Complex evolution of novel red floral color in Petunia

背景回顾：Red flower color has arisen multiple times and is generally associated with hummingbird pollination. The majority of evolutionary transitions to red color proceeded from purple lineages and tend to be genetically simple, almost always involving a few loss-of-function mutations of major phenotypic effect. 

主要研究：Here we report on the complex evolution of a novel red floral color in the hummingbird-pollinated Petunia exserta (Solanaceae) from a colorless ancestor. 

结果1-非功能性AN2：The presence of a red color is remarkable because the genus cannot synthesize red anthocyanins and P. exserta retains a nonfunctional copy of the key MYB transcription factor AN2. 

结果2-关键基因DPL：We show that moderate up-regulation and a shift in tissue specificity of an AN2paralog, DEEP PURPLE (DPL), restores anthocyanin biosynthesis in P. exserta. An essential shift in anthocyanin hydroxylation occurred through re-balancing the expression of three hydroxylating genes. 

结果3-酰基化：Furthermore, the down-regulation of an acyltransferase promotes reddish hues in typically purple pigments by preventing acyl group decoration of anthocyanins. 

结论：This study presents a rare case of a genetically complex evolutionary transition towards the gain of a novel red color.

 摘 要 

在植物演化过程中，红色的花多次出现，且多与蜂鸟授粉有关。大多数向红色花的演化转变是从开紫色花转变的，并且在遗传上十分简单，几乎总是涉及一些负责主要表型效应的功能缺失突变。本文中，作者报道了一种由蜂鸟授粉、并是从无色花祖先演化出的新的红色花矮牵牛。P. exserta的红色花是异常引人注目的，因为该属植物并不能合成红色的花色苷，虽然P. exserta中留存了一个关键的MYB转录因子AN2基因，但属于非功能性拷贝。作者发现，适度上调和改变AN2旁系同源基因DPL的组织特异性，能够恢复P. exserta的花青素生物合成。通过重新平衡三个羟基化基因的表达，导致花青素羟基化的发生了一个重要转变。此外，酰基转移酶的下调通过阻止花青素的酰基修饰来增加典型紫色色素中的红色色调。本文的研究揭示了一个十分罕见的情况，即由遗传上十分复杂的演化转变使得植物获得了红色表型特征。