Profilin as a regulator of the membrane-actin cytoskeleton interface in plant cells

Synergism of vesicle trafficking and cytoskeleton during regulation of plant growth and development: A mechanistic outlook

The cytoskeleton is a fundamental component found in all eukaryotic organisms, serving as a critical factor in various essential cyto-biological mechanisms, particularly in the locomotion and morphological transformations of plant cells. The cytoskeleton is comprised of three main components: microtubules (MT), microfilaments (MF), and intermediate filaments (IF). The cytoskeleton plays a crucial role in the process of cell wall formation and remodeling throughout the growth and development of cells. It is a highly organized and regulated network composed of filamentous components. In the basic processes of intracellular transport, such as mitosis, cytokinesis, and cell polarity, the plant cytoskeleton plays a crucial role according to recent studies. The major flaws in the organization of the cytoskeletal framework are at the root of the aberrant organogenesis currently observed in plant mutants. The regulation of protein compartmentalization and abundance within cells is predominantly governed by the process of vesicle/membrane transport, which plays a crucial role in several signaling cascades.The regulation of membrane transport in eukaryotic cells is governed by a diverse array of proteins. Recent developments in genomics have provided new tools to study the evolutionary relationships between membrane proteins in different plant species. It is known that members of the GTPases, COP, SNAREs, Rabs, tethering factors, and PIN families play essential roles in vesicle transport between plant, animal, and microbial species. This Review presents the latest research on the plant cytoskeleton, focusing on recent developments related to the cytoskeleton and summarizing the role of various proteins in vesicle transport. In addition, the report predicts future research direction of plant cytoskeleton and vesicle trafficking, potential research priorities, and provides researchers with specific pointers to further investigate the significant link between cytoskeleton and vesicle trafficking.

Exploring the Role of the Plant Actin Cytoskeleton: From Signaling to Cellular Functions

The plant actin cytoskeleton is characterized by the basic properties of dynamic array, which plays a central role in numerous conserved processes that are required for diverse cellular functions. Here, we focus on how actins and actin-related proteins (ARPs), which represent two classical branches of a greatly diverse superfamily of ATPases, are involved in fundamental functions underlying signal regulation of plant growth and development. Moreover, we review the structure, assembly dynamics, and biological functions of filamentous actin (F-actin) from a molecular perspective. The various accessory proteins known as actin-binding proteins (ABPs) partner with F-actin to finely tune actin dynamics, often in response to various cell signaling pathways. Our understanding of the significance of the actin cytoskeleton in vital cellular activities has been furthered by comparison of conserved functions of actin filaments across different species combined with advanced microscopic techniques and experimental methods. We discuss the current model of the plant actin cytoskeleton, followed by examples of the signaling mechanisms under the supervision of F-actin related to cell morphogenesis, polar growth, and cytoplasmic streaming. Determination of the theoretical basis of how the cytoskeleton works is important in itself and is beneficial to future applications aimed at improving crop biomass and production efficiency.

Effects of environmental stress factors on the actin cytoskeleton of fungi and plants: Ionizing radiation and ROS

Actin is an abundant and multifaceted protein in eukaryotic cells that has been detected in the cytoplasm as well as in the nucleus. In cooperation with numerous interacting accessory-proteins, monomeric actin (G-actin) polymerizes into microfilaments (F-actin) which constitute ubiquitous subcellular higher order structures. Considering the extensive spatial dimensions and multifunctionality of actin superarrays, the present study analyses the issue if and to what extent environmental stress factors, specifically ionizing radiation (IR) and reactive oxygen species (ROS), affect the cellular actin-entity. In that context, this review particularly surveys IR-response of fungi and plants. It examines in detail which actin-related cellular constituents and molecular pathways are influenced by IR and related ROS. This comprehensive survey concludes that the general integrity of the total cellular actin cytoskeleton is a requirement for IR-tolerance. Actin's functions in genome organization and nuclear events like chromatin remodeling, DNA-repair, and transcription play a key role. Beyond that, it is highly significant that the macromolecular cytoplasmic and cortical actin-frameworks are affected by IR as well. In response to IR, actin-filament bundling proteins (fimbrins) are required to stabilize cables or patches. In addition, the actin-associated factors mediating cellular polarity are essential for IR-survivability. Moreover, it is concluded that a cellular homeostasis system comprising ROS, ROS-scavengers, NADPH-oxidases, and the actin cytoskeleton plays an essential role here. Consequently, besides the actin-fraction which controls crucial genome-integrity, also the portion which facilitates orderly cellular transport and polarized growth has to be maintained in order to survive IR.

Mass Spectrometry-Based Identification of Bioactive Bee Pollen Proteins: Evaluation of Allergy Risk after Bee Pollen Supplementation

Bee pollen, because of its high content of nutrients, is a very valuable medicinal and nutritional product. However, since its composition is not completely studied, the consumption of this product may cause adverse effects, including allergic reactions. Therefore, this study aimed to discover and characterize the bioactive proteins of bee pollen collected in Poland, focusing mainly on the allergens. For this purpose, the purified and concentrated pollen aqueous solutions were analyzed using the nanoLC-MALDI-TOF/TOF MS analytical platform. As a result of the experiments, 197 unique proteins derived from green plants (Viridiplantae) and 10 unique proteins derived from bees (Apis spp.) were identified. Among them, potential plant allergens were discovered. Moreover, proteins belonging to the group of hypothetical proteins, whose expression had not been confirmed experimentally before, were detected. Because of the content of bioactive compounds-both beneficial and harmful-there is a critical need to develop guidelines for standardizing bee pollen, especially intended for consumption or therapeutic purposes. This is of particular importance because awareness of the allergen content of bee pollen and other bee products can prevent health- or life-threatening incidents following the ingestion of these increasingly popular "superfoods".

PFN4 is required for manchette development and acrosome biogenesis during mouse spermiogenesis

Profilin 4 (Pfn4) is expressed during spermiogenesis and localizes to the acrosome-acroplaxome-manchette complex. Here, we generated PFN4-deficient mice, with sperm displaying severe impairment in manchette formation. Interestingly, HOOK1 staining suggests that the perinuclear ring is established; however, ARL3 staining is disrupted, suggesting that lack of PFN4 does not interfere with the formation of the perinuclear ring and initial localization of HOOK1, but impedes microtubular organization of the manchette. Furthermore, amorphous head shape and flagellar defects were detected, resulting in reduced sperm motility. Disrupted cis- and trans-Golgi networks and aberrant production of proacrosomal vesicles caused impaired acrosome biogenesis. Proteomic analysis showed that the proteins ARF3, SPECC1L and FKBP1, which are involved in Golgi membrane trafficking and PI3K/AKT pathway, are more abundant in Pfn4^−/− testes. Levels of PI3K, AKT and mTOR were elevated, whereas AMPK level was reduced, consistent with inhibition of autophagy. This seems to result in blockage of autophagic flux, which could explain the failure in acrosome formation. In vitro fertilization demonstrated that PFN4-deficient sperm is capable of fertilizing zona-free oocytes, suggesting a potential treatment for PFN4-related human infertility.

Summary: PFN4-deficient male mice exhibit impaired acrosome formation and malformation of the manchette, leading to amorphous sperm head shape, flagellar abnormalities and sterility.

An Arabidopsis mutant deficient in phosphatidylinositol-4-phosphate kinases ß1 and ß2 displays altered auxin-related responses in roots

Phosphatidylinositol 4-kinases (PI4Ks) are the first enzymes that commit phosphatidylinositol into the phosphoinositide pathway. Here, we show that Arabidopsis thaliana seedlings deficient in PI4Kβ1 and β2 have several developmental defects including shorter roots and unfinished cytokinesis. The pi4kβ1β2 double mutant was insensitive to exogenous auxin concerning inhibition of root length and cell elongation; it also responded more slowly to gravistimulation. The pi4kß1ß2 root transcriptome displayed some similarities to a wild type plant response to auxin. Yet, not all the genes displayed such a constitutive auxin-like response. Besides, most assessed genes did not respond to exogenous auxin. This is consistent with data with the transcriptional reporter DR5-GUS. The content of bioactive auxin in the pi4kß1ß2 roots was similar to that in wild-type ones. Yet, an enhanced auxin-conjugating activity was detected and the auxin level reporter DII-VENUS did not respond to exogenous auxin in pi4kß1ß2 mutant. The mutant exhibited altered subcellular trafficking behavior including the trapping of PIN-FORMED 2 protein in rapidly moving vesicles. Bigger and less fragmented vacuoles were observed in pi4kß1ß2 roots when compared to the wild type. Furthermore, the actin filament web of the pi4kß1ß2 double mutant was less dense than in wild-type seedling roots, and less prone to rebuilding after treatment with latrunculin B. A mechanistic model is proposed in which an altered PI4K activity leads to actin filament disorganization, changes in vesicle trafficking, and altered auxin homeostasis and response resulting in a pleiotropic root phenotypes.

Identification and validation of reference genes for qRT-PCR based studies in horse gram (Macrotyloma uniflorum)

The quantitative real-time polymerase chain reaction (qRT-PCR) is the most sensitive and commonly used technique for gene expression studies in biological systems. However, the reliability of qRT-PCR results depends on the selection of reference gene(s) for data normalization. Horse gram (Macrotyloma uniflorum) is an important legume crop on which several molecular studies have been reported. However, the stability of reference genes has not been evaluated. In the present study, nine candidate reference genes were identified from horse gram RNA-seq data and evaluated in two horse gram genotypes, HPK4 and HPKM317 under six abiotic stresses viz. cold, drought, salinity, heat, abscisic acid and methyl viologen-induced oxidative stress. The results were evaluated using geNorm, Bestkeeper, Normfinder and delta-delta Ct methods and comprehensive ranking was assigned using RefFinder and RankAggreg software. The overall result showed that TCTP was one of the most stable genes in all samples and in genotype HPK4, while in HPKM317 profilin was most stably expressed. However, PSMA5 was identified as least stable in all the experimental conditions. Expression of target genes dehydrin and early response to dehydration 6 under drought stress was also validated using TCTP and profilin for data normalization, either alone or in combination, which confirmed their suitability for qRT-PCR data normalization. Thus, TCTP and profilin genes may be used for qRT-PCR data normalization for molecular and genomic studies in horse gram.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01104-0.

Transcriptional loss of domestication-driven cytoskeletal GhPRF1 gene causes defective floral and fiber development in cotton (Gossypium)

Constitutive- and fiber-specific RNAi of GhPRF1 gene illustrated strong correlation between domestication-driven profilin genes and floral/fiber architecture in cotton. During morpho-transformation of short-fuzz of wild cotton into the elongating spinnable fibers under the millennia of human selection, actin-polymerizing cytoskeletal profilin genes had undergone significant sequence alterations and spatiotemporal shift in their transcription levels. To comprehend the expression dynamics of profilin genes with their phenotypic implications, transgenic expression modulation of cotton profilin 1 (GhPRF1) gene was performed in the constitutive- and fiber-specific manner in Coker 310FR cotton cultivar. The constitutive GhPRF1-RNAi lines (35S:GhPRF1-RNAi) exhibited distorted 'monadelphous' staminal-tube, reduced pollen-viability and poorly developed fibers, whereas floral and fiber development of fiber-specific GhPRF1-RNAi lines showed no abnormalities. Moreover, the fiber-specific GhPRF1 overexpression lines (FBP7:GhPRF1-Ox) showed increased emergence of fiber-initials on the ovule surface, on the contrary to no fiber-initials in fiber-specific RNAi lines (FBP7:GhPRF1-RNAi). Interestingly, the average seed weight and fiber weight of FBP7:GhPRF1-Ox lines increased > 60% and > 38%, respectively, compared with FBP7:GhPRF1-RNAi lines and untransformed control seeds. On a molecular basis, the aberrant floral and fiber development of 35S:GhPRF1-RNAi lines was largely associated with sugar metabolism and hormone-signaling mechanisms. These observations illustrated the strong correlation between domestication-driven GhPRF genes, and floral/fiber development in cotton. Also, the enhanced agronomic traits in GhPRF1-Ox lines of cotton empowered us to recognize their imperative roles, and their future deployment for the sustainable cotton crop improvement.

The Resistance Responses of Potato Plants to Potato Virus Y Are Associated with an Increased Cellular Methionine Content and an Altered SAM:SAH Methylation Index

Plant-virus interactions are frequently influenced by elevated temperature, which often increases susceptibility to a virus, a scenario described for potato cultivar Chicago infected with potato virus Y (PVY). In contrast, other potato cultivars such as Gala may have similar resistances to PVY at both normal (22 °C) and high (28 °C) temperatures. To elucidate the mechanisms of temperature-independent antivirus resistance in potato, we analysed responses of Gala plants to PVY at different temperatures using proteomic, transcriptional and metabolic approaches. Here we show that in Gala, PVY infection generally upregulates the accumulation of major enzymes associated with the methionine cycle (MTC) independently of temperature, but that temperature (22 °C or 28 °C) may finely regulate what classes accumulate. The different sets of MTC-related enzymes that are up-regulated at 22 °C or 28 °C likely account for the significantly increased accumulation of S-adenosyl methionine (SAM), a key component of MTC which acts as a universal methyl donor in methylation reactions. In contrast to this, we found that in cultivar Chicago, SAM levels were significantly reduced which correlated with the enhanced susceptibility to PVY at high temperature. Collectively, these data suggest that MTC and its major transmethylation function determines resistance or susceptibility to PVY.

GORI, encoding the WD40 domain protein, is required for pollen tube germination and elongation in rice

Successful delivery of sperm cells to the embryo sac in higher plants is mediated by pollen tube growth. The molecular mechanisms underlying pollen germination and tube growth in crop plants remain rather unclear, although these mechanisms are crucial to plant reproduction and seed formation. By screening pollen-specific gene mutants in rice (Oryza sativa), we identified a T-DNA insertional mutant of Germinating modulator of rice pollen (GORI) that showed a one-to-one segregation ratio for wild type (WT) to heterozygous. GORI encodes a seven-WD40-motif protein that is homologous to JINGUBANG/REN4 in Arabidopsis. GORI is specifically expressed in rice pollen, and its protein is localized in the nucleus, cytosol and plasma membrane. Furthermore, a homozygous mutant, gori-2, created through CRISPR-Cas9 clearly exhibited male sterility with disruption of pollen tube germination and elongation. The germinated pollen tube of gori-2 exhibited decreased actin filaments and altered pectin distribution. Transcriptome analysis revealed that 852 pollen-specific genes were downregulated in gori-2 compared with the WT, and Gene Ontology enrichment analysis indicated that these genes are strongly associated with cell wall modification and clathrin coat assembly. Based on the molecular features of GORI, phenotypical observation of the gori mutant and its interaction with endocytic proteins and Rac GTPase, we propose that GORI plays key roles in forming endo-/exocytosis complexes that could mediate pollen tube growth in rice.

Molecular approach to a patient's tailored diagnosis of the oral allergy syndrome

Oral allergy syndrome (OAS) is one of the most common IgE-mediated allergic reactions. It is characterized by a number of symptoms induced by the exposure of the oral and pharyngeal mucosa to allergenic proteins belonging to class 1 or to class 2 food allergens. OAS occurring when patients sensitized to pollens are exposed to some fresh plant foods has been called pollen food allergy syndrome (PFAS). In the wake of PFAS, several different associations of allergenic sources have been progressively proposed and called syndromes. Molecular allergology has shown that these associations are based on IgE co-recognition taking place between homologous allergens present in different allergenic sources. In addition, the molecular approach reveals that some allergens involved in OAS are also responsible for systemic reactions, as in the case of some food Bet v 1-related proteins, lipid transfer proteins and gibberellin regulated proteins. Therefore, in the presence of a convincing history of OAS, it becomes crucial to perform a patient's tailored molecule-based diagnosis in order to identify the individual IgE sensitization profile. This information allows the prediction of possible cross-reactions with homologous molecules contained in other sources. In addition, it allows the assessment of the risk of developing more severe symptoms on the basis of the features of the allergenic proteins to which the patient is sensitized. In this context, we aimed to provide an overview of the features of relevant plant allergenic molecules and their involvement in the clinical onset of OAS. The value of a personalized molecule-based approach to OAS diagnosis is also analyzed and discussed.

LC-MS/MS based comparative proteomics of floral nectars reveal different mechanisms involved in floral defense of Nicotiana spp., Petunia hybrida and Datura stramonium

Tobacco floral nectar (FN) is a biological fluid produced by nectaries composed of sugars, amino acids and proteins called nectarins, involved in the floral defense. FN provides an ideal source of nutrients for microorganisms. Understanding the role of nectar proteins is essential to predict impacts in microbial growth, composition and plants-pollinators interactions. Using LC-MS/MS-based comparative proteomic analysis we identified 22 proteins from P. hybrida, 35 proteins from D. stramonium, and 144 proteins from 23 species of Nicotiana. The data are available at ProteomeXchance (PXD014760). GO analysis and secretory signal prediction demonstrated that defense/stress was the largest group of proteins in the genus Nicotiana. The Nicotiana spp. proteome consisted of 105 exclusive proteins such as lipid transfer proteins (LTPs), Nectar Redox Cycle proteins, proteases inhibitors, and PR-proteins. Analysis by taxonomic sections demonstrated that LTPs were most abundant in Undulatae and Noctiflora, while nectarins were more abundant in Rusticae, Suaveolens, Polydicliae, and Alata sections. Peroxidases (Pox) and chitinases (Chit) were exclusive to P. hybrida, while D. stramonium had only seven unique proteins. Biochemical analysis confirmed these differences. These findings support the hypothesis that, although conserved, there is differential abundance of proteins related to defense/stress which may impact the mechanisms of floral defense. SIGNIFICANCE: This study represents a comparative proteomic analysis of floral nectars of the Nicotiana spp. with two correlated Solanaceous species. Significant differences were identified between the proteome of taxonomic sections providing relevant insights into the group of proteins related to defense/stress associated with Nectar Redox Cycle, antimicrobial proteins and signaling pathways. The activity of FNs proteins is suggested impact the microbial growth. The knowledge about these proteomes provides significant insights into the diversity of proteins secreted in the nectars and the array of mechanisms used by Nicotiana spp. in its floral defense.

Actin Cytoskeleton as Actor in Upstream and Downstream of Calcium Signaling in Plant Cells

In plant cells, calcium (Ca²⁺) serves as a versatile intracellular messenger, participating in several fundamental and important biological processes. Recent studies have shown that the actin cytoskeleton is not only an upstream regulator of Ca²⁺ signaling, but also a downstream regulator. Ca²⁺ has been shown to regulates actin dynamics and rearrangements via different mechanisms in plants, and on this basis, the upstream signaling encoded within the Ca²⁺ transient can be decoded. Moreover, actin dynamics have also been proposed to act as an upstream of Ca²⁺, adjust Ca²⁺ oscillations, and establish cytosolic Ca²⁺ ([Ca²⁺]_cyt) gradients in plant cells. In the current review, we focus on the advances in uncovering the relationship between the actin cytoskeleton and calcium in plant cells and summarize our current understanding of this relationship.

Molecular Responses of Maize Shoot to a Plant Derived Smoke Solution

Plant-derived smoke has effects on plant growth. To find the molecular mechanism of plant-derived smoke on maize, a gel-free/label-free proteomic technique was used. The length of root and shoot were increased in maize by plant-derived smoke. Proteomic analysis revealed that 2000 ppm plant-derived smoke changed the abundance of 69 proteins in 4-days old maize shoot. Proteins in cytoplasm, chloroplast, and cell membrane were altered by plant-derived smoke. Catalytic, signaling, and nucleotide binding proteins were changed. Proteins related to sucrose synthase, nucleotides, signaling, and glutathione were significantly increased; however, cell wall, lipids, photosynthetic, and amino acid degradations related proteins were decreased. Based on proteomic and immunoblot analyses, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was decreased; however, RuBisCO activase was not changed by plant-derived smoke in maize shoot. Ascorbate peroxidase was not affected; however, peroxiredoxin was decreased by plant-derived smoke. Furthermore, the results from enzyme-activity and mRNA-expression analyses confirmed regulation of ascorbate peroxidase and the peroxiredoxinin reactive oxygen scavenging system. These results suggest that increases in sucrose synthase, nucleotides, signaling, and glutathione related proteins combined with regulation of reactive oxygen species and their scavenging system in response to plant-derived smoke may improve maize growth.

Actin filaments regulate the adhesion between the plasma membrane and the cell wall of tobacco guard cells

During the opening and closing of stomata, guard cells undergo rapid and reversible changes in their volume and shape, which affects the adhesion of the plasma membrane (PM) to the cell wall (CW). The dynamics of actin filaments in guard cells are involved in stomatal movement by regulating structural changes and intracellular signaling. However, it is unclear whether actin dynamics regulate the adhesion of the PM to the CW. In this study, we investigated the relationship between actin dynamics and PM-CW adhesion by the hyperosmotic-induced plasmolysis of tobacco guard cells. We found that actin filaments in guard cells were depolymerized during mannitol-induced plasmolysis. The inhibition of actin dynamics by treatment with latrunculin B or jasplakinolide and the disruption of the adhesion between the PM and the CW by treatment with RGDS peptide (Arg-Gly-Asp-Ser) enhanced guard cell plasmolysis. However, treatment with latrunculin B alleviated the RGDS peptide-induced plasmolysis and endocytosis. Our results reveal that the actin depolymerization is involved in the regulation of the PW-CW adhesion during hyperosmotic-induced plasmolysis in tobacco guard cells.

Two Distinct Conformations in Bet v 2 Determine Its Proteolytic Resistance to Cathepsin S

Birch pollen allergy affects more than 20% of the European allergic population. On a molecular level, birch pollen allergy can be linked to the two dominant allergens Bet v 1 and Bet v 2. Bet v 2 belongs to the profilin family, which is abundant in the plant kingdom. Importantly, the homologous plant profilins have a conserved cysteine motif with a currently unknown functional relevance. In particular, it is unknown whether the motif is relevant for disulfide formation and to what extent it would affect the profilins’ structural, functional and immunological properties. Here we present crystal structures of Bet v 2 in the reduced and the oxidized state, i.e., without and with a disulfide bridge. Despite overall structural similarity, the two structures distinctly differ at their termini which are stabilized to each other in the oxidized, i.e., disulfide-linked state. These structural differences translate into differences in their proteolytic resistance. Whereas the oxidized Bet v 2 is rather resistant towards the endolysosomal protease cathepsin S, it is rapidly degraded in the reduced form. By contrast, both Bet v 2 forms exhibit similar immunological properties as evidenced by their binding to IgE antibodies from birch pollen allergic patients and by their ability to trigger histamine release in a humanized rat basophilic leukemia cells (RBL) assay, independent of the presence or absence of the disulfide bridge. Taken together our findings suggest that the oxidized Bet v 2 conformation should be the relevant species, with a much longer retention time to trigger immune responses.

Molecular features of grass allergens and development of biotechnological approaches for allergy prevention

Allergic diseases are characterized by elevated allergen-specific IgE and excessive inflammatory cell responses. Among the reported plant allergens, grass pollen and grain allergens, derived from agriculturally important members of the Poaceae family such as rice, wheat and barley, are the most dominant and difficult to prevent. Although many allergen homologs have been predicted from species such as wheat and timothy grass, fundamental aspects such as the evolution and function of plant pollen allergens remain largely unclear. With the development of genetic engineering and genomics, more primary sequences, functions and structures of plant allergens have been uncovered, and molecular component-based allergen-specific immunotherapies are being developed. In this review, we aim to provide an update on (i) the distribution and importance of pollen and grain allergens of the Poaceae family, (ii) the origin and evolution, and functional aspects of plant pollen allergens, (iii) developments of allergen-specific immunotherapy for pollen allergy using biotechnology and (iv) development of less allergenic plants using gene engineering techniques. We also discuss future trends in revealing fundamental aspects of grass pollen allergens and possible biotechnological approaches to reduce the amount of pollen allergens in grasses.

Guilt by Association: A Phenotype-Based View of the Plant Phosphoinositide Network

Eukaryotic membranes contain small amounts of phospholipids that have regulatory effects on the physiological functions of cells, tissues, and organs. Phosphoinositides (PIs)-the phosphorylated derivatives of phosphatidylinositol-are one example of such regulatory lipids. Although PIs were described in plants decades ago, their contribution to the regulation of physiological processes in plants is not well understood. In the past few years, evidence has emerged that PIs are essential for plant function and development. Recently reported phenotypes associated with the perturbation of different PIs suggest that some subgroups of PIs influence specific processes. Although the molecular targets of PI-dependent regulation in plants are largely unknown, the effects of perturbed PI metabolism can be used to propose regulatory modules that involve particular downstream targets of PI regulation. This review summarizes phenotypes associated with the perturbation of the plant PI network to categorize functions and suggest possible downstream targets of plant PI regulation.

Development of monoclonal antibody-based ELISA for the quantification of orange allergen Cit s 2 in fresh and processed oranges

The aim of this study was to develop a monoclonal antibody (mAb)-based enzyme-linked immunosorbent assay (ELISA) for the quantification of a major allergen (Cit s 2) in fresh and processed oranges. Purified recombinant Cit s 2 (rCit s 2)-small ubiquitin-like modifier (SUMO) was used for the production of mAbs. In the optimized ELISA, the recovery of rCit s 2 from Navel oranges or orange juice was 107-132%, and the intra- and inter-assay coefficients of variation were 3.1-8.8% and 4.4-11%, respectively. The Cit s 2 content in fresh oranges was determined to be 1,800±430ng/g, while this content was much lower in the processed foods. The developed ELISA demonstrated high reproducibility, sensitivity, and accuracy, and this assay may help individuals with orange allergy by determining Cit s 2 quantities in food products and controlling their Cit s 2 intake.

Plant actin depolymerizing factor: actin microfilament disassembly and more

ACTIN DEPOLYMERIZING FACTOR (ADF) is a conserved protein among eukaryotes. The main function of ADF is the severing and depolymerizing filamentous actin (F-actin), thus regulating F-actin organization and dynamics and contributing to growth and development of the organisms. Mammalian genomes contain only a few ADF genes, whereas angiosperm plants have acquired an expanding number of ADFs, resulting in the differentiation of physiological functions. Recent studies have revealed functions of ADFs in plant growth and development, and various abiotic and biotic stress responses. In biotic stress responses, ADFs are involved in both susceptibility and resistance, depending on the pathogens. Furthermore, recent studies have highlighted a new role of ADF in the nucleus, possibly in the regulation of gene expression. In this review, I will summarize the current status of plant ADF research and discuss future research directions.

How relevant is panallergen sensitization in the development of allergies?

Panallergens comprise various protein families of plant as well as animal origin and are responsible for wide IgE cross-reactivity between related and unrelated allergenic sources. Such cross-reactivities include reactions between various pollen sources, pollen and plant-derived foods as well as invertebrate-derived inhalants and foodstuff. Here, we provide an overview on the most clinically relevant panallergens from plants (profilins, polcalcins, non-specific lipid transfer proteins, pathogenesis-related protein family 10 members) and on the prominent animal-derived panallergen family, tropomyosins. In addition, we explore the role of panallergens in the sensitization process and progress of the allergic disease. Emphasis is given on epidemiological aspects of panallergen sensitization and clinical manifestations. Finally, the issues related to diagnosis and therapy of patients sensitized to panallergens are outlined, and the use of panallergens as predictors for cross-reactive allergy and as biomarkers for disease severity is discussed.

Computational Study of the Binding Mechanism of Actin-Depolymerizing Factor 1 with Actin in Arabidopsis thaliana

Actin is a highly conserved protein. It plays important roles in cellular function and exists either in the monomeric (G-actin) or polymeric form (F-actin). Members of the actin-depolymerizing factor (ADF)/cofilin protein family bind to both G-actin and F-actin and play vital roles in actin dynamics by manipulating the rates of filament polymerization and depolymerization. It has been reported that the S6D and R98A/K100A mutants of actin-depolymerizing factor 1 (ADF1) in Arabidopsis thaliana decreased the binding affinity of ADF for the actin monomer. To investigate the binding mechanism and dynamic behavior of the ADF1–actin complex, we constructed a homology model of the AtADF1–actin complex based on the crystal structure of AtADF1 and the twinfilin C-terminal ADF-H domain in a complex with a mouse actin monomer. The model was then refined for subsequent molecular dynamics simulations. Increased binding energy of the mutated system was observed using the Molecular Mechanics Generalized Born Surface Area and Poisson–Boltzmann Surface Area (MM-GB/PBSA) methods. To determine the residues that make decisive contributions to the ADF1 actin-binding affinity, per-residue decomposition and computational alanine scanning analyses were performed, which provided more detailed information on the binding mechanism. Root-mean-square fluctuation and principal component analyses confirmed that the S6D and R98A/K100A mutants induced an increased conformational flexibility. The comprehensive molecular insight gained from this study is of great importance for understanding the binding mechanism of ADF1 and G-actin.

Fatty acid profiles of monofloral clover beebread and pollen and proteomics of red clover (Trifolium pratense) pollen

Fatty acids were identified in monofloral beebread (BB) and bee pollen (BP) loads collected from Trifolium pratense L. A gas chromatography method was used to identify and quantify fatty acids: Thirty-five fatty acids were identified in BB and 42 in BP. A high amount of the healthy n-3 fatty acids was found. The ratio of polyunsaturated fatty acids n-3 to n-6 reached a value of 8.42 and 3.35 in the latter products. The proteomic analysis also was performed on the manually collected T. pratense pollen, and the most abundant protein groups were subjected to mass spectrometry analysis. Proteins identified in T. pratense pollen are involved in the main cellular functions (cell membrane formation, organelles traffic, and mainly metabolic processes). Because of the composition of fatty acids in BB and BP and a variety of proteins present in pollen, these products are considered to be favorable for human nutrition and health.

From filaments to function: The role of the plant actin cytoskeleton in pathogen perception, signaling and immunity

The eukaryotic actin cytoskeleton is required for numerous cellular processes, including cell shape, development and movement, gene expression and signal transduction, and response to biotic and abiotic stress. In recent years, research in both plants and animal systems have described a function for actin as the ideal surveillance platform, linking the function and activity of primary physiological processes to the immune system. In this review, we will highlight recent advances that have defined the regulation and breadth of function of the actin cytoskeleton as a network required for defense signaling following pathogen infection. Coupled with an overview of recent work demonstrating specific targeting of the plant actin cytoskeleton by a diversity of pathogens, including bacteria, fungi and viruses, we will highlight the importance of actin as a key signaling hub in plants, one that mediates surveillance of cellular homeostasis and the activation of specific signaling responses following pathogen perception. Based on the studies highlighted herein, we propose a working model that posits changes in actin filament organization is in and of itself a highly specific signal, which induces, regulates and physically directs stimulus-specific signaling processes, most importantly, those associated with response to pathogens.

HLB1 Is a Tetratricopeptide Repeat Domain-Containing Protein That Operates at the Intersection of the Exocytic and Endocytic Pathways at the TGN/EE in Arabidopsis

The endomembrane system plays essential roles in plant development, but the proteome responsible for its function and organization remains largely uncharacterized in plants. Here, we identified and characterized the HYPERSENSITIVE TO LATRUNCULIN B1 (HLB1) protein isolated through a forward-genetic screen in Arabidopsis thaliana for mutants with heightened sensitivity to actin-disrupting drugs. HLB1 is a plant-specific tetratricopeptide repeat domain-containing protein of unknown function encoded by a single Arabidopsis gene. HLB1 associated with the trans-Golgi network (TGN)/early endosome (EE) and tracked along filamentous actin, indicating that it could link post-Golgi traffic with the actin cytoskeleton in plants. HLB1 was found to interact with the ADP-ribosylation-factor guanine nucleotide exchange factor, MIN7/BEN1 (HOPM INTERACTOR7/BREFELDIN A-VISUALIZED ENDOCYTIC TRAFFICKING DEFECTIVE1) by coimmunoprecipitation. The min7/ben1 mutant phenocopied the mild root developmental defects and latrunculin B hypersensitivity of hlb1, and analyses of ahlb1/ min7/ben1 double mutant showed that hlb1 and min7/ben1 operate in common genetic pathways. Based on these data, we propose that HLB1 together with MIN7/BEN1 form a complex with actin to modulate the function of the TGN/EE at the intersection of the exocytic and endocytic pathways in plants.

Keeping it all together: auxin-actin crosstalk in plant development

Polar auxin transport and the action of the actin cytoskeleton are tightly interconnected, which is documented by the finding that auxin transporters reach their final destination by active movement of secretory vesicles along F-actin tracks. Moreover, auxin transporter polarity and flexibility is thought to depend on transporter cycling that requires endocytosis and exocytosis of vesicles. In this context, we have reviewed the current literature on an involvement of the actin cytoskeleton in polar auxin transport and identify known similarities and differences in its structure, function and dynamics in comparison to non-plant organisms. By describing how auxin modulates actin expression and actin organization and how actin and its stability affects auxin-transporter endocytosis and recycling, we discuss the current knowledge on regulatory auxin-actin feedback loops. We focus on known effects of auxin and of auxin transport inhibitors on the stability and organization of actin and examine the functionality of auxin and/or auxin transport inhibitor-binding proteins with respect to their suitability to integrate auxin/auxin transport inhibitor action. Finally, we indicate current difficulties in the interpretation of organ, time and concentration-dependent auxin/auxin transport inhibitor treatments and formulate simple future experimental guidelines.

An iTRAQ-based proteomics approach to clarify the molecular physiology of somatic embryo development in Prince Rupprecht's larch (Larix principis-rupprechtii Mayr)

Prince Rupprecht's larch (Larix principis-rupprechtii Mayr) is a native high-value forest tree species in North China whose clonal propagation through somatic embryogenesis (SE) has the potential to rapidly capture the benefits of breeding or genetic engineering programs and to improve raw material uniformity and quality. To date, research has focused on clarifying the molecular mechanism of SE, but proteomic studies are still in the early stages. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) analysis was performed on three developmental stages of SE in L. principis-rupprechtii in an attempt to identify a wide range of proteins that are regulated differentially during this process. Proteins were extracted and analyzed from the pro-embryogenic mass (PEM), globular embryo (GE), and cotyledon embryo (CE) stages of embryo development. We detected 503 proteins in total and identified 96 proteins expressed differentially during different developmental stages. The identified proteins were analyzed further to provide information about their expression patterns and functions during SE. Four clusters of proteins based on shared expression profiles were generated. Functional analysis showed that proteins involved in primary metabolism, phosphorylation, and oxidation reduction were upregulated during somatic embryo development. This work provides novel insights into the process of larch embryo development in vitro and a basis for further study of the biological process and opportunities for practical application of this knowledge.

Interactions between plant endomembrane systems and the actin cytoskeleton

Membrane trafficking, organelle movement, and morphogenesis in plant cells are mainly controlled by the actin cytoskeleton. Not all proteins that regulate the cytoskeleton and membrane dynamics in animal systems have functional homologs in plants, especially for those proteins that form the bridge between the cytoskeleton and membrane; the membrane-actin adaptors. Their nature and function is only just beginning to be elucidated and this field has been greatly enhanced by the recent identification of the NETWORKED (NET) proteins, which act as membrane-actin adaptors. In this review, we will summarize the role of the actin cytoskeleton and its regulatory proteins in their interaction with endomembrane compartments and where they potentially act as platforms for cell signaling and the coordination of other subcellular events.

Effects of corn gluten feed inclusion at graded levels in a corn-soybean diet on the ileal and fecal digestibility of growing pigs

BACKGROUND

This study aimed to determine the effect of the inclusion of corn gluten feed (CGF) on the apparent and standardized ileal digestibility of protein and amino acids and the apparent ileal and total tract digestibility of energy in growing pigs. The study was performed using 16 barrows (weight, 45.3 ± 4.5 kg) that were fitted with a T cannula at the terminal ileum. There were four treatments: a corn-soybean diet without CGF and three corn-soybean diets containing increasing levels of CGF (65, 130, and 195 g/kg). Data were analyzed according to a randomized complete block design, four blocks with four pigs each (one pig per treatment). The trend of the response (linear or quadratic) was determined using orthogonal contrasts, and when a linear effect was determined, a linear equation was obtained.

RESULTS

The results showed that the inclusion up to 195 g/kg of CGF in the corn-soybean diet did not diminish the ileal digestibility (apparent and standardized) of protein and amino acids (P > 0.05), except that of phenylalanine, cystine, and proline. A linear decrease (P < 0.05) per gram of CGF added to the diet in the apparent and standardized ileal digestibility of phenylalanine (0.011 and 0.015 percentage units, respectively), cystine (0.048 and 0.043 percentage units, respectively), and proline (0.045 and 0.047 percentage units, respectively) was noted. Similarly, ileal digestibility of dry matter and energy were adversely affected (reduced by 0.028 and 0.025 percentage units, respectively, per gram of CGF increment in the diet). A significant (P < 0.05) linear reduction in total tract digestibility with increase in CGF amount in the diet was observed for energy (0.027 percentage units), dry matter (0.027 percentage units), crude protein (0.020 percentage units), and neutral detergent fiber (0.041 percentage units) per gram of CGF added to the diet.

CONCLUSION

CGF did not affect the ileal digestibility of protein and most amino acids but reduced the ileal and total tract digestibility of energy.