Maize Y9 encodes a product essential for 15-cis-ζ-carotene isomerization
Maize Y9 encodes a product essential for 15-cis-ζ-carotene isomerization
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DOI：
10.1104/pp.107.098996
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发表时间：
2007-06-01
期刊：
影响因子：
7.4
通讯作者：
Wurtzel, Eleanore T.
中科院分区：
文献类型：
--
作者：
Li, Faqiang;Murillo, Christina;Wurtzel, Eleanore T.
类胡萝卜素是在植物、真菌和细菌中发现的一组不同的色素。它们在植物中发挥重要作用，并为人类和动物提供健康益处。在植物中，人们认为，将 C40 类胡萝卜素骨架（15-顺式八氢番茄红素）转化为全反式番茄红素（下游酶所需的几何异构体），除了光介导的 15-顺式双键的光异构化之外，还需要两种去饱和酶（八氢番茄红素去饱和酶和 xi-胡萝卜素去饱和酶 [ZDS]）加上胡萝卜素异构酶 (CRTISO)；细菌只使用一种酶，CRTI。玉米 (Zea mays) 淡黄 9 (y9) 基因座的表征揭示了植物类胡萝卜素生物合成所需的新异构酶。我们报道玉米Y9编码CRTISO上游异构酶活性所需的因子，我们称之为Z-ISO，这种活性催化八氢番茄红素去饱和酶的产物9,15,9'-三顺式-xi-胡萝卜素中的15-顺式键顺式-反式转化，形成9,9'-二-顺式-xi-胡萝卜素，ZDS的底物。我们发现，隐性 y9 等位基因导致 9,15,9'-三顺式 xi-胡萝卜素在深色组织（例如根和黄化叶）中积累，而 ZDS 突变体（胎生9）中则积累了 9,9'-二顺式 xi-胡萝卜素。我们还在眼虫中发现了一个基因座，这对于 Z-ISO 活性同样是必需的。这些数据与进化距离较远的植物中 ZDS 的几何异构体底物需求一起表明，Z-ISO 活性并非玉米所独有，而是在所有高等植物中都存在。进一步分析这一新的基因控制步骤对于理解这一重要生物合成途径的调控至关重要。
Carotenoids are a diverse group of pigments found in plants, fungi, and bacteria. They serve essential functions in plants and provide health benefits for humans and animals. In plants, it was thought that conversion of the C40 carotenoid backbone, 15-cis-phytoene, to all-trans-lycopene, the geometrical isomer required by downstream enzymes, required two desaturases (phytoene desaturase and xi-carotene desaturase [ZDS]) plus a carotene isomerase (CRTISO), in addition to light-mediated photoisomerization of the 15-cis-double bond; bacteria employ only a single enzyme, CRTI. Characterization of the maize (Zea mays) pale yellow9 (y9) locus has brought to light a new isomerase required in plant carotenoid biosynthesis. We report that maize Y9 encodes a factor required for isomerase activity upstream of CRTISO, which weterm Z-ISO, an activity that catalyzes the cis-to trans-conversion of the 15-cis-bond in 9,15,9'-tri-cis-xi-carotene, the product of phytoene desaturase, to form 9,9'-di-cis-xi-carotene, the substrate of ZDS. We show that recessive y9 alleles condition accumulation of 9,15,9'-tri-cis-xi-carotene in dark tissues, such as roots and etiolated leaves, in contrast to accumulation of 9,9'-di-cis-xi-carotene in a ZDS mutant, viviparous9. We also identify a locus in Euglena gracilis, which is similarly required for Z-ISO activity. These data, taken together with the geometrical isomer substrate requirement of ZDS in evolutionarily distant plants, suggest that Z-ISO activity is not unique to maize, but will be found in all higher plants. Further analysis of this new gene-controlled step is critical to understanding regulation of this essential biosynthetic pathway.