title: SYP73 Anchors the ER to the Actin Cytoskeleton for Maintenance of ER Integrity and Streaming in Arabidopsis.
abstract: The endoplasmic reticulum (ER) is an essential organelle that spreads throughout the cytoplasm as one interconnected network of narrow tubules and dilated cisternae that enclose a single lumen. The ER network undergoes extensive remodeling, which critically depends on membrane-cytoskeleton interactions [1]. In plants, the ER is also highly mobile, and its streaming contributes significantly to the movement of other organelles [2, 3]. The remodeling and motility of the plant ER rely mainly on actin [4] and to a minor extent on microtubules [5]. Although a three-way interaction between the ER, cytosolic myosin-XI, and F-actin mediates the plant ER streaming [6], the mechanisms underlying stable interaction of the ER membrane with actin are unknown. Early electron microscopy studies suggested a direct attachment of the plant ER with actin filaments [7, 8], but it is plausible that yet-unknown proteins facilitate anchoring of the ER membrane with the cytoskeleton. We demonstrate here that SYP73, a member of the plant Syp7 subgroup of SNARE proteins [9] containing actin-binding domains, is a novel ER membrane-associated actin-binding protein. We show that overexpression of SYP73 causes a striking rearrangement of the ER over actin and that, similar to mutations of myosin-XI [4, 10, 11], loss of SYP73 reduces ER streaming and affects overall ER network morphology and plant growth. We propose a model for plant ER remodeling whereby the dynamic rearrangement and streaming of the ER network depend on the propelling action of myosin-XI over actin coupled with a SYP73-mediated bridging, which dynamically anchors the ER membrane with actin filaments.
authors.affiliation: MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Pengfei
authors.initials: P
authors.lastname: Cao
authors.affiliation: MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Luciana
authors.initials: L
authors.lastname: Renna
authors.affiliation: MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Stefano
authors.affiliation: MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, MI 48824, USA. Electronic address: fb@msu.edu.
authors.forename: Federica
authors.initials: F
authors.lastname: Brandizzi
mesh_terms: D000199:Actins / Q000502:physiology*; D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003599:Cytoskeleton / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000502:physiology*; D017353:Gene Deletion; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D009154:Mutation
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins
keywords: Arabidopsis thaliana; SYP73; actin; endoplasmic reticulum; myosin