An alternative pathway to β-carotene formation in plant chromoplasts discovered by map-based cloning of Beta and old-gold color mutations in tomato
An alternative pathway to β-carotene formation in plant chromoplasts discovered by map-based cloning of Beta and old-gold color mutations in tomato
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DOI：
10.1073/pnas.190177497
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发表时间：
2000-09-26
影响因子：
11.1
通讯作者：
Hirschberg, J
中科院分区：
文献类型：
--
作者：
Ronen, G;Carmel-Goren, L;Hirschberg, J
类胡萝卜素在植物的光合作用中起着不可或缺的作用。类胡萝卜素作为次生代谢产物在质体中积累，为花和果实提供独特的颜色。在这项工作中，我们研究了番茄果实成熟过程中调节类胡萝卜素积累的遗传机制。我们分析了影响番茄果实色素沉着的两种突变：β（B），一种增加果实中β-胡萝卜素的单一显性基因，和一种消除β-胡萝卜素并增加番茄红素的隐性突变。利用图位克隆方法，我们克隆了基因B和og。分子分析显示，B编码一种新型的番茄红素β-环化酶，这种酶将番茄红素转化为β-胡萝卜素。a的氨基酸序列与辣椒红素-辣椒红素合酶相似。一种在辣椒果实中产生红色叶黄素的酶。我们的研究结果证明，β-胡萝卜素是从头合成番茄果实发育过程中的B番茄红素环化酶。在野生型番茄中，B在成熟的破坏阶段以低水平表达，而在Beta突变体中，其转录显著增加。基因B中的突变导致og中的表型。表明og是B的等位基因。这些结果证实，发育调节的转录是控制成熟水果中番茄红素积累的主要机制。克隆的B基因可用于各种遗传操作，以改变色素和提高植物食品的营养价值。
Carotenoid pigments in plants fulfill indispensable functions in photosynthesis. Carotenoids that accumulate as secondary metabolites in chromoplasts provide distinct coloration to flowers and fruits. In this work we investigated the genetic mechanisms that regulate accumulation of carotenoids as secondary metabolites during ripening of tomato fruits. We analyzed two mutations that affect fruit pigmentation in tomato (Lycopersicon esculentum): Beta (B), a single dominant gene that increases beta-carotene in the fruit, and old-gold log), a recessive mutation that abolishes beta-carotene and increases lycopene. Using a map-based cloning approach we cloned the genes B and og. Molecular analysis revealed that B encodes a novel type of lycopene beta-cyclase, an enzyme that converts lycopene to beta-carotene. The amino acid sequence of a is similar to capsanthin-capsorubin synthase. an enzyme that produces red xanthophylls in fruits of pepper (Capsicum annum). Our results prove that beta-carotene is synthesized de novo during tomato fruit development by the B lycopene cyclase. In wild-type tomatoes B is expressed at low levels during the breaker stage of ripening, whereas in the Beta mutant its transcription is dramatically increased. Null mutations in the gene B are responsible for the phenotype in og. indicating that og is an allele of B. These results confirm that developmentally regulated transcription is the major mechanism that governs lycopene accumulation in ripening fruits. The cloned B genes can be used in various genetic manipulations toward altering pigmentation and enhancing nutritional value of plant foods.