Abstract
Betaine is an important osmoprotectant, synthesized by many plants in response to abiotic stresses. Although almost all known biosynthetic pathways of betaine are two-step oxidations of choline, recently a novel biosynthetic pathway of betaine from glycine, catalyzed by two N-methyltransferase enzymes, was found. Here, the potential role of N-methyltransferase genes for betaine synthesis was examined in a fresh water cyanobacterium Synechococcus sp. PCC 7942 and in Arabidopsis plants. Co-expression of N-methyltransferase genes in Synechococcus caused accumulation of significant amount of betaine, and conferred sufficient salt tolerance to a fresh water cyanobacterium. Arabidopsis plants expressing the N-methyltransferase genes also accumulated betaine to a high level in roots, stems, leaves, and flowers, and improved the seed yield under stress conditions. Betaine levels were higher than those produced by choline-oxidizing enzymes. These results demonstrate the usefulness of glycine N-methyltransferase genes for improvement of abiotic stress tolerance in crop plants.
