Bovy Arnaud, de Vos Ric, Kemper Mark, Schijlen Elio, Almenar Pertejo Maria, Muir Shelagh, Collins Geoff, Robinson Sue, Verhoeyen Martine, Hughes Steve, Santos-Buelga Celestino, van Tunen Arjen
Plant Research International, Droevendaalsesteeg 1, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
Plant Cell. 2002 Oct;14(10):2509-26. doi: 10.1105/tpc.004218.
Flavonoids are a group of polyphenolic plant secondary metabolites important for plant biology and human nutrition. In particular flavonols are potent antioxidants, and their dietary intake is correlated with a reduced risk of cardiovascular diseases. Tomato fruit contain only in their peel small amounts of flavonoids, mainly naringenin chalcone and the flavonol rutin, a quercetin glycoside. To increase flavonoid levels in tomato, we expressed the maize transcription factor genes LC and C1 in the fruit of genetically modified tomato plants. Expression of both genes was required and sufficient to upregulate the flavonoid pathway in tomato fruit flesh, a tissue that normally does not produce any flavonoids. These fruit accumulated high levels of the flavonol kaempferol and, to a lesser extent, the flavanone naringenin in their flesh. All flavonoids detected were present as glycosides. Anthocyanins, previously reported to accumulate upon LC expression in several plant species, were present in LC/C1 tomato leaves but could not be detected in ripe LC/C1 fruit. RNA expression analysis of ripening fruit revealed that, with the exception of chalcone isomerase, all of the structural genes required for the production of kaempferol-type flavonols and pelargonidin-type anthocyanins were induced strongly by the LC/C1 transcription factors. Expression of the genes encoding flavanone-3'-hydroxylase and flavanone-3'5'-hydroxylase, which are required for the modification of B-ring hydroxylation patterns, was not affected by LC/C1. Comparison of flavonoid profiles and gene expression data between tomato leaves and fruit indicates that the absence of anthocyanins in LC/C1 fruit is attributable primarily to an insufficient expression of the gene encoding flavanone-3'5'-hydroxylase, in combination with a strong preference of the tomato dihydroflavonol reductase enzyme to use the flavanone-3'5'-hydroxylase reaction product dihydromyricetin as a substrate.
类黄酮是一类多酚类植物次生代谢产物，对植物生物学和人类营养都很重要。特别是黄酮醇是强效抗氧化剂，其饮食摄入量与心血管疾病风险降低相关。番茄果实仅在其果皮中含有少量类黄酮，主要是柚皮素查耳酮和黄酮醇芦丁（一种槲皮素糖苷）。为了提高番茄中的类黄酮水平，我们在转基因番茄植株的果实中表达了玉米转录因子基因LC和C1。这两个基因的表达对于上调番茄果肉中的类黄酮途径是必需且充分的，而果肉是通常不产生任何类黄酮的组织。这些果实的果肉中积累了高水平的黄酮醇山奈酚，以及少量的黄烷酮柚皮素。检测到的所有类黄酮均以糖苷形式存在。先前报道在几种植物物种中LC表达后会积累花青素，其在LC/C1番茄叶片中存在，但在成熟的LC/C1果实中未检测到。成熟果实的RNA表达分析表明，除查耳酮异构酶外，生产山奈酚型黄酮醇和天竺葵素型花青素所需的所有结构基因均被LC/C1转录因子强烈诱导。编码B环羟基化模式修饰所需的黄烷酮-3'-羟化酶和黄烷酮-3'5'-羟化酶的基因表达不受LC/C1影响。番茄叶片和果实之间类黄酮谱和基因表达数据的比较表明，LC/C1果实中花青素的缺失主要归因于编码黄烷酮-3'5'-羟化酶的基因表达不足，以及番茄二氢黄酮醇还原酶强烈倾向于使用黄烷酮-3'5'-羟化酶反应产物二氢杨梅素作为底物。
