Physiological Role of Endogenous S-adenosyl-L-methionine Synthetase in Chinese Cabbage

S-adenosyl-L-methionine synthetase (SAMS) catalyzes the synthesis of S-adenosyl-L-methionine, a molecule which functions as the methyl group donor in the biosynthesis of nucleic acids, proteins, lipids, polysaccharides, and secondary products. To analyze the physiological role of endogenous S-adenosyl-L-methionine synthetase, Chinese cabbage was transformed with pCSAMS vector for SAMS over-expression and pJJSAMS vector for SAMS down-regulation, respectively. From the results of both quantitative real-time PCR and northern hybridization, SAMS showed a 2.5-fold greater expression in the pCSAMS line and approximately 2-fold suppression in the pJJSAMS line. T-1 progenies of these transgenic lines and a wild type control were analyzed by microarray to evaluate genes that are functionally related to SAMS. Expression level changes of SAMS strongly affected not only genes related to defense response to abiotic stress but also protein, jasmonic acid, and ethylene synthesis. Based on these results, we conclude that SAMS plays an important role in plant metabolic pathways and in the biosynthesis of phytohormones related to plant growth. By phenotype analysis, the SAMS over-expression lines were found to grow rapidly with flattened and serrated leaf margin. The down-regulated SAMS lines, however, could be characterized by stunted growth and the appearance of thick and asymmetric leaves.