Unraveling Different Biological Roles of Plant Synaptotagmins

Endoplasmic Reticulum-Plasma Membrane contact sites (ER-PM CS) are evolutionarily conserved membrane domains found in all eukaryotes, where the endoplasmic reticulum (ER) closely interfaces with the plasma membrane (PM). This short distance is achieved in plants through the action of tether proteins such as Synaptotagmins (SYTs). Arabidopsis comprises five SYT members ( SYT1-SYT5 ), but whether they possess overlapping or distinct biological functions remains elusive. SYT1 , the best-characterized member, plays essential roles in the resistance to abiotic stress. This study reveals that the functionally redundant SYT1 and SYT3 genes, but not SYT5, are involved in salt and cold stress resistance. We also show that, unlike SYT5 , SYT1 and SYT3 are not required for Pseudomonas syringae resistance . Since SYT1 and SYT5 interact in vivo via their SMP domains , the distinct functions of these proteins cannot be caused by differences in their localization. Interestingly, structural phylogenetic analysis indicates that SYT1 and SYT5 clades emerged early in the evolution of land plants. We also show that SYT1 and SYT5 clades exhibit different structural features, rationalizing their distinct biological roles.