Extracellular vesicles: a missing component in plant cell wall remodeling

Extracellular vesicles of Norway spruce contain precursors and enzymes for lignin formation and salicylic acid

Lignin is a phenolic polymer in plants that rigidifies the cell walls of water-conducting tracheary elements and support-providing fibers and stone cells. Different mechanisms have been suggested for the transport of lignin precursors to the site of lignification in the cell wall. Extracellular vesicle (EV)-enriched samples isolated from a lignin-forming cell suspension culture of Norway spruce (Picea abies L. Karst.) contained both phenolic metabolites and enzymes related to lignin biosynthesis. Metabolomic analysis revealed mono-, di-, and oligolignols in the EV isolates, as well as carbohydrates and amino acids. In addition, salicylic acid (SA) and some proteins involved in SA signaling were detected in the EV-enriched samples. A proteomic analysis detected several laccases, peroxidases, β-glucosidases, putative dirigent proteins, and cell wall-modifying enzymes, such as glycosyl hydrolases, transglucosylase/hydrolases, and expansins in EVs. Our findings suggest that EVs are involved in transporting enzymes required for lignin polymerization in Norway spruce, and radical coupling of monolignols can occur in these vesicles.

Plant-derived exosome-like nanoparticles - from Laboratory to factory, a landscape of application, challenges and prospects

Recent decades have witnessed substantial interest in extracellular vesicles (EVs) due to their crucial role in intercellular communication across various biological processes. Among these, plant-derived exosome-like Nanoparticles (ELNs) have rapidly gained recognition as highly promising candidates. ELNs, characterized by diverse sources, cost-effective production, and straightforward isolation, present a viable option for preventing and treating numerous diseases. Furthermore, ELNs hold significant potential as carriers for natural or engineered drugs, enhancing their attractiveness and drawing considerable attention in science and medicine. However, translating ELNs into clinical applications poses several challenges. This study explores these challenges and offers critical insights into potential research directions. Additionally, it provides a forward-looking analysis of the industrial prospects for ELNs. With their broad applications and remarkable potential, ELNs stand at the forefront of biomedical innovation, poised to revolutionize disease management and drug delivery paradigms in the coming years.

The evolving roles of extracellular vesicles in embryo-maternal communication

Mammalian reproduction relies on precise maternal-fetal communication, wherein immune modifications foster tolerance toward the semi-allogeneic embryo. Extracellular vesicles (EVs), including exosomes and microvesicles, have emerged as crucial mediators, transporting molecules like microRNAs securely. EVs influence various reproductive stages, from gamete maturation to implantation, and impact pathologies like pregnancy loss. In the embryo-maternal dialogue, EVs notably affect oviductal interactions, gene expression, and the embryo-endometrial interface, crucial for successful implantation. Key queries persist about EV uptake, cargo delivery, and the specific biomolecules driving communication. Their potential in diagnostics, therapeutics, and understanding environmental impacts on fertility signals an exciting future, reliant on collaborative efforts for transformative strides in reproductive health.

Isolation of Extracellular Vesicles from Agri-Food Wastes: A Novel Perspective in the Valorization of Agri-Food Wastes and By-Products

Agri-food wastes generated by industrial food processing are valorized through the extraction of biomolecules to obtain value-added products useful for various industrial applications. In the present review, we describe the valuable by-products and bioactive molecules that can be obtained from agricultural wastes and propose extracellular vesicles (EVs) as innovative nutraceutical and therapeutic compounds that could be derived from agriculture residues. To support this idea, we described the general features and roles of EVs and focused on plant-derived extracellular vesicles (PDEVs) that are considered natural carriers of bioactive molecules and are involved in intercellular communication between diverse kingdoms of life. Consistently, PDEVs exert beneficial effects (anti-inflammatory, anti-tumor, and immune-modulatory) on mammalian cells. Although this research field is currently in its infancy, in the near future, the isolation of EVs and their use as nutraceutical tools could represent a new and innovative way to valorize waste from the agri-food industry in an ecofriendly way.

Unveiling the Potential of Extracellular Vesicles as Biomarkers and Therapeutic Nanotools for Gastrointestinal Diseases

Extracellular vesicles (EVs), acting as inherent nanocarriers adept at transporting a range of different biological molecules such as proteins, lipids, and genetic material, exhibit diverse functions within the gastroenteric tract. In states of normal health, they participate in the upkeep of systemic and organ homeostasis. Conversely, in pathological conditions, they significantly contribute to the pathogenesis of gastrointestinal diseases (GIDs). Isolating EVs from patients' biofluids facilitates the discovery of new biomarkers that have the potential to offer a rapid, cost-effective, and non-invasive method for diagnosing and prognosing specific GIDs. Furthermore, EVs demonstrate considerable therapeutic potential as naturally targeted physiological carriers for the intercellular delivery of therapeutic cargo molecules or as nanoscale tools engineered specifically to regulate physio-pathological conditions or disease progression. Their attributes including safety, high permeability, stability, biocompatibility, low immunogenicity, and homing/tropism capabilities contribute to their promising clinical therapeutic applications. This review will delve into various examples of EVs serving as biomarkers or nanocarriers for therapeutic cargo in the context of GIDs, highlighting their clinical potential for both functional and structural gastrointestinal conditions. The versatile and advantageous properties of EVs position them as promising candidates for innovative therapeutic strategies in advancing personalized medicine approaches tailored to the gastroenteric tract, addressing both functional and structural GIDs.

Kaempferia parviflora Extracellular Vesicle Loaded with Clarithromycin for the Treatment of Helicobacter pylori Infection

Purpose

Kaempferia parviflora extracellular vesicles (KPEVs) have been reported as promising nanovesicles for drug delivery. This study aimed to load clarithromycin (CLA) into KPEVs (KPEVS-CLA) and determine the physical properties, drug-releasing efficiency, gastric cell uptake, anti-H. pylori activities, and anti-inflammatory responses in comparison with free CLA and KPEVs.

Methods

The size and surface charge of KPEVs-CLA were evaluated using dynamic light scattering and visualized using a transmission electron microscope. The encapsulation efficiency (EE%), loading capacity (LC%), and drug release of KPEVs-CLA were examined using HPLC. Anti-H. pylori growth and anti-adhesion were evaluated. IL-8 gene expression, NF-κB signaling proteins, and anti-inflammatory profiles were examined using qRT-PCR, Western blotting, and Bio-Plex immunoassay, respectively. Anti-chemotaxis was then examined using a Transwell assay.

Results

KPEVs-CLA were intact and showed a negative surface charge similar to that of KPEVs. However, slightly enlarged KPEVs were observed. CLA was successfully loaded into KPEVs with EE of 93.45% ± 2.43%, LC of 9.3% ± 3.02%. CLA release in the PBS and gastric mimic buffer with Fickian diffusion (n ≤ 0.43) according to Korsmeyer-Peppas kinetic model (R2=0.98). KPEVs-CLA was localized in the gastric cells' cytoplasm and perinuclear region. Anti-H. pylori growth and anti-H. pylori adhesion of KPEVs-CLA were compared with those of free CLA with no cytotoxicity to adenocarcinoma gastric cells. KPEVs-CLA significantly reduced IL-8, G-CSF, MIP-1α, and MIP-1β levels. Moreover, KPEVs-CLA showed a superior effect over CLA in reducing G-CSF, MIP-1α, and NF-κB phosphorylation and monocyte chemotactic activities.

Conclusion

KPEVs serve as potential carriers of CLA. They exhibited a higher efficiency in inhibiting gastric cell inflammation mediated by H. pylori infection than free CLA. The establishment of KPEVs-CLA as a nanodrug delivery model for H. pylori treatment could be applied to other plant extracellular vesicles or loaded with other cancer drugs for gastric cancer treatment.

Edible Plant-Derived Extracellular Vesicles for Oral mRNA Vaccine Delivery

Nucleic acid delivery through extracellular vesicles (EVs) is a well-preserved evolutionary mechanism in all life kingdoms including eukaryotes, prokaryotes, and plants. EVs naturally allow horizontal transfer of native as well as exogenous functional mRNAs, which once incorporated in EVs are protected from enzymatic degradation. This observation has prompted researchers to investigate whether EVs from different sources, including plants, could be used for vaccine delivery. Several studies using human or bacterial EVs expressing mRNA or recombinant SARS-CoV-2 proteins showed induction of a humoral and cell mediated immune response. Moreover, EV-based vaccines presenting the natural configuration of viral antigens have demonstrated advantages in conferring long-lasting immunization and lower toxicity than synthetic nanoparticles. Edible plant-derived EVs were shown to be an alternative to human EVs for vaccine delivery, especially via oral administration. EVs obtained from orange juice (oEVs) loaded with SARS-CoV-2 mRNAs protected their cargo from enzymatic degradation, were stable at room temperature for one year, and were able to trigger a SARS-CoV-2 immune response in mice. Lyophilized oEVs containing the S1 mRNA administered to rats via gavage induced a specific humoral immune response with generation of blocking antibodies, including IgA and Th1 lymphocyte activation. In conclusion, mRNA-containing oEVs could be used for developing new oral vaccines due to optimal mucosal absorption, resistance to stress conditions, and ability to stimulate a humoral and cellular immune response.

Bioactive compounds and biological functions of medicinal plant-derived extracellular vesicles

Extracellular vesicles (EVs) are tiny lipid bilayer-enclosed membrane particles released from a variety of cell types into the surrounding environment. These EVs have massive participated in cell-to-cell communication and interspecies communication. In recent years, plant-derived extracellular vesicles (PDEVs) and "exosome-like" EVs populations found in distinct plants have attracted widespread attention. Especially, research on medicinal plant-derived extracellular vesicles (MPDEVs) are increasing, which are considered a kind of promising natural compound. This review summarizes current knowledge on MPDEVs in terms of bioactive compounds, including small RNA, protein, lipid, and metabolite, have been found on the surface and/or in the lumen of MPDEVs. Moreover, both in vitro and in vivo experiments have shown that MPDEVs exert broad biomedical functions, such as anti-inflammatory, anticancer, antioxidant, modulate microbiota, etc. MPDEVs may be a better substitute than animal-derived extracellular vesicles (ADEVs) because of safety and biocompatibility in the future.

Plant Extracellular Vesicles: Current Landscape and Future Directions

Plant cells secrete membrane-enclosed micrometer- and nanometer-sized vesicles that, similarly to the extracellular vesicles (EVs) released by mammalian or bacterial cells, carry a complex molecular cargo of proteins, nucleic acids, lipids, and primary and secondary metabolites. While it is technically complicated to isolate EVs from whole plants or their tissues, in vitro plant cell cultures provide excellent model systems for their study. Plant EVs have been isolated from the conditioned culture media of plant cell, pollen, hairy root, and protoplast cultures, and recent studies have gathered important structural and biological data that provide a framework to decipher their physiological roles and unveil previously unacknowledged links to their diverse biological functions. The primary function of plant EVs seems to be in the secretion that underlies cell growth and morphogenesis, cell wall composition, and cell-cell communication processes. Besides their physiological functions, plant EVs may participate in defence mechanisms against different plant pathogens, including fungi, viruses, and bacteria. Whereas edible and medicinal-plant-derived nanovesicles isolated from homogenised plant materials ex vivo are widely studied and exploited, today, plant EV research is still in its infancy. This review, for the first time, highlights the different in vitro sources that have been used to isolate plant EVs, together with the structural and biological studies that investigate the molecular cargo, and pinpoints the possible role of plant EVs as mediators in plant-pathogen interactions, which may contribute to opening up new scenarios for agricultural applications, biotechnology, and innovative strategies for plant disease management.

Food-Derived Extracellular Vesicles as Multi-Bioactive Complex and Their Versatile Health Effects

Extracellular vesicles (EVs) are membrane-bound organelles that are generally released by eukaryotic cells and enclose various cellular metabolic information, such as RNA, meta-proteins, and versatile metabolites. The physiological properties and diverse functions of food-derived EVs have been extensively elucidated, along with a recent explosive upsurge in EV research. Therefore, a concise review of the health effects of food-derived EVs is necessary. This review summarizes the structural stability and uptake pathways of food-derived EVs to target cells and their health benefits, including antioxidant, anti-inflammatory, and anticarcinogenic effects, gut microbiome modulation, and intestinal barrier enhancement.

Extracellular RNAs released by plant-associated fungi: from fundamental mechanisms to biotechnological applications

Extracellular RNAs are an emerging research topic in fungal-plant interactions. Fungal plant pathogens and symbionts release small RNAs that enter host cells to manipulate plant physiology and immunity. This communication via extracellular RNAs between fungi and plants is bidirectional. On the one hand, plants release RNAs encapsulated inside extracellular vesicles as a defense response as well as for intercellular and inter-organismal communication. On the other hand, recent reports suggest that also full-length mRNAs are transported within fungal EVs into plants, and these fungal mRNAs might get translated inside host cells. In this review article, we summarize the current views and fundamental concepts of extracellular RNAs released by plant-associated fungi, and we discuss new strategies to apply extracellular RNAs in crop protection against fungal pathogens. KEY POINTS: • Extracellular RNAs are an emerging topic in plant-fungal communication. • Fungi utilize RNAs to manipulate host plants for colonization. • Extracellular RNAs can be engineered to protect plants against fungal pathogens.

A nonclassically secreted effector of Magnaporthe oryzae targets host nuclei and plays important roles in fungal growth and plant infection

Rice blast caused by Magnaporthe oryzae is one of the most destructive diseases and poses a growing threat to food security worldwide. Like many other filamentous pathogens, rice blast fungus releases multiple types of effector proteins to facilitate fungal infection and modulate host defence responses. However, most of the characterized effectors contain an N-terminal signal peptide. Here, we report the results of the functional characterization of a nonclassically secreted nuclear targeting effector in M. oryzae (MoNte1). MoNte1 has no signal peptide, but can be secreted and translocated into plant nuclei driven by a nuclear targeting peptide. It could also induce hypersensitive cell death when transiently expressed in Nicotiana benthamiana. Deletion of the MoNTE1 gene caused a significant reduction of fungal growth and conidiogenesis, partially impaired appressorium formation and host colonization, and also dramatically attenuated the pathogenicity. Taken together, these findings reveal a novel effector secretion pathway and deepen our understanding of rice-M. oryzae interactions.

Plant Exosome-like Nanovesicles and Their Role in the Innovative Delivery of RNA Therapeutics

Exosomes are single membrane-bound spheres released from cells carrying complex cargoes, including lipids, proteins, and nucleic acids. Exosomes transfer specific cargoes from donor to acceptor cells, playing important roles in cell-to-cell communication. Current studies have reported that plant exosomes are prominent in transferring small RNA between host and pathogens in a cross-kingdom manner. Plant exosomes are excellent RNA interference (RNAi) delivery agents with similar physical and chemical properties to mammalian exosomes and have potential applications in therapeutic delivery systems. Recent data have suggested that plant exosome-like nanovesicles (PENVs) and artificial PENV-derived nano-vectors (APNVs) are beneficial for delivering therapeutic small RNA in mammalian systems and exhibit excellent competitiveness in future clinical applications. This review features their preparation methods, composition, roles in small RNA delivery for health functionalities, and their potency as functional nanomedicine.

Plant-Derived Vesicle-Like Nanoparticles as Promising Biotherapeutic Tools: Present and Future

Extracellular vesicles (EVs) are heterogeneous, phospholipid bilayer-enclosed biological particles that regulate cell communication by molecular cargo delivery and surface signaling. EVs are secreted by almost all living cells, including plant cells. Plant-derived vesicle-like nanoparticles (PDVLNs) is a generic term referring to vesicle-like nanostructure particles isolated from plants. Their low immunogenicity and wide availability make PDVLNs safer and more economical to be developed as therapeutic agents and drug carriers. Accumulating evidence indicates the key roles of PDVLNs in regulating interkingdom crosstalk between humans and plants. PDVLNs are capable of entering the human-body systemand delivering effector molecules to cells that modulate cell-signaling pathways. PDVLNs released by or obtained from plants thus have great influenceon human health and diseases. In this review, the biogenesis, detailed preparation methods, various physical and biochemical characteristics, biosafety, and preservation of PDVLNs are introduced, along with how these characteristics pertain to their biosafety and preservability. The potential applications of PDVLNs on different plant and mammalian diseases and PDVLN research standardization are then systematically discussed.

Do photosynthetic cells communicate with each other during cell death? From cyanobacteria to vascular plants

As in metazoans, life in oxygenic photosynthetic organisms relies on the accurate regulation of cell death. During development and in response to the environment, photosynthetic cells activate and execute cell death pathways that culminate in the death of a specific group of cells, a process known as regulated cell death (RCD). RCD control is instrumental, as its misregulation can lead to growth penalties and even the death of the entire organism. Intracellular molecules released during cell demise may act as 'survival' or 'death' signals and control the propagation of cell death to surrounding cells, even in unicellular organisms. This review explores different signals involved in cell-cell communication and systemic signalling in photosynthetic organisms, in particular Ca2+, reactive oxygen species, lipid derivates, nitric oxide, and eATP. We discuss their possible mode-of-action as either 'survival' or 'death' molecules and their potential role in determining cell fate in neighbouring cells. By comparing the knowledge available across the taxonomic spectrum of this coherent phylogenetic group, from cyanobacteria to vascular plants, we aim at contributing to the identification of conserved mechanisms that control cell death propagation in oxygenic photosynthetic organisms.

Plant-derived extracellular vesicles: Recent advancements and current challenges on their use for biomedical applications

Extracellular vesicles (EVs) represent a diverse class of lipid bilayer membrane vesicles released by both animal and plant cells. These ubiquitous vesicles are involved in intercellular communication and transport of various biological cargos, including proteins, lipids, and nucleic acids. In recent years, interest in plant-derived EVs has increased tremendously, as they serve as a scalable and sustainable alternative to EVs derived from mammalian sources. In vitro and in vivo findings have demonstrated that these plant-derived vesicles (PDVs) possess intrinsic therapeutic activities that can potentially treat diseases and improve human health. In addition, PDVs can also act as efficient and biocompatible drug carriers. While preclinical studies have shown promising results, there are still several challenges and knowledge gaps that have to be addressed for the successful translation of PDVs into clinical applications, especially in view of the lack of standardised protocols for material handling and PDV isolation from various plant sources. This review provides the readers with a quick overview of the current understanding and research on PDVs, critically analysing the current challenges and highlighting the immense potential of PDVs as a novel class of therapeutics to treat human diseases. It is expected that this work will guide scientists to address the knowledge gaps currently associated with PDVs and promote new advances in plant-based therapeutic solutions.

Spotlight on plant RNA-containing extracellular vesicles

Extracellular vesicles (EVs) carrying RNA have attracted growing attention in plant cell biology. For a long time, EV release or uptake through the rigid plant cell wall was considered to be impossible and RNA outside cells to be unstable. Identified EV biomarkers have brought new insights into functional roles of EVs to transport their RNA cargo for systemic spread in plants and into plant-invading pathogens. RNA-binding proteins supposedly take over key functions in EV-mediated RNA secretion and transport, but the mechanisms of RNA sorting and EV translocation through the plant cell wall and plasma membrane are not understood. Characterizing the molecular players and the cellular mechanisms of plant RNA-containing EVs will create new knowledge in cell-to-cell and inter-organismal communication.

Role of extracellular vesicles in intercellular communication during reproduction

The mammalian reproduction is a process of controlled cellular growth and development regulated by constant communication between the gametes, the subsequent embryo and the maternal system. Extracellular vesicles (EVs) are involved in these communications to a significant degree from the gamete production and maturation to fertilization, embryo development and implantation. They regulate the cellular physiology and the immune reaction to bring about a favourable environment for a successful pregnancy. Deciphering the mechanisms employed in EV-mediated embryo maternal communication could improve our knowledge in mammalian reproduction and increase the efficiency of animal breeding.

Immunological Effects of Aster yomena Callus-Derived Extracellular Vesicles as Potential Therapeutic Agents against Allergic Asthma

Plant-derived extracellular vesicles, (EVs), have recently gained attention as potential therapeutic candidates. However, the varying properties of plants that are dependent on their growth conditions, and the unsustainable production of plant-derived EVs hinder drug development. Herein, we analyzed the secondary metabolites of Aster yomena callus-derived EVs (AYC-EVs) obtained via plant tissue cultures and performed an immune functional assay to assess the potential therapeutic effects of AYC-EVs against inflammatory diseases. AYC-EVs, approximately 225 nm in size, were isolated using tangential flow filtration (TFF) and cushioned ultracentrifugation. Metabolomic analysis, using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS), revealed that AYC-EVs contained 17 major metabolites. AYC-EVs inhibited the phenotypic and functional maturation of LPS-treated dendritic cells (DCs). Furthermore, LPS-treated DCs exposed to AYC-EVs showed decreased immunostimulatory capacity during induction of CD4+ and CD8+ T-cell proliferation and activation. AYC-EVs inhibited T-cell reactions associated with the etiology of asthma in asthmatic mouse models and improved various symptoms of asthma. This regulatory effect of AYC-EVs resembled that of dexamethasone, which is currently used to treat inflammatory diseases. These results provide a foundation for the development of plant-derived therapeutic agents for the treatment of various inflammatory diseases, as well as providing an insight into the possible mechanisms of action of AYC-EVs.

Plant hairy roots for the production of extracellular vesicles with antitumor bioactivity

Plant extracellular vesicles (EVs) concentrate and deliver different types of bioactive molecules in human cells and are excellent candidates for a next-generation drug delivery system. However, the lack of standard protocols for plant EV production and the natural variations of their biomolecular cargo pose serious limitation to their use as therapeutics. To overcome these issues, we set up a versatile and standardized procedure to purify plant EVs from hairy root (HR) cultures, a versatile biotechnological system, already successfully employed as source of bioactive molecules with pharmaceutical and nutraceutical relevance. Herewith, we report that HR of Salvia dominica represent an excellent platform for the production of plant EVs. In particular, EVs derived from S. dominica HRs are small round-shaped vesicles carrying typical EV-associated proteins such as cytoskeletal components, chaperon proteins and integral membrane proteins including the tetraspanin TET-7. Interestingly, the HR-derived EVs showed selective and strong pro-apoptotic activity in pancreatic and mammary cancer cells. These results reveal that plant hairy roots may be considered a new promising tool in plant biotechnology for the production of extracellular vesicles for human health.

Plant-derived extracellular vesicles: a novel nanomedicine approach with advantages and challenges

BACKGROUND

Many eukaryote cells produce membrane-enclosed extracellular vesicles (EVs) to establish cell-to-cell communication. Plant-derived EVs (P-EVs) contain proteins, RNAs, lipids, and other metabolites that can be isolated from the juice, the flesh, and roots of many species.

METHODS

In the present review study, we studied numerous articles over the past two decades published on the role of P-EVs in plant physiology as well as on the application of these vesicles in different diseases.

RESULTS

Different types of EVs have been identified in plants that have multiple functions including reorganization of cell structure, development, facilitating crosstalk between plants and fungi, plant immunity, defense against pathogens. Purified from several edible species, these EVs are more biocompatible, biodegradable, and extremely available from many plants, making them useful for cell-free therapy. Emerging evidence of clinical and preclinical studies suggest that P-EVs have numerous benefits over conventional synthetic carriers, opening novel frontiers for the novel drug-delivery system. Exciting new opportunities, including designing drug-loaded P-EVs to improve the drug-delivery systems, are already being examined, however clinical translation of P-EVs-based therapies faces challenges.

CONCLUSION

P-EVs hold great promise for clinical application in the treatment of different diseases. In addition, despite enthusiastic results, further scrutiny should focus on unravelling the detailed mechanism behind P-EVs biogenesis and trafficking as well as their therapeutic applications. Video Abstract.

Unconventional Pathways of Protein Secretion: Mammals vs. Plants

In eukaryotes, many proteins contain an N-terminal signal peptide that allows their translocation into the endoplasmic reticulum followed by secretion outside the cell according to the classical secretory system. However, an increasing number of secreted proteins lacking the signal peptide sequence are emerging. These proteins, secreted in several alternative ways collectively known as unconventional protein secretion (UPS) pathways, exert extracellular functions including cell signaling, immune modulation, as well as moonlighting activities different from their well-described intracellular functions. Pathways for UPS include direct transfer across the plasma membrane, secretion from endosomal/multivesicular body-related components, release within plasma membrane-derived microvesicles, or use of elements of autophagy. In this review we describe the mammals and plants UPS pathways identified so far highlighting commonalities and differences.

Extracellular vesiculo-tubular structures associated with suberin deposition in plant cell walls

Suberin is a fundamental plant biopolymer, found in protective tissues, such as seed coats, exodermis and endodermis of roots. Suberin is deposited in most suberizing cells in the form of lamellae just outside of the plasma membrane, below the primary cell wall. How monomeric suberin precursors, thought to be synthesized at the endoplasmic reticulum, are transported outside of the cell, for polymerization into suberin lamellae has remained obscure. Using electron-microscopy, we observed large numbers of extracellular vesiculo-tubular structures (EVs) to accumulate specifically in suberizing cells, in both chemically and cryo-fixed samples. EV presence correlates perfectly with root suberization and we could block suberin deposition and vesicle accumulation by affecting early, as well as late steps in the secretory pathway. Whereas many previous reports have described EVs in the context of biotic interactions, our results suggest a developmental role for extracellular vesicles in the formation of a major cell wall polymer.

Suberizing plant cells export suberin monomers outside of the cell to form a hydrophobic barrier. Here the authors propose a role for extracellular vesiculo-tubular structures in the deposition of suberin monomers.

A novel chicory fructanase can degrade common microbial fructan product profiles and displays positive cooperativity

Fructan metabolism in bacteria and plants relies on fructosyltransferases and fructanases. Plant fructanases (fructan exohydrolase, FEH) only hydrolyse terminal fructose residues. Levan (β-2,6 linkages) is the most abundant fructan type in bacteria. Dicot fructan accumulators, such as chicory (Cichorium intybus), accumulate inulin (β-2,1 linkages), harbouring several 1-FEH isoforms for their degradation. Here, a novel chicory fructanase with high affinity for levan was characterized, providing evidence that such enzymes widely occur in higher plants. It is adapted to common microbial fructan profiles, but has low affinity towards chicory inulin, in line with a function in trimming of microbial fructans in the extracellular environment. Docking experiments indicate the importance of an N-glycosylation site close to the active site for substrate specificity. Optimal pH and temperature for levan hydrolysis are 5.0 and 43.7 °C, respectively. Docking experiments suggested multiple substrate binding sites and levan-mediated enzyme dimerization, explaining the observed positive cooperativity. Alignments show a single amino acid shift in the position of a conserved DXX(R/K) couple, typical for sucrose binding in cell wall invertases. A possible involvement of plant fructanases in levan trimming is discussed, in line with the emerging 'fructan detour' concepts, suggesting that levan oligosaccharides act as signalling entities during plant-microbial interactions.

Technology insight: Plant-derived vesicles-How far from the clinical biotherapeutics and therapeutic drug carriers?

Within the past decades, extracellular vesicles (EVs) have emerged as important mediators of intercellular communication in both prokaryotes and higher eukaryotes to regulate a diverse range of biological processes. Besides EVs, exosome-like nanoparticles (ELNs) derived from plants were also emerging. Comparing to EVs, ELNs are source-widespread, cost-effective and easy to obtain. Their definite activities can be utilized for potential prevention/treatment of an abundance of diseases, including metabolic syndrome, cancer, colitis, alcoholic hepatitis and infectious diseases, which highlights ELNs as promising biotherapeutics. In addition, the potential of ELNs as natural or engineered drug carriers is also attractive. In this review, we tease out the timeline of plant EVs and ELNs, introduce the arising separation, purification and characterization techniques, state the stability and transport manner, discuss the therapeutic opportunities as well as the potential as novel drug carriers. Finally, the challenges and the direction of efforts to realize the clinical transformation of ELNs are also discussed.

Characterizing Kaempferia parviflora extracellular vesicles, a nanomedicine candidate

Plant-derived extracellular vesicles (EVs) are a promising candidate for nanomedicine delivery due to their bioactive cargos, high biocompatibility to human cells, biodegradability, low cytotoxicity, and potential for large-scale production. However, the research on EVs derived from medicinal plants is very limited. In this study, Kaempferia parviflora extracellular vesicles (KPEVs) were isolated by differential and sucrose density gradient centrifugation, and their size, morphology, and surface charge were characterized using transmission electron microscopy and dynamic light scattering. The biological properties of KPEVs, including their bioactive compound composition, gastric uptake, cytotoxicity, acid tolerance, and storage stability, were also examined. In addition, KPEVs had an average and uniform size of 200–300 nm and a negative surface charge of 14.7 ± 3.61 mV. Moreover, 5,7-dimethoxyflavone, the major bioactive compound of KP, was packaged into KPEVs. Meanwhile, KPEVs were resistant to gastric digestion and stably maintained at −20°C and −80°C for 8 weeks with no freeze-thaw cycle. The lipid hydrolysis during EVs storage at room temperature and 4°C were also demonstrated for the first time. Furthermore, the labeled KPEVs were internalized into adenocarcinoma gastric cells, and the cell viability was reduced in a dose-dependent manner, according to the results of the thiazolyl blue tetrazolium assay. Our study supports the potential application of KPEVs as a vehicle for anticancer or oral drugs.

Aloe derived nanovesicle as a functional carrier for indocyanine green encapsulation and phototherapy

Background

Cancer is one of the devastating diseases in the world. The development of nanocarrier provides a promising perspective for improving cancer therapeutic efficacy. However, the issues with potential toxicity, quantity production, and excessive costs limit their further applications in clinical practice.

Results

Herein, we proposed a nanocarrier obtained from aloe with stability and leak-proofness. We isolated nanovesicles from the gel and rind of aloe (gADNVs and rADNVs) with higher quality and yield by controlling the final centrifugation time within 20 min, and modulating the viscosity at 2.98 mPa S and 1.57 mPa S respectively. The gADNVs showed great structure and storage stability, antioxidant and antidetergent capacity. They could be efficiently taken up by melanoma cells, and with no toxicity in vitro or in vivo. Indocyanine green (ICG) loaded in gADNVs (ICG/gADNVs) showed great stability in both heating system and in serum, and its retention rate exceeded 90% after 30 days stored in gADNVs. ICG/gADNVs stored 30 days could still effectively damage melanoma cells and inhibit melanoma growth, outperforming free ICG and ICG liposomes. Interestingly, gADNVs showed prominent penetrability to mice skin which might be beneficial to noninvasive transdermal administration.

Conclusions

Our research was designed to simplify the preparation of drug carrier, and reduce production cost, which provided an alternative for the development of economic and safe drug delivery system.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01195-7.

Extracellular Vesicles: Emerging Players in Plant Defense Against Pathogens

Communication between plants and interacting microorganisms requires functional molecule trafficking, which is essential for host defense and pathogen virulence. Extracellular vesicles (EVs) are single membrane-bound spheres that carry complex cargos, including lipids, proteins, and nucleic acids. They mediate cell-to-cell communication via the transfer of molecules between cells. Plant EVs have been isolated from many plant species and play a prominent role in immune system modulation and plant defense response. Recent studies have shown that plant EVs are emerging players in cross-kingdom regulation and contribute to plant immunity by mediating the trafficking of regulatory small RNA into pathogens, leading to the silencing of pathogen virulence-related genes. This review summarizes the current understanding of plant EV isolation technologies, the role of plant EVs in plant immunity, and the mechanism of plant EV biogenesis, as well as approaches for how these findings can be developed into innovative strategies for crop protection.

Induction of Proline Iminopeptidase by Nitric Oxide May Result in the Proline Accumulation in the Pea Roots

The nitric oxide (NO) donor sodium nitroprusside upregulated the proline iminopeptidase content in the pea seedling roots. It is assumed that NO activates deprolinization of the proline-rich proteins, as evidenced by an increase in the content of free proline, which is known to protect plants from the abiotic and biotic stressors.

Communication is key: Extracellular vesicles as mediators of infection and defence during host-microbe interactions in animals and plants

Extracellular vesicles (EVs) are now understood to be ubiquitous mediators of cellular communication. In this review, we suggest that EVs have evolved into a highly regulated system of communication with complex functions including export of wastes, toxins and nutrients, targeted delivery of immune effectors and vectors of RNA silencing. Eukaryotic EVs come in different shapes and sizes and have been classified according to their biogenesis and size distributions. Small EVs (or exosomes) are released through fusion of endosome-derived multivesicular bodies with the plasma membrane. Medium EVs (or microvesicles) bud off the plasma membrane as a form of exocytosis. Finally, large EVs (or apoptotic bodies) are produced as a result of the apoptotic process. This review considers EV secretion and uptake in four eukaryotic kingdoms, three of which produce cell walls. The impacts cell walls have on EVs in plants and fungi are discussed, as are roles of fungal EVs in virulence. Contributions of plant EVs to development and innate immunity are presented. Compelling cases are sporophytic self-incompatibility and cellular invasion by haustorium-forming filamentous pathogens. The involvement of EVs in all of these eukaryotic processes is reconciled considering their evolutionary history.

Cell Walls Are Remodeled to Alleviate nY2O3 Cytotoxicity by Elaborate Regulation of de Novo Synthesis and Vesicular Transport

Yttrium oxide nanoparticles (nY2O3), one of the broadly used rare earth nanoparticles, can interact with plants and possibly cause plant health and environmental impacts, but the plant defense response particularly at the nanoparticle-cell interface is largely unknown. To elucidate this, Bright Yellow 2 (BY-2) tobacco (Nicotiana tabacum L.) suspension-cultured cells were exposed to 50 mg L-1 nY2O3 (30 nm) for 12 h. Although 42.2% of the nY2O3 remained outside of protoplasts, nY2O3 could still traverse the cell wall and was partially deposited inside the vacuole. In addition to growth inhibition, morphological and compositional changes in cell walls occurred. Together with a locally thickened (7-13-fold) cell wall, increased content (up to 58%) of pectin and reduction in (up to 29%) hemicellulose were observed. Transcriptome analysis revealed that genes involved in cell wall metabolism and remodeling were highly regulated in response to nY2O3 stress. Expression of genes for pectin synthesis and degradation was up- and down-regulated by 31-78% and 13-42%, respectively, and genes for xyloglucan and pectin modifications were up- and down-regulated by 82% and 81-92%, respectively. Interestingly, vesicle trafficking seemed to be activated, enabling the repair and defense against nY2O3 disturbance. Our findings indicate that, although nY2O3 generated toxicity on BY-2 cells, it is very likely that during the recovery process cell wall remodeling was initiated to gain resistance to nY2O3 stress, demonstrating the plant's cellular regulatory machinery regarding repair and adaptation to nanoparticles like nY2O3.

Nanovesicles from Organic Agriculture-Derived Fruits and Vegetables: Characterization and Functional Antioxidant Content

Dietary consumption of fruits and vegetables is related to a risk reduction in a series of leading human diseases, probably due to the plants' antioxidant content. Plant-derived nanovesicles (PDNVs) have been recently receiving great attention regarding their natural ability to deliver several active biomolecules and antioxidants. To investigate the presence of active antioxidants in fruits, we preliminarily analyzed the differences between nanovesicles from either organic or conventional agriculture-derived fruits, at equal volumes, showing a higher yield of nanovesicles with a smaller size from organic agriculture-derived fruits as compared to conventional ones. PDNVs from organic agriculture also showed a higher antioxidant level compared to nanovesicles from conventional agriculture. Using the PDNVs from fruit mixes, we found comparable levels of Total Antioxidant Capacity, Ascorbic Acid, Catalase, Glutathione and Superoxide Dismutase 1. Finally, we exposed the nanovesicle mixes to either chemical or physical lytic treatments, with no evidence of effects on the number, size and antioxidant capacity of the treated nanovesicles, thus showing a marked resistance of PDNVs to external stimuli and a high capability to preserve their content. Our study provides for the first time a series of data supporting the use of plant-derived nanovesicles in human beings' daily supplementation, for both prevention and treatment of human diseases.

Molecular self-organization of wood lignin-carbohydrate matrix

The analysis of the state of research on the chemical composition, functional nature and structure of the main components of the lignin-carbohydrate matrix allows considering the wood substance as a thermodynamically self-organizing nanobiocomposite system. Features of biosynthesis of the wood matrix main biopolymers, the formation of their functional nature and structure determine the complex hierarchical organization of cell walls. The supramolecular level of biosynthesis considers the interaction of cell wall components. On the one hand, these are questions of dynamics of cell walls synthesis and processes of self-organization that control the formation of chaotic objects of biological origin; on the other hand, it is the question of thermodynamic compatibility of plant tissue components. Various models of structural organization are currently being considered, focusing on various features (biological, chemical, structural) of wood substance. At the same time, the lignin-carbohydrate matrix is a three-component system of natural polymers: lignin-hemicelluloses-cellulose, the state of which is described by specific values of thermodynamic parameters that characterize the degree of its stability. The new approach proposed in this paper allows considering the plant lignin-carbohydrate matrix from the standpoint of physical chemistry of polymer as quasi-equilibrium, thermodynamically limited ordered system of biopolymers. Thus, the biochemical processes of synthesis and self-organization lead to the formation of a complex multicomponent system of wood substance, considered as a nanobiocomposite. This determines the need to study the applicability of the fundamental cycle "structure-functional nature-properties" from the standpoint of physical chemistry of biopolymers both for the investigation of plant objects and for the development of modern technologies for complex processing based on the principles of "green chemistry".

Plant-Derived Nano and Microvesicles for Human Health and Therapeutic Potential in Nanomedicine

Plants produce different types of nano and micro-sized vesicles. Observed for the first time in the 60s, plant nano and microvesicles (PDVs) and their biological role have been inexplicably under investigated for a long time. Proteomic and metabolomic approaches revealed that PDVs carry numerous proteins with antifungal and antimicrobial activity, as well as bioactive metabolites with high pharmaceutical interest. PDVs have also been shown to be also involved in the intercellular transfer of small non-coding RNAs such as microRNAs, suggesting fascinating mechanisms of long-distance gene regulation and horizontal transfer of regulatory RNAs and inter-kingdom communications. High loading capacity, intrinsic biological activities, biocompatibility, and easy permeabilization in cell compartments make plant-derived vesicles excellent natural or bioengineered nanotools for biomedical applications. Growing evidence indicates that PDVs may exert anti-inflammatory, anti-oxidant, and anticancer activities in different in vitro and in vivo models. In addition, clinical trials are currently in progress to test the effectiveness of plant EVs in reducing insulin resistance and in preventing side effects of chemotherapy treatments. In this review, we concisely introduce PDVs, discuss shortly their most important biological and physiological roles in plants and provide clues on the use and the bioengineering of plant nano and microvesicles to develop innovative therapeutic tools in nanomedicine, able to encompass the current drawbacks in the delivery systems in nutraceutical and pharmaceutical technology. Finally, we predict that the advent of intense research efforts on PDVs may disclose new frontiers in plant biotechnology applied to nanomedicine.

Panax ginseng-Derived Extracellular Vesicles Facilitate Anti-Senescence Effects in Human Skin Cells: An Eco-Friendly and Sustainable Way to Use Ginseng Substances

Ginseng is a traditional herbal medicine in eastern Asian countries. Most active constituents in ginseng are prepared via fermentation or organic acid pretreatment. Extracellular vesicles (EVs) are released by most organisms from prokaryotes to eukaryotes and play central roles in intra- and inter-species communications. Plants produce EVs upon exposure to microbes; however, their direct functions and utility for human health are barely known, except for being proposed as delivery vehicles. In this study, we isolated EVs from ginseng roots (GrEVs) or the culture supernatants of ginseng cells (GcEVs) derived from Panax ginseng C.A. Meyer and investigated their biological effects on human skin cells. GrEV or GcEV treatments improved the replicative senescent or senescence-associated pigmented phenotypes of human dermal fibroblasts or ultraviolet B radiation-treated human melanocytes, respectively, by downregulating senescence-associated molecules and/or melanogenesis-related proteins. Based on comprehensive lipidomic analysis using liquid chromatography mass spectrometry, the lipidomic profile of GrEVs differed from that of the parental root extracts, showing significant increases in 70 of 188 identified lipid species and prominent increases in diacylglycerols, some phospholipids (phosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine), and sphingomyelin, revealing their unique vesicular properties. Therefore, our results imply that GEVs represent a novel type of bioactive and sustainable nanomaterials that can be applied to human tissues for improving tissue conditions and targeted delivery of active constituents.

Grapefruit-Derived Micro and Nanovesicles Show Distinct Metabolome Profiles and Anticancer Activities in the A375 Human Melanoma Cell Line

Fruit juice is one of the most easily accessible resources for the isolation of plant-derived vesicles. Here we found that micro- and nano-sized vesicles (MVs and NVs) from four Citrus species, C. sinensis, C. limon, C. paradisi and C. aurantium, specifically inhibit the proliferation of lung, skin and breast cancer cells, with no substantial effect on the growth of non-cancer cells. Cellular and molecular analyses demonstrate that grapefruit-derived vesicles cause cell cycle arrest at G2/M checkpoint associated with a reduced cyclins B1 and B2 expression levels and the upregulation of cell cycle inhibitor p21. Further data suggest the inhibition of Akt and ERK signalling, reduced intercellular cell adhesion molecule-1 and cathepsins expressions, and the presence of cleaved PARP-1, all associated with the observed changes at the cellular level. Gas chromatography-mass spectrometry-based metabolomics reveals distinct metabolite profiles for the juice and vesicle fractions. NVs exhibit a high relative amount of amino acids and organic acids whereas MVs and fruit juice are characterized by a high percentage of sugars and sugar derivatives. Grapefruit-derived NVs are in particular rich in alpha–hydroxy acids and leucine/isoleucine, myo-inositol and doconexent, while quininic acid was detected in MVs. Our findings reveal the metabolite signatures of grapefruit-derived vesicles and substantiate their potential use in new anticancer strategies.

Plant Exosome-like Nanovesicles: Emerging Therapeutics and Drug Delivery Nanoplatforms

Plant exosome-like nanovesicles, being innately replete with bioactive lipids, proteins, RNA, and other pharmacologically active molecules, offer unique morphological and compositional characteristics as natural nanocarriers. Furthermore, their compelling physicochemical traits underpin their modulative role in physiological processes, all of which have fostered the concept that these nanovesicles may be highly proficient in the development of next-generation biotherapeutic and drug delivery nanoplatforms to meet the ever-stringent demands of current clinical challenges. This review systemically deals with various facets of plant exosome-like nanovesicles ranging from their origin and isolation to identification of morphological composition, biological functions, and cargo-loading mechanisms. Efforts are made to encompass their biotherapeutic roles by elucidating their immunological modulating, anti-tumor, regenerative, and anti-inflammatory roles. We also shed light on re-engineering these nanovesicles into robust, innocuous, and non-immunogenic nanovectors for drug delivery through multiple stringent biological hindrances to various targeted organs such as intestine and brain. Finally, recent advances centered around plant exosome-like nanovesicles along with new insights into transdermal, transmembrane and targeting mechanisms of these vesicles are also elucidated. We expect that the continuing development of plant exosome-like nanovesicle-based therapeutic and delivery nanoplatforms will promote their clinical applications.

Arabidopsis leaf extracellular vesicles in wound-induced jasmonate accumulation

The plant extracellular vesicles (EVs) are lipid-enveloped nano-particles containing proteins, nucleic acids and metabolites and function in plant development and response. The Arabidopsis four transmembrane protein TETRASPANIN 8 (TET8) knock-out mutant tet8 secreted less EVs than the wild-type (WT). In this report, we show that the tet8 mutant was attenuated in the plant hormone jasmonate (JA) accumulation in response to mechanical wounding treatment. We also noticed that the EVs contained a high level of phospholipids phosphatidic acids (PAs) which may serve as precursors of JA biosynthesis during wound-triggered-self-healing processes. Thus, we propose an open question about a potential role of EVs or TET8 or both in damage-associated JA response.

Expression Kinetics of Regulatory Genes Involved in the Vesicle Trafficking Processes Operating in Tomato Flower Abscission Zone Cells during Pedicel Abscission

The abscission process occurs in a specific abscission zone (AZ) as a consequence of the middle lamella dissolution, cell wall degradation, and formation of a defense layer. The proteins and metabolites related to these processes are secreted by vesicle trafficking through the plasma membrane to the cell wall and middle lamella of the separating cells in the AZ. We investigated this process, since the regulation of vesicle trafficking in abscission systems is poorly understood. The data obtained describe, for the first time, the kinetics of the upregulated expression of genes encoding the components involved in vesicle trafficking, occurring specifically in the tomato (Solanum lycopersicum) flower AZ (FAZ) during pedicel abscission induced by flower removal. The genes encoding vesicle trafficking components included soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), SNARE regulators, and small GTPases. Our results clearly show how the processes of protein secretion by vesicle trafficking are regulated, programmed, and orchestrated at the level of gene expression in the FAZ. The data provide evidence for target proteins, which can be further used for affinity purification of plant vesicles in their natural state. Such analyses and dissection of the complex vesicle trafficking networks are essential for further elucidating the mechanism of organ abscission.

Deciphering the Novel Role of AtMIN7 in Cuticle Formation and Defense against the Bacterial Pathogen Infection

The cuticle is the outermost layer of plant aerial tissue that interacts with the environment and protects plants against water loss and various biotic and abiotic stresses. ADP ribosylation factor guanine nucleotide exchange factor proteins (ARF-GEFs) are key components of the vesicle trafficking system. Our study discovers that AtMIN7, an Arabidopsis ARF-GEF, is critical for cuticle formation and related leaf surface defense against the bacterial pathogen Pseudomonas syringae pathovar tomato (Pto). Our transmission electron microscopy and scanning electron microscopy studies indicate that the atmin7 mutant leaves have a thinner cuticular layer, defective stomata structure, and impaired cuticle ledge of stomata compared to the leaves of wild type plants. GC–MS analysis further revealed that the amount of cutin monomers was significantly reduced in atmin7 mutant plants. Furthermore, the exogenous application of either of three plant hormones—salicylic acid, jasmonic acid, or abscisic acid—enhanced the cuticle formation in atmin7 mutant leaves and the related defense responses to the bacterial Pto infection. Thus, transport of cutin-related components by AtMIN7 may contribute to its impact on cuticle formation and related defense function.

The Multiple Facets of Plant-Fungal Interactions Revealed Through Plant and Fungal Secretomics

The plant secretome is usually considered in the frame of proteomics, aiming at characterizing extracellular proteins, their biological roles and the mechanisms accounting for their secretion in the extracellular space. In this review, we aim to highlight recent results pertaining to secretion through the conventional and unconventional protein secretion pathways notably those involving plant exosomes or extracellular vesicles. Furthermore, plants are well known to actively secrete a large array of different molecules from polymers (e.g. extracellular RNA and DNA) to small compounds (e.g. ATP, phytochemicals, secondary metabolites, phytohormones). All of these play pivotal roles in plant-fungi (or oomycetes) interactions, both for beneficial (mycorrhizal fungi) and deleterious outcomes (pathogens) for the plant. For instance, recent work reveals that such secretion of small molecules by roots is of paramount importance to sculpt the rhizospheric microbiota. Our aim in this review is to extend the definition of the plant and fungal secretomes to a broader sense to better understand the functioning of the plant/microorganisms holobiont. Fundamental perspectives will be brought to light along with the novel tools that should support establishing an environment-friendly and sustainable agriculture.

A Diverse Membrane Interaction Network for Plant Multivesicular Bodies: Roles in Proteins Vacuolar Delivery and Unconventional Secretion

Vesicle trafficking between the membrane-bound organelles in plant cells plays crucial roles in the precise transportation of various materials, and thus supports cell proliferation and cellular polarization. Conventionally, plant prevacuolar compartments (PVCs), identified as multivesicular bodies (MVBs), play important roles in both the secretory pathway as intermediate compartments and the endocytic pathway as late endosomes. In recent years, the PVC/MVBs have been proposed to play important roles in both protein vacuolar delivery and unconventional secretion, but several important questions on the new regulators and environmental cues that coordinate the PVC/MVB-organelle membrane interactions and their biological significances remain. In this review, we first summarize the identity and nature of the plant PVC/MVBs, and then we present an update on our current understanding on the interaction of PVC/MVBs with other organelles in the plant endomembrane system with focus on the vacuole, autophagosome, and plasma membrane (PM) in plant development and stress responses. Finally, we raise some open questions and present future perspectives in the study of PVC/MVB-organelle interactions and associated biological functions.

Plant extracellular vesicles

Exocytosis is a key mechanism for delivering materials into the extracellular space for cell function and communication. In plant cells, conventional protein secretion (CPS) is achieved via an ER (endoplasmic reticulum)-Golgi-TGN (trans-Golgi network)-PM (plasma membrane) pathway. Unconventional protein secretion (UPS) bypassing these secretory organelles is also in operation and can potentially lead to the formation of extracellular vesicles (EVs) in plant cells. Although multiple types of EVs have been identified and shown to play important roles in mediating intercellular communications in mammalian cells, there has been a long debate about the possible existence of EVs in plants because of the presence of the cell wall. However, increasing evidence suggests that plants also release EVs having various functions including unconventional protein secretion, RNA transport, and defense against pathogens. In this review, we present an update on the current knowledge about the nature, secretory mechanism, and function of various types of EVs in plants. The key regulators involved in EV secretion are also summarized and discussed. We pay special attention to the function of EVs in plant defense and symbiosis.

Cell Wall Proteome of Wheat Grain Endosperm and Outer Layers at Two Key Stages of Early Development

The cell wall is an important compartment in grain cells that fulfills both structural and functional roles. It has a dynamic structure that is constantly modified during development and in response to biotic and abiotic stresses. Non-structural cell wall proteins (CWPs) are key players in the remodeling of the cell wall during events that punctuate the plant life. Here, a subcellular and quantitative proteomic approach was carried out to identify CWPs possibly involved in changes in cell wall metabolism at two key stages of wheat grain development: the end of the cellularization step and the beginning of storage accumulation. Endosperm and outer layers of wheat grain were analyzed separately as they have different origins (maternal and seed) and functions in grains. Altogether, 734 proteins with predicted signal peptides were identified (CWPs). Functional annotation of CWPs pointed out a large number of proteins potentially involved in cell wall polysaccharide remodeling. In the grain outer layers, numerous proteins involved in cutin formation or lignin polymerization were found, while an unexpected abundance of proteins annotated as plant invertase/pectin methyl esterase inhibitors were identified in the endosperm. In addition, numerous CWPs were accumulating in the endosperm at the grain filling stage, thus revealing strong metabolic activities in the cell wall during endosperm cell differentiation, while protein accumulation was more intense at the earlier stage of development in outer layers. Altogether, our work gives important information on cell wall metabolism during early grain development in both parts of the grain, namely the endosperm and outer layers. The wheat cell wall proteome is the largest cell wall proteome of a monocot species found so far.

A safe ride in extracellular vesicles - small RNA trafficking between plant hosts and pathogens

Communication between plants and pathogens requires the transport of regulatory molecules across cellular boundaries, which is essential for host defense and pathogen virulence. Previous research has largely focused on protein transport, but, which other molecules function in communication, and how they are transported remains under explored. Recent studies discovered that small RNAs (sRNAs) are transported between plants and pathogens, which can silence target genes in the interacting organisms and regulate host immunity and pathogen infection, a mechanism called 'cross-kingdom RNA interference (RNAi)'. Further studies indicate that plant extracellular vesicles (EVs) are essential for sRNA trafficking and host-pathogen communication. This review will focus on the latest advances in our understanding of plant EVs and their roles in transporting regulatory molecules, especially sRNAs, between hosts and pathogens.

Exosomes in the phloem and xylem of woody plants

Exosomes in the secondary phloem and secondary xylem of angiosperms and gymnosperms have physiological roles in the storage and transport of endoglucanases. Knowledge of plant extracellular vesicles (EVs) is limited by their presence in the apoplastic fluid of seeds and leaves. The contents of plant EVs and their biological functions are unclear. The aim of the present study was to expand our knowledge of EVs in woody plants. Sample splits were prepared from branch and stem samples from angiosperms and gymnosperms after cryomechanical destruction with liquid nitrogen. The study methods included scanning electron (SEM), atomic force microscopy (AFM), endoglucanase activity measurement. EVs visualized on the internal layers of the cell walls proved to be exosomes according to their diameter (65-145 nm). SEM revealed cup-shaped structures characteristic of exosomes in a dry state. Plant exosomes in the form of globules in the native state were visualized for the first time by AFM. Exosomes were present both in the active and dormant cambium. Erosion zones were observed at the sites of exosome localization. The activity of endo-1,4-β-glucanase was detected in Picea xylem, while the RNA level was very low, suggesting that endo-1,4-β-glucanases were preserved in the exosomes. There are grounds to assert that endo-1,4-β-glucanases delivered by exosomes participated in pit cavity formation in the S₁ layer of xylary fibres. A possible mechanism of endo-1,4-β-glucanase action in the biosynthesis of the secondary wall is proposed. These results demonstrate that the physiological role of the exosomes in the phloem and xylem is the storage and transport of endo-1,4-β-glucanases participating in cell wall remodeling in woody plants. Present study expands our knowledge about plant exosomes.

Specific trophoblast transcripts transferred by extracellular vesicles affect gene expression in endometrial epithelial cells and may have a role in embryo-maternal crosstalk

Background

Successful establishment of pregnancy hinges on appropriate communication between the embryo and the uterus prior to implantation, but the nature of this communication remains poorly understood. Here, we tested the hypothesis that the endometrium is receptive to embryo-derived signals in the form of RNA.

Methods

We have utilized a non-contact co culture system to simulate the conditions of pre implantation environment of the uterus. We bioorthogonally tagged embryonic RNA and tracked the transferred transcripts to endometrium. Transferred transcripts were separated from endometrial transcripts and sequenced. Changes in endometrial transcripts were quantified using quantitative PCR.

Results

We show that three specific transcripts are transferred to endometrial cells. We subsequently demonstrate a role of extracellular vesicles (EVs) in this process, as EVs obtained from cultured trophoblast spheroids incubated with endometrial cells induced down-regulation of all the three identified transcripts in endometrial cells.

Finally, we show that EVs/nanoparticles captured from conditioned culture media of viable embryos as opposed to degenerating embryos induce ZNF81 down-regulation in endometrial cells, hinting at the functional importance of this intercellular communication.

Conclusion

Ultimately, our findings demonstrate the existence of an RNA-based communication which may be of critical importance for the establishment of pregnancy.

Answers to naysayers regarding microbial extracellular vesicles

It is now over 30 years since the discovery of extracellular vesicles (EVs) in Gram-negative bacteria. However, for cell-walled microbes such as fungi, mycobacteria and Gram-positive bacteria it was thought that EV release would be impossible, since such structures were not believed to cross the thick cell wall. This notion was disproven 10 years ago with the discovery of EVs in fungi, mycobacteria, and gram-positive bacteria. Today, EVs have been described in practically every species tested, ranging from Fungi through Bacteria and Archaea, suggesting that EVs are a feature of every living cell. However, there continues to be skepticism in some quarters regarding EV release and their biological significance. In this review, we list doubts that have been verbalized to us and provide answers to counter them. In our opinion, there is no doubt as to existence and physiological function of EVs and we take this opportunity to highlight the most pressing topics in our understanding of the biological processes underlying these structures.

The Dynamics of the Cell Wall Proteome of Developing Alfalfa Stems

In this study, the cell-wall-enriched subproteomes at three different heights of alfalfa stems were compared. Since these three heights correspond to different states in stem development, a view on the dynamics of the cell wall proteome during cell maturation is obtained. This study of cell wall protein-enriched fractions forms the basis for a description of the development process of the cell wall and the linking cell wall localized proteins with the evolution of cell wall composition and structure. The sequential extraction of cell wall proteins with CaCl2, EGTA, and LiCl-complemented buffers was combined with a gel-based proteome approach and multivariate analysis. Although the highest similarities were observed between the apical and intermediate stem regions, the proteome patterns are characteristic for each region. Proteins that bind carbohydrates and have proteolytic activity, as well as enzymes involved in glycan remobilization, accumulate in the basal stem region. Beta-amylase and ferritin likewise accumulate more in the basal stem segment. Therefore, remobilization of nutrients appears to be an important process in the oldest stem segment. The intermediate and apical regions are sites of cell wall polymer remodeling, as suggested by the high abundance of proteins involved in the remodeling of the cell wall, such as xyloglucan endoglucosylase, beta-galactosidase, or the BURP-domain containing polygalacturonase non-catalytic subunit. However, the most striking change between the different stem parts is the strong accumulation of a DUF642-conserved domain containing protein in the apical region of the stem, which suggests a particular role of this protein during the early development of stem tissues.