Plant exosomes: using an unconventional exit to prevent pathogen entry?

Exosome-like Nanoparticles, High in Trans-δ-Viniferin Derivatives, Produced from Grape Cell Cultures: Preparation, Characterization, and Anticancer Properties

Background: Recent interest in plant-derived exosome-like nanoparticles (ENs) has surged due to their therapeutic potential, which includes antioxidant, anti-inflammatory, and anticancer activities. These properties are attributed to their cargo of bioactive metabolites and other endogenous molecules. However, the properties of ENs isolated from plant cell cultures remain less explored. Methods: In this investigation, grape callus-derived ENs (GCENs) were isolated using differential ultracentrifugation techniques. Structural analysis through electron microscopy, nanoparticle tracking analysis, and western blotting confirmed that GCENs qualify as exosome-like nanovesicles. Results: These GCENs contained significant amounts of microRNAs and proteins characteristic of plant-derived ENs, as well as trans-δ-viniferin, a notable stilbenoid known for its health-promoting properties. Functional assays revealed that the GCENs reduced the viability of the triple-negative breast cancer cell line MDA-MB-231 in a dose-dependent manner. Moreover, the GCENs exhibited negligible effects on the viability of normal human embryonic kidney (HEK) 293 cells, indicating selective cytotoxicity. Notably, treatment with these GCENs led to cell cycle arrest in the G1 phase and triggered apoptosis in the MDA-MB-231 cell line. Conclusions: Overall, this study underscores the potential of grape callus-derived nanovectors as natural carriers of stilbenoids and proposes their application as a novel and effective approach in the management of cancer.

Vesicle trafficking pathways in defence-related cell wall modifications: papillae and encasements

Filamentous pathogens that cause plant diseases such as powdery mildew, rust, anthracnose, and late blight continue to represent an enormous challenge for farmers worldwide. Interestingly, these pathogens, although phylogenetically distant, initiate pathogenesis in a very similar way by penetrating the cell wall and establishing a feeding structure inside the plant host cell. To prevent pathogen ingress, the host cell responds by forming defence structures known as papillae and encasements that are thought to mediate pre- and post-invasive immunity, respectively. This form of defence is evolutionarily conserved in land plants and is highly effective and durable against a broad selection of non-adapted filamentous pathogens. As most pathogens have evolved strategies to overcome the defences of only a limited range of host plants, the papilla/encasement response could hold the potential to become an optimal transfer of resistance from one plant species to another. In this review I lay out current knowledge of the involvement of membrane trafficking that forms these important defence structures and highlight some of the questions that still need to be resolved.

Ginseng root-derived exosome-like nanoparticles protect skin from UV irradiation and oxidative stress by suppressing activator protein-1 signaling and limiting the generation of reactive oxygen species

Background

Recently, plant-derived exosome-like nanoparticles (PDENs) have been isolated, and active research was focusing on understanding their properties and functions. In this study, the characteristics and molecular properties of ginseng root-derived exosome-like nanoparticles (GrDENs) were examined in terms of skin protection.

Methods

HPLC-MS protocols were used to analyze the ginsenoside contents in GrDENs. To investigate the beneficial effect of GrDENs on skin, HaCaT cells were pre-treated with GrDENs (0-2 × 109 particles/mL), and followed by UVB irradiation or H2O2 exposure. In addition, the antioxidant activity of GrDENs was measured using a fluorescence microscope or flow cytometry. Finally, molecular mechanisms were examined with immunoblotting analysis.

Results

GrDENs contained detectable levels of ginsenosides (Re, Rg1, Rb1, Rf, Rg2 (S), Gyp17, Rd, C-Mc1, C-O, and F2). In UVB-irradiated HaCaT cells, GrDENs protected cells from death and reduced ROS production. GrDENs downregulated the mRNA expression of proapoptotic genes, including BAX, caspase-1, -3, -6, -7, and -8 and the ratio of cleaved caspase-8, -9, and -3 in a dose-dependent manner. In addition, GrDENs reduced the mRNA levels of aging-related genes (MMP2 and 3), proinflammatory genes (COX-2 and IL-6), and cellular senescence biomarker p21, possibly by suppressing activator protein-1 signaling.

Conclusions

This study demonstrates the protective effects of GrDENs against skin damage caused by UV and oxidative stress, providing new insights into beneficial uses of ginseng. In particular, our results suggest GrDENs as a potential active ingredient in cosmeceuticals to promote skin health.

Plant-derived exosomes: a green approach for cancer drug delivery

Plant-derived exosomes (PDEs) are natural extracellular vesicles (EVs). In the current decade, they have been highlighted for cancer therapeutic development. Cancer is a global health crisis and it requires an effective, affordable, and less side effect-based treatment. Emerging research based on PDEs suggests that they have immense potential to be considered as a therapeutic option. Research evidences indicate that PDEs' internal molecular cargos show impressive cancer prevention activity with less toxicity. PDEs-based drug delivery systems overcome several limitations of traditional drug delivery tools. Extraction of PDEs from plant sources employ diverse methodologies, encompassing ultracentrifugation, immunoaffinity, size-based isolation, and precipitation, each with distinct advantages and limitations. The core constituents of PDEs comprise of lipids, proteins, DNA, and RNA. Worldwide, a few clinical trials on plant-derived exosomes are underway, and regulatory affairs for their use as therapeutic agents are still not understood with clarity. This review aims to comprehensively analyze the current state of research on plant-derived exosomes as a promising avenue for drug delivery, highlighting anticancer activity, challenges, and future orientation in effective cancer therapeutic development.

Evaluation of Antioxidant Activity and Drug Delivery Potential of Cell-Derived Extracellular Vesicles from Citrus reticulata Blanco cv. 'Dahongpao'

Plant extracellular vesicles (PEVs) have attracted increasing attention due to their rich composition, good antioxidant and anti-inflammatory activity, and ability to transport drugs. As a common fruit, citrus is an ideal material for extracting PEVs because of the diversity and abundance of bioactive substances in it. In our study, citrus-derived extracellular vesicles (CEVs) were extracted from red mandarin (Citrus reticulata Blanco cv. 'Dahongpao') and it was found that they contain high levels of lipids, proteins, and carbohydrates. The high levels of total phenols and total flavonoids suggest that CEVs have good chemical antioxidant properties. We also demonstrated through cell experiments that CEVs have significant antioxidant and anti-inflammatory effects. Furthermore, we found that CEVs have an encapsulation rate of 71.5 ± 0.19% and a high drug-carrying capacity of 4.96 ± 0.22% and can enhance antioxidant and anti-inflammatory activity when loaded with tangeretin. Our results show that CEVs contain abundant bioactive components, have low toxicity, exhibit good antioxidant and anti-inflammatory properties, and can serve as drug delivery agents. This study has important implications for utilizing citrus materials and developing natural anti-oxidative and anti-inflammatory biomaterials.

Rgl-exomiR-7972, a novel plant exosomal microRNA derived from fresh Rehmanniae Radix, ameliorated lipopolysaccharide-induced acute lung injury and gut dysbiosis

Plant-derived exosome-like nanoparticles (ELNs) have been proposed as a novel therapeutic tool for preventing human diseases. However, the number of well-verified plant ELNs remains limited. In this study, the microRNAs in ELNs derived from fresh Rehmanniae Radix, a well-known traditional Chinese herb for treating inflammatory and metabolic diseases, were determined by using microRNA sequencing to investigate the active components in the ELNs and the protection against lipopolysaccharide (LPS)-induced acute lung inflammation in vivo and in vitro. The results showed that rgl-miR-7972 (miR-7972) was the main ingredient in ELNs. It exerted stronger protective activities against LPS-induced acute lung inflammation than catalpol and acteoside, which are two well-known chemical markers in this herb. Moreover, miR-7972 decreased the production of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), reactive oxygen species (ROS) and nitric oxide (NO) in LPS-exposed RAW264.7 cells, thereby facilitating M2 macrophage polarization. Mechanically, miR-7972 downregulated the expression of G protein-coupled receptor 161 (GPR161), activating the Hedgehog pathway, and inhibited the biofilm form of Escherichia coli via targeting virulence gene sxt2. Therefore, miR-7972 derived from fresh R. Radix alleviated LPS-induced lung inflammation by targeting the GPR161-mediated Hedgehog pathway, recovering gut microbiota dysbiosis. It also provided a new direction for gaining novel bioactivity nucleic acid drugs and broadening the knowledge on cross-kingdom physiological regulation through miRNAs.

Engineered Plant-Derived Nanovesicles Facilitate Tumor Therapy: Natural Bioactivity Plus Drug Controlled Release Platform

Tumors are the second-most common disease in the world, killing people at an alarming rate. As issues with drug resistance, lack of targeting, and severe side effects are revealed, there is a growing demand for precision-targeted drug delivery systems. Plant-derived nanovesicles (PDNVs), which arecomposed of proteins, lipids, RNA, and metabolites, are widely distributed and readily accessible. The potential for anti-proliferative, pro-apoptotic, and drug-resistant-reversing effects on tumor cells, as well as the ability to alter the tumor microenvironment (TME) by modulating tumor-specific immune cells, make PDNVs promising anti-tumor therapeutics. With a lipid bilayer structure that allows drug loading and a transmembrane capacity readily endocytosed by cells, PDNVs are also expected to become a new drug delivery platform. Exogenous modifications of PDNVs enhance their circulating stability, tumor targeting ability, high cell endocytosis rate, and controlled-release capacity. In this review, we summarize PDNVs' natural antitumor activity, as well as engineered PDNVs as efficient precision-targeted drug delivery tools that enhance therapeutic effects. Additionally, we discuss critical considerations related to the issues raised in this area, which will encourage researchers to improve PDNVs as better anti-tumor therapeutics for clinic applications.

Development of Blueberry-Derived Extracellular Nanovesicles for Immunomodulatory Therapy

Over the past decade, there has been a significant expansion in the development of plant-derived extracellular nanovesicles (EVs) as an effective drug delivery system for precision therapy. However, the lack of effective methods for the isolation and characterization of plant EVs hampers progress in the field. To solve a challenge related to systemic separation and characterization in the plant-derived EV field, herein, we report the development of a simple 3D inner filter-based method that allows the extraction of apoplastic fluid (AF) from blueberry, facilitating EV isolation as well as effective downstream applications. Class I chitinase (PR-3) was found in blueberry-derived EVs (BENVs). As Class I chitinase is expressed in a wide range of plants, it could serve as a universal marker for plant-derived EVs. Significantly, the BENVs exhibit not only higher drug loading capacity than that reported for other EVs but also possess the ability to modulate the release of the proinflammatory cytokine IL-8 and total glutathione in response to oxidative stress. Therefore, the BENV is a promising edible multifunctional nano-bio-platform for future immunomodulatory therapies.

Genome-wide identification and analysis of a cotton secretome reveals its role in resistance against Verticillium dahliae

BACKGROUND

The extracellular space between the cell wall and plasma membrane is a battlefield in plant-pathogen interactions. Within this space, the pathogen employs its secretome to attack the host in a variety of ways, including immunity manipulation. However, the role of the plant secretome is rarely studied for its role in disease resistance.

RESULTS

Here, we examined the secretome of Verticillium wilt-resistant Gossypium hirsutum cultivar Zhongzhimian No.2 (ZZM2, encoding 95,327 predicted coding sequences) to determine its role in disease resistance against the wilt causal agent, Verticillium dahliae. Bioinformatics-driven analyses showed that the ZZM2 genome encodes 2085 secreted proteins and that these display disequilibrium in their distribution among the chromosomes. The cotton secretome displayed differences in the abundance of certain amino acid residues as compared to the remaining encoded proteins due to the localization of these putative proteins in the extracellular space. The secretome analysis revealed conservation for an allotetraploid genome, which nevertheless exhibited variation among orthologs and comparable unique genes between the two sub-genomes. Secretome annotation strongly suggested its involvement in extracellular stress responses (hydrolase activity, oxidoreductase activity, and extracellular region, etc.), thus contributing to resistance against the V. dahliae infection. Furthermore, the defense response genes (immunity marker NbHIN1, salicylic acid marker NbPR1, and jasmonic acid marker NbLOX4) were activated to varying degrees when Nicotina benthamiana leaves were agro-infiltrated with 28 randomly selected members, suggesting that the secretome plays an important role in the immunity response. Finally, gene silencing assays of 11 members from 13 selected candidates in ZZM2 displayed higher susceptibility to V. dahliae, suggesting that the secretome members confer the Verticillium wilt resistance in cotton.

CONCLUSIONS

Our data demonstrate that the cotton secretome plays an important role in Verticillium wilt resistance, facilitating the development of the resistance gene markers and increasing the understanding of the mechanisms regulating disease resistance.

TETRASPANIN 8-1 from Phaseolus vulgaris plays a key role during mutualistic interactions

Arbuscular mycorrhizal (AM) fungi and rhizobia form two of the most important plant-microbe associations for the assimilation of phosphorus (P) and nitrogen (N). Symbiont-derived signals are able to coordinate the infection process by triggering multiple responses in the plant root, such as calcium influxes and oscillations, increased reactive oxygen species (ROS), cytoskeletal rearrangements and altered gene expression. An examination was made of the role of tetraspanins, which are transmembrane proteins that self-organize into tetraspanin web regions, where they recruit specific proteins into platforms required for signal transduction, membrane fusion, cell trafficking, and ROS generation. In plant cells, tetraspanins are scaffolding proteins associated with root radial patterning, biotic and abiotic stress responses, cell fate determination, plasmodesmata and hormonal regulation. Some plant tetraspanins, such as Arabidopsis thaliana TETRASPANIN 8 and TETRASPANIN 9 (AtTET8 and AtTET9) are associated with exosomes during inter-kingdom communication. In this study, a homolog of AtTET8, PvTET8-1, in common bean (Phaseolus vulgaris L. var. Negro Jamapa) was examined in roots during interactions with Rhizobium tropici and Rhizophagus irregularis. The promoter of PvTET8-1 contained several cis-acting regulatory DNA elements potentially related to mutualistic interactions, and PvTET8-1 was transcriptionally activated during AM fungal and rhizobial associations. Silencing it decreased the size and number of nodules, nitrogen fixation, and mycorrhizal arbuscule formation, whereas overexpressing it increased the size and number of nodules, and mycorrhizal arbuscule formation but decreased nitrogen fixation. PvTET8-1 appears to be an important element in both of these mutualistic interactions, perhaps through its interaction with NADPH oxidase and the generation of ROS during the infection processes.

Novel Technologies for Exosome and Exosome-like Nanovesicle Procurement and Enhancement

Exosomes are extracellular nanovesicles commonly produced by mammalian cells that in recent years have risen as a novel strategy for drug delivery systems and cancer therapy because of their innate specificity and high bioavailability. However, there are limitations that undermine their potential. Among them is the lack of mass production capacity with the current available sources and the failure to reach the intended therapeutic effect because of their insufficient uptake or their rapid clearance once administered. This review aims to show the current advances in overcoming these limitations by presenting, firstly, reported strategies to improve exosome and exosome-like nanovesicle extraction from possible novel eukaryotic sources, including animals, plants, and protozoa; and secondly, alternative modification methods that functionalize exosomes by conferring them higher targeting capacity and protection from organism defenses, which results in an increase in the attachment of ligands and cellular uptake of inorganic materials. However, even when these strategies might address some of the obstacles in their procurement and therapeutic use, there are still several aspects that need to be addressed, so several perspectives of the matter are also presented and analyzed throughout this work.

The multifaceted interactions between pathogens and host ESCRT machinery

The Endosomal Sorting Complex Required for Transport (ESCRT) machinery consists of multiple protein complexes that coordinate vesicle budding away from the host cytosol. ESCRTs function in many fundamental cellular processes including the biogenesis of multivesicular bodies and exosomes, membrane repair and restoration, and cell abscission during cytokinesis. Work over the past 2 decades has shown that a diverse cohort of viruses critically rely upon host ESCRT machinery for virus replication and envelopment. More recent studies reported that intracellular bacteria and the intracellular parasite Toxoplasma gondii benefit from, antagonize, or exploit host ESCRT machinery to preserve their intracellular niche, gain resources, or egress from infected cells. Here, we review how intracellular pathogens interact with the ESCRT machinery of their hosts, highlighting the variety of strategies they use to bind ESCRT complexes using short linear amino acid motifs like those used by ESCRTs to sequentially assemble on target membranes. Future work exposing new mechanisms of this molecular mimicry will yield novel insight of how pathogens exploit host ESCRT machinery and how ESCRTs facilitate key cellular processes.

Garlic-derived exosomes regulate PFKFB3 expression to relieve liver dysfunction in high-fat diet-fed mice via macrophage-hepatocyte crosstalk

BACKGROUND

Although macrophage-mediated low-grade chronic inflammation and liver dysfunction have been found to be associated with the development of non-alcoholic fatty (NAFLD) and widely reported, but strategies and drugs targeting macrophages for the treatment of NAFLD are limited.

HYPOTHESIS/PURPOSE

Garlic-derived exosomes (GDE) can be useful for NAFLD due to its anti-inflammatory activity. Clarify whether GDE improves liver dysfunction through macrophage-hepatocyte crosstalk.

METHODS

GDE was isolated with PEG precipitation and ultracentrifuge. Inflammatory cytokines were detected by qRT-PCR and ELISA. Expression of 6-phosphofructo-2-kinase/fructose-2, 6-biphosphatase 3 (PFKFB3) was determined using qRT-PCR and western blot. Crosstalk between macrophages and hepatocytes was identified through a co-culture experiment. Small RNA sequencing and bioinformatic analysis were used to identify the key element of GDE regulating the expression of PFKFB3 gene.

RESULTS

GDE regulated the expression of PFKFB3 to reduce the inflammatory response in LPS-treated differentiated THP-1 macrophages. Data from small RNA sequencing and bioinformatics analysis reveal that miR-396e, one of the most abundant miRNAs of GDE, is the key component to regulate PFKFB3 expression. Mechanistically, miR-396e-mediating PFKFB3 expression plays a crucial role in GDE inhibiting inflammatory response and enhancing lipid metabolism in hepatocytes via the macrophage-hepatocyte crosstalk. Notably, GDE supplementation reduced the inflammatory response and improved liver dysfunction in high-fat diet-fed mice.

CONCLUSION

GDE may be useful for improving the symptoms of NAFLD via macrophage-hepatocyte crosstalk and its role in PFKFB3 expression.

Callose metabolism and the regulation of cell walls and plasmodesmata during plant mutualistic and pathogenic interactions

Cell walls are essential for plant growth and development, providing support and protection from external environments. Callose is a glucan that accumulates in specialized cell wall microdomains including around intercellular pores called plasmodesmata. Despite representing a small percentage of the cell wall (~0.3% in the model plant Arabidopsis thaliana), callose accumulation regulates important biological processes such as phloem and pollen development, cell division, organ formation, responses to pathogenic invasion and to changes in nutrients and toxic metals in the soil. Callose accumulation modifies cell wall properties and restricts plasmodesmata aperture, affecting the transport of signaling proteins and RNA molecules that regulate plant developmental and environmental responses. Although the importance of callose, at and outside plasmodesmata cell walls, is widely recognized, the underlying mechanisms controlling changes in its synthesis and degradation are still unresolved. In this review, we explore the most recent literature addressing callose metabolism with a focus on the molecular factors affecting callose accumulation in response to mutualistic symbionts and pathogenic elicitors. We discuss commonalities in the signaling pathways, identify research gaps and highlight opportunities to target callose in the improvement of plant responses to beneficial versus pathogenic microbes.

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

Introduction

In the last decade, it has been discovered that allergen-bearing extracellular nanovesicles, termed "pollensomes", are released by pollen during germination. These extracellular vesicles (EVs) may play an important role in pollen-pistil interaction during fertilization, stabilizing the secreted bioactive molecules and allowing long-distance signaling. However, the molecular composition and the biological role of these EVs are still unclear. The present study had two main aims: (I) to clarify whether pollen germination is needed to release pollensomes, or if they can be secreted also in high humidity conditions; and (II) to investigate the molecular features of pollensomes following the most recent guidelines for EVs isolation and identification.

Methods

To do so, pollensomes were isolated from hydrated and germinated kiwi (Actinidia chinensis Planch.) pollen, and characterized using imaging techniques, immunoblotting, and proteomics.

Results

These analyses revealed that only germinated kiwi pollen released detectable concentrations of nanoparticles compatible with small EVs for shape and protein content. Moreover, a plant homolog of ALIX, which is a well-recognized and accepted marker of small EVs and exosomes in mammals, was found in pollensomes.

Discussion

The presence of this protein, along with other proteins involved in endocytosis, is consistent with the hypothesis that pollensomes could comprehend a prominent subpopulation of plant exosome-like vesicles.

Peltate trichomes in the dormant shoot apex of Metrodorea nigra, a Rutaceae species with rhythmic growth

In Metrodorea nigra, a Rutaceae species with rhythmic growth, the shoot apex in the dormant stage is enclosed by modified stipules. The young organs are fully covered with peltate secretory trichomes, and these structures remain immersed in a hyaline exudate within a hood-shaped structure. Our study focused on the morpho-functional characterization of the peltate trichomes and cytological events associated with secretion. Shoot apices were collected during both dormant and active stages and processed for anatomical, cytochemical and ultrastructural studies. Trichomes initiate secretion early on, remain active throughout leaf development, but collapse as the leaves expand; at which time secretory cavities start differentiation in the mesophyll and secretion increases as the leaf reaches full expansion. The subcellular apparatus of the trichome head cells is consistent with hydrophilic and lipophilic secretion. Secretion involves two vesicle types: the smaller vesicles are PATAg-positive (periodic acid/thiocarbohydrazide/silver proteinate) for carbohydrates and the larger ones are PATAg-negative. In the first phase of secretory activity, the vesicles containing polysaccharides discharge their contents through exocytosis with the secretion accumulating beneath the cuticle, which detaches from the cell wall. Later, a massive discharge of lipophilic substances (lipids and terpenes/phenols) results in their accumulation between the wall and cuticle. Release of the secretions occurs throughout the cuticular microchannels. Continued protection of the leaves throughout shoot development is ensured by replacement of the collapsed secretory trichomes by oil-secreting cavities. Our findings provide new perspectives for understanding secretion regulation in shoot apices of woody species with rhythmic growth.

Barley endosomal MONENSIN SENSITIVITY1 is a target of the powdery mildew effector CSEP0162 and plays a role in plant immunity

Encasements formed around haustoria and biotrophic hyphae as well as hypersensitive reaction (HR) cell death are essential plant immune responses to filamentous pathogens. In this study we examine the components that may contribute to the absence of these responses in susceptible barley attacked by the powdery mildew fungus. We find that the effector CSEP0162 from this pathogen targets plant MONENSIN SENSITIVITY1 (MON1), which is important for the fusion of multivesicular bodies to their target membranes. Overexpression of CSEP0162 and silencing of barley MON1 both inhibit encasement formation. We find that the Arabidopsis ecotype No-0 has resistance to powdery mildew, and that this is partially dependent on MON1. Surprisingly, we find the MON1-dependent resistance in No-0 not only includes an encasement response, but also an effective HR. Similarly, silencing of MON1 in barley also blocks Mla3-mediated HR-based powdery mildew resistance. Our results indicate that MON1 is a vital plant immunity component, and we speculate that the barley powdery mildew fungus introduces the effector CSEP0162 to target MON1 and hence reduce encasement formation and HR.

Characterization of microRNAs in the cyst nematode Heterodera glycines identifies possible candidates involved in cross-kingdom interactions with its host Glycine max

The soybean cyst nematode (SCN - Heterodera glycines) is one of the most damaging pests to the cultivated soybean worldwide. Using a wide array of stylet-secreted effector proteins, this nematode can restructure its host cells into a complex and highly active feeding structure called the syncytium. Tight regulation of these proteins is thought to be essential to the successful formation of this syncytium. To date, multiple mechanisms have been proposed to regulate the expression of these proteins including through post-transcriptional regulation. MicroRNAs (miRNAs) are a class of small, roughly 22-nucleotide-long, non-coding RNA shown to regulate gene expression through its interaction with the 3' untranslated region of genes. These same small RNAs have also been hypothesized to be able to cross over kingdom barriers and regulate genes in other species in a process called cross-kingdom interactions. In this study, we characterized the miRNome of the SCN via sequencing of small-RNAs isolated from whole nematodes and exosomes representing all developmental stages. We identified 121 miRNA loci encoding 96 distinct miRNA families including multiple lineage- and species-specific candidates. Using a combination of plant- and animal-specific miRNA target predictors, we generated a unique repertoire of miRNA:mRNA interacting partners in the nematode and its host plant leading to the identification of a set of nine probable cross-kingdom miRNA candidates.

Mobility of the syntaxin PEN1 in Arabidopsis reflects functional specialization of the conserved SYP12 clade

Plant innate immunity toward cell-wall penetrating filamentous pathogens relies on the conserved SYP12 clade of secretory syntaxins. In Arabidopsis, the two closely related SYP12 clade members, PEN1 and SYP122, play an overlapping role in this general immunity, which can be complemented by two SYP12 clade members from Marchantia (MpSYP12A and MpSYP12B). However, in addition to the conserved SYP12 clade function, PEN1 alone mediates pre-invasive immunity toward powdery mildew fungi, which likely reflects a specialization of its functionality. Here, we show that the PEN1-specific specialization in immunity correlates with a continuous BFA-sensitive recycling and the ability to accumulate strongly at the growing cell plate. This contrasts with the behavior of SYP122, MpSYP12A, and MpSYP12B, all being more stable at the plasma membrane. We suggest that the highly mobile SYP12 specialization observed for PEN1 is required for a fast pre-invasive immune response to resist attack from powdery mildew fungi.

Extracellular vesicles of cannabis with high CBD content induce anticancer signaling in human hepatocellular carcinoma

Plant-derived extracellular vesicles (EVs) have been the topic of interest in recent years due to their proven therapeutic properties. Intact or manipulated plant EVs have shown antioxidant, anti-inflammatory, and anti-cancerous activities as a result of containing bioactive metabolites and other endogenous molecules. Less is known about the EV efficacy with high levels of bioactive secondary metabolites derived from medicinal or non-edible plants. Numerous data suggest the functionality of Cannabis sativa extract and its phytocannabinoids in cancer treatment. Here, two chemotypes of cannabis with different levels of D-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) were selected. EVs were isolated from each chemotype via differential ultracentrifugation. HPLC analysis was illustrative of the absence of THC in EVs derived from both plants. Therefore, two types of EVs were classified according to their CBD content into high- (H.C-EVs) and low-CBD EVs (L.C-EVs). Electron microscopy and DLS showed both cannabis-derived EVs (CDEVs) can be considered as exosome-like nanovesicles. Cytotoxicity assay showed that H.C-EVs strongly decreased the viability of two hepatocellular carcinoma (HCC) cell lines, HepG2 and Huh-7, in a dose and time-dependent manner compared with L.C-EVs. H.C-EVs had no significant effect on HUVECs normal cell growth. The finding showed that the H.C-EVs arrested the G0/G1 phase in the cell cycle and significantly induced cell death by activating mitochondrial-dependent apoptosis signaling pathways in both HCC cell lines. Altogether, the current study highlights that CDEVs can be an ideal natural vehicle for bioactive phytocannabinoids and a promising strategy in cancer management.

Exosomes: Insights and therapeutic applications in cancer

Cancer refers to the division of abnormal cells at an uncontrollable rate that possesses the ability to infiltrate and destroy normal tissues. It frequently spreads to normal tissues throughout the body, a condition known as metastasis, which is a significant concern. It is the second leading cause of mortality globally and treatment therapy can assist in improving survival rates. Exosomes are the extracellular vesicles secreted by several cells that act as messengers between cells. When engineered, exosomes act as promising drug delivery vehicles that help achieve targeted action at the tumour site and reduce the limitations of conventional treatments such as castration, chemotherapy, radiation, etc. The present review provides an overview of exosomes, the biogenesis, sources, isolation methods and characterization. The current status and applications of chemotherapeutic agents loaded, engineered exosomes in cancer treatment were convoluted.

Unconventional Secretion of Plant Extracellular Vesicles and Their Benefits to Human Health: A Mini Review

Mechanisms devoted to the secretion of proteins via extracellular vesicles (EVs) have been found in mammals, yeasts, and plants. Since they transport a number of leader-less proteins to the plasma membrane or the extracellular space, EVs are considered part of Unconventional protein secretion (UPS) routes. UPS involving EVs are a relatively new field in plants. Aside from their role in plant physiology and immunity, plant extracts containing EVs have also been shown to be beneficial for human health. Therefore, exploring the use of plant EVs in biomedicine and their potential as drug delivery tools is an exciting avenue. Here we give a summary of the state of knowledge on plant EVs, their crosstalk with mammalian systems and potential research routes that could lead to practical applications in therapeutic drug delivery.

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.

Immunity functions of Arabidopsis pathogenesis-related 1 are coupled but not confined to its C-terminus processing and trafficking

The pathogenesis-related 1 (PR1) proteins are members of the cross-kingdom conserved CAP superfamily (from Cysteine-rich secretory protein, Antigen 5, and PR1 proteins). PR1 mRNA expression is frequently used for biotic stress monitoring in plants; however, the molecular mechanisms of its cellular processing, localization, and function are still unknown. To analyse the localization and immunity features of Arabidopsis thaliana PR1, we employed transient expression in Nicotiana benthamiana of the tagged full-length PR1 construct, and also disrupted variants with C-terminal truncations or mutations. We found that en route from the endoplasmic reticulum, the PR1 protein transits via the multivesicular body and undergoes partial proteolytic processing, dependent on an intact C-terminal motif. Importantly, only nonmutated or processing-mimicking variants of PR1 are secreted to the apoplast. The C-terminal proteolytic cleavage releases a protein fragment that acts as a modulator of plant defence responses, including localized cell death control. However, other parts of PR1 also have immunity potential unrelated to cell death. The described modes of the PR1 contribution to immunity were found to be tissue-localized and host plant ontogenesis dependent.

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.

Biogenesis and Biological Functions of Extracellular Vesicles in Cellular and Organismal Communication With Microbes

Extracellular vesicles (EVs) represent a prominent mechanism of transport and interaction between cells, especially microbes. Increasing evidence indicates that EVs play a key role in the physiological and pathological processes of pathogens and other symbionts. Recent research has focused on the specific functions of these vesicles during pathogen-host interactions, including trans-kingdom delivery of small RNAs, proteins and metabolites. Much current research on the function of EVs is focused on immunity and the interactions of microbes with human cells, while the roles of EVs during plant-microbe interactions have recently emerged in importance. In this review, we summarize recent research on the biogenesis of these vesicles and their functions in biology and pathology. Many key questions remain unclear, including the full structural and functional diversity of EVs, the roles of EVs in communication among microbes within microbiomes, how specific cargoes are targeted to EVs, whether EVs are targeted to specific destinations, and the full scope of EVs' transport of virulence effectors and of RNA and DNA molecules.

Plant SYP12 syntaxins mediate an evolutionarily conserved general immunity to filamentous pathogens

Filamentous fungal and oomycete plant pathogens that invade by direct penetration through the leaf epidermal cell wall cause devastating plant diseases. Plant preinvasive immunity toward nonadapted filamentous pathogens is highly effective and durable. Pre- and postinvasive immunity correlates with the formation of evolutionarily conserved and cell-autonomous cell wall structures, named papillae and encasements, respectively. Yet, it is still unresolved how papillae/encasements are formed and whether these defense structures prevent pathogen ingress. Here, we show that in Arabidopsis the two closely related members of the SYP12 clade of syntaxins (PEN1 and SYP122) are indispensable for the formation of papillae and encasements. Moreover, loss-of-function mutants were hampered in preinvasive immunity toward a range of phylogenetically distant nonadapted filamentous pathogens, underlining the versatility and efficacy of this defense. Complementation studies using SYP12s from the early diverging land plant, Marchantia polymorpha, showed that the SYP12 clade immunity function has survived 470 million years of independent evolution. These results suggest that ancestral land plants evolved the SYP12 clade to provide a broad and durable preinvasive immunity to facilitate their life on land and pave the way to a better understanding of how adapted pathogens overcome this ubiquitous plant defense strategy.

Elaboration of a Phytoremediation Strategy for Successful and Sustainable Rehabilitation of Disturbed and Degraded Land

Humans are dependent upon soil which supplies food, fuel, chemicals, medicine, sequesters pollutants, purifies and conveys water, and supports the built environment. In short, we need soil, but it has little or no need of us. Agriculture, mining, urbanization and other human activities result in temporary land-use and once complete, used and degraded land should be rehabilitated and restored to minimize loss of soil carbon. It is generally accepted that the most effective strategy is phyto-remediation. Typically, phytoremediation involves re-invigoration of soil fertility, physicochemical properties, and its microbiome to facilitate establishment of appropriate climax cover vegetation. A myco-phytoremediation technology called Fungcoal was developed in South Africa to achieve these outcomes for land disturbed by coal mining. Here we outline the contemporary and expanded rationale that underpins Fungcoal, which relies on in situ bio-conversion of carbonaceous waste coal or discard, in order to explore the probable origin of humic substances (HS) and soil organic matter (SOM). To achieve this, microbial processing of low-grade coal and discard, including bio-liquefaction and bio-conversion, is examined in some detail. The significance, origin, structure, and mode of action of coal-derived humics are recounted to emphasize the dynamic equilibrium, that is, humification and the derivation of soil organic matter (SOM). The contribution of plant exudate, extracellular vesicles (EV), extra polymeric substances (EPS), and other small molecules as components of the dynamic equilibrium that sustains SOM is highlighted. Arbuscular mycorrhizal fungi (AMF), saprophytic ectomycorrhizal fungi (EMF), and plant growth promoting rhizobacteria (PGPR) are considered essential microbial biocatalysts that provide mutualistic support to sustain plant growth following soil reclamation and restoration. Finally, we posit that de novo synthesis of SOM is by specialized microbial consortia (or ‘humifiers’) which use molecular components from the root metabolome; and, that combinations of functional biocatalyst act to re-establish and maintain the soil dynamic. It is concluded that a bio-scaffold is necessary for functional phytoremediation including maintenance of the SOM dynamic and overall biogeochemistry of organic carbon in the global ecosystem

Algal Cells-Derived Extracellular Vesicles: A Review With Special Emphasis on Their Antimicrobial Effects

Extracellular vesicles (EVs) originated from different cells of approximately all kinds of organisms, recently got more attention because of their potential in the treatment of diseases and reconstructive medicine. To date, lots of studies have been performed on mammalian-derived vesicles, but little attention has been paid to algae and marine cells as valuable sources of EVs. Proving the promising role of EVs in medicine requires sufficient resources to produce qualified microvesicles. Algae, same as its other sister groups, such as plants, have stem cells and stem cell niches. Previous studies showed the EVs in plants and marine cells. So, this study was set out to talk about algal extracellular vesicles. EVs play a major role in cell-to-cell communication to convey molecules, such as RNA/DNA, metabolites, proteins, and lipids within. The components of EVs depends on the origin of the primitive cells or tissues and the isolation method. Sufficient resources are needed to produce high-quality, stable, and compatible EVs as a drug or drug delivery system. Plant stem cells have great potential as a new controllable resource for the production of EVs. The EVs secreted from stem cells can easily be extracted from the cell culture medium and evaluated for medicinal uses. In this review, the aim is to introduce algae stem cells as well as EVs derived from algal cells. In the following, the production of the EVs¸ the properties of EVs extracted from these sources and their antimicrobial effects will be discussed.

Arabidopsis PLDζ1 and PLDζ2 localize to post-Golgi membrane compartments in a partially overlapping manner

Arabidopsis PLDζ1 and PLDζ2 localize to the trans-Golgi network and to compartments including the trans-Golgi network, multi-vesicular bodies, and the tonoplast, respectively, depending on their N-terminal regions containing PX-PH domains. Phospholipase D (PLD) is involved in dynamic cellular processes, including membrane trafficking, cytoskeletal reorganization, and signal transduction for gene expression, through the production of phosphatidic acid in membrane compartments specific to each process. Although PLD plays crucial roles in various plant phenomena, the underlying processes involving PLD for each phenomenon remain largely elusive, partly because the subcellular localization of PLD remains obscure. In this study, we performed comparative subcellular localization analyses of the Arabidopsis thaliana PX-PH-PLDs PLDζ1 and PLDζ2. In mature lateral root cap cells, own promoter-driven fluorescence protein fusions of PLDζ1 localized to the entire trans-Golgi network (TGN) while that of PLDζ2 localized to punctate structures including part of the TGN and multi-vesicular bodies as well as the tonoplast. These localization patterns were reproduced using N-terminal partial proteins, which contain PX-PH domains. An inducibly overexpressed fluorescence protein fusion of the PLDζ2 partial protein first localized to punctate structures, and then accumulated predominantly on the tonoplast. Further domain dissection analysis revealed that the N-terminal moiety preceding the PX-PH domain of PLDζ2 was required for the tonoplast-predominant accumulation. These findings suggest that PLDζ1 and PLDζ2 play partially overlapping but nonetheless distinctive roles in post-Golgi compartments along the membrane trafficking pathway from the TGN to the tonoplast.

Trends in the biological functions and medical applications of extracellular vesicles and analogues

Natural extracellular vesicles (EVs) play important roles in many life processes such as in the intermolecular transfer of substances and genetic information exchanges. Investigating the origins and working mechanisms of natural EVs may provide an understanding of life activities, especially regarding the occurrence and development of diseases. Additionally, due to their vesicular structure, EVs (in small molecules, nucleic acids, proteins, etc.) could act as efficient drug-delivery carriers. Herein, we describe the sources and biological functions of various EVs, summarize the roles of EVs in disease diagnosis and treatment, and review the application of EVs as drug-delivery carriers. We also assess the challenges and perspectives of EVs in biomedical applications.

Identification of viral particles in the apoplast of Nicotiana benthamiana leaves infected by potato virus X

The apoplast is the extracellular space for signalling, nutrient transport, and plant-microbe interactions, but little is known about how plant viruses use the foliar apoplast. Proteomic analysis of the apoplasts isolated from potato virus X (PVX)-infected Nicotiana benthamiana plants showed that the coat protein (CP) is the dominant viral component. The presence of the CP in the apoplast was confirmed by western blot, viral nucleic acid was detected by reverse transcription-PCR and northern blot, and viral particles were observed by transmission electron microscopy (TEM). The apoplast from infected leaves was infectious if rubbed onto healthy leaves but not when infiltrated into them. The exosomes were separated from the apoplast fluid by high-speed centrifugation and TEM showed that PVX particles were not associated with the exosomes. These results suggest that PVX virions are released to the N. benthamiana apoplast in a one-way manner and do not share the bidirectional transport of exosomes.

RNAs on the Go: Extracellular Transfer in Insects with Promising Prospects for Pest Management

RNA-mediated pathways form an important regulatory layer of myriad biological processes. In the last decade, the potential of RNA molecules to contribute to the control of agricultural pests has not been disregarded, specifically via the RNA interference (RNAi) mechanism. In fact, several proofs-of-concept have been made in this scope. Furthermore, a novel research field regarding extracellular RNAs and RNA-based intercellular/interorganismal communication is booming. In this article, we review key discoveries concerning extracellular RNAs in insects, insect RNA-based cell-to-cell communication, and plant-insect transfer of RNA. In addition, we overview the molecular mechanisms implicated in this form of communication and discuss future biotechnological prospects, namely from the insect pest-control perspective.

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.

Simultaneous visualization of callose deposition and plasma membrane for live-cell imaging in plants

The appropriate combination of fluorescent probes enabled the simultaneous visualization of callose deposition and plasma membrane in living Arabidopsis and can be useful for the cell biological study of papilla formation in plants. Localized callose deposition at the site of fungal infection is a central part of papilla formation, which creates a barrier between the host plasma membrane and the cell wall and plays an important role in preventing the penetration of fungal hyphae into the host cells. Using chitin-induced callose deposition as a model system, we examined suitable conditions for the simultaneous visualization of callose deposition and plasma membrane dynamics in living Arabidopsis cotyledons. We found that aniline blue fluorochrome (ABF) for callose staining selectively interferes with FM dyes for membrane visualization depending on the structure of the latter compounds and the proper combination of these fluorescent dyes and staining conditions is a key for successful live-cell imaging. The established conditions enabled the live-cell imaging of chitin-induced callose deposition and host membrane systems. The established system/conditions would also be useful for the cell biological studies on the localized callose deposition in other stress/development-associated processes. The finding that the slight difference in the structure of FM dyes affects the interaction with another fluorescent dye, ABF, would also give useful suggestions for the studies where multiple fluorescent dyes are utilized for live-cell imaging.

A Review of Exosomal Isolation Methods: Is Size Exclusion Chromatography the Best Option?

Extracellular vesicles (EVs) are membranous vesicles secreted by both prokaryotic and eukaryotic cells and play a vital role in intercellular communication. EVs are classified into several subtypes based on their origin, physical characteristics, and biomolecular makeup. Exosomes, a subtype of EVs, are released by the fusion of multivesicular bodies (MVB) with the plasma membrane of the cell. Several methods have been described in literature to isolate exosomes from biofluids including blood, urine, milk, and cell culture media, among others. While differential ultracentrifugation (dUC) has been widely used to isolate exosomes, other techniques including ultrafiltration, precipitating agents such as poly-ethylene glycol (PEG), immunoaffinity capture, microfluidics, and size-exclusion chromatography (SEC) have emerged as credible alternatives with pros and cons associated with each. In this review, we provide a summary of commonly used exosomal isolation techniques with a focus on SEC as an ideal methodology. We evaluate the efficacy of SEC to isolate exosomes from an array of biological fluids, with a particular focus on its application to adipose tissue-derived exosomes. We argue that exosomes isolated via SEC are relatively pure and functional, and that this methodology is reproducible, scalable, inexpensive, and does not require specialized equipment or user expertise. However, it must be noted that while SEC is a good candidate method to isolate exosomes, direct comparative studies are required to support this conclusion.

Plant Cells under Attack: Unconventional Endomembrane Trafficking during Plant Defense

Since plants lack specialized immune cells, each cell has to defend itself independently against a plethora of different pathogens. Therefore, successful plant defense strongly relies on precise and efficient regulation of intracellular processes in every single cell. Smooth trafficking within the plant endomembrane is a prerequisite for a diverse set of immune responses. Pathogen recognition, signaling into the nucleus, cell wall enforcement, secretion of antimicrobial proteins and compounds, as well as generation of reactive oxygen species, all heavily depend on vesicle transport. In contrast, pathogens have developed a variety of different means to manipulate vesicle trafficking to prevent detection or to inhibit specific plant responses. Intriguingly, the plant endomembrane system exhibits remarkable plasticity upon pathogen attack. Unconventional trafficking pathways such as the formation of endoplasmic reticulum (ER) bodies or fusion of the vacuole with the plasma membrane are initiated and enforced as the counteraction. Here, we review the recent findings on unconventional and defense-induced trafficking pathways as the plant´s measures in response to pathogen attack. In addition, we describe the endomembrane system manipulations by different pathogens, with a focus on tethering and fusion events during vesicle trafficking.

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.

Negative Regulation of Age-Related Developmental Leaf Senescence by the IAOx Pathway, PEN1, and PEN3

Early age-related developmental senescence was observed in Arabidopsis cyp79B2/cyp79B3 double mutants that cannot produce indole-3-acetaldoxime (IAOx), the precursor to indole glucosinolates (IGs), camalexin and auxin. The early senescence phenotype was not observed when senescence was induced by darkness. The cyp79B2/cyp79B3 mutants had lower auxin levels, but did not display auxin-deficient phenotypes. Camalexin biosynthesis mutants senesced normally; however, IG transport and exosome-related pen1/pen3 double mutants displayed early senescence. The early senescence in pen1/pen3 mutants depended on salicylic acid and was not observed in pen1 or pen3 single mutants. Quantitation of IGs showed reduced levels in cyp79B2/cyp79B3 mutants, but unchanged levels in pen1/pen3, even though both of these double mutants display early senescence. We discuss how these genetic data provide evidence that IAOx metabolites are playing a protective role in leaf senescence that is dependent on proper trafficking by PEN1 and PEN3, perhaps via the formation of exosomes.

Dietary non-coding RNAs from plants: Fairy tale or treasure?

The past two decades have witnessed soaring interest in the field of non-coding RNAs, largely attributed by its regulatory role in controlling two third of human transcriptional output. Though, there are several classes of non-coding RNAs found in nature, microRNAs takes the central stage because of their pleiotropic roles. In particular, extracellular microRNAs are gaining traction due to their relative stability and bio availability. Extracellular microRNAs has been shown to occur in all living organisms, including dietary plants. Some of the recent reports suggest that these dietary microRNAs pass through the gut, enter systemic circulation and exert biological effects on animal physiology. However, evidences against this hypothesis are also presented in literature and hence this area has been strongly debated. In this review, I will briefly summarise the evidences accumulated for and against this hypothesis and discuss potential implications of such findings in human health.

Exosomes: An emerging factor in atherosclerosis

Atherosclerosis is the main reason for morbidity and death caused by cardiovascular disease which leads to approximately 20% of total death around the world. Exosomes secreted by the cells is a kind of extracellular vesicles with lipid bilayer structure, containing a variety of cell specific lipid, nucleic acid and protein, involved in intercellular communication, plays an important role in different physiological and pathological process. In recent years, with the deepening of research, the role of exosomes in cardiovascular diseases has received extensive attention. This review summarizes the roles of exosomes and exosome-derived from microRNAs, proteins and DNA as biomarkers in the development of atherosclerosis, and explores the mechanism of exosome-mediated intercellular crosstalk in atherosclerosis, providing potential roles for diagnosis and treatment.

Tethering of Multi-Vesicular Bodies and the Tonoplast to the Plasma Membrane in Plants

Tethering of the plasma membrane (PM) and many organelles to the endoplasmic reticulum (ER) for communication and lipid exchange has been widely reported. However, despite growing interest in multi-vesicular bodies (MVBs) as possible sources of exosomes, tethering of MVBs to the PM has not been reported. Here we show that MVBs and the vacuolar membrane (tonoplast) could be tethered to the PM (PM-MVB/TP tethering) by artificial protein fusions or bimolecular fluorescence complementation (BiFC) complexes that contain a peripheral membrane protein that binds the PM and also a protein that binds MVBs or the tonoplast. PM-binding proteins capable of participating in PM-MVB/TP tethering included StRem1.3, BIK1, PBS1, CPK21, and the PtdIns(4)-binding proteins FAPP1 and Osh2. MVB/TP-binding proteins capable of participating in tethering included ARA6, ARA7, RHA1, RABG3f, and the PtdIns(3)P-binding proteins Vam7p and Hrs-2xFYVE. BiFC complexes or protein fusions capable of producing PM-MVB/TP tethering were visualized as large well-defined patches of fluorescence on the PM that could displace PM proteins such as AtFlotillin1 and also could displace cytoplasmic proteins such as soluble GFP. Furthermore, we identified paralogous ubiquitin E3 ligase proteins, SAUL1 (AtPUB44), and AtPUB43 that could produce PM-MVB/TP tethering. SAUL1 and AtPUB43 could produce tethering in uninfected tissue when paired with MVB-binding proteins or when their E3 ligase domain was deleted. When Nicotiana benthamiana leaf tissue was infected with Phytophthora capsici, full length SAUL1 and AtPUB43 localized in membrane patches consistent with PM-MVB/TP tethering. Our findings define new tools for studying PM-MVB/TP tethering and its possible role in plant defense.

SIGNIFICANCE STATEMENT

Although not previously observed, the tethering of multi-vesicular bodies to the plasma membrane is of interest due to the potential role of this process in producing exosomes in plants. Here we describe tools for observing and manipulating the tethering of multi-vesicular bodies and the tonoplast to the plant plasma membrane, and describe two plant proteins that may naturally regulate this process during infection.

Milk-Derived Exosomes and Metabolic Regulation

Exosomes are natural nanoparticles that play an important role in cell-to-cell communication. Communication is achieved through the transfer of cargos, such as microRNAs, from donor to recipient cells and binding of exosomes to cell surface receptors. Exosomes and their cargos are also obtained from dietary sources, such as milk. Exosome and cell glycoproteins are crucial for intestinal uptake. A large fraction of milk exosomes accumulates in the brain, whereas the tissue distribution of microRNA cargos varies among distinct species of microRNA. The fraction of milk exosomes that escapes absorption elicits changes in microbial communities in the gut. Dietary depletion of exosomes and their cargos causes a loss of circulating microRNAs and elicits phenotypes such as loss of cognitive performance, increase in purine metabolites, loss of fecundity, and changes in the immune response. Milk exosomes meet the definition of bioactive food compounds.