Redirection of flavonoid biosynthesis through the down-regulation of an anthocyanidin glucosyltransferase in ripening strawberry fruit
Redirection of flavonoid biosynthesis through the down-regulation of an anthocyanidin glucosyltransferase in ripening strawberry fruit
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DOI：
10.1104/pp.107.114280
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发表时间：
2008-04-01
期刊：
影响因子：
7.4
通讯作者：
Schwab, Wilfried
中科院分区：
文献类型：
--
作者：
Griesser, Markus;Hoffmann, Thomas;Schwab, Wilfried
草莓（Fragaria x ananassa）果实含有几种花青素，使成熟的果实呈现迷人的红色。在花青素途径中催化形成第一个稳定中间体的酶是花青素-3- o -葡萄糖基转移酶。从草莓果实cDNA文库中克隆了一个假定的糖基转移酶序列（FaGT1），重组的FaGT1将udp -葡萄糖转移到花青素上，并在较小程度上转移到黄酮醇上，生成相应的3- o -糖苷。定量聚合酶链反应显示，在青果中几乎检测不到FaGT1的转录本，但在转果和成熟的红果中，该基因的表达量都显著增加，这与果实成熟过程中花青素的积累密切相关。FaGT1的表达与果实相关，受生长素负调控。为了阐明FaGT1在植物中的功能，将含有部分FaGT1序列内含子发夹结构的根癌农杆菌细胞注入中型成熟果实中。在大约三分之一的注射果实中，这导致FaGT1转录物水平显著下调，这与成熟草莓果实中花青素色素浓度降低相对应。相比之下，在FaGT1沉默的果实中发现了大量由花青素还原酶（ANR）生成的epiafzelecin，这表明FaGT1和FaANR对共同的花青素底物进行了竞争。因此，FaGT1代表了一个重要的分支点酶，因为它是黄酮类化合物途径到花青素的通道。这些结果证明了一种将花青素生物合成转向黄烷-3-醇生产的方法，以增加生物活性天然产物的水平或修饰植物组织中的色素。
Strawberry (Fragaria x ananassa) fruit contains several anthocyanins that give the ripe fruits their attractive red color. The enzyme that catalyzes the formation of the first stable intermediate in the anthocyanin pathway is anthocyanidin-3-O-glucosyltransferase. A putative glycosyltransferase sequence (FaGT1) was cloned from a strawberry fruit cDNA library and the recombinant FaGT1 transferred UDP-glucose to anthocyanidins and, to a lesser extent, flavonols, generating the respective 3-O-glucosides. Quantitative polymerase chain reaction revealed that transcripts of FaGT1 were almost undetectable in green fruits, but gene expression increased dramatically in both turning and ripe red fruit, corresponding closely to the accumulation of anthocyanins during fruit ripening. The expression of FaGT1 is fruit associated and negatively regulated by auxin. To elucidate the in planta function of FaGT1, Agrobacterium tumefaciens cells harboring an intron-hairpin construct of a partial FaGT1 sequence were injected into midsized ripening fruits. In about one-third of the injected fruits, this led to significant down-regulation of FaGT1 transcript levels that corresponded to reduced concentrations of anthocyanin pigments in ripe strawberry fruits. In contrast, significant levels of epiafzelechin-formed by anthocyanidin reductase (ANR) from pelargonidin-were identified in FaGT1-silenced fruits, indicating competition of FaGT1 and FaANR for the common anthocyanidin substrate. Thus, FaGT1 represents an important branching-point enzyme because it is channeling the flavonoid pathway to anthocyanins. These results demonstrate a method to redirect the anthocyanin biosynthesis into flavan-3-ol production to increase the levels of bioactive natural products or modify pigments in plant tissues.