Cárdenas-Conejo Yair, Carballo-Uicab Víctor, Lieberman Meric, Aguilar-Espinosa Margarita, Comai Luca, Rivera-Madrid Renata
Centro de Investigación Científica de Yucatán, A. C. Calle 43 No. 130, Col. Chuburná de Hidalgo, 97200, Mérida, Yucatán, Mexico.
Plant Biology and Genome Center, University of California, Davis, CA, 95616, USA.
BMC Genomics. 2015 Oct 28;16:877. doi: 10.1186/s12864-015-2065-4.
Bixin or annatto is a commercially important natural orange-red pigment derived from lycopene that is produced and stored in seeds of Bixa orellana L. An enzymatic pathway for bixin biosynthesis was inferred from homology of putative proteins encoded by differentially expressed seed cDNAs. Some activities were later validated in a heterologous system. Nevertheless, much of the pathway remains to be clarified. For example, it is essential to identify the methylerythritol phosphate (MEP) and carotenoid pathways genes.
In order to investigate the MEP, carotenoid, and bixin pathways genes, total RNA from young leaves and two different developmental stages of seeds from B. orellana were used for the construction of indexed mRNA libraries, sequenced on the Illumina HiSeq 2500 platform and assembled de novo using Velvet, CLC Genomics Workbench and CAP3 software. A total of 52,549 contigs were obtained with average length of 1,924 bp. Two phylogenetic analyses of inferred proteins, in one case encoded by thirteen general, single-copy cDNAs, in the other from carotenoid and MEP cDNAs, indicated that B. orellana is closely related to sister Malvales species cacao and cotton. Using homology, we identified 7 and 14 core gene products from the MEP and carotenoid pathways, respectively. Surprisingly, previously defined bixin pathway cDNAs were not present in our transcriptome. Here we propose a new set of gene products involved in bixin pathway.
The identification and qRT-PCR quantification of cDNAs involved in annatto production suggest a hypothetical model for bixin biosynthesis that involve coordinated activation of some MEP, carotenoid and bixin pathway genes. These findings provide a better understanding of the mechanisms regulating these pathways and will facilitate the genetic improvement of B. orellana.
胭脂树素或胭脂红是一种具有重要商业价值的天然橙红色色素，由番茄红素衍生而来，存在于红木（Bixa orellana L.）的种子中并在其中产生和储存。通过差异表达的种子cDNA编码的假定蛋白质的同源性推断出了胭脂树素生物合成的酶促途径。后来在异源系统中验证了一些活性。然而，该途径的许多方面仍有待阐明。例如，鉴定甲基赤藓糖醇磷酸（MEP）和类胡萝卜素途径基因至关重要。
为了研究MEP、类胡萝卜素和胭脂树素途径基因，使用来自红木幼叶和两个不同发育阶段种子的总RNA构建索引mRNA文库，在Illumina HiSeq 2500平台上进行测序，并使用Velvet、CLC Genomics Workbench和CAP3软件进行从头组装。共获得52,549个重叠群，平均长度为1,924 bp。对推断蛋白质进行的两种系统发育分析，一种由13个通用单拷贝cDNA编码，另一种来自类胡萝卜素和MEP cDNA，表明红木与姐妹锦葵目物种可可和棉花密切相关。通过同源性，我们分别从MEP和类胡萝卜素途径中鉴定出7个和14个核心基因产物。令人惊讶的是，我们的转录组中不存在先前定义的胭脂树素途径cDNA。在这里，我们提出了一组参与胭脂树素途径的新基因产物。
参与胭脂红生产的cDNA的鉴定和qRT-PCR定量提出了一种胭脂树素生物合成的假设模型，该模型涉及一些MEP、类胡萝卜素和胭脂树素途径基因的协同激活。这些发现有助于更好地理解调节这些途径的机制，并将促进红木的遗传改良。
