SYP73 Is a Novel Membrane-Associated Actin-Binding Protein that Anchors the ER to the Actin Cytoskeleton in Arabidopsis

The endoplasmic reticulum (ER) is an essential organelle that spreads throughout the cytoplasm and undergoes extensive remodeling. In plants, the remodeling and motility of the ER rely mainly on actin and to a minor extent on microtubules. Although the actomyosin system has been suggested functional for ER streaming in plant cells, the mechanisms underlying stable interaction of the ER membrane with actin are unknown. We demonstrate that SYP73, a member of the plant Syp7 subgroup of SNARE proteins 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 loss of SYP73 reduces ER streaming and affects overall ER network morphology and plant growth. A potential mechanism that regulates SYP73 functions has been investigated. Although conserved domain prediction tools did not detect any actin‐binding domain in SYP73, we identified a fragment that is mainly responsible for SYP73 actin binding. Furthermore, the role of SYP73 in regulating actin reorganization has also been examined. 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. Support or Funding Information This work is support by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy, the National Science Foundation, and MSU AgBioResearch. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .