Phytoene synthase-2 enzyme activity in tomato does not contribute to carotenoid synthesis in ripening fruit
Phytoene synthase-2 enzyme activity in tomato does not contribute to carotenoid synthesis in ripening fruit
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DOI：
10.1023/a:1006256302570
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发表时间：
1999-07-01
影响因子：
5.1
通讯作者：
Bramley, PM
中科院分区：
文献类型：
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作者：
Fraser, PD;Kiano, JW;Bramley, PM
r，r突变体和Psy-1（八氢番茄红素合酶-1）反义番茄的特征性黄色果实表型分别是由于突变或下调的八氢番茄红素合酶蛋白，导致类胡萝卜素的实际缺乏。基于详细的类胡萝卜素测定Psy-1似乎几乎没有贡献的类胡萝卜素在含叶绿体的组织中的形成。尽管在成熟的果实中类胡萝卜素的虚拟情况下，在体外八氢番茄红素的形成检测在两个突变体的果实。当[C-14]异戊烯焦磷酸（IPP）用作八氢番茄红素合成酶的底物时，观察到八氢番茄红素形成的减少（例如r，r突变体，5倍），同时直接前体香叶基香叶基焦磷酸（GGPP）的积累（例如r，r突变体，2倍）。相反，当[H-3]GGPP用作底物时，没有检测到八氢番茄红素合酶活性降低。在成熟过程中的八氢番茄红素形成的配置文件也是不同的下调突变体相比，野生型。使用特异性引物，RT-PCR分析检测Psy-2转录本的存在下，在整个果实发育和成熟的下调突变体和野生型。这些数据得到了八氢番茄红素合成酶蛋白质的蛋白质印迹检测的支持。在这些突变体中GGPP形成和八氢番茄红素去饱和都升高。因此，尽管成熟果实中缺乏类胡萝卜素，但两种突变体都具有在该组织中合成类胡萝卜素的酶促能力。类胡萝卜素的形成和番茄（及其潜在的操纵）的异戊二烯基脂质前体的通道的调节方面的数据的影响进行了讨论。
The characteristic yellow fruit phenotype of the r,r mutant and Psy-1 (phytoene synthase-1) antisense tomatoes is due to a mutated or down-regulated phytoene synthase protein, respectively, resulting in the virtual absence of carotenoids. Based on detailed carotenoid determinations Psy-1 appeared to barely contribute to the formation of carotenoids in chloroplast-containing tissues. Despite the virtual absence of carotenoids in ripe fruit the formation of phytoene in vitro was detected in fruit of both mutants. When [C-14]isopentenyl pyrophosphate (IPP) was used as the substrate for phytoene synthase a reduction (e.g. r,r mutant, 5-fold) in the formation of phytoene was observed with an accumulation (e.g. r,r mutant, 2-fold) of the immediate precursor geranylgeranyl pyrophosphate (GGPP). Contrastingly, reduced phytoene synthase activity was not detected when [H-3]GGPP was used as the substrate. The profile of phytoene formation during ripening was also different in the down-regulated mutants compared to the wild-type. Using specific primers, RT-PCR analysis detected the presence of Psy-2 transcripts in the down-regulated mutants and wild-type throughout fruit development and ripening. These data were supported by the detection of phytoene synthase protein on western blots. Both GGPP formation and phytoene desaturation were elevated in these mutants. Therefore, it appears that despite the absence of carotenoids in ripe fruit, both the mutants have the enzymic capability to synthesize carotenoids in this tissue. Implications of the data with respect to the regulation of carotenoid formation and the channelling of prenyl lipid precursors in tomato (and its potential manipulation) are discussed.