SLAC1

SLAC1, which stands for Slow Anion Channel-Associated 1, is a plasma membrane protein encoded by the SLAC1 gene in Arabidopsis thaliana. It functions as a guard cell S-type anion channel that mediates the efflux of anions, such as chloride and nitrate, across the guard cell plasma membrane—a key step in the regulation of stomatal aperture.

SLAC1 belongs to the SLAC/ALMT family of ion channels and is predominantly expressed in guard cells of aerial tissues. The channel is regulated by phosphorylation, with the ABA-activated protein kinase OST1/SnRK2.6 playing a central role. Calcium signaling and other kinases can modulate activity as part of the broader ABA signaling network. Phosphorylation relieves autoinhibition by the cytosolic C-terminal domain and promotes channel opening, enabling anion efflux that drives osmotic and turgor changes in guard cells.

Functionally, SLAC1 activity contributes to ABA- and CO2-induced stomatal closure. When activated, anion efflux leads to water efflux, guard cell shrinkage, and stomatal closure, reducing water loss during drought. In loss-of-function slac1 mutants, ABA- and CO2-responsive stomatal closure is impaired, resulting in higher transpirational water loss and altered drought responses. Proper SLAC1 function is thus important for plant water use efficiency under water-limited conditions.

Structurally, SLAC1 is a multi-pass transmembrane protein localized to the guard cell plasma membrane. It is thought to form functional channels as multimers and contains cytosolic regulatory regions that integrate multiple signaling cues, coordinating environmental and hormonal signals to control stomatal movements.