![]() ![]() ![]() The relative importance of such large-effect mutations, however, remains contentious ( Rockman, 2012) highlighting the need to examine genetic mechanisms with a critical eye.Ī prime example of the relevance of mutations of large phenotypic effect has been pollinator-mediated selection on floral traits. At the same time, evidence for adaptation proceeding via few loci of large effect also abounds ( Doebley, 2004 Hoekstra et al., 2006 Nadeau et al., 2016 Todesco et al., 2020). Today, there is abundant experimental evidence that the genetic basis of natural variation in individual traits can be extremely complex with many loci involved ( Atwell et al., 2010 Chan et al., 2010 Turchin et al., 2012 Kooke et al., 2016 Guo et al., 2018 Sohail et al., 2019). However, contemporaries of Fisher as well as more recent theory suggest that a single bout of adaptation could involve loci with a distribution of effect sizes, with both large-effect and small-effect mutations ( Orr, 1998 Orteu and Jiggins, 2020). In his theoretical work, Fisher predicted that mutations of small effect were most likely to produce phenotypes with increased fitness ( Fisher, 1918, 1930). Whether adaptation involves single genes of large phenotypic effect or proceeds through many genes with small individual effects is a crucial question in evolutionary biology ( Orr and Coyne, 1992 Orr, 2005 Chevin and Beckerman, 2012 Barton et al., 2016 Boyle et al., 2017). This study presents a rare case of a genetically complex evolutionary transition toward the gain of a novel red color. Furthermore, the downregulation of an acyltransferase promotes reddish hues in typically purple pigments by preventing acyl group decoration of anthocyanins. An essential shift in anthocyanin hydroxylation occurred through rebalancing the expression of three hydroxylating genes. ![]() We show that moderate upregulation and a shift in tissue specificity of an AN2 paralog, DEEP PURPLE, restores anthocyanin biosynthesis in P. exserta retains a nonfunctional copy of the key MYB transcription factor AN2. The presence of a red color is remarkable because the genus cannot synthesize red anthocyanins and P. Here we report on the complex evolution of a novel red floral color in the hummingbird-pollinated Petunia exserta (Solanaceae) from a colorless ancestor. 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. Red flower color has arisen multiple times and is generally associated with hummingbird pollination. ![]()
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