背景1：Understanding the molecular basis of reproductive isolation and speciation is a key goal of evolutionary genetics. In the South American genus Petunia, the R2R3-MYB transcription factor MYB-FL regulates the biosynthesis of UV-absorbing flavonol pigments, a major determinant of pollinator preference. 

背景2：MYB-FL is highly expressed in the hawkmoth-pollinated P. axillaris, but independent losses of its activity in sister taxa P. secreta and P. exserta led to UV-reflective flowers and associated pollinator shifts in each lineage (bees and hummingbirds, respectively). 

主要研究：We created a myb-fl CRISPR mutant in P. axillaris and studied the effect of this single gene on innate pollinator preference. 

结果1-突变影响黄酮醇和花色苷：The mutation strongly reduced the expression of the two key flavonol-related biosynthetic genes but only affected the expression of few other genes. The mutant flowers were UV reflective as expected but additionally contained low levels of visible anthocyanin pigments. 

结果2-突变影响传粉者偏好：Hawkmoths strongly preferred the wild-type P. axillaris over the myb-fl mutant, whereas both social and solitary beepreference depended on the level of visible color of the mutants. 

结论：MYB-FL, with its specific expression pattern, small number of target genes, and key position at the nexus of flavonol and anthocyanin biosynthetic pathways, provides a striking example of evolution by single mutations of large phenotypic effect.

理解生殖隔离和物种形成的分子基础是进化遗传学的一个关键目标。在南美洲矮牵牛属中，R2R3-MYB转录因子MYB-FL调控能够吸收紫外线的植物色素黄酮醇的生物合成，这是决定传粉者偏好性的主要因素。MYB-FL在依靠天蛾传粉的夜香矮牵牛（P. axillaris）中高表达，但在其姊妹类群P. secreta和P. exserta中活性丢失，导致形成了能够反射紫外线的花，这与各自谱系中传粉者的改变相关，分别换成了蜜蜂和蜂鸟。作者利用CRISPR技术在夜香矮牵牛中创制了一个myb-fl突变体，并研究了这一单基因突变对于夜香矮牵牛先天传粉者偏好的影响。结果发现，该突变显著降低了两个与黄酮醇相关的关键生物合成基因的表达，但几乎不影响其他基因的表达。如预期所料，突变体的花具有紫外线反射性，还也含有低水平的可见花色苷。与myb-fl突变体相比，天蛾更加偏爱野生型的夜香矮牵牛，而群居蜂和独居蜂的偏好则依赖于突变体的可见色程度。MYB-FL以其独特的表达模式、少量的靶基因以及在黄酮醇和花色苷生物合成途径中的关键位置，为单个基因突变剧烈影响表型提供了一个十分明显的演化案例。