Perianth phyllotaxis and symmetry in Lamiales

ABSTRACT

Genetic studies of floral development have essentially focused on events within the floral meristem. By contrast, phyllotaxis models have shown that sepal arrangement is determined by the structure of the inflorescence. In this study, we assess the interplay between the genetic program underlying floral symmetry and phyllotaxic determination, which together shape the flower. We used a phyllotaxic model for the initiation of sepals and petals in six species of Lamiales and studied the impact of the zygomorphic genetic program on their pattern at anthesis. The initiation pattern of floral organs is determined by hormone signaling and contact pressure acting during organogenesis, while the genetic program underlying zygomorphy forces the bilateral symmetry of the initiation of organ primordia. The integration of phyllotaxic and genetic studies allows to deepen our understanding of the mechanisms producing actinomorphic or zygomorphic flowers. In any case, these mechanisms respect Curie’s symmetry principle which states that “when certain causes (here, expression of CYC-like genes) produce certain effects, the elements of symmetry of the causes must be found in the effects produced (here, perianth symmetry)”.

KEYWORDS:

• Phyllotaxis
• bracteoles
• zygomorphy
• actinomorphy
• Lamiales
• CYC gene

Acknowledgments

We thank Catherine Damerval, Senior Researcher at the Centre National de la Recherche Scientifique, Université Paris-Saclay and Florian Jabbour, Associate professor, Muséum National d’Histoire Naturelle, Paris, for their encouragement, advice and critical review of the manuscript, Hélène Citerne for her review of the manuscript and Line Walch for her superb drawings.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

JPW performed genetic analysis, modeling and wrote the manuscript; SB contributed to botanical aspects and reviewed the manuscript.

Additional information

Funding

This work received no specific grant from any funding agency in the public, commercial or not-for-profit sector.