Hibiscus bullseyes reveal mechanisms controlling petal pattern proportions that influence plant-pollinator interactions

Colourful flower patterns are key signals to attract pollinators. To
produce such motifs, plants specify boundaries dividing petals into
subdomains where cells develop distinctive pigmentations, shapes and
textures. While some transcription factors and biosynthetic pathways
behind these characteristics are well-studied, the upstream processes
restricting their activities to specific petal regions remain enigmatic.
Here, we unveil that the petal surface of Hibiscus trionum, an emerging
model featuring a bullseye on its corolla, is pre-patterned as the
bullseye boundary position is specified long before it becomes visible.
Using a computational model, we explore how pattern proportions are
maintained while petals experience a 100-fold size increase. Exploiting
transgenic lines and natural variants, we show that plants can regulate
boundary position during the pre-patterning phase or modulate growth
either side of this boundary later in development to vary bullseye
proportions. Such modifications are functionally relevant, as buff-tailed
bumblebees (Bombus terrestris) can reliably identify food sources based on
bullseye size and prefer certain pattern proportions.