Maize phytoene desaturase and ζ-carotene desaturase catalyse a poly-Z desaturation pathway:: implications for genetic engineering of carotenoid content among cereal crops
Maize phytoene desaturase and ζ-carotene desaturase catalyse a poly-Z desaturation pathway:: implications for genetic engineering of carotenoid content among cereal crops
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DOI：
10.1093/jxb/erg235
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发表时间：
2003-10-01
影响因子：
6.9
通讯作者：
Wurtzel, ET
中科院分区：
文献类型：
--
作者：
Matthews, PD;Luo, RB;Wurtzel, ET
胡萝卜素去饱和是有色类胡萝卜素生物合成中的一个重要步骤，受到了广泛关注：(1) 作为漂白除草剂作用的目标，(2) 作为类胡萝卜素及其代谢物几何异构体状态的决定因素，(3) 作为类胡萝卜素积累和结构变异的关键调节剂。先前已分离并功能表征了编码玉米胡萝卜素去饱和中第一种酶八氢番茄红素去饱和酶 (PDS) 的 cDNA，本文报道了第二种去饱和酶的分离和功能表征，即编码泽塔胡萝卜素去饱和酶 (ZDS) 的玉米胚乳 cDNA (2265 bp)。对玉米 PDS 和 ZDS 异位协同作用的功能分析表明，这些酶介导主要几何异构体 7,9,7',9'-四 Z-番茄红素（多 Z-番茄红素或丙番茄红素）的多 Z 去饱和途径，而不是下游番茄红素环化酶所需的全反式底物。这一发现表明，与胡萝卜素去饱和酶相关的速率控制异构酶是玉米植物中活跃的默认多 Z 类胡萝卜素生物合成途径的必然结果。玉米和水稻的基因比较分析表明，编码PDS和ZDS的基因是单拷贝；这里表征的 Zds cDNA 被定位到玉米染色体 7S，并且建议 vp9 作为结构基因的候选基因座，而 y9 被排除。使用经典遗传资源进一步剖析去饱和步骤，并将羟苯丙酮酸双加氧酶与 vp2 基因座连接，将玉米中专性异构酶的候选基因座缩小到只有几个。由于本文报道了谷类作物的配对胡萝卜素去饱和酶的首次功能分析，因此讨论了水稻和玉米等谷类作物中维生素 A 原含量的遗传修饰的影响。
Carotene desaturation, an essential step in the biosynthesis of coloured carotenoids, has received much attention (1) as a target of bleaching herbicide action, (2) as a determinant of geometric isomer states of carotenoids and their metabolites, and (3) as a key modulator of accumulation and structural variability of carotenoids. Having previously isolated and functionally characterized the cDNA encoding the first enzyme in maize carotene desaturation, phytoene desaturase (PDS), the isolation and functional characterization of the second desaturase, a maize endosperm cDNA (2265 bp) encoding zetacarotene (zeta-carotene) desaturase (ZDS) is reported here. Functional analysis of the concerted actions of maize PDS and ZDS ex situ showed these enzymes to mediate a poly-Z desaturation pathway to the predominate geometric isomer 7,9,7',9'-tetra-Z-lycopene (poly-Z-lycopene or prolycopene), and not the all-trans substrate required of the downstream lycopene cyclase enzymes. This finding suggests a rate-controlling isomerase associated with the carotene desaturases as a corollary of a default poly-Z carotenoid biosynthetic pathway active in planta for maize. Comparative gene analysis between maize and rice revealed that genes encoding PDS and ZDS are single copy; the Zds cDNA characterized here was mapped to maize chromosome 7S and vp9 is suggested as a candidate locus for the structural gene while y9 is ruled out. Classical genetic resources were used to dissect the desaturation steps further and hydroxyphenylpyruvate dioxygenase was linked to the vp2 locus, narrowing candidate loci for an obligate isomerase in maize to only a few. Since the first functional analysis of the paired carotene desaturases for a cereal crop is reported here, the implications for the genetic modification of the pro-vitamin A content in cereal crops such as rice and maize, are discussed.