Phosphatase ABI1 and okadaic acid-sensitive phosphoprotein phosphatases inhibit salt stress-activated SnRK2.4 kinase.

Background SNF1-related protein kinases 2 (SnRK2s) are key regulators of the plant response to osmotic stress. They are transiently activated in response to drought and salinity. Based on a phylogenetic analysis SnRK2s are divided into three groups. The classification correlates with their response to abscisic acid (ABA); group 1 consists SnRK2s non-activated in response to ABA, group 2, kinases non-activated or weakly activated (depending on the plant species) by ABA treatment, and group 3, ABA-activated kinases. The activity of all SnRK2s is regulated by phosphorylation. It is well established that clade A phosphoprotein phosphatases 2C (PP2Cs) are negative regulators of ABA-activated SnRK2s, whereas regulators of SnRK2s from group 1 remain unidentified.