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Cereal endosperm is a short-lived tissue adapted for nutrient storage, containing specialized organelles, such as protein bodies (PBs) and protein storage vacuoles (PSVs), for the accumulation of storage proteins. During development, protein trafficking and storage require an extensive reorganization of the endomembrane system. Consequently, endomembrane-modifying proteins will influence the final grain quality and yield. However, little is known about the molecular mechanism underlying endomembrane system remodeling during barley grain development. By using label-free quantitative proteomics profiling, we quantified 1,822 proteins across developing barley grains. Based on proteome annotation and a homology search, 94 proteins associated with the endomembrane system were identified that exhibited significant changes in abundance during grain development. Clustering analysis allowed characterization of three different development phases; notably, integration of proteomics data with in situ subcellular microscopic analyses showed a high abundance of cytoskeleton proteins associated with acidified PBs at the early development stages. Moreover, endosomal sorting complex required for transport (ESCRT)-related proteins and their transcripts are most abundant at early and mid-development. Specifically, multivesicular bodies (MVBs), and the ESCRT-III HvSNF7 proteins are associated with PBs during barley endosperm development. Together our data identified promising targets to be genetically engineered to modulate seed storage protein accumulation that have a growing role in health and nutritional issues.

The multivesicular body (MVB) sorting pathway provides a mechanism for the delivery of cargo destined for degradation to the vacuole or lysosome. The endosomal sorting complex required for transport (ESCRT) is essential for the MVB sorting pathway by driving the cargo sorting to its destination. Many efforts in plant research have identified the ESCRT machinery and functionally characterised the first plant ESCRT proteins. However, most studies have been performed in the model plant Arabidopsis thaliana that is genetically and physiologically different to crops. Cereal crops are important for animal feed and human nutrition and have further been utilized as promising candidates for recombinant protein production. In this review, I summarize the role of plant ESCRT components in cereals that are involved in efficient adaptation to environmental stress and grain development. A special focus is on barley ( Hordeum vulgare L.) ESCRT proteins, where recent studies show their quantitative mapping during grain development, e.g. associating HvSNF7.1 with protein trafficking to protein bodies (PBs) in starchy endosperm. Thus, it is indispensable to identify the molecular key-players within the endomembrane system including ESCRT proteins to optimize and possibly enhance tolerance to environmental stress, grain yield and recombinant protein production in cereal grains.

Cereal endosperm is a short-lived tissue adapted for nutrient storage, containing specialized organelles, such as protein bodies (PBs) and protein storage vacuoles (PSVs), for the accumulation of storage proteins. PBs can be used as efficient biotechnological systems to produce high yields of stable recombinant proteins. During development, protein trafficking and storage require an extensive reorganization of the endomembrane system. Consequently, endomembrane-modifying proteins will influence the final grain quality, yield and recombinant protein production. Barley, a cereal crop of worldwide importance for the brewing industry, animal feed and to a lesser extent, human nutrition, has been identified as promising candidate for recombinant protein production. However, little is known about the molecular mechanism underlying endomembrane system remodeling during barley grain development. By usingin vivolabel-free quantitative proteomics profiling, we quantified 1,822 proteins across developing barley grains. Based on proteome annotation and a homology search, 95 proteins associated with the endomembrane system were identified, and 83 of these exhibited significant changes in abundance during grain development. Clustering analysis allowed characterization of three different development stages; notably, integration of proteomics data within situsubcellular microscopic analyses showed a high abundance of cytoskeleton proteins associated with acidified protein bodies at the early development stages. Endosomal sorting complex required for transport (ESCRT)-related proteins and their transcripts are most abundant at early and mid-development. Specifically, multivesicular bodies (MVBs), and the ESCRT-III HvSNF7 proteins are associated with protein bodies (PBs) during barley endosperm development. Taken together, our proteomics results specifically identified members of the cytoskeleton, MVBs, and ESCRT as putative key players for protein sorting into PBs during barley endosperm development. These results present a comprehensive overview of proteins involved in the rearrangement of the endomembrane system during barley early grain development and will provide the basis for future work on engineering the endomembrane system to optimize nutrient content and to produce high yields of recombinant proteins.

The cereal endosperm is a complex structure comprising distinct cell types, characterized by specialized organelles for the accumulation of storage proteins. Protein trafficking in these cells is complicated by the presence of several different storage organelles including protein bodies (PBs) derived from the endoplasmic reticulum (ER) and dynamic protein storage vacuoles (PSVs). In addition, trafficking may follow a number of different routes depending on developmental stage, showing that the endomembrane system is capable of massive reorganization. Thus, developmental sequences involve progressive changes of the endomembrane system of endosperm tissue and are characterized by a high structural plasticity and endosomal activity.Given the technical dexterity required to access endosperm tissue and study subcellular structures and (seed storage protein) SSP trafficking in cereal seeds, static images are the state of the art providing a bulk of information concerning the cellular composition of seed tissue. In view of the highly dynamic endomembrane system in cereal endosperm cells, it is reasonable to expect that live cell imaging will help to characterize the spatial and temporal changes of the system. The high resolution achieved with electron microscopy perfectly complements the live cell imaging.We therefore established an imaging platform for TEM as well as for live cell imaging. Here, we describe the preparation of different cereal seed tissues for live cell imaging concomitant with immunolocalization studies and ultrastructure.

The cereal endosperm is a complex structure comprising distinct cell types, characterized by specialized organelles for the accumulation of storage proteins. Protein trafficking in these cells is complicated by the presence of several different storage organelles including protein bodies (PBs) derived from the endoplasmic reticulum (ER) and dynamic protein storage vacuoles (PSVs). In addition, trafficking may follow a number of different routes depending on developmental stage, showing that the endomembrane system is capable of massive reorganization. Thus, developmental sequences involve progressive changes of the endomembrane system of endosperm tissue and are characterized by a high structural plasticity and endosomal activity.Given the technical dexterity required to access endosperm tissue and study subcellular structures and (seed storage protein) SSP trafficking in cereal seeds, static images are the state of the art providing a bulk of information concerning the cellular composition of seed tissue. In view of the highly dynamic endomembrane system in cereal endosperm cells, it is reasonable to expect that live cell imaging will help to characterize the spatial and temporal changes of the system. The high resolution achieved with electron microscopy perfectly complements the live cell imaging.We therefore established an imaging platform for TEM as well as for live cell imaging. Here, we describe the preparation of different cereal seed tissues for live cell imaging concomitant with immunolocalization studies and ultrastructure.

A method for the immunological visualization of plant polysaccharides in native plant tissues was adopted for the histological investigation of xylan on kraft pulp and xylan-enriched viscose fibers. The method consisted of the selective labeling of xylan structures through the binding of specific monoclonal primary antibodies and fluorescein isothiocyanate (FITC)-carrying secondary antibodies. This indirect immunolabeling method was adapted for pulp and viscose fibers through the blockage of unspecific binding sites with bovine serum albumin (BSA), which allowed a selective localization of xylan. The combination of this technique with high resolution confocal laser scanning microscopy (CLSM) rendered a parallel detection of morphological changes of pulp fibers alongside various processing steps possible. Within this study, kraft pulps from birch, beech, and eucalyptus were investigated throughout a purification process that enabled an upgrade from paper pulps to dissolving pulps by caustic hemicellulose extraction and xylan-enriched viscose fibers. The method demonstrated its potential for gaining novel insights into pulp purification, as well as fiber modification through the application of an immunolabeling method.

Summary The article provides in vivo imaging data on the morphological changes in the endomembrane architecture of developing barley seeds, focussing on the fate of protein storage vacuoles along endosperm development., Cereal endosperm is a highly differentiated tissue containing specialized organelles for the accumulation of storage proteins. The endosperm of barley contains hordeins, which are ultimately deposited within protein storage vacuoles (PSVs). These organelles have been characterized predominantly by the histochemical analysis of fixed immature tissue samples. However, little is known about the fate of PSVs during barley endosperm development, and in vivo imaging has not been attempted in order to gain further insight. In this report, young seeds were followed through development to characterize the dynamic morphology of PSVs from aleurone, subaleurone, and central starchy endosperm cells. TIP3-GFP was used as a PSV membrane marker and several fluorescent tracers were used to identify membranes and monitor endomembrane organelles in real time. Whereas the spherical appearance of strongly labelled TIP3-GFP PSVs in the aleurone remained constant, those in the subaleurone and central starchy endosperm underwent substantial morphological changes. Fusion and rupture events were observed in the subaleurone, and internal membranes derived from both the tonoplast and endoplasmic reticulum were identified within these PSVs. TIP3-GFP-labelled PSVs in the starchy endosperm cells underwent a dramatic reduction in size, so that finally the protein bodies were tightly enclosed. Potential desiccation-related membrane-altering processes that may be causally linked to these dynamic endomembrane events in the barley endosperm are discussed.

Seed storage proteins (SSPs) have been studied for more than 250 years because of their nutritional value and their impact on the use of grain in food processing. More recently, the use of seeds for the production of recombinant proteins has rekindled interest in the behavior of SSPs and the question how they are able to accumulate as stable storage reserves. Seed cells produce vast amounts of SSPs with different subcellular destinations creating an enormous logistic challenge for the endomembrane system. Seed cells contain several different storage organelles including the complex and dynamic protein storage vacuoles (PSVs) and other protein bodies (PBs) derived from the endoplasmic reticulum (ER). Storage proteins destined for the PSV may pass through or bypass the Golgi, using different vesicles that follow different routes through the cell. In addition, trafficking may depend on the plant species, tissue and developmental stage, showing that the endomembrane system is capable of massive reorganization. Some SSPs contain sorting signals or interact with membranes or with other proteins en route in order to reach their destination. The ability of SSPs to form aggregates is particularly important in the formation or ER-derived PBs, a mechanism that occurs naturally in response to overloading with proteins that cannot be transported and that can be used to induce artificial storage bodies in vegetative tissues. In this review, we summarize recent findings that provide insight into the formation, function, and fate of storage organelles and describe tools that can be used to study them.

Birch pollen-related apple allergy is the most frequent IgE-mediated food allergy in Central-Northern Europe with Mal d 1 as major allergen. Its concentration in apples varies with the cultivar and storage time. Year-round appealing, hypoallergenic cultivars still are needed to satisfy the nutritional needs of affected individuals. We characterized three promising cultivars by multidisciplinary in vitro assays including long-term storage and by clinical challenges of allergic individuals before and after the birch pollen season.Proteins were extracted from fruits of 'Santana', 'Golden Delicious' (GD), and three genuine cultivars in November 2018 and April 2019. Mal d 1-levels were analysed by mass spectrometry, SDS-PAGE, immunoblotting, competitive ELISA, and basophil activation tests. Twenty-eight allergic individuals underwent single-blinded open food challenges and skin testing with the cultivars and birch pollen in November 2018 and May 2019. Allergen-specific IgE-levels were determined.After storage all cultivars except 'Santana' were of appealing appearance and taste. Their Mal d 1 content had increased, also reflected by significantly amplified basophil activation and stronger reactions in clinical challenges. Besides, individuals showed boosted reactivity after pollen exposure indicated by enhanced allergen-specific IgE-levels and skin reactions to birch pollen. Still, all cultivars remained significantly less allergenic than GD and comparable to Santana in November 2018 in all assessments except for skin testing.Combined expertise in pomology and allergology identified promising new cultivars for allergic consumers. The evaluation of hypoallergenic apples should incorporate long-term storage and birch pollen exposure. Basophil activation tests may be suitable in the selection of promising cultivars for oral challenges.