Salt- and osmotic stress-induced choline monooxygenase expression in Kochia scoparia is ABA-independent

Choline monooxygenase (CMO) is the first regulatory enzyme in the biosynthetic pathway for glycine betaine, an effective osmoprotectant in Kochia scoparia, a highly drought- and salt-tolerant species. In seedlings, CMO transcript levels are rapidly increased in response to both NaCl and osmotic stress treatments. The mRNA level in shoots was substantially higher than in roots. The rapid induction seen in whole plants was in contrast to the apparent down-regulation observed in suspension-cultured K. scoparia cells in response to the same salt stress. Treatment with exogenous abscisic acid (ABA) or fluridone shows that CMO induction proceeds via an ABA-independent signal transduction pathway. Examination of the CMO upstream regulatory region reveals a number of stress response-related elements, some of which may be involved in the stress tolerance shown by this species.