An Update on Coat Protein Complexes for Vesicle Formation in Plant Post-Golgi Trafficking

Abstract

Endomembrane trafficking is an evolutionarily conserved process for all eukaryotic organisms. It is a fundamental and essential process for the transportation of proteins, lipids, or cellular metabolites. The aforementioned cellular components are sorted across multiple membrane-bounded organelles. In plant cells, the endomembrane mainly consists of the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, trans-Golgi network or early endosome (TGN/EE), prevacuolar compartments or multivesicular bodies (PVCs/MVBs), and vacuole. Among them, Golgi apparatus and TGN represent two central sorting intermediates for cargo secretion and recycling from other compartments by anterograde or retrograde trafficking. Several protein sorting machineries have been identified to function in these pathways for cargo recognition and vesicle assembly. Exciting progress has been made in recent years to provide novel insights into the sorting complexes and also the underlying sorting mechanisms in plants. Here, we will highlight the recent findings for the adaptor protein (AP) complexes, retromer, and retriever complexes, and also their functions in the related coated vesicle formation in post-Golgi trafficking.

Sorting motifs target the movement protein of ourmia melon virus to the trans-Golgi network and plasmodesmata

“…A key question emerging from this observation is whether the Y motif in OuMV MP is a functional internalization motif. Y motifs are recognized by msubunits of APs 1-4 (24,63,64). In plants, clathrin-mediated endocytosis (CME) of plasma membrane proteins is achieved by the recognition of Y motifs in their cytoplasmic domains by AP2M (56-59), and it has been previously shown that CaMV MP is able to bind Arabidopsis AP2M through three Y motifs (16).…”

The sorting of cargo proteins in the plant trans-Golgi network

“…AP complexes typically consist of two large subunits (β and α/γ/δ/ε/ζ), a medium subunit (μ), and a small subunit (σ). They sort membrane-bound or transmembrane cargo proteins by recognizing and binding to sorting motifs or signals, such as the tyrosine motif, dileucine motif, and ubiquitin, which are present in the cytoplasmic domains of cargo proteins ( Arora and Van Damme, 2021 ; Law et al, 2022 ). Various AP complexes interact with clathrin to form clathrin-coated vesicles.…”

“…First, Arf/Sar GTPases activated by their guanine-nucleotide exchange factor (GEF) promote the recruitment of coat proteins on the donor membrane. Coat proteins play important roles in cargo protein recognition and membrane distortion ( Singh and Jürgens, 2018 ; Arora and Van Damme, 2021 ; Law et al, 2022 ). RAB GTPases are involved in various trafficking events, such as tethering ( Saito and Ueda, 2009 ; Minamino and Ueda, 2019 ).…”

An Update on the Key Factors Required for Plant Golgi Structure Maintenance

“…During CCVs formation, Arf GTPases recruit adaptor protein (AP) complex, which serve as an intermediate between clathrin coat components and cargo receptors. Clathrin triskelions are recruited by AP complexes and assembled to form clathrin-coated vesicles, which are pinched from the donor membrane with the aid of the polymerizing GTPase dynamins ( Jin et al, 2001 ; Backues et al, 2010 ; Law et al, 2022 ). AP1-4 in plants have been found to be heterotetrametric complexes, comprising two large subunits (α/γ/δ/ε and β), one medium subunit (μ) and one small subunit (σ).…”

“…AP1-4 in plants have been found to be heterotetrametric complexes, comprising two large subunits (α/γ/δ/ε and β), one medium subunit (μ) and one small subunit (σ). In Arabidopsis, several studies show that AP1, AP3, and AP4 participate in anterograde transport from the TGN to the vacuole/PM ( Niihama et al, 2009 ; Park et al, 2013 ; Robinson and Pimpl, 2014 ; Fuji et al, 2016 ; Hatsugai et al, 2018 ; Law et al, 2022 ).…”