Factors Involved in Pollen Germination Playing a Critical Role also in Allergic Sensitization

Pollen is a useful system for the studies of tip growth and cell wall deposition. For this reason, it was chosen as a promising model for studying how external stimuli are integrated within the cell and how several signalling molecules are interconnected. In particular, understanding how the overall shaping of the pollen tube tip and how several well-known factors are interconnected were the main goals of this study. As the proper growth of the pollen tube depends on an elaborate mechanism that integrates several molecular and cytological sub-processes its growth mechanism is controlled by several signaling molecules such as polyamines (PAs), which control different aspects of pollen tube germination. In pollen, the homeostasis of PAs is finely regulated and the perturbation of this balance has provided, over the years, interesting evidences about how PAs carry out some of their functions in the cell. For these reasons, PAs ware taken into consideration to be used as perturbing molecules, used to spread light in understanding not only the reciprocal interactions among factors, but also the timing of the events. Besides the great interest about pollen as a model of study, pollen is a relevant topic also because it is the main trigger of seasonal allergies. It often happens that the only “pollen count” does not completely mirror the potential allergenicity of the air. Here from, the necessity to integrate the forecasting of allergenic pollen in the atmosphere with the monitoring of airborne allergenic proteins. In these studies, the amount of airborne allergens were put in correlation not only with pollen counts but also with meteorological factors in order to obtain a broad panel of evidences about factors that may affect pollen and allergen dispersion. Finally, in vitro studies also focused on the characterization of allergens, deeply involved in pollen cell wall organization

Pollen-Pistil Interaction

The aim of this Special Issue is to highlight the molecular dialogue between the pollen tube and the pistil. This is achieved with original articles and reviews which show how this dialogue is controlled at the genomic and molecular levels. During the angiosperm’s double fertilization, the pollen tube must enter female tissues, bypass numerous physical barriers to reach the micropyle, and release gametes to complete the fertilization process with the final fusion between male and female gametes. There are molecular signals produced by the pistil that are intercepted by the receptors located primarily at the tip of the tube, which generate effects that modulate its growth activity; in turn, the pollen tube releases molecules that determine effects on the pistil cells. Thus, a complex dialogue develops between the female and male counterparts, whose language is made up of an expansive molecular alphabet that includes proteins, glycoproteins, arabinogalactan-proteins, lipid-binding proteins, nanovesicles, ions, amino acids, sugars, hormones, reactive oxygen species (ROS), and modulators of gene expression

Pollen-Pistil Interaction

The aim of this Special Issue is to highlight the molecular dialogue between the pollen tube and the pistil. This is achieved with original articles and reviews which show how this dialogue is controlled at the genomic and molecular levels. During the angiosperm’s double fertilization, the pollen tube must enter female tissues, bypass numerous physical barriers to reach the micropyle, and release gametes to complete the fertilization process with the final fusion between male and female gametes. There are molecular signals produced by the pistil that are intercepted by the receptors located primarily at the tip of the tube, which generate effects that modulate its growth activity; in turn, the pollen tube releases molecules that determine effects on the pistil cells. Thus, a complex dialogue develops between the female and male counterparts, whose language is made up of an expansive molecular alphabet that includes proteins, glycoproteins, arabinogalactan-proteins, lipid-binding proteins, nanovesicles, ions, amino acids, sugars, hormones, reactive oxygen species (ROS), and modulators of gene expression

Environment-oriented selection criteria to overcome controversies in breeding for drought resistance in wheat

Wheat is one of the most important cereal crops, representing a fundamental source of calories and protein for the global human population. Drought stress (DS) is a widespread phenomenon, already affecting large wheat-growing areas worldwide, and a major threat for cereal productivity, resulting in consistent losses in average grain yield (GY). Climate change is projected to exacerbate DS incidence and severity by increasing temperatures and changing rainfall patterns. Estimating that wheat production has to substantially increase to guarantee food security to a demographically expanding human population, the need for breeding programs focused on improving wheat drought resistance is manifest. Drought occurrence, in terms of time of appearance, duration, frequency, and severity, along the plant's life cycle varies significantly among different environments and different agricultural years, making it difficult to identify reliable phenological, morphological, and functional traits to be used as effective breeding tools. The situation is further complicated by the presence of confounding factors, e.g., other concomitant abiotic stresses, in an open-field context. Consequently, the relationship between morpho-functional traits and GY under water deficit is often contradictory; moreover, controversies have emerged not only on which traits are to be preferred, but also on how one specific trait should be desired. In this review, we attempt to identify the possible causes of these disputes and propose the most suitable selection criteria in different target environments and, thus, the best trait combinations for breeders in different drought contexts. In fact, an environment-oriented approach could be a valuable solution to overcome controversies in identifying the proper selection criteria for improving wheat drought resistance

Allergenic risk assessment of urban parks: Towards a standard index.

Allergenicity indices are a powerful tool to assess the health hazard posed by urban parks to pollen allergic subjects. Nonetheless, only few indices have been developed and applied to urban vegetation in the last decade, and they were never compared nor standardised over the same dataset. To address this issue, in this paper the two best-known allergenicity indices, the Urban Green Zones Allergenicity Index (IUGZA) and the Specific Allergenicity Index (SAI), have been calculated for the same park (the Botanical Garden of Bologna), collecting vegetation data through both systematic sampling and arboreal census. The results obtained with the two data collection methods were comparable for both indices, indicating systematic sampling as a reliable approximation of the total census. Besides, the allergenic risk resulted moderate to high according to SAI, and very low according to IUGZA. Since SAI does not consider the total volume of the vegetation, it was deemed less reliable than IUGZA in evaluating the allergenicity of an enclosed green space

Cytoskeleton, Transglutaminase and Gametophytic Self-Incompatibility in the Malinae (Rosaceae)

Self-incompatibility (SI) is a complex process, one out of several mechanisms that prevent plants from self-fertilizing to maintain and increase the genetic variability. This process leads to the rejection of the male gametophyte and requires the co-participation of numerous molecules. Plants have evolved two distinct SI systems, the sporophytic (SSI) and the gametophytic (GSI) systems. The two SI systems are markedly characterized by different genes and proteins and each single system can also be divided into distinct subgroups; whatever the mechanism, the purpose is the same, i.e., to prevent self-fertilization. In Malinae, a subtribe in the Rosaceae family, i.e., Pyrus communis and Malus domestica, the GSI requires the production of female determinants, known as S-RNases, which penetrate the pollen tube to interact with the male determinants. Beyond this, the penetration of S-RNase into the pollen tube triggers a series of responses involving membrane proteins, such as phospholipases, intracellular variations of cytoplasmic Ca2+, production of reactive oxygen species (ROS) and altered enzymatic activities, such as that of transglutaminase (TGase). TGases are widespread enzymes that catalyze the post-translational conjugation of polyamines (PAs) to different protein targets and/or the cross-linking of substrate proteins leading to the formation of cross-linked products with high molecular mass. When actin and tubulin are the substrates, this destabilizes the cytoskeleton and inhibits the pollen-tube's growth process. In this review, we will summarize the current knowledge of the relationship between S-RNase penetration, TGase activity and cytoskeleton function during GSI in the Malinae

New bread formulation with improved rheological properties and longer shelf-life by the combined use of transglutaminase and sourdough

The combined use of the protein reticulating enzyme transglutaminase (TGase) and a selected microbial consortium of Lactobacillus sanfranciscensis and Candida milleri for improving the rheological properties, aroma, and shelf-life of a bakery product was evaluated. A microbial TGase, showing the highest activity over a wide temperature range on different protein substrates, was selected among different types. Results showed that this TGase was able to produce isodipeptide bonds, especially in the gluten fraction, leading to the formation of protein aggregates, which improved the structure of a sourdough bakery product. The microbial TGase in combination with sourdough exhibited a positive synergistic effect allowing the production of flavor-enriched bread, with rheological properties similar to those of standard bread

Spermine Regulates Pollen Tube Growth by Modulating Ca2+-Dependent Actin Organization and Cell Wall Structure

Proper growth of the pollen tube depends on an elaborate mechanism that integrates severalmolecularandcytologicalsub-processesandensuresacellshapeadaptedtothe transport of gametes. This growth mechanism is controlled by several molecules among which cytoplasmic and apoplastic polyamines. Spermine (Spm) has been correlated with various physiological processes in pollen, including structuring of the cell wall and modulation of protein (mainly cytoskeletal) assembly. In this work, the effects of Spm on the growth of pear pollen tubes were analyzed. When exogenous Spm (100 µM) was supplied to germinating pollen, it temporarily blocked tube growth, followed by the induction of apical swelling. This reshaping of the pollen tube was maintained also after growth recovery, leading to a 30–40% increase of tube diameter. Apical swelling was also accompanied by a transient increase in cytosolic calcium concentration and alteration of pH values, which were the likely cause for major reorganization of actin filaments and cytoplasmic organelle movement. Morphological alterations of the apical and subapical region also involved changes in the deposition of pectin, cellulose, and callose in the cell wall. Thus, results point to the involvement of Spm in cell wall construction as well as cytoskeleton organization during pear pollen tube growth

Small extracellular vesicles released from germinated kiwi pollen (pollensomes) present characteristics similar to mammalian exosomes and carry a plant homolog of ALIX

Introduction: In the last decade, it has been discovered that allergen-bearing extracellular nanovesicles, termed “pollensomes”, are released by pollen during germination. These extracellular vesicles (EVs) may play an important role in pollen-pistil interaction during fertilization, stabilizing the secreted bioactive molecules and allowing long-distance signaling. However, the molecular composition and the biological role of these EVs are still unclear. The present study had two main aims: (I) to clarify whether pollen germination is needed to release pollensomes, or if they can be secreted also in high humidity conditions; and (II) to investigate the molecular features of pollensomes following the most recent guidelines for EVs isolation and identification. Methods: To do so, pollensomes were isolated from hydrated and germinated kiwi (Actinidia chinensis Planch.) pollen, and characterized using imaging techniques, immunoblotting, and proteomics. Results: These analyses revealed that only germinated kiwi pollen released detectable concentrations of nanoparticles compatible with small EVs for shape and protein content. Moreover, a plant homolog of ALIX, which is a well-recognized and accepted marker of small EVs and exosomes in mammals, was found in pollensomes. Discussion: The presence of this protein, along with other proteins involved in endocytosis, is consistent with the hypothesis that pollensomes could comprehend a prominent subpopulation of plant exosome-like vesicles