Tethers and Transporters: The Molecular Fingerprint of Plant ER–PM Contact Sites

Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) are central hubs that coordinate lipid metabolism, membrane remodelling, calcium signalling and stress responses in plant cells. This review summarizes current knowledge on the molecular architecture and functions of ER-PM CS, with emphasis on the three tether families (synaptotagmins/SYTs, multiple-C2-domain and transmembrane region proteins/MCTPs, and VAMP-associated protein 27/VAP27 proteins) and the lipid-transfer proteins (SMP-domain proteins and oxysterol-binding protein-related/ORPs) described to date. SYTs and MCTPs use C2 domains to read PM phosphoinositides and Ca2+ signals to dynamically modulate tethering, while VAP27s scaffold multimeric complexes via MSP-FFAT interactions and link the ER to the cytoskeleton. Lipid transfer at ER-PM CS sustain the phosphatidylinositol (PI) cycle and prevents accumulation of cone-shaped lipids such as diacylglycerol (DAG) at the PM. In plants, SYT1/SYT3 form a module with diacylglycerol kinases (DGKs) to clear DAG from the PM and to channel DAG into metabolism. ORP family members function as PI/PS (and sterol) exchangers and integrate contact-site lipid exchange with signalling and autophagy. ER-PM CS also intersect with endocytosis, autophagosome biogenesis, plasmodesmata function and unfolded protein response signalling, underlining their multi-functional roles in cellular homeostasis and stress adaptation.