Cell-Free Science and Technology Research Center, Ehime University, Matsuyama, Ehime, Japan.
Planta. 2010 Jun;232(1):209-18. doi: 10.1007/s00425-010-1166-1. Epub 2010 Apr 16.
Some flavonoids are considered as beneficial compounds because they exhibit anticancer or antioxidant activity. In higher plants, flavonoids are secondary metabolites that are derived from phenylpropanoid biosynthetic pathway. A large number of phenylpropanoids are generated from p-coumaric acid, which is a derivative of the primary metabolite, phenylalanine. The first two steps in the phenylpropanoid biosynthetic pathway are catalyzed by phenylalanine ammonia-lyase and cinnamate 4-hydroxylase, and the coupling of these two enzymes forms a rate-limiting step in the pathway. For the generation of p-coumaric acid, the conversion from phenylalanine to p-coumaric acid that is catalyzed by two enzymes can be theoretically performed by a single enzyme, tyrosine ammonia-lyase (TAL) that catalyzes the conversion of tyrosine to p-coumaric acid in certain bacteria. To modify the p-coumaric acid pathway in plants, we isolated a gene encoding TAL from a photosynthetic bacterium, Rhodobacter sphaeroides, and introduced the gene (RsTAL) in Arabidopsis thaliana. Analysis of metabolites revealed that the ectopic over-expression of RsTAL leads to higher accumulation of anthocyanins in transgenic 5-day-old seedlings. On the other hand, 21-day-old seedlings of plants expressing RsTAL showed accumulation of higher amount of quercetin glycosides, sinapoyl and p-coumaroyl derivatives than control. These results indicate that ectopic expression of the RsTAL gene in Arabidopsis enhanced the metabolic flux into the phenylpropanoid pathway and resulted in increased accumulation of flavonoids and phenylpropanoids.
一些类黄酮被认为是有益的化合物，因为它们具有抗癌或抗氧化活性。在高等植物中，类黄酮是由苯丙烷生物合成途径衍生而来的次生代谢物。大量的苯丙烷类化合物是由对香豆酸衍生而来的，对香豆酸是苯丙氨酸的一种代谢物。苯丙烷生物合成途径的前两步由苯丙氨酸解氨酶和肉桂酸 4-羟化酶催化，这两种酶的偶联形成了途径中的限速步骤。对于对香豆酸的生成，由两种酶催化的苯丙氨酸转化为对香豆酸的转化在理论上可以由一种酶，即酪氨酸解氨酶（TAL）来完成，该酶在某些细菌中催化酪氨酸转化为对香豆酸。为了修饰植物中的对香豆酸途径，我们从光合细菌 Rhodobacter sphaeroides 中分离出编码 TAL 的基因，并将该基因（RsTAL）导入拟南芥中。代谢物分析表明，RsTAL 的异位过表达导致转基因 5 天大的幼苗中花色苷的积累增加。另一方面，表达 RsTAL 的植物 21 天大的幼苗中积累的槲皮素糖苷、芥子酰和对香豆酰衍生物的量高于对照。这些结果表明，RsTAL 基因在拟南芥中的异位表达增强了苯丙烷途径的代谢通量，导致类黄酮和苯丙烷类化合物的积累增加。
