Characterization of an O-methyltransferase specific to guaiacol-type benzenoids from the flowers of loquat (Eriobotrya japonica)

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• 作者：Takao Koeduka¹ ; ^{takaori@yamaguchi-u.ac.jp} ; Mami Kajiyama¹ ; Takumi Furuta² ; Hideyuki Suzuki³ ; Tomohiko Tsuge² ; Kenji Matsui¹
• 关键词：O-Methyltransferase ; Volatile benzenoid ; Loquat ; Guaiacol ; Eriobotrya japonica
• 刊名：Journal of Bioscience and Bioengineering
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：122
• 期：6
• 页码：679-684
• 全文大小：1445 K
• 卷排序：122

文摘

Volatile benzenoids, including methyl p-methoxybenzoate, p-anisaldehyde, and p-anisalcohol, are responsible for the sweet and characteristic fragrance of loquat (Eriobotrya japonica, Rosaceae) flowers. Although the full pathway of volatile benzenoid synthesis has yet to be elucidated, their chemical structures suggest that O-methyltransferases are present in loquat and function in the methylation of the para-OH groups. In the present study, we used RNA-sequencing to identify four loquat genes (EjOMT1, EjOMT2, EjOMT3, and EjOMT4) that encode O-methyltransferases. We found that EjOMT1 was highly expressed in floral tissues, with an expression pattern that coincided with changes in intracellular volatile benzenoids during flower development. Recombinant EjOMT1 protein expressed in Escherichia coli showed the highest activity towards guaiacol with a Km value of 35 μM. Furthermore, the protein also showed lesser activities towards guaiacol-type benzenoids including eugenol, isoeugenol, vanillin, and ferulic acid, in addition to much weaker activities towards catechol and p-hydroxybenzenoid derivatives. However, no activity was shown towards phenylpropenes without m-methoxy substitution, t-anol and chavicol. Taken together, our findings indicate that EjOMT1 has a broad substrate specificity towards compounds with both para-OH and meta-OCH3 groups, unlike previously characterized O-methyltransferases for volatile benzenoid/phenylpropanoid biosynthesis.