Sasaki Kanako, Mito Kouji, Ohara Kazuaki, Yamamoto Hirobumi, Yazaki Kazufumi
Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan.
Plant Physiol. 2008 Mar;146(3):1075-84. doi: 10.1104/pp.107.110544. Epub 2008 Jan 24.
Prenylated flavonoids are natural compounds that often represent the active components in various medicinal plants and exhibit beneficial effects on human health. Prenylated flavonoids are hybrid products composed of a flavonoid core mainly attached to either 5-carbon (dimethylallyl) or 10-carbon (geranyl) prenyl groups derived from isoprenoid (terpenoid) metabolism, and the prenyl groups are crucial for their biological activity. Prenylation reactions in vivo are crucial coupling processes of two major metabolic pathways, the shikimate-acetate and isoprenoid pathways, in which these reactions are also known as a rate-limiting step. However, none of the genes responsible for the prenylation of flavonoids has been identified despite more than 30 years of research in this field. We have isolated a prenyltransferase gene from Sophora flavescens, SfN8DT-1, responsible for the prenylation of the flavonoid naringenin at the 8-position, which is specific for flavanones and dimethylallyl diphosphate as substrates. Phylogenetic analysis shows that SfN8DT-1 has the same evolutionary origin as prenyltransferases for vitamin E and plastoquinone. The gene expression of SfN8DT-1 is strictly limited to the root bark where prenylated flavonoids are solely accumulated in planta. The ectopic expression of SfN8DT-1 in Arabidopsis thaliana resulted in the formation of prenylated apigenin, quercetin, and kaempferol, as well as 8-prenylnaringenin. SfN8DT-1 represents the first flavonoid-specific prenyltransferase identified in plants and paves the way for the identification and characterization of further genes responsible for the production of this large and important class of secondary metabolites.
异戊烯基黄酮是一类天然化合物，常为多种药用植物中的活性成分，对人体健康具有有益作用。异戊烯基黄酮是一种混合产物，其黄酮类核心主要连接着源自类异戊二烯（萜类）代谢的5碳（二甲基烯丙基）或10碳（香叶基）异戊烯基，而异戊烯基对其生物活性至关重要。体内的异戊烯基化反应是莽草酸 - 乙酸途径和类异戊二烯途径这两条主要代谢途径的关键偶联过程，在这些反应中，该步骤也是限速步骤。然而，尽管在该领域进行了30多年的研究，但尚未鉴定出负责黄酮类异戊烯基化的基因。我们从苦参中分离出一个异戊烯基转移酶基因SfN8DT - 1，它负责黄酮类化合物柚皮素在8位的异戊烯基化，该基因以黄烷酮和二甲基烯丙基二磷酸作为底物具有特异性。系统发育分析表明，SfN8DT - 1与维生素E和质体醌的异戊烯基转移酶具有相同的进化起源。SfN8DT - 1的基因表达严格局限于根皮，在植物中，异戊烯基黄酮仅在根皮中积累。SfN8DT - 1在拟南芥中的异位表达导致了异戊烯基化芹菜素、槲皮素、山奈酚以及8 - 异戊烯基柚皮素的形成。SfN8DT - 1是在植物中鉴定出的首个黄酮类特异性异戊烯基转移酶，为进一步鉴定和表征负责这类大量且重要的次生代谢产物合成的基因铺平了道路。
