Plant Endocytosis Requires the ER Membrane-Anchored Proteins VAP27-1 and VAP27-3

Abstract

Through yet-undefined mechanisms, the plant endoplasmic reticulum (ER) has a critical role in endocytosis. The plant ER establishes a close association with endosomes and contacts the plasma membrane (PM) at ER-PM contact sites (EPCSs) demarcated by the ER membrane-associated VAMP-associated-proteins (VAP). Here, we investigated two plant VAPs, VAP27-1 and VAP27-3, and found an interaction with clathrin and a requirement for the homeostasis of clathrin dynamics at endocytic membranes and endocytosis. We also demonstrated direct interaction of VAP27-proteins with phosphatidylinositol-phosphate lipids (PIPs) that populate endocytic membranes. These results support that, through interaction with PIPs, VAP27-proteins bridge the ER with endocytic membranes and maintain endocytic traffic, likely through their interaction with clathrin.

Low Water Potential and At14a-Like1 (AFL1) Effects on Endocytosis and Actin Filament Organization

“…Given the pattern of AFL1-actin filament colocalization, it seems likely that AFL1 is also present on the cytoplasmic side of the ER membrane. Interestingly, there is recent evidence that ER-associated proteins can directly participate in endocytosis (Stefano et al, 2018). Whether AFL1 is involved in such a mechanism, as well as the mechanism connecting AFL1 to actin filaments, is under investigation in our laboratory.…”

Ionic stress enhances ER–PM connectivity via phosphoinositide-associated SYT1 contact site expansion in Arabidopsis

“…In recent years, the functional characterization of EPCS components in Arabidopsis has uncovered their critical roles in essential cellular processes, including the activation of immune secretory pathways (25), the regulation of viral movement at plasmodesmata (16,17,35), the stabilization of the cER network (32), the Ca 2+ -dependent responses to environmental stresses (23,36,37), endocytosis (35,38), and pollen, seeds, and root hairs development (24). However, the environmental triggers and molecular mechanisms that regulate ER-PM connectivity at those EPCS microdomains remain unexplored.…”

A putative ER-PM contact site complex relocalizes in response to Rare Earth Elements –induced endocytosis

“…Since REEs are internalized via endocytosis upon long-term treatments, and REEs are known to act as allosteric regulators of the activity of Calmodulins [47] and C2 containing proteins [60] , we propose that endocytosed REEs promote changes in ER-PM communication by either activating Calmodulin signaling or through direct binding to the SSC complex Ca 2+ -binding domains. Still, it is unclear whether EPCS microdomains have an active role in REE endocytosis, following the models proposed in [61, 62] , and which molecular components confer specificity to the EPCS tethers’ responses. Given the growing number of EPCS components, Calmodulins, and C2 containing proteins described in Arabidopsis, the elucidation of specific mechanisms underlying REE-induced EPCS reorganization will likely require genetic strategies, such as REEs-resistance screens and/or mutant analyses beyond the scope of this study.…”