The Arabidopsis thaliana SOS2 gene encodes a protein kinase that is required for salt tolerance.

Liu J, Ishitani M, Halfter U, Kim CS, Zhu JK.

Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA.

In Arabidopsis thaliana, the Salt Overly Sensitive 2 (SOS2) gene is required for intracellular Na(+) and K(+) homeostasis. Mutations in SOS2 cause Na(+) and K(+) imbalance and render plants more sensitive toward growth inhibition by high Na(+) and low K(+) environments. We isolated the SOS2 gene through positional cloning. SOS2 is predicted to encode a serine/threonine type protein kinase with an N-terminal catalytic domain similar to that of the yeast SNF1 kinase. Sequence analyses of sos2 mutant alleles reveal that both the N-terminal catalytic domain and the C-terminal regulatory domain of SOS2 are functionally essential. The steady-state level of SOS2 transcript is up-regulated by salt stress in the root. Autophosphorylation assays show that SOS2 is an active protein kinase. In the recessive sos2-5 allele, a conserved glycine residue in the kinase catalytic domain is changed to glutamate. This mutation abolishes SOS2 autophosphorylation, indicating that SOS2 protein kinase activity is required for salt tolerance.