Bai Chao, Capell Teresa, Berman Judit, Medina Vicente, Sandmann Gerhard, Christou Paul, Zhu Changfu
Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Lleida, Spain.
Institute of Molecular Bioscience, J. W. Goethe University, Frankfurt am Main, Germany.
Plant Biotechnol J. 2016 Jan;14(1):195-205. doi: 10.1111/pbi.12373. Epub 2015 Apr 7.
The profile of secondary metabolites in plants reflects the balance of biosynthesis, degradation and storage, including the availability of precursors and products that affect the metabolic equilibrium. We investigated the impact of the precursor-product balance on the carotenoid pathway in the endosperm of intact rice plants because this tissue does not normally accumulate carotenoids, allowing us to control each component of the pathway. We generated transgenic plants expressing the maize phytoene synthase gene (ZmPSY1) and the bacterial phytoene desaturase gene (PaCRTI), which are sufficient to produce β-carotene in the presence of endogenous lycopene β-cyclase. We combined this mini-pathway with the Arabidopsis thaliana genes AtDXS (encoding 1-deoxy-D-xylulose 5-phosphate synthase, which supplies metabolic precursors) or AtOR (the ORANGE gene, which promotes the formation of a metabolic sink). Analysis of the resulting transgenic plants suggested that the supply of isoprenoid precursors from the MEP pathway is one of the key factors limiting carotenoid accumulation in the endosperm and that the overexpression of AtOR increased the accumulation of carotenoids in part by up-regulating a series of endogenous carotenogenic genes. The identification of metabolic bottlenecks in the pathway will help to refine strategies for the creation of engineered plants with specific carotenoid profiles.
植物中次生代谢产物的概况反映了生物合成、降解和储存之间的平衡，包括影响代谢平衡的前体和产物的可用性。我们研究了前体-产物平衡对完整水稻植株胚乳中类胡萝卜素途径的影响，因为该组织通常不积累类胡萝卜素，这使我们能够控制该途径的每个组成部分。我们构建了表达玉米八氢番茄红素合酶基因（ZmPSY1）和细菌八氢番茄红素去饱和酶基因（PaCRTI）的转基因植物，在存在内源性番茄红素β-环化酶的情况下，这些基因足以产生β-胡萝卜素。我们将这个微型途径与拟南芥基因AtDXS（编码1-脱氧-D-木酮糖5-磷酸合酶，提供代谢前体）或AtOR（橙色基因，促进代谢库的形成）相结合。对所得转基因植物的分析表明，来自MEP途径的类异戊二烯前体的供应是限制胚乳中类胡萝卜素积累的关键因素之一，并且AtOR的过表达部分通过上调一系列内源性类胡萝卜素生成基因来增加类胡萝卜素的积累。确定该途径中的代谢瓶颈将有助于完善创建具有特定类胡萝卜素谱的工程植物的策略。
