Co-expression of calcium-dependent protein kinase with the inward rectified guard cell K+ channel KAT1 alters current parameters in Xenopus laevis oocytes.
by Berkowitz G., Zhang X., Mercie R., Leng Q., Lawton M. (2000)
in Plant Cell Physiol 41: 785–790 – DOI: https://doi.org/10.1093/pcp/41.6.785 –
Guard cell calcium-dependent protein kinase (CDPK) has been shown to phosphorylate KAT1; such phosphorylation is known to modulate other K+ channels involved in signal transduction cascades.
The work reported here focused on demonstrating CDPK-dependent inhibition of KAT1 currents. A cDNA encoding soybean CDPK was generated and it’s translation product was shown to be functional; demonstrating Ca2+-dependent autophosphorylation and phosphorylation of a target protein. Ion currents were monitored using voltage clamp techniques upon expression of KAT1 in Xenopus laevis oocytes.
Co-expression of recombinant CDPK with KAT1 in oocytes altered the kinetics and magnitude of induced K+ currents; at a given hyperpolarizing command voltage, the magnitude of KAT1 currents was reduced and the half-time for channel activation was increased.
This finding supports a model of Ca2+-dependent ABA inhibition of inward K+ currents in guard cells as being mediated by CDPK phosphorylation of KAT1.