Abstract

Have you ever wondered what the spirals in sunflower heads are and how they emerge? Flower heads (i.e. inflorescences) in the sunflower family, Asteraceae, are iconic examples of geometric beauty found in nature. They superficially mimic solitary flowers but are in fact tightly packed structures, often composed of tens or hundreds of florets. The individual florets emerge on an enlarged meristem in regular left and right winding spirals whose numbers follow the two consecutive numbers in a mathematical Fibonacci sequence. My focus here is on molecular level studies to understand phyllotactic patterning of flower heads. Using the DR5 auxin reporter lines of the model plant Gerbera hybrida, we have shown how patterning is established de novo at early stages of meristem development and how the expansion growth of the meristem drives the emergence of high spiral numbers. The molecular data has been integrated into a computational model that was extended also to cases of non-circular (fasciated) heads. We have also applied synchrotron-based micro-CT imaging to explore the role vascular networks on patterning. Additionally, I will discuss how our work contributes to understanding of the evolutionary origin of capitula.