A haustorial-expressed lytic polysaccharide monooxygenase from the cucurbit powdery mildew pathogen Podosphaera xanthii contributes to the suppression of chitin-triggered immunity.

Podosphaera xanthii is the main causal agent of cucurbit powdery mildew and a limiting factor of crop productivity. The lifestyle of this fungus is determined by the development of specialized parasitic structures inside epidermal cells, termed haustoria, that are responsible for the acquisition of nutrients and the release of effectors. A typical function of fungal effectors is the manipulation of host immunity, for example the suppression of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). Chitin is a major component of fungal cell walls, and chitin oligosaccharides are well-known PAMP elicitors. In this work, we examined the role of PHEC27213, the most highly expressed, haustorium-specific effector candidate of P. xanthii. According to different computational predictions, the protein folding of PHEC27213 was similar to that of lytic polysaccharide monooxygenases (LPMOs) and included a conserved histidine brace; however, PHEC27213 had low sequence similarity with LPMO proteins and displayed a putative chitin-binding domain that was different from the canonical carbohydrate-binding module. Binding and enzymatic assays demonstrated that PHEC27213 was able to bind and catalyse colloidal chitin, as well as chitooligosaccharides, acting as an LPMO. Furthermore, RNAi silencing experiments showed the potential of this protein to prevent the activation of chitin-triggered immunity. Moreover, proteins with similar features were found in other haustorium-forming fungal pathogens. Our results suggest that this protein is a new fungal LPMO that catalyses chitooligosaccharides, thus contributing to the suppression of plant immunity during haustorium development. To our knowledge, this is the first mechanism identified in the haustorium to suppress chitin signalling.

Medicinal bioactivites and allergenic properties of pumpkin seeds: review upon a pediatric food anaphylaxis case report.

SUMMARY: Food allergy to pumpkin seed is considered very rare, and only some isolated case reports have so far been published. We report here a case of food anaphylaxis to pumpkin seed in an eight-year-old boy, who tolerated all other edible seeds, peanut and tree nuts, as well as pulp of different kinds of pumpkins and other fruits of the Cucurbitaceae family. From this observation, a review of the botanical, historical, medicinal and allergenic aspects of pumpkin and its seeds is proposed. With the advent of diets rich in omega-3 and omega-6 polyunsaturated fatty acids, edible seeds like pumpkin seed have been incorporated in the modern diet. Their incremental use in the food-processing industry might contribute to an increase in food allergy to pumpkin seed in the future.

Disease interactions in a shared host plant: effects of pre-existing viral infection on cucurbit plant defense responses and resistance to bacterial wilt disease.

Both biotic and abiotic stressors can elicit broad-spectrum plant resistance against subsequent pathogen challenges. However, we currently have little understanding of how such effects influence broader aspects of disease ecology and epidemiology in natural environments where plants interact with multiple antagonists simultaneously. In previous work, we have shown that healthy wild gourd plants (Cucurbita pepo ssp. texana) contract a fatal bacterial wilt infection (caused by Erwinia tracheiphila) at significantly higher rates than plants infected with Zucchini yellow mosaic virus (ZYMV). We recently reported evidence that this pattern is explained, at least in part, by reduced visitation of ZYMV-infected plants by the cucumber beetle vectors of E. tracheiphila. Here we examine whether ZYMV-infection may also directly elicit plant resistance to subsequent E. tracheiphila infection. In laboratory studies, we assayed the induction of key phytohormones (SA and JA) in single and mixed infections of these pathogens, as well as in response to the feeding of A. vittatum cucumber beetles on healthy and infected plants. We also tracked the incidence and progression of wilt disease symptoms in plants with prior ZYMV infections. Our results indicate that ZYMV-infection slightly delays the progression of wilt symptoms, but does not significantly reduce E. tracheiphila infection success. This observation supports the hypothesis that reduced rates of wilt disease in ZYMV-infected plants reflect reduced visitation by beetle vectors. We also documented consistently strong SA responses to ZYMV infection, but limited responses to E. tracheiphila in the absence of ZYMV, suggesting that the latter pathogen may effectively evade or suppress plant defenses, although we observed no evidence of antagonistic cross-talk between SA and JA signaling pathways. We did, however, document effects of E. tracheiphila on induced responses to herbivory that may influence host-plant quality for (and hence pathogen acquisition by) cucumber beetles.

A case of allergy to zucchini.

A case of mono-sensitization to a heat- and pepsin-stable allergen in zucchini is described.

Identification of Cucumisin (Cuc m 1), a subtilisin-like endopeptidase, as the major allergen of melon fruit.

BACKGROUND: Allergenic components in melon extracts have not been described in spite of the fact that melon (Cucumis melo) is a frequent allergy-eliciting fruit. The aim of this study was to evaluate allergenic components in melon extract and to report the identification of cucumisin as a major melon allergen. MATERIALS AND METHODS: Sera from 35 patients allergic to melon were selected on the basis of clinical symptoms, skin prick tests and oral challenge test. Allergenic components were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting. Molecular characterization of IgE-binding bands was performed by N-terminal amino acid sequencing. RESULTS: More than 10 IgE-binding bands, between 10 and 80 kDa, were identified in melon extract. Out of them, four IgE-binding bands were major allergens: 14 kDa, 36 kDa, 54 kDa and 67 kDa. These major allergens, except 14 kDa band, showed the same N-terminal sequence: T-T-R-S-W-D-F-L. Research conducted with protein databases identified this N-terminal sequence as cucumisin, an alkaline serine protease, which shares structural homology with microbial subtilisin. The molecular mass of the identified bands corresponds with different molecular forms of cucumisin produced during the processing or degradation of the enzyme: 67 kDa native cucumisin, 54 kDa mature cucumisin and 36 kDa NH2-terminal cucumisin fragment. CONCLUSION: Cucumisin (Cuc m 1) and several N-terminal cucumisin fragments are the major allergens of melon. The ubiquitous distribution of this protein family (cucumisin-like proteases) in many plant species and its high structural similarity suggest its potential role as a new panallergen in plant foods.