Lao Yong M, Jin Hui, Zhou Jin, Zhang Huai J, Cai Zhong H
Shenzhen Public Platform of Screening and Application of Marine Microbial ResourcesGuangdong, China.
The Division of Ocean Science and Technology, Graduate School at Shenzhen, Tsinghua UniversityShenzhen, China.
Front Plant Sci. 2017 Aug 2;8:1341. doi: 10.3389/fpls.2017.01341. eCollection 2017.
Cyclization of acyclic lycopene by cyclases marks an important regulatory point in carotenoid biosynthesis. Though some algal lycopene epsilon cyclases (LCYEs) have been predicted computationally, very few have been functionally identified. Little is known about the regulation mechanisms of algal LCYEs. Recent comparative genomic analysis suggested that contained only the β type cyclase (HpLCYB). However, in this study, carotenoid profiling found trace α-carotene in the salt-treated cells, indicating the activity of HpLCYE, a missing component for α-branch carotenoids. Thus, genes coding for HpLCYB and HpLCYE were isolated and functionally complemented in . Substrate specificity assays revealed an exclusive cyclization order of HpLCYE to HpLCYB for the biosynthesis of heterocyclic carotenoids. Expression pattern studies and bioinformatic analysis of promoter regions showed that both cyclases were differentially regulated by the regulatory -acting elements in promoters to correlate with primary and secondary carotenoid biosynthesis under environmental stresses. Characterization of the branch components in algal carotenoid biosynthesis revealed a mechanism for control of metabolic flux into α- and β-branch by the competition and cooperation between HpLCYE and HpLCYB; and supplied a promising route for molecular breeding of cyclic carotenoid biosynthesis.
环化酶将无环番茄红素环化是类胡萝卜素生物合成中的一个重要调控点。虽然通过计算预测了一些藻类番茄红素ε环化酶（LCYEs），但功能鉴定的却很少。关于藻类LCYEs的调控机制知之甚少。最近的比较基因组分析表明，[具体物种]仅含有β型环化酶（HpLCYB）。然而，在本研究中，类胡萝卜素谱分析在盐处理的细胞中发现了微量的α-胡萝卜素，这表明存在HpLCYE的活性，而HpLCYE是α-分支类胡萝卜素缺失的组分。因此，分离出了编码HpLCYB和HpLCYE的基因，并在[具体物种]中进行了功能互补。底物特异性分析揭示了在杂环类胡萝卜素生物合成中，HpLCYE对HpLCYB具有独特的环化顺序。启动子区域的表达模式研究和生物信息学分析表明，在环境胁迫下，两种环化酶均受启动子中调控作用元件的差异调节，与初级和次级类胡萝卜素生物合成相关。藻类类胡萝卜素生物合成中分支组分的表征揭示了一种通过HpLCYE和HpLCYB之间的竞争与合作来控制代谢流进入α-和β-分支的机制；并为环状类胡萝卜素生物合成的分子育种提供了一条有前景的途径。
