title: Functional interaction of the SNARE protein NtSyp121 in Ca2+ channel gating, Ca2+ transients and ABA signalling of stomatal guard cells.
abstract: There is now growing evidence that membrane vesicle trafficking proteins, especially of the superfamily of SNAREs, are critical for cellular signalling in plants. Work from this laboratory first demonstrated that a soluble, inhibitory (dominant-negative) fragment of the SNARE NtSyp121 blocked K+ and Cl- channel responses to the stress-related hormone abscisic acid (ABA), but left open a question about functional impacts on signal intermediates, especially on Ca2+-mediated signalling events. Here, we report one mode of action for the SNARE mediated directly through alterations in Ca2+ channel gating and its consequent effects on cytosolic-free [Ca2+] ([Ca2+]i) elevation. We find that expressing the same inhibitory fragment of NtSyp121 blocks ABA-evoked stomatal closure, but only partially suppresses stomatal closure in the presence of the NO donor, SNAP, which promotes [Ca2+]i elevation independently of the plasma membrane Ca2+ channels. Consistent with these observations, Ca2+ channel gating at the plasma membrane is altered by the SNARE fragment in a manner effective in reducing the potential for triggering a rise in [Ca2+]i, and we show directly that its expression in vivo leads to a pronounced suppression of evoked [Ca2+]i transients. These observations offer primary evidence for the functional coupling of the SNARE with Ca2+ channels at the plant cell plasma membrane and, because [Ca2+]i plays a key role in the control of K+ and Cl- channel currents in guard cells, they underscore an important mechanism for SNARE integration with ion channel regulation during stomatal closure.
authors.affiliation: Laboratory of Plant Physiology and Biophysics, IBLS-Plant Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Sergei
authors.initials: S
authors.lastname: Sokolovski
authors.forename: Adrian
authors.initials: A
authors.lastname: Hills
authors.forename: Robert A
authors.initials: RA
authors.lastname: Gay
authors.forename: Michael R
authors.initials: MR
authors.lastname: Blatt
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003907:Dexamethasone / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D030821:Plants, Genetically Modified / Q000187:drug effects; D050600:SNARE Proteins / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014026:Nicotiana / Q000187:drug effects / Q000502:physiology; D031306:Vicia / Q000187:drug effects / Q000502:physiology*
chemical_list: D010446:Peptide Fragments; D050600:SNARE Proteins; D000040:Abscisic Acid; D003907:Dexamethasone; D002118:Calcium