S-acylation of YKT61 modulates its unconventional participation in the formation of SNARE complexes in Arabidopsis

Hetero-tetrameric soluble N-ethylmaleimide-sensitive factor attachment protein receptors(SNAREs)complexes are critical for vesicle-target membrane fusion within the endomembrane system of eukaryotic cells.SNARE assembly involves four different SNARE motifs,Qa,Qb,Qc,and R,providedby three orfour SNARE proteins.YKT6 is an atypical R-SNARE that lacks a transmembrane domain and is involved in multiple vesicle-target membrane fusions.Although YKT6 is evolutionarily conserved and essential,its function and regulation in different phyla seem distinct.Arabidopsis YKT61,the yeast and metazoan YKT6 homologue,is essential for gametophytic development,plays a critical role in sporophytic cells,and me-diates multiple vesicle-target membrane fusion.However,its molecular regulation is unclear.We report here that YKT61 is S-acylated.Abolishing its S-acylation by a C195S mutation dissociates YKT61 from endomembrane structures and causes its functional loss.Although interacting with various SNARE pro-teins,YKT61functions not as a canonical R-SNAREbut coordinates with otherR-SNAREs to participate in theformationof SNAREcomplexes.Phylum-specific molecular regulation of YKT6 may be evolvedto allow more efficient SNARE assembly in different eukaryotic cells.