Endocytosis, secretion, and endosomal trafficking are key cellular processes that control the composition of the plasma membrane. Through the coordination of these trafficking pathways, cells can adjust the composition, localization, and turnover of proteins and lipids in response to developmental or environmental cues. Upon being incorporated into vesicles and internalized through endocytosis, plant plasma membrane proteins are delivered to the trans‐Golgi network (TGN). At the TGN, plasma membrane proteins are recycled back to the plasma membrane or transferred to multivesicular endosomes (MVEs), where they are further sorted into intralumenal vesicles for degradation in the vacuole. Both types of plant endosomes, TGN and MVEs, act as sorting organelles for multiple endocytic, recycling, and secretory pathways. Molecular assemblies such as retromer, ESCRT (endosomal sorting complex required for transport) machinery, small GTPases, adaptor proteins, and SNAREs associate with specific domains of endosomal membranes to mediate different sorting and membrane‐budding events. In this review, we discuss the mechanisms underlying the recognition and sorting of proteins at endosomes, membrane remodeling and budding, and their implications for cellular trafficking and physiological responses in plants.
- Award ID(s):
- 2114603
- NSF-PAR ID:
- 10337441
- Date Published:
- Journal Name:
- The Plant Cell
- ISSN:
- 1532-298X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract In eukaryotes, clathrin-coated vesicles (CCVs) facilitate the internalization of material from the cell surface as well as the movement of cargo in post-Golgi trafficking pathways. This diversity of functions is partially provided by multiple monomeric and multimeric clathrin adaptor complexes that provide compartment and cargo selectivity. The adaptor-protein assembly polypeptide-1 (AP-1) complex operates as part of the secretory pathway at the trans-Golgi network (TGN), while the AP-2 complex and the TPLATE complex jointly operate at the plasma membrane to execute clathrin-mediated endocytosis. Key to our further understanding of clathrin-mediated trafficking in plants will be the comprehensive identification and characterization of the network of evolutionarily conserved and plant-specific core and accessory machinery involved in the formation and targeting of CCVs. To facilitate these studies, we have analyzed the proteome of enriched TGN/early endosome-derived and endocytic CCVs isolated from dividing and expanding suspension-cultured Arabidopsis (Arabidopsis thaliana) cells. Tandem mass spectrometry analysis results were validated by differential chemical labeling experiments to identify proteins co-enriching with CCVs. Proteins enriched in CCVs included previously characterized CCV components and cargos such as the vacuolar sorting receptors in addition to conserved and plant-specific components whose function in clathrin-mediated trafficking has not been previously defined. Notably, in addition to AP-1 and AP-2, all subunits of the AP-4 complex, but not AP-3 or AP-5, were found to be in high abundance in the CCV proteome. The association of AP-4 with suspension-cultured Arabidopsis CCVs is further supported via additional biochemical data.
-
SUMMARY Plant cell walls are essential for defining plant growth and development, providing structural support to the main body and responding to abiotic and biotic cues. Cellulose, the main structural polymer of plant cell walls, is synthesized at the plasma membrane by cellulose synthase complexes (CSCs). The construction and transport of CSCs to and from the plasma membrane is poorly understood but is known to rely on the coordinated activity of cellulose synthase‐interactive protein 1 (CSI1), a key regulator of CSC trafficking. In this study, we found that Trs85, a TRAPPIII complex subunit, interacted with CSI1
in vitro . Using functional genetics and live‐cell imaging, we have shown thattrs85‐1 mutants have reduced cellulose content, stimulated CSC delivery, an increased population of static CSCs and deficient clathrin‐mediated endocytosis in the primary cell wall. Overall, our findings suggest that Trs85 has a dual role in the trafficking of CSCs, by negatively regulating the exocytosis and clathrin‐mediated endocytosis of CSCs. -
Abstract Heterotetrameric clathrin adaptor protein complexes (APs) orchestrate the formation of coated vesicles for transport among organelles of the cell periphery. AP1 binds membranes enriched for phosphatidylinositol 4‐phosphate, such as the
trans Golgi network, while AP2 associates with phosphatidylinositol 4,5‐bisphosphate of the plasma membrane. At their respective membranes, AP1 and AP2 bind the cytoplasmic tails of transmembrane protein cargo and clathrin triskelions, thereby coupling cargo recruitment to coat polymerization. Structural, biochemical and genetic studies have revealed that APs undergo conformational rearrangements and reversible phosphorylation to cycle between different activity states. While membrane, cargo and clathrin have been demonstrated to promote AP activation, growing evidence supports that membrane‐associated proteins such as Arf1 and FCHo also stimulate this transition. APs may be returned to the inactive state via a regulated process involving phosphorylation and a protein called NECAP. Finally, because antiviral mechanisms often rely on appropriate trafficking of membrane proteins, viruses have evolved novel strategies to evade host defenses by influencing the conformation of APs. This review will cover recent advances in our understanding of the molecular inputs that stimulate AP1 and AP2 to adopt structurally and functionally distinct configurations. -
Abstract It has become increasingly apparent that G protein-coupled receptor (GPCR) localization is a master regulator of cell signaling. However, the molecular mechanisms involved in this process are not well understood. To date, observations of intracellular GPCR activation can be organized into two categories: a dependence on OCT3 cationic channel-permeable ligands or the necessity of endocytic trafficking. Using CXC chemokine receptor 4 (CXCR4) as a model, we identified a third mechanism of intracellular GPCR signaling. We show that independent of membrane permeable ligands and endocytosis, upon stimulation, plasma membrane and internal pools of CXCR4 are post-translationally modified and collectively regulate EGR1 transcription. We found that β-arrestin-1 (arrestin 2) is necessary to mediate communication between plasma membrane and internal pools of CXCR4. Notably, these observations may explain that while CXCR4 overexpression is highly correlated with cancer metastasis and mortality, plasma membrane localization is not. Together these data support a model where a small initial pool of plasma membrane-localized GPCRs are capable of activating internal receptor-dependent signaling events.