The canonical alpha-SNAP is essential for gametophytic development in Arabidopsis

The development of male and female gametophytes is a pre-requisite for successful reproduction of angiosperms. Factors mediating vesicular trafficking are among the key regulators controlling gametophytic development. Fusion between vesicles and target membranes requires the assembly of a fusogenic soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) complex, whose disassembly in turn ensures the recycle of individual SNARE components. The disassembly of post-fusion SNARE complexes is controlled by the AAA(+) ATPase N-ethylmaleimide-sensitive factor (Sec18/NSF) and soluble NSF attachment protein (Sec17/alpha-SNAP) in yeast and metazoans. Although non-canonical alpha-SNAPs have been functionally characterized in soybeans, the biological function of canonical alpha-SNAPs has yet to be demonstrated in plants. We report here that the canonical alpha-SNAP in Arabidopsis is essential for male and female gametophytic development. Functional loss of the canonical alpha-SNAP in Arabidopsis results in gametophytic lethality by arresting the first mitosis during gametogenesis. We further show that Arabidopsis alpha-SNAP encodes two isoforms due to alternative splicing. Both isoforms interact with the Arabidopsis homolog of NSF whereas have distinct subcellular localizations. The presence of similar alternative splicing of human alpha-SNAP indicates that functional distinction of two alpha-SNAP isoforms is evolutionarily conserved. Author summary Vesicular trafficking among different endomembrane compartments ensures membrane homeostasis, protein targeting, and finally the survival of eukaryotic cells. Fusion between vesicle and target membranes is mediated by tetrameric SNARE complexes, whose disassembly ensures the recycle of individual SNARE components. The disassembly of post-fusion SNARE complexes is controlled by NSF/Sec18 and alpha-SNAP/Sec17 both in yeast and metazoans. Recent reports show that a naturally occurring, truncated alpha-SNAP allele suppresses parasitic nematode infection in soybeans. However, a role of the canonical alpha-SNAP has yet to be demonstrated in plants. We report here that the canonical alpha-SNAP in Arabidopsis is essential for fertility. Mutations in alpha-SNAP arrest mitosis and causes gametophytic lethality. In addition, we demonstrated that Arabidopsis alpha-SNAP encodes two functional isoforms. Interesting, the single alpha-SNAP gene in human also encodes two similarly distinct isoforms. Thus, the study