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Sar1 is a small GTPase of the ARF family. Upon exchange of GDP for GTP, Sar1 associates with the endoplasmic reticulum (ER) membrane and recruits COPII components, orchestrating cargo concentration and membrane deformation. Many aspects of the role of Sar1 and regulation of its GTP cycle remain unclear, especially as complexity increases in higher organisms that secrete a wider range of cargoes. This review focusses on the regulation of GTP hydrolysis and its role in coat assembly, as well as the mechanism of Sar1-induced membrane deformation and scission. Finally, we highlight the additional specialisation in higher eukaryotes and the outstanding questions on how Sar1 functions are orchestrated., (© 2023 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

GEFs are generally multidomain proteins with conformational plasticity and often assemble in multisubunit complexes that interact with membranes to activate small GTPases attached to membranes. Insights regarding guanine nucleotide exchange from the structure of a DENN-domain protein complexed with its Rab GTPase substrate. GDP/GTP alternation is exquisitely regulated by two main classes of regulators: guanine nucleotide exchange factors or guanine nucleotide exchange factors (GEFs), which activate small GTPases by stimulating GDP/GTP exchange, and GTPase-activating proteins or GTPase-activating proteins (GAPs), which terminate their activity by stimulating the hydrolysis of GTP into GDP [[4]]. Most small GTPases carry post-translational modifications by lipids, whereby GDP/GTP alternation combines with cytosol/membrane alternation, itself regulated by guanine nucleotide dissociation inhibitors (GDIs) or functionally related proteins [[4]]. [Extracted from the article]

In eukaryotes, the endomembrane system allows for spatiotemporal compartmentation of complicated cellular processes. The plant endomembrane system consists of the endoplasmic reticulum, the Golgi apparatus, the trans‐Golgi network, the multivesicular body and the vacuole. Anterograde traffic from the endoplasmic reticulum to the Golgi apparatus is mediated by coat protein complex II (COPII) vesicles. Autophagy, an evolutionarily conserved catabolic process that turns over cellular materials upon nutrient deprivation or in adverse environments, exploits double‐membrane autophagosomes to recycle unwanted constituents in the lysosome/vacuole. Accumulating evidence reveals novel functions of plant COPII vesicles in autophagy and their regulation by abiotic stresses. Here, we summarize current knowledge about plant COPII vesicles in endomembrane trafficking and then highlight recent findings showing their distinct roles in modulating the autophagic flux and stress responses. [ABSTRACT FROM AUTHOR]

The synthesis, quality control, and trafficking of a third of the eukaryotic proteome takes place at the endoplasmic reticulum (ER), which is the largest cellular organelle. Thus, biosynthetic trafficking from the ER, although constitutive, has to be tightly controlled. Increasing evidence indicates that the ER acts as a platform that initiates signaling events. In this review, we focus on signaling pathways that target components of the ER export machinery to regulate protein export. In addition, we discuss how signaling generated at the ER regulates various homeostatic cellular processes such as cell growth and proliferation, and how the deregulation thereof is involved in disease. [ABSTRACT FROM AUTHOR]