Functional Interaction of the SNARE Protein NtSyp121 in Ca^2＋ Channel Gating, Ca^2＋ Transientsand ABA Signalling of Stomatal Guard Cells

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 CI^- channel responses to the stress-related hormone abscisic acid （ABA）, but left open a question about functional impacts on signal intermediates, especially on Ca^2＋-mediated signalling events. Here, we report one mode of action for the SNARE mediated directly through alterations in Ca^2＋ channel gating and its consequent effects on cytosolic-free [Ca^2＋] （[Ca^2＋]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 [Ca^2＋]i elevation independently of the plasma membrane Ca^2＋ channels. Consistent with these observations, Ca^2＋ 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 [Ca^2＋]i, and we show directly that its expression in vivo leads to a pronounced suppression of evoked [Ca^2＋]i transients. These observations offer primary evidence for the functional coupling of the SNARE with Ca^2＋ channels at the plant cell plasma membrane and, because [Ca^2＋]i plays a key role in the control of K^＋ and CI^- channel currents in guard cells, they underscore an important mechanism for SNARE integration with ion channel regulation during stomatal closure.

Distributed Differences Structures Underlie Gating between the Kin Channel KAT1 and the Kout Channel SKOR

The family of voltage-gated （Shaker-like） potassium channels in plants includes both inward-rectifying （Kin） channels that allow plant cells to accumulate K＋ and outward-rectifying （Kout） channels that mediate K＋ efflux. Despite their dose structural similarities, Kin and Kout channels differ in their gating sensitivity towards voltage and the extracellular K＋ concentration. We have carried out a systematic program of domain swapping between the Kout channel SKOR and the Kin channel KAT1 to examine the impacts on gating of the pore regions, the S4, S5, and the S6 helices. We found that, in particular, the N-terminal part of the S5 played a critical role in KAT1 and SKOR gating. Our findings were supported by molecular dynamics of KAT1 and SKOR homology models. In silico analysis revealed that during channel opening and closing, displacement of certain residues, especially in the S5 and S6 segments, is more pronounced in KAT1 than in SKOR. From our analysis of the S4-S6 region, we conclude that gating （and K＋-sensing in SKOR） depend on a number of structural elements that are dispersed over this -145-residue sequence and that these place additional constraints on configurational rearrangement of the channels during gating.

Speedy Grass Stomata： Emerging Molecular anc Evolutionary Features

Stomata in most land plants are formed by a pair of guard cells, controlling the water loss and the carbon dioxide uptake. The development, patterning, and density of stomata are fundamental traits for stomatal function, contributing to plant growth and productivity （Pillitteri and Torii, 2012）.