Format: ORAL

Paula Elomaa1, Teng Zhang1, Feng Wang1 Andrew Owens2, Mikolaj Cieslak2, Przemyslaw Prusinkiewicz2

1 Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, Finland 2 Department of Computer Science, University of Calgary, Canada

Asteraceae (sunflower family) represents one of the largest and most diverse families of plants. The inflorescences of Asteraceae mimic solitary flowers but are in fact compressed, head-like structures typically comprised of multiple florets with specialized functions. This unique architecture has been considered as a key innovation behind the evolutionary success of the family. Flower heads are also iconic examples of geometric regularity found in nature; the involucral bracts and florets are arranged in regular left- and right-curving spirals whose numbers follow the mathematical Fibonacci series. We have explored the growth dynamics and patterning of the enlarged inflorescence meristem in the model plant Gerbera hybrida and shown with DR5 auxin reporter lines how the high spiral numbers emerge. The molecular data was integrated into a computational model to explain phyllotactic patterning of Asteraceae heads. We have extended our studies to explore how head vasculature is associated with organ phyllotaxis. By applying synchrotron-based micro-CT imaging, we have explored the vascular networks in heads of diverse Asteraceae species. The observed diversity and irregularities of vasculature stand in contrast with the regularity of phyllotactic patterns, confirming that phyllotaxis in heads in not driven by the vasculature. We will discuss how our recent discoveries on meristem patterning relate to distinct scenarios of the evolutionary origin of Asteraceae heads.