ER-associated retrograde SNAREs and the Dsl1 complex mediate an alternative, Sey1p-independent homotypic ER fusion pathway.

Citation:

Rogers, J.V., McMahon, C., Baryshnikova, A., Hughson, F.M. & Rose, M.D. ER-associated retrograde SNAREs and the Dsl1 complex mediate an alternative, Sey1p-independent homotypic ER fusion pathway. Mol Biol Cell 25, 21, 3401-12 (2014).

Date Published:

2014 Nov 01

ISSN:

1939-4586

Abstract:

The peripheral endoplasmic reticulum (ER) network is dynamically maintained by homotypic (ER-ER) fusion. In Saccharomyces cerevisiae, the dynamin-like GTPase Sey1p can mediate ER-ER fusion, but sey1Δ cells have no growth defect and only slightly perturbed ER structure. Recent work suggested that ER-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediate a Sey1p-independent ER-ER fusion pathway. However, an alternative explanation--that the observed phenotypes arose from perturbed vesicle trafficking--could not be ruled out. In this study, we used candidate and synthetic genetic array (SGA) approaches to more fully characterize SNARE-mediated ER-ER fusion. We found that Dsl1 complex mutations in sey1Δ cells cause strong synthetic growth and ER structure defects and delayed ER-ER fusion in vivo, additionally implicating the Dsl1 complex in SNARE-mediated ER-ER fusion. In contrast, cytosolic coat protein I (COPI) vesicle coat mutations in sey1Δ cells caused no synthetic defects, excluding perturbed retrograde trafficking as a cause for the previously observed synthetic defects. Finally, deleting the reticulons that help maintain ER architecture in cells disrupted for both ER-ER fusion pathways caused almost complete inviability. We conclude that the ER SNAREs and the Dsl1 complex directly mediate Sey1p-independent ER-ER fusion and that, in the absence of both pathways, cell viability depends upon membrane curvature-promoting reticulons.

DOI:

10.1091/mbc.E14-07-1220

Alternate Journal:

Mol. Biol. Cell