The membrane trafficking system is responsible for precise transportation and localization of proteins, lipids, and polysaccharides among single membrane-bound organelles, the plasma membrane, and ...the extracellular space. While the exocytic trafficking pathway is considered to be a default transport pathway in many organisms, including land plants, research has shown that evolutionary processes led to an increase in the number of machinery components involved in the plant exocytic pathway. This study provides an overview of the diversification of exocytic trafficking pathways in plants, which mediate the formation and maintenance of cell polarity, interaction with symbiotic and pathogenic microbes, and cytokinesis. To fulfill these functions, distinct strategies have been employed to reroute secretory/exocytic transport during land plant evolution.
Subcellular localization of proteins acting on the endomembrane system is primarily regulated via membrane trafficking. To obtain and maintain the correct protein composition of the plasma membrane ...and membrane‐bound organelles, the loading of selected cargos into transport vesicles is critically regulated at donor compartments by adaptor proteins binding to the donor membrane, the cargo molecules and the coat‐protein complexes, including the clathrin coat. The ANTH/ENTH/VHS domain‐containing protein superfamily generally comprises a structurally related ENTH, ANTH, or VHS domain in the N‐terminal region and a variable C‐terminal region, which is thought to act as an adaptor during transport vesicle formation. This protein family is involved in various plant processes, including pollen tube growth, abiotic stress response and development. In this review, we provide an overview of the recent findings on ANTH/ENTH/VHS domain‐containing proteins in plants.
AP180 N‐terminal homology (ANTH) domain‐containing PICALM proteins mediate endocytic and exocytic transport of plasma membrane proteins in plant cells.
The trans-Golgi network (TGN) is an important organelle for protein transport at the post-Golgi network, which functions as a sorting station that directs cargo proteins to a variety of destinations ...including post-Golgi compartments and the extracellular space. However, the functions and dynamics of the TGN in plant cells have not been well understood yet. To elucidate the dynamics of the plant TGN, we established transgenic plants expressing green fluorescent protein (GFP)-SYP43, the ortholog of Tlg2/syntaxin16, which is localized to the TGN in yeast and mammalian cells, under the control of the native promoter as a TGN marker. Observation by confocal laser scanning microscopy and super-resolution confocal live imaging microscopy revealed two types of TGN in Arabidopsis root: the GA-TGNs (Golgi-associated TGNs), located on the trans-side of the Golgi apparatus, and the GI-TGNs (Golgi-released independent TGNs), located away from the Golgi apparatus and behaving independently. The GI-TGNs is derived from a population of GA-TGNs by segregation, although the core of the GA-TGN remains even after the generation of the GI-TGN. We further found that the abundance of the GI-TGNs differs between observed tissues. Our results indicate that the dynamic features of the TGN in plant cells differ from those of animal and yeast cells.
Eukaryotic cells acquired novel organelles during evolution through mechanisms that remain largely obscure. The existence of the unique oil body compartment is a synapomorphy of liverworts that ...represents lineage-specific acquisition of this organelle during evolution, although its origin, biogenesis, and physiological function are yet unknown. We find that two paralogous syntaxin-1 homologs in the liverwort Marchantia polymorpha are distinctly targeted to forming cell plates and the oil body, suggesting that these structures share some developmental similarity. Oil body formation is regulated by an ERF/AP2-type transcription factor and loss of the oil body increases M. polymorpha herbivory. These findings highlight a common strategy for the acquisition of organelles with distinct functions in plants, via periodical redirection of the secretory pathway depending on cellular phase transition.
Rab GTPases serve as multifaceted organizers during vesicle trafficking. Rab7, a member of the Rab GTPase family, has been shown to perform various essential functions in endosome trafficking and in ...endosome-to-lysosome trafficking in mammalian systems. The Arabidopsis thaliana genome encodes eight putative Rab7 homologs; however, the detailed function and activation mechanism of Rab7 in plants remain unknown. Here, we demonstrate that Arabidopsis RABG3f, a member of the plant Rab7 small GTPase family, localizes to prevacuolar compartments (PVCs) and the tonoplast. The proper activation of Rab7 is essential for both PVC-to-vacuole trafficking and vacuole biogenesis. Expression of a dominant-negative Rab7 mutant (RABG3fT22N) induces the formation of enlarged PVCs and affects vacuole morphology in plant cells. We also identify Arabidopsis MON1 (MONENSIN SENSITIVITY1) and CCZ1 (CALCIUM CAFFEINE ZINC SENSITIVITY1) proteins as a dimeric complex that functions as the Rab7 guanine nucleotide exchange factor. The MON1-CCZ1 complex also serves as the Rab5 effector to mediate Rab5-to-Rab7 conversion on PVCs. Loss of functional MON1 causes the formation of enlarged Rab5-positive PVCs that are separated from Rab7-positive endosomes. Similar to the dominant-negative Rab7 mutant, the mon1 mutants show pleiotropic growth defects, fragmented vacuoles, and altered vacuolar trafficking. Thus, Rab7 activation by the MON1-CCZ1 complex is critical for vacuolar trafficking, vacuole biogenesis, and plant growth.
Sensing of potential pathogenic bacteria is of critical importance for immunity. In plants, this involves plasma membrane-resident pattern recognition receptors, one of which is the FLAGELLIN SENSING ...2 (FLS2) receptor kinase. Ligand-activated FLS2 receptors are internalized into endosomes. However, the extent to which these spatiotemporal dynamics are generally present among pattern recognition receptors (PRRs) and their regulation remain elusive. Using live-cell imaging, we show that at least three other receptor kinases associated with plant immunity, PEP RECEPTOR 1/2 (PEPR1/2) and EF-TU RECEPTOR (EFR), internalize in a ligand-specific manner. In all cases, endocytosis requires the coreceptor BRI1-ASSOCIATED KINASE 1 (BAK1), and thus depends on receptor activation status. We also show the internalization of liganded FLS2, suggesting the transport of signaling competent receptors. Trafficking of activated PRRs requires clathrin and converges onto the same endosomal vesicles that are also shared with the hormone receptor BRASSINOSTERIOD INSENSITIVE 1 (BRI1). Importantly, clathrin-dependent endocytosis participates in plant defense against bacterial infection involving FLS2-mediated stomatal closure and callose deposition, but is uncoupled from activation of the flagellin-induced oxidative burst and MAP kinase signaling. In conclusion, immunity mediated by pattern recognition receptors depends on clathrin, a critical component for the endocytosis of signaling competent receptors into a common endosomal pathway.
Penetration resistance to powdery mildew fungi, conferred by localized cell wall appositions (papillae), is one of the best-studied processes in plant innate immunity. The syntaxin PENETRATION (PEN)1 ...is required for timely appearance of papillae, which contain callose and extracellular membrane material, as well as PEN1 itself. Appearance of membrane material in papillae suggests secretion of exosomes. These are potentially derived from multivesicular bodies (MVBs), supported by our observation that ARA6-labeled organelles assemble at the fungal attack site. However, the trafficking components that mediate delivery of extracellular membrane material are unknown. Here, we show that the delivery is independent of PEN1 function. Instead, we find that application of brefeldin (BF)A blocks the papillary accumulation of GFP-PEN1-labeled extracellular membrane and callóse, while impeding penetration resistance. We subsequently provide evidence indicating that the responsible BFA-sensitive ADP ribosylation factor-GTP exchange factor (ARF-GEF) is GNOM. Firstly, analysis of the transheterozygote gnom B404a/emb30-1 (gnomB/E) mutant revealed a delay in papilla formation and reduced penetration resistance. Furthermore, a BFA-resistant version of GNOM restored the BFA-sensitive papillary accumulation of GFP-PEN1 and callose. Our data, therefore, provide a link between GNOM and disease resistance. We suggest that papilla formation requires rapid reorganization of material from the plasma membrane mediated by GNOM. The papilla material is subsequently presumed to be sorted into MVBs and directed to the site of fungal attack, rendering the epidermal plant cell inaccessible for the invading powdery mildew fungus.
An 87-year-old man experiencing lower abdominal discomfort resulting from the ingestion of a fish bone underwent conservative management involving endoscopic extraction of the fish bone lodged in the ...sigmoid colon. Most patients with lower gastrointestinal tract perforations typically develop peritonitis or abscesses, necessitating surgical intervention. Notably, endoscopic management of lower gastrointestinal tract perforations is infrequently employed. Patients presenting with localized abdominal symptoms along with a stable overall health condition may benefit from conservative therapeutic approaches that utilize endoscopic methods. Notably, the transition from endoscopic procedures for foreign body removal to surgical intervention requires close collaboration with a surgeon and must be executed judiciously.
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