more tolerable for patients allergic to apple, the Mal d 1 content of four apple cultivars ('Boskoop', 'Elise', 'Pinova', 'Santana' and 'Topaz') were analyzed, to identify apple cultivars with only a low Mal d 1 content. Further, the development of Mal d 1 content of low-allergenic cultivars should be investigated during long-term storage.

RESULTS

The lowest Mal d 1 content was measured for fruits of the cultivar 'Santana' at harvest, followed by 'Pinova' and 'Elise' after storage without 1-MCP. Nearly all fruits treated with 1-MCP had a significantly lower Mal d 1 content than fruits without 1-MCP, except for 'Boskoop' fruits after 44 weeks of storage. Apple cultivars with a low Mal d 1 content are not a cross of 'Golden Delicious' with another cultivar, with the exception of 'Pinova' which is a cultivar from the so-called 'Pi-series', which have a moderate resistance to scab and mildew. First experiments on tomatoes and peanuts have shown a reduction of allergic proteins in older and child generations after transfer of RNA. This reduction is probably based on an alteration of gene expression regulating the synthesis of allergic proteins, leading to changes in protein composition in the fruit.

CONCLUSION

Individuals allergic to apple should choose the described cultivars with relative low Mal d 1 content. If breeders want to breed cultivars with low allergy, they should avoid crossings with 'Golden Delicious'.

Dynamic changes in proteins during apple (Malus x domestica) fruit ripening and storage

A proteomic study, using two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight, was conducted in apple fruit (cv. 'Golden Delicious') starting at 10 days prior to harvest through 50 days in storage. Total protein was extracted using a phenol/sodium dodecyl sulfate protocol. More than 400 protein spots were detected in each gel and 55 differentially expressed proteins (p<0.05) were subjected to matrix-assisted laser desorption/ionization time-of-flight/time-of-flight analysis. Fifty-three of these proteins were finally identified using an apple expressed sequence tag database downloaded from Genome Database for Rosaceae and placed into six categories. The categories and the percentage of proteins placed in each category were stress response and defense (49.0%), energy and metabolism (34.0%), fruit ripening and senescence (5.6%), signal transduction (3.8%), cell structure (3.8%) and protein synthesis (3.8%). Proteins involved in several multiple metabolic pathways, including glycolysis, pentose-phosphate pathway, anti-oxidative systems, photosynthesis and cell wall synthesis, were downregulated, especially during the climacteric burst in respiration and during the senescent stages of fruit development. Proteins classified as allergens or involved in cell wall degradation were upregulated during the ripening process. Some protein spots exhibited a mixed pattern (increasing to maximal abundance followed by a decrease), such as 1-aminocyclopropane-1-carboxylate oxidase, L-ascorbate peroxidase and abscisic acid response proteins. The identification of differentially expressed proteins associated with physiological processes identified in the current study provides a baseline of information for understanding the metabolic processes and regulatory mechanisms that occur in climacteric apple fruit during ripening and senescence.

Early induction of apple fruitlet abscission is characterized by an increase of both isoprene emission and abscisic acid content

Apple (Malus domestica) fruitlet abscission represents an interesting model system to study the early phases of the shedding process, during which major transcriptomic changes and metabolic rearrangements occur within the fruit. In apple, the drop of fruits at different positions within the cluster can be selectively magnified through chemical thinners, such as benzyladenine and metamitron, acting as abscission enhancers. In this study, different abscission potentials were obtained within the apple fruitlet population by means of the above-cited thinners. A metabolomic study was conducted on the volatile organic compounds emitted by abscising fruitlets, allowing for identification of isoprene as an early marker of abscission induction. A strong correlation was also observed between isoprene production and abscisic acid (ABA) levels in the fruit cortex, which were shown to increase in abscising fruitlets with respect to nonabscising ones. Transcriptomic evidence indicated that abscission-related ABA is biologically active, and its increased biosynthesis is associated with the induction of a specific ABA-responsive 9-cis-epoxycarotenoid dioxygenase gene. According to a hypothetical model, ABA may transiently cooperate with other hormones and secondary messengers in the generation of an intrafruit signal leading to the downstream activation of the abscission zone. The shedding process therefore appears to be triggered by multiple interdependent pathways, whose fine regulation, exerted within a very short temporal window by both endogenous and exogenous factors, determines the final destiny of the fruitlets.

A qRT-PCR assay for the expression of all Mal d 1 isoallergen genes

BACKGROUND

A considerable number of individuals suffer from oral allergy syndrome (OAS) to apple, resulting in the avoidance of apple consumption. Apple cultivars differ greatly in their allergenic properties, but knowledge of the causes for such differences is incomplete. Mal d 1 is considered the major apple allergen. For Mal d 1, a wide range of isoallergens and variants exist, and they are encoded by a large gene family. To identify the specific proteins/genes that are potentially involved in the allergy, we developed a PCR assay to monitor the expression of each individual Mal d 1 gene. Gene-specific primer pairs were designed for the exploitation of sequence differences among Mal d 1 genes. The specificity of these primers was validated using both in silico and in vitro techniques. Subsequently, this assay was applied to the peel and flesh of fruits from the two cultivars 'Florina' and 'Gala'.

RESULTS

We successfully developed gene-specific primer pairs for each of the 31 Mal d 1 genes and incorporated them into a qRT-PCR assay. The results from the application of the assay showed that 11 genes were not expressed in fruit. In addition, differential expression was observed among the Mal d 1 genes that were expressed in the fruit. Moreover, the expression levels were tissue and cultivar dependent.

CONCLUSION

The assay developed in this study facilitated the first characterisation of the expression levels of all known Mal d 1 genes in a gene-specific manner. Using this assay on different fruit tissues and cultivars, we obtained knowledge concerning gene relevance in allergenicity. This study provides new perspectives for research on both plant breeding and immunotherapy.

Oral challenges with four apple cultivars result in significant differences in oral allergy symptoms

BACKGROUND

We analyzed the hypoallergenic potential of a recently bred apple selection with unusually low content of Mal d 1, using an oral challenge model with three additional apple cultivars for comparison.

METHODS

Sixty-six birch pollen-allergic individuals with a history of oral allergy syndrome after apple intake were subjected to a double-blind oral provocation with two apple cultivars (B:0654 and 'Discovery'). Thirteen also tested two other apple cultivars ('Ingrid Marie' and 'Gloster'). Three doses were given consecutively, 30 min apart: 10 g without peel, and 10 and 50 g with peel. A final assessment was conducted 30 min after the last intake. Oral symptoms were graded from 0 to 5. Total oral symptom score (TOS) included all scores for each cultivar at all time points.

RESULTS

B:0654 induced significantly higher TOS than 'Discovery' when tested by 66 individuals, in spite of its lower Mal d 1 content. TOS values were higher in females and increased with increasing age of the individuals when challenged with 'Discovery'. Among the 13 individuals who tested all four cultivars, B:0654 produced a higher score after the second dose compared to 'Ingrid Marie'. This was also the case after the third dose compared to 'Ingrid Marie' and 'Gloster', and again 30 min after the last intake compared to each of the other three cultivars, as well as a higher TOS compared to each of the other three cultivars (all p < 0.01).

CONCLUSIONS

Our test was safe and well tolerated, and produced significant differences among the apple cultivars. Contrary to expectations, B:0654 was less well tolerated than the other three cultivars.

The impact of catechin and epicatechin, total phenols and PPO activity on the Mal d 1 content in apple fruit

The most important apple allergen in Central Europe and North America is Mal d 1. Apples are a very important source of secondary plant metabolites like polyphenols in human nutrition. It is known that oxidised phenols can bind proteins. These irreversible bindings can lead to a reduced allergenicity. The most important phenols in apple are epicatechin, catechin and their polymeric structures, which have been identified as substrates of the polyphenoloxidase (PPO). The aim of this study was to analyse the influence of naturally occurring catechin and epicatechin contents in apple on the allergenicity of apple fruits. Fruits of the cultivars 'Elstar', 'Diwa' and 'Boskoop' were harvested and stored for 8 and 12 weeks in a cold-chamber at 2 °C. Mal d 1-, catechin-, epicatechin- and total phenol content as well as the activity of PPO were determined. Correlation analysis showed that naturally occurring catechin as well as epicatechin has no impact on the Mal d 1 content of the tested cultivars: correlation coefficient ranged from -0.203 to 0.501 for the correlation between Mal d 1 and catechin. The results further indicated that the activity of PPO is more important than the content of total phenols to reduce the Mal d 1 level. If there is a high PPO activity, Mal d 1 could be reduced even if the total phenol concentration is low.

LC/MS analysis of proteolytic peptides in wheat extracts for determining the content of the allergen amylase/trypsin inhibitor CM3: influence of growing area and variety

Food allergy from wheat is triggered by several protein classes, such as LTPs, ω5-gliadins and α-amylase/trypsin inhibitors. The latter proteins, belonging to the prolamin superfamily, are mostly involved in baker's asthma, a form of occupational allergy in which the sensitization occurs through the respiratory tract. α-Amylase/trypsin inhibitors were also found to be involved in wheat-related atopic dermatitis. In this work, the allergen Tri a 30 (the CM3 α-amylase/trypsin inhibitor) was quantified in durum wheat salt soluble extracts using a peptidomic approach. CM3 protein identification was confirmed by using LTQ-OrbiTrap analysis on peptides obtained from the enzymatically digested protein separated by gel electrophoresis. Then, marker peptides derived from the protein after enzymatic cleavage of the full wheat extracts were identified by LC-MS/MS. One of them was used as marker for quantitative determination on an UPLC/ESI-MS system by using its isotopically labelled analogue as internal standard, allowing to assess the protein content in the different samples. The CM3 allergenic proteins were found to greatly vary among different cultivation areas.

A proteomic investigation of apple fruit during ripening and in response to ethylene treatment

A proteomic approach employing a two dimensional electrophoresis (2-DE) technique with SYPRO Ruby, a fluorescent stain with improved sensitivity and quantitative accuracy, was performed to separate the total proteins from apple fruit at different stages of ripening and senescence. After imaging and statistical analyses were performed on 2340 spots, a total of 316 spots, or approximately 13.5% of the total protein population, was found to be significantly changed in this study. Of the 316 proteins, 219 spots were only present at a specific ripening stage, while 97 spots were significantly different (p<0.05) throughout fruit ripening and in response to ethylene treatment. From 316 candidate spots, 221 proteins were further identified by liquid chromatography and mass spectrometry analysis with protein sequence and express sequence tag (EST) data searching. Analysis and identification of proteins revealed that apple fruit ripening is associated with increase of abundance of many proteins with functions such as ethylene production, antioxidation and redox, carbohydrate metabolism, oxidative stress, energy, and defense response. Ethylene treatment increased a group of unique proteins that were not present during normal fruit ripening and have not been previously reported. It also reduced some proteins involved in primary metabolism, including those of the last few steps of the glycolytic pathway. This study demonstrated the complexity and dynamic changes of protein profiles of apple fruit during ripening and in response to exogenous ethylene treatment. Identifying and tracking protein changes may allow us to better understand the mechanism of ripening in climacteric fruit.

BIOLOGICAL SIGNIFICANCE

Postharvest physiology and biochemistry has been conducted on apple fruit for many years. Ethylene plays an important role in ripening and senescence in many climacteric fruit. However, little information is available at the proteome level to investigate fruit ripening and effect of ethylene treatment. The significance of this paper is that it is the first study employing 2-DE and fluorescent dye in the investigation of the apple fruit ripening and influence of ethylene treatment. It reveals some significant biological changes in association with these events and demonstrates significant changed proteins under these conditions. Therefore, our study links the biological events with proteomic information and provides detailed peptide information on all identified proteins. Through the function analysis, those significantly changed proteins are also analyzed. These findings from this paper provide not only proteome information on fruit ripening, but also pave the ground for further quantitative studies using SMR to investigate certain proteins and pathways under the hypothesis involved in fruit ripening. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Genomic organisation of the Mal d 1 gene cluster on linkage group 16 in apple

European populations exhibit progressive sensitisation to food allergens, and apples are one of the foods for which sensitisation is observed most frequently. Apple cultivars vary greatly in their allergenic characteristics, and a better understanding of the genetic basis of low allergenicity may therefore allow allergic individuals to increase their fruit intake. Mal d 1 is considered to be a major apple allergen, and this protein is encoded by the most complex allergen gene family. Not all Mal d 1 members are likely to be involved in allergenicity. Therefore, additional knowledge about the existence and characteristics of the different Mal d 1 genes is required. In the present study, we investigated the genomic organisation of the Mal d 1 gene cluster in linkage group 16 of apple through the sequencing of two bacterial artificial chromosome clones. The results provided new information on the composition of this family with respect to the number and orientation of functional and pseudogenes and their physical distances. The results were compared with the apple and peach genome sequences that have recently been made available. A broad analysis of the whole apple genome revealed the presence of new genes in this family, and a complete list of the observed Mal d 1 genes is supplied. Thus, this study provides an important contribution towards a better understanding of the genetics of the Mal d 1 family and establishes the basis for further research on allelic diversity among cultivars in relation to variation in allergenicity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-011-9588-4) contains supplementary material, which is available to authorized users.

Signaling pathways mediating the induction of apple fruitlet abscission

Apple (Malus × domestica) represents an interesting model tree crop for studying fruit abscission. The physiological fruitlet drop occurring in this species can be easily magnified by using thinning chemicals, such as benzyladenine (BA), to obtain fruits with improved quality and marketability. Despite the economic importance of this process, the molecular determinants of apple fruitlet abscission are still unknown. In this research, BA was used to obtain fruitlet populations with different abscission potentials to be analyzed by means of a newly released 30K oligonucleotide microarray. RNAs were extracted from cortex and seed of apple fruitlets sampled over a 4-d time course, during which BA triggers fruit drop, and used for microarray hybridization. Transcriptomic profiles of persisting and abscising fruitlets were tested for statistical association with abscission potential, allowing us to identify molecular signatures strictly related to fruit destiny. A hypothetical model for apple fruitlet abscission was obtained by putting together available transcriptomic and metabolomic data. According to this model, BA treatment would establish a nutritional stress within the tree that is primarily perceived by the fruitlet cortex whose growth is blocked by resembling the ovary growth inhibition found in other species. In weaker fruits, this stress is soon visible also at the seed level, likely transduced via reactive oxygen species/sugar and hormones signaling cross talk, and followed by a block of embryogenesis and the consequent activation of the abscission zone.

Humic substances induce lateral root formation and expression of the early auxin-responsive IAA19 gene and DR5 synthetic element in Arabidopsis

Humic substances (HS) have positive effects on plant physiology, but the molecular mechanisms underlying these events are only partially understood. HS exert auxin-like activity, but data supporting this hypothesis are under debate. To investigate the auxin-like activity of HS, we studied their biological effect on lateral root initiation in Arabidopsis thaliana. To this aim we characterised HS by means of DRIFT and (13)C CP/MAS NMR spectroscopy, and measured their endogenous content of IAA. We then utilised a combination of genetic and molecular approaches to unravel HS auxin activity in the initiation of lateral roots. The data obtained using specific inhibitors of auxin transport or action showed that HS induce lateral root formation mostly through their 'auxin activity'. These findings were further supported by the fact that HS used in this study activated the auxin synthetic reporter DR5::GUS and enhanced transcription of the early auxin responsive gene IAA19.

Apple (Malus domestica L. Borkh.) allergen Mal d 1: effect of cultivar, cultivation system, and storage conditions

It has been reported on the basis of skin prick tests and gene expression studies that apple cultivars differ in their allergenic potential. Only a few studies have tried to measure the amount of the major apple allergen Mal d 1 so far. Mal d 1 belongs to the pathogenesis-related proteins, a family of proteins that are induced by pathogens and environmental stress. Due to cross-reactivity between Bet v 1 and proteins present in several plant-derived foods, birch pollen allergic patients develop food allergies, most frequently to apples. Mal d 1 content was quantified in different apple cultivars, cultivated at the research stations Klein-Altendorf and Bavendorf, dependent on cultivation method and storage conditions by sandwich-ELISA. Apple cultivars differ considerably in their Mal d 1 content. A high variability in Mal d 1 content was determined within one cultivar and between the two locations for the same apple cultivar. In most cases organically cultivated fruit showed lower Mal d 1 content in comparison to fruit from integrated production. At harvest the detected concentration of Mal d 1 was low, but during storage the Mal d 1 content increased significantly.

Peach ( Prunus persica L. Batsch) allergen-encoding genes are developmentally regulated and affected by fruit load and light radiation

The fruits of Rosaceae species may frequently induce allergic reactions in both adults and children, especially in the Mediterranean area. In peach, true allergens and cross-reactive proteins may cause hypersensitive reactions involving a wide diversity of symptoms. Three known classes of allergenic proteins, namely, Pru p 1, Pru p 3, and Pru p 4, have been reported to be mostly involved, but an exhaustive survey of the proteins determining the overall allergenic potential, their biological functions, and the factors affecting the expression of the related genes is still missing. In the present study, the expression profiles of some selected genes encoding peach allergen isoforms were studied during fruit growth and development and upon different fruit load and light radiation regimens. The results indicate that the majority of allergen-encoding genes are expressed at their maximum during the ripening stage, therefore representing a potential risk for peach consumers. Nevertheless, enhancing the light radiation and decreasing the fruit load achieved a reduction of the transcription rate of most genes and a possible decrease of the overall allergenic potential at harvest. According to these data, new growing practices could be set up to obtain hypoallergenic peach fruits and eventually combined with the cultivation of hypoallergenic genotypes to obtain a significant reduction of the allergenic potential.

Genomic characterization of putative allergen genes in peach/almond and their synteny with apple

Background

Fruits from several species of the Rosaceae family are reported to cause allergic reactions in certain populations. The allergens identified belong to mainly four protein families: pathogenesis related 10 proteins, thaumatin-like proteins, lipid transfer proteins and profilins. These families of putative allergen genes in apple (Mal d 1 to 4) have been mapped on linkage maps and subsequent genetic study on allelic diversity and hypoallergenic traits has been carried out recently. In peach (Prunus persica), these allergen gene families are denoted as Pru p 1 to 4 and for almond (Prunus dulcis)Pru du 1 to 4. Genetic analysis using current molecular tools may be helpful to establish the cause of allergenicity differences observed among different peach cultivars. This study was to characterize putative peach allergen genes for their genomic sequences and linkage map positions, and to compare them with previously characterized homologous genes in apple (Malus domestica).

Results

Eight Pru p/du 1 genes were identified, four of which were new. All the Pru p/du 1 genes were mapped in a single bin on the top of linkage group 1 (G1). Five Pru p/du 2 genes were mapped on four different linkage groups, two very similar Pru p/du 2.01 genes (A and B) were on G3, Pru p/du 2.02 on G7,Pru p/du 2.03 on G8 and Pru p/du 2.04 on G1. There were differences in the intron and exon structure in these Pru p/du 2 genes and in their amino acid composition. Three Pru p/du 3 genes (3.01–3.03) containing an intron and a mini exon of 10 nt were mapped in a cluster on G6. Two Pru p/du 4 genes (Pru p/du 4.01 and 4.02) were located on G1 and G7, respectively. The Pru p/du 1 cluster on G1 aligned to the Mal d 1 clusters on LG16; Pru p/du 2.01A and B on G3 to Mal d 2.01A and B on LG9; the Pru p/du 3 cluster on G6 to Mal d 3.01 on LG12; Pru p/du 4.01 on G1 to Mal d 4.03 on LG2; and Pru p/du 4.02 on G7 to Mal d 4.02 on LG2.

Conclusion

A total of 18 putative peach/almond allergen genes have been mapped on five linkage groups. Their positions confirm the high macro-synteny between peach/almond and apple. The insight gained will help to identify key genes causing differences in allergenicity among different cultivars of peach and other Prunus species.

Assessment of allelic diversity in intron-containing Mal d 1 genes and their association to apple allergenicity

BACKGROUND

Mal d 1 is a major apple allergen causing food allergic symptoms of the oral allergy syndrome (OAS) in birch-pollen sensitised patients. The Mal d 1 gene family is known to have at least 7 intron-containing and 11 intronless members that have been mapped in clusters on three linkage groups. In this study, the allelic diversity of the seven intron-containing Mal d 1 genes was assessed among a set of apple cultivars by sequencing or indirectly through pedigree genotyping. Protein variant constitutions were subsequently compared with Skin Prick Test (SPT) responses to study the association of deduced protein variants with allergenicity in a set of 14 cultivars.

RESULTS

From the seven intron-containing Mal d 1 genes investigated, Mal d 1.01 and Mal d 1.02 were highly conserved, as nine out of ten cultivars coded for the same protein variant, while only one cultivar coded for a second variant. Mal d 1.04, Mal d 1.05 and Mal d 1.06 A, B and C were more variable, coding for three to six different protein variants. Comparison of Mal d 1 allelic composition between the high-allergenic cultivar Golden Delicious and the low-allergenic cultivars Santana and Priscilla, which are linked in pedigree, showed an association between the protein variants coded by the Mal d 1.04 and -1.06A genes (both located on linkage group 16) with allergenicity. This association was confirmed in 10 other cultivars. In addition, Mal d 1.06A allele dosage effects associated with the degree of allergenicity based on prick to prick testing. Conversely, no associations were observed for the protein variants coded by the Mal d 1.01 (on linkage group 13), -1.02, -1.06B, -1.06C genes (all on linkage group 16), nor by the Mal d 1.05 gene (on linkage group 6).

CONCLUSION

Protein variant compositions of Mal d 1.04 and -1.06A and, in case of Mal d 1.06A, allele doses are associated with the differences in allergenicity among fourteen apple cultivars. This information indicates the involvement of qualitative as well as quantitative factors in allergenicity and warrants further research in the relative importance of quantitative and qualitative aspects of Mal d 1 gene expression on allergenicity. Results from this study have implications for medical diagnostics, immunotherapy, clinical research and breeding schemes for new hypo-allergenic cultivars.