EMAC, Retromer, and VSRs: do they connect?
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NEW IDEAS IN CELL BIOLOGY
EMAC, Retromer, and VSRs: do they connect? Rumen Ivanov 1
&
David G. Robinson 2
Received: 7 June 2020 / Accepted: 6 August 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Eukaryotic organisms share many common features in terms of endomembrane trafficking. This fact has helped plant scientists to propose testable hypotheses on how plant intracellular membrane trafficking is achieved and regulated based on knowledge from yeast and mammals. However, when a new compartment has been identified in a plant cell that has a vesicle tethering complex located at a position which is completely different to its counterpart in yeast and mammalian cells, caution is demanded when interpreting possible interactions with other trafficking elements. This is exemplified by the recently discovered EMAC (ER and microtubule-associated compartment). It has been postulated that this compartment is the recipient of vacuolar sorting receptors (VSRs) transported retrogradely via “retromer vesicles” from a post-Golgi location. Unfortunately, this suggestion was based entirely on our knowledge of retromer from yeast and mammalian cells, and did not take into account the available literature on the composition, localization, and function of the plant retromer. It also lacked reference to recent contradictory findings on VSR trafficking. In this short article, we have tried to rectify this situation, pointing out that plant retromer may not function as a pentameric complex of two subunits: the retromer core and the sorting nexins. Keywords Endomembrane trafficking . Retromer . VPS26-VPS35-VPS29 . Sorting nexin . SNX . Subcellular localization
Exchange of material between intracellular membrane compartments is mediated by vesicles and is essential for the function of eukaryotic organisms. Endomembrane vesicular transport is orchestrated by regulatory protein complexes, whose subunits are often evolutionary conserved between distantly related organisms (Bethune and Wieland 2018; Brandizzi 2018; Heucken and Ivanov 2018). However, evidence shows that protein complex composition and subunit function might significantly differ between species, making inference of functions a tricky task. In a recently reported elegant screen for plant vacuolar trafficking regulators, Delgadillo et al. (2020) identified a number of proteins, including vacuolar sorting receptors (VSRs) and the Arabidopsis VPS51 and VPS54 homologs. Since VSP51 and Handling Editor: Peter Nick * Rumen Ivanov [email protected] 1
Institute of Botany, Heinrich Heine University, 40225 Düsseldorf, Germany
2
Centre for Organismal Studies, University of Heidelberg, 69117 Heidelberg, Germany
VPS54 are components of the GARP tethering complex, transient expression studies were performed on tobacco epidermal cells with RFP-VPS51 and VPS54-GFP to elucidate the nature and localization of the plant GARP complex. In yeast and mammals, the GARP complex locates strictly to the trans-Golgi network (TGN) where it serves to tether i
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