Search for the regulatory site of the SLAC1 anion channel involved in stomatal CO₂ response

Abstract

SLAC1 is a slow-anion channel which has a central role in the control of stomatal closure and its activity is regulated by ABA and CO₂. Regarding ABA sensing mechanism of SLAC1, it has been reported that this channel is activated by phosphorylation of Ser 120 in its N-terminal region from the OST1 kinase which is a positive regulator of ABA signaling. In contrast, its CO₂ sensing mechanism remains unknown. To search for the regulatory region involved in the CO₂ response, N- or C-terminal deletion SLAC1 genes (S1ΔN, S1ΔC ) were introduced into slac1-2 mutant. S1ΔN and S1ΔC can complement the CO₂-insensitive phenotype of slac1-2. This result suggests that transmembrane region of SLAC1 (180~504 a.a.) have some regulatory site involved in stomatal CO₂ response, and we hypothesized that direct phosphorylation of this transmembrane region is critical in CO₂ signaling. Based on a 3D structural model of the SLAC1 channel, we discuss phosphprylation sites in the SLAC1 transmembrane region.