Sunnadeniya Rasika, Bean Alexander, Brown Matthew, Akhavan Neda, Hatlestad Gregory, Gonzalez Antonio, Symonds V Vaughan, Lloyd Alan
Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, United States of America.
Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
PLoS One. 2016 Feb 18;11(2):e0149417. doi: 10.1371/journal.pone.0149417. eCollection 2016.
Yellow and red-violet betalain plant pigments are restricted to several families in the order Caryophyllales, where betacyanins play analogous biological roles to anthocyanins. The initial step in betalain biosynthesis is the hydroxylation of tyrosine to form L-DOPA. Using gene expression experiments in beets, yeast, and Arabidopsis, along with HPLC/MS analysis, the present study shows that two novel cytochrome P450 (CYP450) enzymes, CYP76AD6 and CYP76AD5, and the previously described CYP76AD1 can perform this initial step. Co-expressing these CYP450s with DOPA 4,5-dioxygenase in yeast, and overexpression of these CYP450s in yellow beets show that CYP76AD1 efficiently uses L-DOPA leading to red betacyanins while CYP76AD6 and CYP76AD5 lack this activity. Furthermore, CYP76AD1 can complement yellow beetroots to red while CYP76AD6 and CYP76AD5 cannot. Therefore CYP76AD1 uniquely performs the beet R locus function and beets appear to be genetically redundant for tyrosine hydroxylation. These new functional data and ancestral character state reconstructions indicate that tyrosine hydroxylation alone was the most likely ancestral function of the CYP76AD alpha and beta groups and the ability to convert L-DOPA to cyclo-DOPA evolved later in the alpha group.
黄色和红紫色的甜菜红素植物色素仅限于石竹目（Caryophyllales）中的几个科，在这些科中，花青素苷发挥着与花青素类似的生物学作用。甜菜红素生物合成的第一步是酪氨酸羟基化形成L-多巴。通过在甜菜、酵母和拟南芥中进行基因表达实验以及高效液相色谱/质谱分析，本研究表明，两种新的细胞色素P450（CYP450）酶，即CYP76AD6和CYP76AD5，以及先前描述的CYP76AD1可以执行这一初始步骤。在酵母中使这些CYP450与多巴4,5-双加氧酶共表达，以及在黄色甜菜中过表达这些CYP450，结果表明CYP76AD1能有效地利用L-多巴生成红色花青素苷，而CYP76AD6和CYP76AD5缺乏这种活性。此外，CYP76AD1能使黄色甜菜根变成红色，而CYP76AD6和CYP76AD5则不能。因此，CYP76AD1独特地执行了甜菜R位点的功能，并且甜菜在酪氨酸羟基化方面似乎存在基因冗余。这些新的功能数据和祖先性状状态重建表明，单独的酪氨酸羟基化最有可能是CYP76ADα和β组的祖先功能，而将L-多巴转化为环多巴的能力是在α组中较晚进化出来的。
