SOS4 (SALT OVERLY SENSITIVE 4); kinase/ pyridoxal kinase; Encodes a pyridoxal kinase required for root hair development. Mutants are hypersensitive to Na+, K+ and Li+. ; Catalyzes the transfer of a phosphate group from ATP to the 5-hydroxylmethyl group of pyridoxal to form the biologically active pyridoxal phosphate (343 aa)