Lucie Riglet

Understanding how flowering plants build communication devices on their petal

Keywords: Petal patterns, Morphogenesis, Pollinators, Genetics, Computational modelling.

Flowers are not just beautiful to our eyes - they have evolved complex mechanisms to for capturing pollinator attention, promoting pollen transfer, plant reproduction and seed production. My postdoc research explores how flowers develop patterns on their petals and how these patterns influence pollinator behaviour.

To investigate this, we used the emergent model system Hibiscus trionum, whose flowers feature a target-like ‘bullseye’ pattern consisting of a dark purple centre surrounded by a white periphery. To understand how this pattern forms, I developed a quantitative imaging pipeline and tracked petal growth and pattern formation during early stages of development, when petals are still enclosed in the floral bud. Our research reveals that the H. trionum bullseye begins forming early, before the colour becomes visible to the human eye. This early “prepatterning” establishes the mature bullseye boundary, and is later maintained as the petal undergoes a 100-fold increase in size before reaching its final dimensions.

This early prepatterning poses a developmental challenge: how does the plant maintain the pattern proportions as the petal expand so dramatically to its mature size? To investigate this, we developed mathematical models to test how cells coordinate their behaviour to maintain the boundary position during petal growth. Our models demonstrated how different rates of cell growth and expansion across the different petal domains can either maintain the bullseye’s proportions or alter the pattern size.

In the wild, H. trionum belongs to a group of closely related species that exhibit bullseye of different sizes. To explore how these variations are designed, we studied both natural variants and genetically modified Hibiscus lines that produce either small or large bullseyes. By combining our imaging pipeline with genetic analysis, we found that plants can vary the size of their bullseyes in at least two ways: either by establishing the boundary position early in development, or by adjusting cell growth on either side of the boundary after it is set, thus adjusting the bullseye size as the petal develops.

Petal patterns are thought to enhance flower attractiveness, but it was previously unknown whether pollinators have a preference for specific bullseye proportions. We tested bumblebee behaviour using artificial flowers with varying bullseyes sizes and found that bumblebees could distinguish different proportions. Our results showed that bees prefer Hibiscus with medium to larger bullseye patterns and flew 25% faster between them, indicating that bullseye size influences flower detectability. Altogether, this indicates that bumblebees use bullseye proportion as a cue to identify targets.

This research relied on a combination of interdisciplinary methods, including high-resolution flowers imaging, genetics, mathematical modelling, and pollinators behavioural experiments. This integrated approach was essential to uncover how the bullseye pattern forms and to understand why floral bullseyes – and petal patterns more generally – are functionally important.

How the work contributes to bridge fields of biology, physics and/or mathematics: 

Using quantitative imaging, we demonstrated that Hibiscus petals are prepatterned, with the characteristic bullseye established early in development and maintained during growth. Combining imaging and genetics, we found that plants can vary bullseye size by positioning the boundary early or adjusting growth on either side of the bullseye domains later. To mechanistically explore how this early-set boundary is maintained and how proportions can vary, we developed mathematical models to test how differential cell growth affects boundary proportions, and create different bullseye sizes. Finally, behavioural experiment showed how bullseye pattern proportions impact bumblebee attraction, highlighting the adaptive significance of petal patterning.

Sainsbury Laboratory, Cambridge University

Dr Edwige Moyroud Lab