Unique and conserved features of the plant ER-shaping GTPase RHD3.

The architectural integrity of the endoplasmic reticulum (ER) network depends on the function of membrane-associated dynamin-like GTPases that include metazoan atlastins, plant RHD3 and yeast Sey1p. The evidence that these proteins are sufficient to drive membrane fusion of reconstituted proteoliposomes, and that loss-of-function mutations lead to conspicuous ER shape defects indicates that atlastins, RHD3 and Sey1p promote ER membrane fusion. However, complementation experiments in reciprocal loss-of-function backgrounds have also suggested that RHD3 and Sey1p may be not functionally equivalent, supporting that ER fusion mechanisms may be not entirely conserved in eukaryotes. In this Letter, we provide a brief overview of the field as well as evidence that may explain the functional differences of the plant and yeast ER-shaping dynamin-like GTPases.