25. イネコーヒー酸3-O-メチルトランスフェラーゼのクローニング及び機能解析

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A putative O-methyltransferase cDNA was cloned from UV-irradiated rice leaves based on the amino acid sequence reported as that of naringenin 7-O-methyltransferase, which is involved in the biosynthesis of rice phytoalexin, sakuranetin [Plant Sci., 155, 213-221 (2000)]. However, the recombinant protein (approximately 41 kDa) expressed in Escherichia coli showed no naringenin 7-O-methyltransferase (NOMT) activity but showed caffeic acid 3-O-methyltransferase (COMT) activity. Thus the gene was designated as caffeic acid 3-O-methyltransferase gene (OsCOMT1). The result of the tblastn search of the GenBank rice genome DNA database indicated that the rice plant contained only one copy of the COMT gene. And it was found to be located at 27.1 cM on chromosome 8 by searching the rice EST map. The result of the quantitative RT-PCR showed that OsCOMT1 was expressed in all tissues tested and was not affected by CuCl_2, jasmonic acid and UV treatments. The optimal pH was found to be 7.5 in Tris-HCl buffer. The apparent K_m values for caffeic acid and S-adenosyl-L-methionine were 69 and 51μM, respectively. The enzyme also methylated flavonoids which have adjacent two hydroxyl groups in the B ring. The COMT activity of crude protein extract was detected at almost a constant level in different plant growth stages and different leaf positions; only a slight increase was detected with increasing age. No induction effect was found by CuCl_2, jasmonic acid and UV treatments.
植物化学調節学会の論文
2005-10-13

25. イネコーヒー酸3-O-メチルトランスフェラーゼのクローニング及び機能解析

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