Physiological Role of Endogenous S-adenosyl-L-methionine Synthetase in Chinese Cabbage Jae-Gyeong Yu, Gi-Ho Lee, and Young-Doo Park * Department of Horticultural Biotechnology, Kyung Hee University, Yongin 446-701, Korea *Corresponding author: ydpark@khu.ac.kr Received February 19, 2012 / Revised April 17, 2012 / Accepted April 30, 2012 Korean Society for Horticultural Science and Springer 2012 Abstract. 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. T1 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. Additional key words: Agrobacterium tumefaciens, down-regulation, microarray, over-expression, phenotype, T1 progenies Hort. Environ. Biotechnol. 53(3):247-255. 2012. DOI 10.1007/s13580-012-0021-7 Research Report Introduction S-Adenosyl-L-methionine synthetase (SAMS) catalyzes the conversion of ATP and L-methionine into S-adenosyl -L-methionine (SAM) (Boerjan et al., 1994). The gene encoding SAMS has been cloned from many plant species including Arabidopsis thaliana (Peleman et al., 1989), car- nation (Dianthus caryophyllus) (Larsen and Woodson, 1991), parsley (Petroselinum crispum) (Kawalleck et al., 1992), poplar (Liriodendron tulipifera) (Van Doorsselaere et al., 1993), rice (Oryza sartiva) (Van Breusegem et al., 1994), tomato (Lycopericum esculentum) (Espartero et al., 1994), tobacco (Nicotiana tabacum) (Boerjan et al., 1994), kiwifruit ( Actinidia chinensis ) (Whittaker et al., 1995), mustard ( Brassica juncea) (Lim et al., 2002; Mo and Pua, 2002; Wen et al., 1995), Madagascar periwinkle ( Catharanthus roseu s) (Schröder et al., 1997), and pea (Pisum sativum) (Gómez-Gómez and Carrasco, 1998). Transgenic tobacco plants over-expressing SAMS have been found previously to display abnormal coloration and flattening in the leaves, whereas highly elevated levels of SAMS leads to reduced plant height and necrotic lesions. In contrast, highly reduced SAMS activity has been shown to produce stunted plants with thick, leather-like, asymmetric, and torn leaves (Boerjan et al., 1994). SAMS is a ubiquitous enzyme that is well conserved between eukaryotes and prokaryotes and is suggested to be expressed constitutively in some tissues and controlled by developmental and/or environmental factors in others. The expression of genes encoding SAMS is therefore affected by the tissue and organ type, the growth stage in the case of plants, and by exposure to stress conditions. In plants, many biochemical reactions involve the transfer of a methyl group from SAM (Barbara and Elizabeth, 2001). SAM serves as a methyl group donor in the transmethylation of DNA, RNA, protein, lipids, polysaccharides, and secondary products (Galston, 1989; Galston and Kaur-Sawhney, 1995). The methylated sulfur (sulfonium) moiety of SAMS is estimated