Calcium-Dependent Freezing Tolerance in Arabidopsis Involves Membrane Resealing via Synaptotagmin SYT1

Abstract

Plant freezing tolerance involves the prevention of lethal freeze-induced damage to the plasma membrane. We hypothesized that plant freezing tolerance involves membrane resealing, which, in animal cells, is accomplished by calcium-dependent exocytosis following mechanical disruption of the plasma membrane. In Arabidopsis thaliana protoplasts, extracellular calcium enhanced not only freezing tolerance but also tolerance to electroporation, which typically punctures the plasma membrane. However, calcium did not enhance survival when protoplasts were exposed to osmotic stress that mimicked freeze-induced dehydration. Calcium-dependent freezing tolerance was also detected with leaf sections in which ice crystals intruded into tissues. Interestingly, calcium-dependent freezing tolerance was inhibited by extracellular addition of an antibody against the cytosolic region of SYT1, a homolog of synaptotagmin known to be a calcium sensor that initiates exocytosis. This inhibition indicates that the puncture allowing the antibody to flow into the cytoplasm occurs during freeze/ thawing. Thus, we propose that calcium-dependent freezing tolerance results from resealing of the punctured site. Protoplasts or leaf sections isolated from Arabidopsis SYT1-RNA interference (RNAi) plants lost calcium-dependent freezing tolerance, and intact SYT1-RNAi plants had lower freezing tolerance than control plants. Taken together, these findings suggest that calcium-dependent freezing tolerance results from membrane resealing and that this mechanism involves SYT1 function.

Plasma Membrane Localization of Solanum tuberosum Remorin from Group 1, Homolog 3 Is Mediated by Conformational Changes in a Novel C-Terminal Anchor and Required for the Restriction of Potato Virus X Movement

“…The recent report of the role of Arabidopsis (Arabidopsis thaliana) synaptotagmin1 in the control of Begomovirus and Tobamovirus cell-to-cell movement (Lewis and Lazarowitz, 2010) sheds new light on the involvement of host membrane proteins in virus movement. Arabidopsis synaptotagmin1 resides in the cortical endoplasmic reticulum, endosomes, DIMs at the PM, and plasmodesmata (PDs; Schapire et al, 2008;Minami et al, 2009;Lewis and Lazarowitz, 2010;Yamazaki et al, 2010), and regulates endocytosis and PM repair processes (Schapire et al, 2008;Yamazaki et al, 2008;Lewis and Lazarowitz, 2010). These studies support a link between DIMs and PDs, and provide evidence for a role of DIM proteins in cell-to-cell communication via PDs.…”

The Arabidopsis Synaptotagmin1 Is Enriched in Endoplasmic Reticulum-Plasma Membrane Contact Sites and Confers Cellular Resistance to Mechanical Stresses

“…According to the tensegrity model, the SYT1-labeled ER-PM contact sites might function as deformable platforms that coordinate the cortical ER and cytoskeleton responses to minimize the mechanical loads at the PM. This model would not require the activation of transcriptional programs and can explain the instantaneous PM instability observed upon exposure to multiple stresses, including freezing, osmotic, and mechanical challenge (Yamazaki et al, 2008;Schapire et al, 2008;this study). This model could also explain the enhanced cytoskeleton depolymerization observed in the syt1 mutant due to the limited ability of SYT1-depleted contact sites to properly transfer mechanical cues to the cortical cytoskeleton (Fig.…”

“…In previous reports, SYT1 has been described as an essential component for PM integrity maintenance, especially under conditions of high potential for membrane disruption such as freezing or salt stresses (Schapire et al, 2008(Schapire et al, , 2009Yamazaki et al, 2008). In these reports, SYT1 was proposed to act as a Ca 2+ -dependent regulator of membrane fusion, in analogy to the classical animal SYTs that mediate Ca 2+ -triggered vesicle fusion during neurotransmission (Carr and Munson, 2007).…”

Oil-Body-Membrane Proteins and Their Physiological Functions in Plants

“…31) These stresses damage membrane of plant cells. 32,33) Freezing stress may cause undetectable damage to oleosindeficient membrane of oil bodies, which causes oil bodies to fuse additionally. The additionally enlarged oil bodies of ole1 seeds are similar to oil bodies of ole1 ole2 seeds.…”