Structural and functional relationships between plasmodesmata and plant endoplasmic reticulum–plasma membrane contact sites consisting of three synaptotagmins

Abstract

Summary Synaptotagmin 1 (SYT1) has been recognised as a tethering factor of plant endoplasmic reticulum (ER)–plasma membrane (PM) contact sites (EPCSs) and partially localises to around plasmodesmata (PD). However, other components of EPCSs associated with SYT1 and functional links between the EPCSs and PD have not been identified. We explored interactors of SYT1 by immunoprecipitation and mass analysis. The dynamics, morphology and spatial arrangement of the ER in Arabidopsis mutants lacking the EPCS components were investigated using confocal microscopy and electron microscopy. PD permeability of EPCS mutants was assessed using a virus movement protein and free green fluorescent protein (GFP) as indicators. We identified two additional components of the EPCSs, SYT5 and SYT7, that interact with SYT1. The mutants of the three SYTs were defective in the anchoring of the ER to the PM. The ER near the PD entrance appeared to be weakly squeezed in the triple mutant compared with the wild‐type. The triple mutant suppressed cell‐to‐cell movement of the virus movement protein, but not GFP diffusion. We revealed major additional components of EPCS associated with SYT1 and suggested that the EPCSs arranged around the PD squeeze the ER to regulate active transport via PD.

Rare earth elements induce cytoskeleton-dependent and PI4P-associated rearrangement of SYT1/SYT5 endoplasmic reticulum–plasma membrane contact site complexes in Arabidopsis

“…In this study, we corroborate a recent report describing the establishment of a putative tethering complex between the synaptotagmins 1 and 5, and the Ca 2+ -dependent lipid binding protein CLB1/SYT7 (hereafter CLB1) at EPCSs ( Ishikawa et al , 2020 ), and we expand their analysis by showing that SYT1 and SYT5 can form homo- and heterodimers in vivo . We also show that changes in extracellular Ca 2+ have a limited effect in EPCS organization with the exception of treatments with salts of the rare earth elements (REEs) lanthanum (La 3+ ) and gadolinium (Gd 3+ ).…”

“…ER–mitochondria and ER–plastid contact sites; Xu et al , 2008 ; Block and Jouhet, 2015 ; Fan et al , 2015 ; Michaud et al , 2016 ), intercellular communication (e.g. plasmodesmata; Uchiyama et al , 2014 ; Levy et al , 2015 ; Tilsner et al , 2016 ; Ishikawa et al , 2020 ), organelle distribution (e.g. ER–peroxisome, ER–plastid, and ER–Golgi contact sites; Andersson et al , 2007 ; Sparkes et al , 2009 ; Barton et al , 2013 ), and the Ca 2+ -dependent regulation of stress responses [ER–plasma membrane (PM) contact sites (EPCSs); Schapire et al , 2008 ; Yamazaki et al , 2008 ; P. Wang et al, 2014 , 2016 ; Pérez-Sancho et al , 2015 ; Kim et al , 2016 ; Lee et al , 2019 ).…”

“…This study expands on existing research on the Arabidopsis SYT1, which is an EPCS tether that localizes in immobile cortical ER tubules, and docks the PM through Ca 2+ -dependent interactions between its C2 domains and negatively charged phospholipids ( Schapire et al , 2008 ; Yamazaki et al , 2010 ; Pérez-Sancho et al, 2015 , 2016b ; Ishikawa et al , 2018 ). Genetic studies using syt1 loss-of-function mutants have shown that SYT1 is required for the control of immune secretory pathways ( Kim et al , 2016 ), maintenance of the cortical ER stability ( Siao et al , 2016 ), the regulation of cell to cell communication ( Lewis and Lazarowitz, 2010 ; Uchiyama et al , 2014 ; Levy et al , 2015 ; Ishikawa et al , 2020 ), and the tolerance to ionic, mechanical, and freezing stresses ( Schapire et al , 2008 ; Yamazaki et al , 2010 ; Pérez-Sancho et al , 2015 ). To achieve such diverse functions, SYT1 establish interactions with elements of the exocytic soluble SNAREs ( Kim et al , 2016 ), phytosterol-binding proteins ( Dalal et al , 2016 ), and reticulon proteins ( Kriechbaumer et al , 2015 ).…”

Creating Contacts Between Replication and Movement at Plasmodesmata – A Role for Membrane Contact Sites in Plant Virus Infections?

“…The association between viral MPs and SYTA/1 was studied in detail. SYTA/1 was found to be required for the movement of viruses from the Tobamovirus [TMV, TVCV, and Youcai mosaic virus (YoMV) (Uchiyama et al, 2014;Cabanillas et al, 2018;Ishikawa et al, 2020). SYTA/1 forms a complex with SYTE/5 and SYT7 that likely also involves actin (Ishikawa et al, 2020), and was shown to localize at PD entrances (Levy et al, 2015;Ishikawa et al, 2020).…”

The Tobamoviral Movement Protein: A “Conditioner” to Create a Favorable Environment for Intercellular Spread of Infection

“…Analysis of cellular factors involved in interactions with MP PLS revealed its ability to bind plant synaptotagmin A (SYTA) (Yuan et al, 2018). SYTA is localized to the plasma membrane (PM), concentrated around Pd and recognized as a tethering factor of ER-PM contact sites (Uchiyama et al, 2014;Levy et al, 2015;Yuan et al, 2018;Ishikawa et al, 2020;Liu et al, 2020).…”