Cloning and Nucleotide Sequence of a cDNA Encoding 5-Adenosyl-L-Methionine Synthetase from Mustard (Brassica juncea L Czern Coss)

摘要

Ethylene, a gaseous hormone in plants, is involved in the regulation of a wide range of plant physiological processes, including leaf abscission, fruit ripening, and flower senescence (Yang and Hoffman, 1984). SAM or Adomet syn-thetase (ATP:L-methionine S-adenosyltransferase; EC 2.5.1-6) catalyzes the conversion of Met to SAM in the presence of ATP and Mg~(2+), which is the first step in ethylene biosynthesis. Changes in the level of endogenous SAM can greatly affect ethylene synthesis. In tomato (Ly-copersicon esculentum), transgenic plants that overproduced bacteriophage T3 SAM hydrolase, the enzyme that degrades SAM to a-ketobutyrate and ammonia, showed a 60 to 80 decrease in ethylene production (Kellogg et al., 1994). Apart from being a precursor in ethylene biosynthesis, SAM also serves as a propylamine group donor in polyamine synthesis and as a methyl group donor in a variety of reactions including transmethylation of proteins, nucleic acids, lipids, and polysaccharides (Tabor and Tabor, 1984).