KIRA1 and ORESARA1 terminate flower receptivity by promoting cell death in the stigma of Arabidopsis

Flowers have a species-specific functional life span that determines the time window in which pollination, fertilization and seed set can occur. The stigma tissue plays a key role in flower receptivity by intercepting pollen and initiating pollen tube growth toward the ovary. In this article, we show that a developmentally controlled cell death programme terminates the functional life span of stigma cells in Arabidopsis. We identified the leaf senescence regulator ORESARA1 (also known as ANAC092) and the previously uncharacterized KIRA1 (also known as ANAC074) as partially redundant transcription factors that modulate stigma longevity by controlling the expression of programmed cell death-associated genes. KIRA1 expression is sufficient to induce cell death and terminate floral receptivity, whereas lack of both KIRA1 and ORESARA1 substantially increases stigma life span. Surprisingly, the extension of stigma longevity is accompanied by only a moderate extension of flower receptivity, suggesting that additional processes participate in the control of the flower's receptive life span

Interactions and reactions between different types of proteins and their importance in wheat-based model and noodle systems

Proteins impact the structural quality of wheat-based food products. The main proteins of wheat are gluten proteins. These consist of monomeric gliadin and polymeric glutenin. They form a network when wheat flour is mixed with water and polymerize even further upon heating, mainly through disulfide bond formation. Gluten network formation is responsible for inter alia the visco-elastic properties of wheat-based dough, the crumb structure of bread and the cooking properties of pasta or noodles. In many wheat-based food products including some cake, cookie, pancake, waffle, bread, tortilla, pasta and noodle systems wheat proteins coexist with globular proteins from egg, soy or milk. Under specific conditions, different proteins interact or react differently than similar proteins. Literature provides examples of changes in food systems as a result of the impact of different types of proteins on each other which are called “co-protein effects”. These can be either synergistic or antagonistic. For example, when speaking about polymerization of proteins, a synergistic (or antagonistic) effect occurs when more (or less) proteins polymerize in mixtures of two proteins than expected based on observations made with separate proteins. Even though interactions and reactions between proteins impact on food systems, the occurrence of co-protein effects is not well understood. This is unfortunate as more fundamental knowledge on the impact of egg, soy or whey proteins on protein network formation in wheat dough and later processing steps, can open perspectives for creating cost-effective food products with enhanced properties. Against the above background, this doctoral work aimed to study interactions and reactions between different types of proteins and their importance for wheat-based food products. In a first part, the impacts of different co-solvents in extraction and elution media on non-size effects in size-exclusion chromatography were studied. Most techniques for studying proteins require them to be soluble. Egg, soy and whey proteins are soluble in water or salt solutions while wheat gluten proteins are not. Co-solvents are necessary to solubilize gluten proteins but these in some cases interact with size exclusion resins altering the separation and apparent molecular weight distribution. An in-depth study indicated that the use of sodium dodecyl sulfate (SDS) containing medium as extraction and elution medium minimized non-size effects. A method for studying heat-induced covalent network formation of different protein types was developed. It is based on their loss in extractability in SDS containing medium and changes in molecular weight distributions during heating. In a second part, heat-induced polymerization (100 °C) was studied in model systems for isolated wheat, egg, soy and whey protein (fractions) in water or aqueous ethanol. Proteins polymerized to a larger extent in water than in aqueous ethanol. The results of isolated protein (fractions) were compared with those of their mixtures with gluten proteins. A synergistic co-protein effect was observed in some cases, namely when proteins polymerized to a larger extent in their mixture with gluten than what would be expected based on the weight-averaged results of the isolated proteins. Phase-separation of proteins did not limit the occurrence of synergistic co-protein effects. Both in water and aqueous ethanol different protein types impacted each other’s denaturation and/or polymerization. A model was developed to predict co-protein effects between globular and wheat gluten proteins during heating at 100 °C in water. The amount of hydrophobic protein sites and accessible sulfhydryl groups of unfolded globular proteins are key parameters determining co-protein effects in their mixtures with gluten. In a third part, non-covalent interactions were found to dominate the properties of fresh noodles while covalent cross-links and hydrogen bonds mainly determined the properties of cooked noodles. Ionic and hydrophobic interactions had some impact on cooked noodles but probably by hindering covalent network formation. The addition of whole egg positively impacted the properties of wheat-based noodles even more than that of egg white and egg yolk. Protein (fractions) with a high amount of accessible sulfhydryl groups rapidly initiated disulfide bond formation which reduced the flexibility of the protein network to cope with starch swelling during cooking. However, insufficient cross-linking during cooking lead to noodles with a weak structure and high levels of material leaching into the cooking water. In conclusion, different types of protein can impact each other’s network formation through non-covalent interactions and covalent cross-links. High amounts of accessible sulfhydryl groups and hydrophobic protein sites in globular protein enhance the rate of gluten protein incorporation in the protein network. However, fast and excessive polymerization can reduce noodle quality. An optimal extent of protein network formation is necessary in wheat-based noodles to obtain superior quality. Addition of whole egg, soy glycinin or bovine serum albumin enhanced the properties of cooked noodles.nrpages: 178status: publishe

Denaturation and covalent network formation of wheat gluten, globular proteins and mixtures thereof in aqueous ethanol and water

Food processing often includes heating and/or exposure to solvents as unit operations. Here, the impact of heating at 100 °C in water or aqueous ethanol [10 or 50% (v/v)] on denaturation and covalent network formation of three model proteins [bovine serum albumin (BSA), soy glycinin and wheat gliadin] was examined. Already at room temperature 50% (v/v) ethanol induced disulfide cross-linking between BSA proteins. Increased ethanol concentrations reduced heat-induced polymerization of soy glycinin and wheat gliadin. The use of aqueous ethanol limited the extent of β-elimination, sulfhydryl-disulfide exchange reactions and sulfhydryl oxidation. Gliadin and soy glycinin had higher colloidal stability in 50% (v/v) ethanol than in water. The conformation of BSA and soy glycinin already changed at lower temperatures in 50% (v/v) ethanol than in water. In all media, different proteins influenced each other’s denaturation and/or polymerization. During heating in water but not in 50% (v/v) ethanol, gliadin-BSA and gliadin-soy glycinin mixtures polymerized more than expected than the isolated proteins. Thus, phase-separation of proteins did not limit intermolecular disulfide formation. Pretreatment of proteins with aqueous ethanol did not substantially influence their subsequent polymerization during prolonged heating in water. However, ethanol pretreatment of gluten impacted heat-induced polymerization of BSA in gluten-BSA mixtures.status: publishe

Impact of extraction and elution media on separation of proteins by size exclusion high performance liquid chromatography

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Identification of lanthionine and lysinoalanine in heat-treated wheat gliadin and bovine serum albumin using tandem mass spectrometry with higher-energy collisional dissociation

The present manuscript reports on the identification of various dehydroamino acid-derived bonds and cross-links resulting from thermal treatment (excess water, 240 min, 130 °C) of two model food proteins, bovine serum albumin, and wheat gliadin. S-Carbamidomethylated tryptic and chymotryptic digests of unheated (control) and heated serum albumin and gliadin, respectively, were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC–ESI–MS/MS) with higher-energy collisional dissociation (HCD). Heat-induced β-elimination of cystine, serine and threonine, and subsequent Michael addition of cysteine and lysine to dehydroalanine and 3-methyl-dehydroalanine were demonstrated. Lanthionine, lysinoalanine, 3-methyl-lanthionine, and 3-methyl-lysinoalanine were identified. The detection of inter-chain lanthionine in both bovine serum albumin and wheat gliadin suggests the significance of these cross-links for food texture.status: publishe

Impact of hydrothermal treatment on quinoa protein network formation

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Globular proteins influence protein network formation in and quality of wheat-based noodles

To address the demand for healthy protein-rich food, nutritious protein sources (e.g. egg, soy or milk) are sometimes included in wheat noodle recipes. Interactions and reactions between different types of proteins can impact complex food systems and are referred to as co-protein effects. They can be synergistic or antagonistic. The relation between protein characteristics, protein network formation and wheat noodle properties was studied. Globular model protein such as bovine serum albumin (BSA), soy glycinin, hen egg ovalbumin, S-ovalbumin and lysozyme were included in the recipe of wheat-based noodles. The characteristics of these non-wheat proteins impacted the type, rate and extent of protein network formation during noodle dough preparation and boiling, and thereby the properties of fresh (i.e. raw) and boiled noodles. None of the added proteins enhanced the properties of fresh noodles. BSA and soy glycinin enhanced Kieffer-rig extensibility parameters of cooked noodles. Addition of ovalbumin or S-ovalbumin led to excessive protein polymerization in cooked noodles and lowered their extensibility and cooking quality. Inclusion of lysozyme lowered the rate and extent of polymerization during boiling. Experiments in which salt, olive oil or urea were added in the recipe showed that non-covalent interactions dominate the properties of fresh noodles while covalent cross-links and hydrogen bonds mainly impact the properties of boiled noodles. In addition, synergistic or antagonistic co-protein effects of binary proteins mixtures in model systems were linked to the rate/extent of polymerization, optimal cooking time, cooking quality and Kieffer-rig extensibility of wheat-based noodles. Proteins from different sources cannot only enhance the nutritional value but also the quality of wheat-based noodles.status: publishe

The impact of protein characteristics on the protein network in and properties of fresh and cooked wheat-based noodles

The relation between protein characteristics, protein network formation and wheat noodle properties was studied. Bovine serum albumin (BSA), soy glycinin, ovalbumin, S-ovalbumin and lysozyme were included in the recipe of wheat-based noodles. The characteristics of these non-wheat proteins impacted the type, rate and extent of protein network formation during noodle dough preparation and cooking, and thereby the properties of fresh and cooked noodles. None of the added proteins enhanced the properties of fresh noodles. BSA and soy glycinin enhanced Kieffer-rig extensibility parameters of cooked noodles. Addition of ovalbumin or S-ovalbumin led to excessive protein polymerization in cooked noodles and lowered their quality. Inclusion of lysozyme lowered the rate and extent of polymerization during cooking. Experiments in which urea, olive oil or urea were added in the recipe showed that non-covalent interactions dominate the properties of fresh noodles while covalent cross-links and hydrogen bonds mainly impact the properties of cooked noodles.status: publishe

Heat-induced network formation between proteins of different sources in model systems, wheat-based noodles and pound cakes

Proteins impact the structure and quality of various food products. Disulfide based heat-induced covalent networks are often linked to food product quality. Each single protein source has a unique ability to react and interact under specific processing conditions. In mixed protein systems, proteins from different sources can influence each other’s polymerization. Such co-protein effects are inter alia relevant for a variety of wheat-based food products in which gluten proteins coexist with globular proteins from egg, soy or milk, especially since recipe changes can be desired from economical and/or ecological perspectives. In this paper, heat-induced network formation of wheat, egg, soy, or whey proteins and mixtures thereof is reviewed. Furthermore, the impact of proteins from different sources on protein network formation in and properties of noodles and pound cake are reviewed. It is outlined that globular proteins impact the rate and extent of protein network formation in a similar way both in model and in noodle systems. The level of accessible sulfhydryl groups and the surface hydrophobicity of unfolded proteins are the main protein characteristics determining co-protein effects between globular proteins and gluten during heating. Also in pound cake, these factors impact network formation between wheat and egg proteins. In both egg noodles and pound cake, egg proteins enhance the incorporation of wheat gliadin into the protein network during heating. Replacing egg by other protein sources in wheat-based food products is not evident due to co-protein effects which impact the timing and extent of protein polymerization.status: publishe