SYP73 Anchors the ER to the Actin Cytoskeleton for Maintenance of ER Integrity and Streaming in Arabidopsis

• Published in: Current biology Vol. 26; no. 23; pp. 3245 - 3254
• Main Authors: Cao, Pengfei, Renna, Luciana, Stefano, Giovanni, Brandizzi, Federica
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 05.12.2016; Elsevier
• Subjects: actin; Actins - physiology; Arabidopsis - cytology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Cytoskeleton - physiology; endoplasmic reticulum; Endoplasmic Reticulum - physiology; Gene Deletion; Gene Expression Regulation, Plant - physiology; Mutation; myosin; SYP73; Arabidopsis thaliana; myosin; actin; SYP73; endoplasmic reticulum
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2016.10.024

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. •Overexpression of SYP73 causes rearrangement of the ER over actin•SYP73 associates with the ER membrane and binds actin directly•Functional SYP73 is required for homeostasis of ER dynamics and plant development•We propose new models connecting ER movement and actin Cao et al. identify a new player involved in the connection between the ER and actin in plant cells. SYP73 is an ER membrane-associated actin-binding protein. Overexpression of SYP73 reshapes ER to overlay actin, while SYP73 loss-of-function mutant displays defects in both plant development and ER dynamics.