Arabidopsis SOS3 plays an important role in salt tolerance by mediating calcium-dependent microfilament reorganization.

KEY MESSAGE : SOS3 mediates calcium dependent actin filament reorganization that plays important roles in plant responses to salt stress. Arabidopsis salt overly sensitive 3 (SOS3) plays an important role in plant salt tolerance by regulation of Na(+)/K(+) homeostasis. Plants lacking SOS3 are hypersensitive to salt stress and this phenomenon can be partially rescued by the addition of calcium. However the mechanism underlying remains elusive. We here report that the organization of actin filaments in sos3 mutant differs from that in wild-type plant. Under salt stress abnormal actin assembly and arrangement in sos3 are more pronounced, which can be partially complemented by addition of external calcium or low concentration of latrunculin A, an actin monomer-sequestering agent. The effects of calcium and Lat A on actin filament organization of sos3 mutant are accordant with their effects on sos3 salt sensitivity under salt stress. These findings indicate that the salt-hypersensitivity of sos3 mutant partially results from its disordered actin filaments, and SOS3 mediated actin filament reorganization plays important roles in plant responses to salt stress.