Production of the allergenic protein Alt a 1 by Alternaria isolates from working environments

Assessment of Resistance Induction in Mungbean against Alternaria alternata through RNA Interference

A comprehensive survey of mungbean-growing areas was conducted to observe leaf spot disease caused by Alternaria alternata. Alternaria leaf spot symptoms were observed on the leaves. Diversity of 50 genotypes of mungbean was assessed against A. alternata and data on pathological traits was subjected to cluster analysis. The results showed that genotypes of mungbean were grouped into four clusters based on resistance parameters under the influence of disease. The principal component biplot demonstrated that all the disease-related parameters (% disease incidence, % disease intensity, lesion area, and % of infection) were strongly correlated with each other. Alt a 1 gene that is precisely found in Alternaria species and is responsible for virulence and pathogenicity. Alt a 1 gene was amplified using gene specific primers. The isolated pathogen produced similar symptoms when inoculated on mungbean and tobacco. The sequence analysis of the internal transcribed spacer (ITS) region, a 600 bp fragment amplified using specific primers, ITS1 and ITS2 showed 100% identity with A. alternata. Potato virus X (PVX) -based silencing vector expressing Alt a 1 gene was constructed to control this pathogen through RNA interference in tobacco. Out of 50 inoculated plants, 9 showed delayed onset of disease. Furthermore, to confirm our findings at molecular level semi-quantitative reverse transcriptase polymerase chain reaction was used. Both phenotypic and molecular investigation indicated that RNAi induced through the VIGS vector was efficacious in resisting the pathogen in the model host, Tobacco (Nicotiana tabacum). To the best of our knowledge, this study has been reported for the first time.

Identification and genetic diversity of Alternaria species recovered from the air of Ahvaz city, the Southwestern part of Iran

The Alternaria genus has pathogenic, endophytic, and saprobic characteristics. Alternaria genus causes respiratory diseases, fungal allergenicity and the production of mycotoxin in food. Ahvaz city is one of the areas where the presence of dust and high humidity cause the growth and spread of fungal species in the air. Identification of Alternaria species is difficult based on morphology solely. For the first time in Ahvaz, the classification of this fungus was performed using ITS region, alta1 gene, and morphology. For the identification of Alternaria isolates in the Ahvaz city air using morphological and molecular characteristics, potato dextrose agar (PDA) media were used to culture 40 Alternaria isolates recovered from the Ahvaz city air. Afterward, the appearance of the colonies was examined. The DNAs of the isolates were extracted and amplified using the specific primers of the ITS and, Alt a1 regions. The amplified DNA products were sequenced. Then, they were compared with the sequences in the NCBI GeneBank. Based on the morphological results, the isolates included four different species and A. alternata had the highest frequency. Alt a1 gene was present in all the isolates of Alternaria species recovered in our research. Finally, identifying the varieties of Alternaria species based on morphological characteristics as well as ITS or Alt a1 regions is useful but difficult.

Occupational Exposure to β-d-Glucans, Mould Allergens, Endotoxins and Cultivable Fungi in Pig Farms

Airborne concentrations of organic dust on animal farms are known to be very high. This dust is partly composed of microorganisms such as bacteria, fungi and their components [endotoxins, (1→3)-β-d-glucans, mould allergens, mycotoxins], recognised as being responsible for numerous health effects. Several cross-sectional studies have measured levels of airborne bacteria, fungi and endotoxins on pig farms. However, the temporal dynamics of organic dust's components throughout the year have rarely been assessed, and airborne concentrations of (1→3)-β-d-glucans and mould allergens remain poorly understood in these work environments. This longitudinal, four-season study measured cultivable fungi, endotoxins, (1→3)-β-d-glucans, Aspergillus versicolor (AveX), Aspergillus fumigatus (Asp f1) and Alternaria sp (Alt a1) allergens on 31 pig farms in Switzerland. Results showed that exposure to AveX occurred in all four seasons. Total mean airborne concentration of endotoxins were between 3 and 4 times higher than the Swiss recommended limit value of 1000 EU m-3 and mean airborne concentrations of fungi were between 30 and 50 times higher than the Swiss recommended limit value of 1000 cfu m-3. Finally, accumulations of faecal matter on floors, humidity and dusty pathways were associated with increased concentrations of (1→3)-β-d-glucans. In conclusion, pig farmers require better information about biological occupational risks, and measures to improve air quality should be implemented, especially in winter.

Gene profiling and expression of major allergen Alt a 1 in Alternaria alternata and related members of the Pleosporaceae family

BACKGROUND

Members of the Pleosporaceae family are known as important sources of airborne allergens which are responsible for asthma and allergic diseases.

AIMS

The purpose of this study was to investigate the gene profiling and expression pattern of Alt a 1 in Alternaria alternata and other members of the Pleosporaceae family including Stemphylium botryosum, Ulocladium chartarum, Curvularia lunata, Cladosporium cladosporioides, and Epicoccum nigrum.

METHODS

Alternaria alternata and related genera were cultured on Czapek-Dox broth medium at 25°C for 21 days. The presence of Alt a 1 was assessed in fungal culture filtrates by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and then confirmed by immunoblot analysis. Real-time PCR was carried out for quantitation of the Alt a 1 gene encoding corresponding protein at the transcriptional level using cDNA prepared from fungal RNA.

RESULTS

SDS-PAGE showed protein bands ranging from 14 to 100kDa. A 14kDa band corresponding to Alt a 1 was present in A. alternata, S. botryosum and U. chartarum. The gene expression of Alt a 1 was reported in A. alternata and some other related genera. The C_t mean value recorded for A. alternata strains ranged from 24.70 to 27.84 while it was in the range 23.62-32.09 for other related taxa. No apparent transcription or expression was revealed in C. cladosporioides.

CONCLUSIONS

The presence and efficient expression of Alt a 1 gene in A. alternata and other related taxa indicate that Alt a 1 protein is a major component of the secretory machinery of Pleosporaceae family members, and it may play a crucial role in its allergenicity.

Temporal variability in the allergenicity of airborne Alternaria spores

The concentration of fungal spores in the air is traditionally considered as a proxy of allergen exposure. However, in vitro experiments have shown that the allergenicity of Alternaria spores varies depending on ecophysiological and developmental factors. Despite the potential clinical significance of these findings, it has never been verified in outdoor environments. This study, therefore, aims to investigate variability in the amount of the major allergen (Alt a 1) released from Alternaria spores in outdoor air. During the 3-year monitoring study (2014-2016), the median seasonal allergenicity of Alternaria spores exceeded 8.6 × 10-3 pg Alt a 1/spore. The most allergenic spores were collected during the driest and the most polluted season (with respect to seasonal concentrations of ozone, sulphur dioxide, and particulate matter). Within the season, daily spore allergenicity ranged from 2.4 to 34.7 × 10-3 pg Alt a 1/spore (5th-95th percentile). No repeatable effects of weather and pollution on short-term variations in Alternaria spore allergenicity were found. However, during the episodes when high-potency spores were recorded, the air masses arrived from eastern directions. Contrary, the spores with the lowest allergenicity were related to western winds. This suggests that factors such as source area (habitat types) and species diversity could be responsible for the varying exposure to Alternaria allergens. Our findings show that high and low-potency spores are recorded in the air; therefore, the airborne concentrations of fungal spores alone may not be sufficient to provide allergy sufferers and healthcare professionals with information about allergen exposure.

Innate Immunity Induced by the Major Allergen Alt a 1 From the Fungus Alternaria Is Dependent Upon Toll-Like Receptors 2/4 in Human Lung Epithelial Cells

Allergens are molecules that elicit a hypersensitive inflammatory response in sensitized individuals and are derived from a variety of sources. Alt a 1 is the most clinically important secreted allergen of the ubiquitous fungus, Alternaria. It has been shown to be a major allergen causing IgE-mediated allergic response in the vast majority of Alternaria-sensitized individuals. However, no studies have been conducted in regards to the innate immune eliciting activities of this clinically relevant protein. In this study, recombinant Alt a 1 was produced, purified, labeled, and incubated with BEAS-2B, NHBE, and DHBE human lung epithelial cells. Alt a 1 elicited strong induction of IL-8, MCP-1, and Gro-a/b/g. Using gene-specific siRNAs, blocking antibodies, and chemical inhibitors such as LPS-RS, it was determined that Alt a 1-induced immune responses were dependent upon toll-like receptors (TLRs) 2 and 4, and the adaptor proteins MYD88 and TIRAP. Studies utilizing human embryonic kidney cells engineered to express single receptors on the cell surface such as TLRs, further confirmed that Alt a 1-induced innate immunity is dependent upon TLR4 and to a lesser extent TLR2.

Secreted protein extract analyses present the plant pathogen Alternaria alternata as a suitable industrial enzyme toolbox

Lignocellulosic plant biomass is the most abundant carbon source in the planet, which makes it a potential substrate for biorefinery. It consists of polysaccharides and other molecules with applications in pharmaceutical, food and feed, cosmetics, paper and textile industries. The exploitation of these resources requires the hydrolysis of the plant cell wall, which is a complex process. Aiming to discover novel fungal natural isolates with lignocellulolytic capacities, a screening for feruloyl esterase activity was performed in samples taken from different metal surfaces. An extracellular enzyme extract from the most promising candidate, the natural isolate Alternaria alternata PDA1, was analyzed. The feruloyl esterase activity of the enzyme extract was characterized, determining the pH and temperature optima (pH 5.0 and 55-60 °C, respectively), thermal stability and kinetic parameters, among others. Proteomic analyses derived from two-dimensional gels allowed the identification and classification of 97 protein spots from the extracellular proteome. Most of the identified proteins belonged to the carbohydrates metabolism group, particularly plant cell wall degradation. Enzymatic activities of the identified proteins (β-glucosidase, cellobiohydrolase, endoglucanase, β-xylosidase and xylanase) of the extract were also measured. These findings confirm A. alternata PDA1 as a promising lignocellulolytic enzyme producer.

SIGNIFICANCE

Although plant biomass is an abundant material that can be potentially utilized by several industries, the effective hydrolysis of the recalcitrant plant cell wall is not a straightforward process. As this hydrolysis occurs in nature relying almost solely on microbial enzymatic systems, it is reasonable to infer that further studies on lignocellulolytic enzymes will discover new sustainable industrial solutions. The results included in this paper provide a promising fungal candidate for biotechnological processes to obtain added value from plant byproducts and analogous substrates. Moreover, the proteomic analysis of the secretome of a natural isolate of Alternaria sp. grown in the presence of one of the most used vegetal substrates on the biofuels industry (sugar beet pulp) sheds light on the extracellular enzymatic machinery of this fungal plant pathogen, and can be potentially applied to developing new industrial enzymatic tools. This work is, to our knowledge, the first to analyze in depth the secreted enzyme extract of the plant pathogen Alternaria when grown on a lignocellulosic substrate, identifying its proteins by means of MALDI-TOF/TOF mass spectrometry and characterizing its feruloyl esterase, cellulase and xylanolytic activities.

Alternaria alternata (Fr.) Keissl with mutation G143A in the Cyt b gene is the source of a difficult-to-control allergen

The saprotrophic fungus Alternaria alternata is widespread in the agro-environment and produces more than ten allergenic proteins, mostly protein Alt a 1. The frequency of the Alt a 1 gene was analyzed in a group of A. alternata isolates from winter wheat kernels obtained in Poland, and the effectiveness of various fungicides targeting the pathogen was evaluated. The Alt a 1 gene was identified in four of the seven tested isolates. A. alternata colonized 35.67% kernels on average, but its frequency increased in stored grain where the presence of epiphytes was noted on 23.09 to 51.38% kernels, and endophytes-in 26.21 to 42.01% of kernels. The efficacy of field-applied fungicides did not exceed 50%, despite the fact that A. alternata is highly sensitive to propiconazole, fenpropimorph, and tebuconazole under in vitro conditions. The analyzed isolates were characterized by limited sensitivity to azoxystrobin (EC₅₀ ranged from 0.505 to 1.350 μg cm^-3) due to a mutation at codon 143 of the CYT b gene, responsible for resistance to quinone outside inhibitor fungicides, which was noted in all isolates. The spread of A. alternata can be effectively controlled with suitable fungicides and by monitoring the prevalence of pathogenic isolates in the environment.

The Incidence of Alternaria Species Associated with Infected Sesamum indicum L. Seeds from Fields of the Punjab, Pakistan

Sesame (Sesamum indicum) is an important oil seed crop of Asia. Yields can be negatively impacted by various factors, including disease, particularly those caused by fungi which create problems in both production and storage. Foliar diseases of sesame such as Alternaria leaf blight may cause significant yield losses, with reductions in plant health and seed quality. The work reported here determined the incidence of Alternaria species infecting sesame seeds grown in the Punjab, Pakistan. A total of 428 Alternaria isolates were obtained from 105 seed samples and grouped into 36 distinct taxonomic groups based on growth pattern and morphological characters. Isolation frequency and relative density of surface sterilized and non-surface sterilized seeds showed that three isolates (A13, A47 and A215) were the most common morphological groups present. These isolates were further identified using sequencing of the Internal Transcribed Spacer (ITS) region of ribosomal DNA (rDNA) and the Alternaria major allergen gene (Alt a 1). Whilst ITS of rDNA did not resolve the isolates into Alternaria species, the Alt a 1 sequences exhibited > 99% homology with Alternaria alternata (KP123850.1) in GenBank accessions. The pathogenicity and virulence of these isolates of Alternaria alternata was confirmed in inoculations of sesame plants resulting in typical symptoms of leaf blight disease. This work confirms the identity of a major source of sesame leaf blight in Pakistan which will aid in formulating effective disease management strategies.

Validation of reference genes for normalization of gene expression by qRT-PCR in a resveratrol-producing entophytic fungus (Alternaria sp. MG1)

Alternaria sp. MG1, an endophytic fungus isolated from Vitis vinifera, can independently produce resveratrol, indicating that this species contains the key genes for resveratrol biosynthesis. Identification of these key genes is essential to understand the resveratrol biosynthesis pathway in this strain, which is currently unknown in microorganisms. qRT-PCR is an efficient and widely used method to identify the key genes related to unknown pathways at the level of gene expression. Verification of stable reference genes in this strain is essential for qRT-PCR data normalization, although results have been reported for other Alternaria sp. strains. In this study, nine candidate reference genes including TUBA, EF1, EF2, UBC, UFD, RPS5, RPS24, ACTB and 18S were evaluated for expression stability in a diverse set of six samples representing different growth periods. We compared cell culture conditions and an optimized condition for resveratrol production. The comparison of the results was performed using four statistical softwares. A combination of TUBA and EF1 was found to be suitable for normalization of Alternaria sp. MG1 in different developmental stages, and 18S was found to be the least stable. The reference genes verified in this study will facilitate further research to explore gene expression and molecular mechanisms as well as the improvement of secondary metabolite yields in Alternaria sp. MG1. To our knowledge, this is the first validation of reference genes in Alternaria with the capability to produce resveratrol. Additionally, these results provide useful guidelines for the selection of reference genes in other Alternaria species.

Characterisation of a flavonoid ligand of the fungal protein Alt a 1

Spores of pathogenic fungi are virtually ubiquitous and cause human disease and severe losses in crops. The endophytic fungi Alternaria species produce host-selective phytotoxins. Alt a 1 is a strongly allergenic protein found in A. alternata that causes severe asthma. Despite the well-established pathogenicity of Alt a 1, the molecular mechanisms underlying its action and physiological function remain largely unknown. To gain insight into the role played by this protein in the pathogenicity of the fungus, we studied production of Alt a 1 and its activity in spores. We found that Alt a 1 accumulates inside spores and that its release with a ligand is pH-dependent, with optimum production in the 5.0-6.5 interval. The Alt a 1 ligand was identified as a methylated flavonoid that inhibits plant root growth and detoxifies reactive oxygen species. We also found that Alt a 1 changes its oligomerization state depending on the pH of the surrounding medium and that these changes facilitate the release of the ligand. Based on these results, we propose that release of Alt a 1 should be a pathogenic target in approaches used to block plant defenses and consequently to favor fungal entry into the plant.