R2R3‐MYB genes control petal pigmentation patterning in Clarkia gracilis ssp. sonomensis (Onagraceae)

Abstract

Petal pigmentation patterning is widespread in flowering plants. The genetics of these pattern elements has been of great interest for understanding the evolution of phenotypic diversification. Here, we investigate the genetic changes responsible for the evolution of an unpigmented petal element on a colored background. We used transcriptome analysis, gene expression assays, cosegregation in F 2 plants and functional tests to identify the gene(s) involved in petal coloration in Clarkia gracilis ssp. sonomensis. We identified an R2R3-MYB transcription factor (CgsMYB12) responsible for anthocyanin pigmentation of the basal region ('cup') in the petal of C. gracilis ssp. sonomensis. A functional mutation in CgsMYB12 creates a white cup on a pink petal background. Additionally, we found that two R2R3-MYB genes (CgsMYB6 and CgsMYB11) are also involved in petal background pigmentation. Each of these three R2R3-MYB genes exhibits a different spatiotemporal expression pattern. The functionality of these R2R3-MYB genes was confirmed through stable transformation of Arabidopsis. Distinct spatial patterns of R2R3-MYB expression have created the possibility that pigmentation in different sections of the petal can evolve independently. This finding suggests that recent gene duplication has been central to the evolution of petal pigmentation patterning in C. gracilis ssp. sonomensis.

Ancient gene duplications, rather than polyploidization, facilitate diversification of petal pigmentation patterns inClarkia gracilis(Onagraceae)

“…albicaulis ). Lin and Rausher (2021) showed that three R2R3-MYB genes, CgsMYB6 , CgsMYB11 and CgsMYB12 , are involved in petal background coloration in C . g .…”

“…g . sonomensis (Lin and Rausher 2021) reveal only one copy of each of the four paralogs, the second copy of each gene has most likely been lost or downregulated in C . gracilis .…”

“…g . sonomensis (Lin and Rausher 2021). In these three (sub)species, MYB6 is expressed early during flower-bud development and remains expressed in all petal sections throughout bud maturation.…”

“…Previous studies have demonstrated that in C . g. sonomensis , each of the distinctive pattern elements (background, spot, cup) is controlled by different sets of R2R3-MYB transcriptional regulators (hereafter “ MYB ”) (Martins et al 2017; Lin and Rausher 2021). MYB1 regulates spot formation, while MYB6 , MYB11 and MYB12 control background pigmentation (hereafter “background MYB s”), including presence/absence of the white cup (fig.…”

“…( A ) In conjunction with MYB6 , MYB11 and MYB12 produce pigmentation in the distal and cup regions, respectively. ( B ) In individuals with a white cup, a nonfunctional MYB12 W is expressed in the cup (Lin and Rausher 2021).…”