Abstract

The genus Petunia comprises species that are pollinated by different animal pollinators including bees, nocturnal hawkmoths and hummingbirds. Transitions in adaptation to these different pollinators have helped drive speciation within the genus. Such transitions require the modification of multiple floral traits, among them visible colour, ultra-violet (UV) absorbance, scent, nectar production and morphology. How can such complex changes happen again and again over short periods of evolutionary time? To help answer this question, I looked at the genes and mutations responsible for transitions in floral colour. Two classes of flavonoids are important for Petunia floral colour: anthocyanins produce the reds and purples, whereas flavonols absorb UV light. In general, differences in anthocyanin and flavonol levels between Petunia species are caused by a limited number of mutations of large phenotypic effect. For instance, mutations in MYB -FL, encoding a R2R3 -MYB transcription factor, are responsible for both gain and loss of UV absorbance. Modifications to MYB -FL also affect anthocyanin levels, imposing constraints on possible colour combinations and providing insight into the possible order of trait changes.