Poster: Secondary Metabolism

Abs # 280: Cloning and Properties of Five Glucosyltransferases Reacting on Phenolic Compounds in Tobacco

Presenter:	Taguchi, Goro , gtagtag@giptc.shinshu-u.ac.jp
Authors	Taguchi, Goro  (A)   Ubukata, Takahisa  (A)   Hayashida, Nobuaki  (A)   Yamamoto, Hirobumi  (B)   Okazaki, Mitsuo  (A)
Affiliations:	(A): Gene Research Center, Shinshu University (B): Medical Plant Garden, School of Pharmaceutical Science, Nagasaki University

Many glucosyltransferases (GTases) adapting to variety of substrates are known in plants. We cloned five cDNAs encoding GTases (NtGT1a, 1b, 2, 3, 4) from tobacco cells (Nicotiana tabacum L. cv Bright Yellow). The proteins encoded by these genes (NTGTs) are classified into three GTase-families according to their sequences. The enzymes expressed in E. coli (rNTGTs) showed glucosylation activity upon scopoletin, which is a major phenolics accumulated as its glucoside in tobacco cells. NTGT1a, NTGT1b and NTGT 3 form a novel GTase family. These enzymes reacted upon several phenolic compounds, especially 3-hydroxyl group (OH) of flavonoids. The K_m value of rNTGT1a and rNTGT3 were 13.1 micro M and 3.5 micro M for 3-OH of kaempferol, 35.5 micro M and 68.1 micro M for 2-naphthol, respectively. They were induced by plant hormones, such as auxin or salicylic acid, and were also induced by xenobiotic compound naphthols. The results suggested that NTGT1 and NTGT3 might relate to the xenobiotic metabolism in tobacco. NTGT4 are classified into another GTase family, but rNTGT4 reacted upon flavonoids and coumarins as similer as rNTGT3. NTGT2 shows 60-70 % identity to anthocyanin 5-O- GTases. The rNTGT2 reacted upon several phenollic-compounds, especially 7-OH of flavonoids. The K_m value of rNTGT2 against 7-OH of kaempferol was 3.7 micro M. NtGT2 was induced by salicylic acid. NTGT2 is a novel inducible GTase that has flavonoid 7-O-GTase activity.