Phyllotactic patterning of gerbera flower heads

Abstract

Phyllotaxis, the distribution of organs such as leaves and flowers on their support, is a key attribute of plant architecture. The geometric regularity of phyllotaxis has attracted multidisciplinary interest for centuries, resulting in an understanding of the patterns in the model plants Arabidopsis and tomato down to the molecular level. Nevertheless, the iconic example of phyllotaxis, the arrangement of individual florets into spirals in the heads of the daisy family of plants (Asteraceae), has not been fully explained. We integrate experimental data and computational models to explain phyllotaxis in Gerbera hybrida. We show that phyllotactic patterning in gerbera is governed by changes in the size of the morphogenetically active zone coordinated with the growth of the head. The dynamics of these changes divides the patterning process into three phases: the development of an approximately circular pattern with a Fibonacci number of primordia near the head rim, its gradual transition to a zigzag pattern, and the development of a spiral pattern that fills the head on the template of this zigzag pattern. Fibonacci spiral numbers arise due to the intercalary insertion and lateral displacement of incipient primordia in the first phase. Our results demonstrate the essential role of the growth and active zone dynamics in the patterning of flower heads.

Shaping the Organ: A Biologist Guide to Quantitative Models of Plant Morphogenesis

“…The beautiful geometry of phyllotaxis has attracted the attention of botanists and mathematicians since ancient times ( Adler et al, 1997 ), and the process is known to be driven by the interaction between the phytohormone auxin and tissue growth to optimize light capture ( Strauss et al, 2020 ). Phyllotaxis has been the subject of many attempts to formalize its mechanism through computational modeling techniques ( Mitchison, 1977 ; Jönsson et al, 2006 ; Smith et al, 2006a ; Zhang et al, 2021 ).…”

Understanding capitulum development: Gerbera hybrida inflorescence meristem as an experimental system

“…Exploring meristem patterning has proven to be most informative to understand capitulum development. The gerbera inflorescence meristems (IM) initiate hundreds of florets in an iconic phyllotactic pattern forming regular left-and right-cur ving spirals (Zhang et al, 2021a). Intriguingly, the spiral numbers represent two consecutive numbers of the Fibonacci series.…”

“…We have visualized the plant hormone auxin in transgenic gerbera using the DR5rev::3XVENUS-N7 repor ter (Heisler et al, 2005) scanning electron microscopy (SEM). Combining the in vivo microscopic data with X-ray micro-computed tomography (micro-CT) based growth analysis, a 3D computational model for capitulum phyllotaxis was established in collaboration with Prof. Prusinkiewicz's team at the University of Calgar y (Zhang et al, 2021a). Our recent molecular data shows that many genes regulating flower development have been recruited to regulate IM development in gerbera (Zhao et al, 2016;Zhang et al, 2017;Zhao et al, 2020).…”

Sepal Identity of the Pappus and Floral Organ Development in the Common Dandelion (Taraxacum officinale; Asteraceae)

“…The capitulum is surrounded by involucral bracts or scales, the phyllaries, which resemble sepals of individual flowers and have a protective function. The true individual flowers, named florets in Asteraceae, are placed closely together on a common receptacle [ 23 ]. The florets vary among species mainly in terms of the shape of their corolla, which always consists of five petals, and fertility [ 24 ].…”