How petals change their spots: cis‐regulatory re‐wiring in Clarkia (Onagraceae)

Abstract

A long-standing question in evolutionary developmental biology is how new traits evolve. Although most floral pigmentation studies have focused on how pigment intensity and composition diversify, few, if any, have explored how a pattern element can shift position. In the present study, we examine the genetic changes underlying shifts in the position of petal spots in Clarkia. Comparative transcriptome analyses were used to identify potential candidate genes responsible for spot formation. Co-segregation analyses in F individuals segregating for different spot positions, quantitative PCR, and pyrosequencing, were used to confirm the role of the candidate gene in determining spot position. Transient expression assays were used to identify the expression domain of different alleles. An R2R3Myb transcription factor (CgMyb1) activated spot formation, and different alleles of CgMyb1 were expressed in different domains, leading to spot formation in different petal locations. Reporter assays revealed that promoters from different alleles determine different locations of expression. The evolutionary shift in spot position is due to one or more cis-regulatory changes in the promoter of CgMyb1, indicating that shifts in pattern element position can be caused by changes in a single gene, and that cis-regulatory rewiring can be used to alter the relative position of an existing character.

Identification and functional analysis of three new anthocyanin R2R3‐MYB genes in Petunia

“…SG6 MYBs are encoded in each species by a small family of genes with different expression patterns, contributing to the color of different plant parts (Albert et al., ; Gonzalez et al., ; Quattrocchio et al., ; Schwinn et al., ). The spotted pattern of the petals of Lilium hybrids has been shown to be associated with LhMYB6 or LhMYB12 (Yamagishi, Shimoyamada, Nakatsuka, & Masuda, ), while in Clarkia , the expression domain of an SG6 MYB, CgMYB1 , determines the position of a spot in the flower (Martins, Berg, Blinka, Rausher, & Baum, ; Martins, Jiang, & Rausher, ). These examples show that duplication and diversification of R2R3‐MYB genes controlling anthocyanin synthesis result in different expression patterns of these regulators, leading to considerable possibilities of variation in temporal and spatial anthocyanin accumulation in plants (Albert et al., ; Bombarely et al., ; Schwinn et al., ).…”

The CYCLOIDEA–RADIALIS module regulates petal shape and pigmentation, leading to bilateral corolla symmetry in Torenia fournieri (Linderniaceae)

“…R2R3-MYB transcription factors have been recruited in the control of various pigmentation patterns (Schwinn et al, 2006;Albert et al, 2011;Shang et al, 2011;Martins et al, 2013Martins et al, , 2016Nishijima et al, 2013;Hsu et al, 2015). In A. majus, pigmentation is often associated with veins and is determined by an R2R3-MYB factor encoded by Venosa (Schwinn et al, 2006;Shang et al, 2011).…”

“…(Orchidaceae), three R2R3-MYBs -PeMYB2, PeMYB11, and PeMYB12are responsible for background pigmentation, petal spots, and venation patterns, respectively (Hsu et al, 2015). In Clarkia (Myrtales), different alleles of an R2R3-MYB transcription factor gene, CgMYB1, are expressed in different regions of the petal and are responsible for the variations in spot pigmentation (Martins et al, 2016). Despite these findings, it remains unclear how these R2R3-MYBs became so diverse in their regulation of different pigmentation patterns.…”

Elena M. Kramer

“…Moyroud & Glover, ; Wilts et al ., ), which has revealed new and surprising aspects of flower–pollinator interactions. Of course, I love a good evo‐devo story, such as Mark Rausher's work on petal spots in Clarkia (Martins et al ., ) or Francois Parcy's study of LEAFY function in Welwitschia (Moyroud et al ., ). What all these papers have in common is a fearless willingness to ask ambitious questions and then figure out how to get the answers, even in Welwitschia !…”