Cloning and characterization of the cDNA for lycopene beta-cyclase from tomato reveals decrease in its expression during fruit ripening
Cloning and characterization of the cDNA for lycopene beta-cyclase from tomato reveals decrease in its expression during fruit ripening
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DOI：
10.1007/bf00019013
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发表时间：
1996-02-01
影响因子：
5.1
通讯作者：
Hirschberg, J
中科院分区：
文献类型：
--
作者：
Pecker, I;Gabbay, R;Hirschberg, J
从番茄（Lycopersicon esculentum cv.）中克隆到了编码番茄红素环化酶（CrtL）的cDNA。VF36)和烟草(Nicotiana tabacum cv。Samsun NN)，并在大肠杆菌中功能性表达。这种酶通过在线性胡萝卜素的两端催化形成两个β环，将番茄红素转化为β -胡萝卜素。这种酶与一半的类胡萝卜素分子相互作用，需要在c -7,8（或c -7,8'）位置有一个双键。在大肠杆菌中的抑制作用表明番茄红素环化酶是2-（4-甲基苯氧基）三乙胺盐酸盐抑制剂MPTA的靶点。高等植物番茄红素环化酶的一级结构与蓝藻酶有明显的保守性，但与非光合细菌欧文菌的结构不同。测定了番茄叶片、花和成熟果实中编码植物烯去饱和酶的CrtL和Pds的mRNA表达水平。与编码类胡萝卜素生物合成途径早期步骤酶的基因相反，其转录在果实成熟的“破坏”阶段增加，CrtL mRNA水平在这一阶段下降。因此，番茄红素在番茄果实中的积累显然是由于番茄红素环化酶基因的下调，这种下调发生在果实发育的破坏阶段。这一结论支持了基因表达的转录调控是调控胡萝卜素生成的主要机制的假设。
The cDNA which encodes lycopene cyclase, CrtL, was cloned from tomato (Lycopersicon esculentum cv. VF36) and tobacco (Nicotiana tabacum cv. Samsun NN) and functionally expressed in Escherichia coli. This enzyme converts lycopene to beta-carotene by catalyzing the formation of two beta-rings at each end of the linear carotene. The enzyme interacts with half of the carotenoid molecule and requires a double bond at the C-7,8 (or C-7,8') position. Inhibition in E. coli indicated that lycopene cyclase is the target site for the inhibitor MPTA, 2-(4-methylphenoxy)tri-ethylamine hydrochloride. The primary structure of lycopene cyclase in higher plants is significantly conserved with the enzyme from cyanobacteria but different from that of from the non-photosynthetic bacteria Erwinia. mRNA of CrtL and Pds, which encodes phytoene desaturase, was measured in leaves, flowers and ripening fruits of tomato. In contrast to genes which encode enzymes of early steps in the carotenoid biosynthesis pathway, whose transcription increases during the 'breaker' stage of fruit ripening, the level of CrtL mRNA decreases at this stage. Hence, the accumulation of lycopene in tomato fruits is apparently due to a down-regulation of the lycopene cyclase gene that occurs at the breaker stage of fruit development. This conclusion supports the hypothesis that transcriptional regulation of gene expression is a predominant mechanism of regulating carotenogenesis.