The evolution of flower development: current understanding and future challenges

Abstract

One of the most fascinating questions in evolutionary biology is understanding how novelties such as new organs or novel body plans arise. Answering this question is all the more challenging as obvious predecessors cannot always be identified in the incomplete fossil record. Evolutionary developmental (evo-devo) studies address this issue by examining how developmental mechanisms have evolved over time. To undertake such studies, rigorous assessment of trait homology (i.e. inherited from a common ancestral trait) is necessary, and this can now be conducted in a robust phylogenetic framework thanks to the remarkable recent progress in molecular systematics (e.g. APG III, 2009; Moore et al., 2010). Close examination of the sequence of developmental events underlying homologous traits, and the genes regulating developmental changes, is critical to our understanding of the present state and evolution of biodiversity. Indeed, the emergence of novel body plans or organs very often coincides with the rise of a wealth of new species, suggesting that evo-devo concepts can revolutionize our understanding of macro-evolutionary events. The flower is doubtlessly the most beautiful example of an evolutionary innovation that is believed to have been a major contributor to the diversification of angiosperms. Flowering plants nowadays dominate terrestrial ecosystems and, as a major food source, are of outstanding importance for mankind. Floral structure is generally conserved with four main organ types (sepals, petals, stamens and carpel); however, the variation on this theme is breathtaking. The types of variation include abortion of organs, radial versus bilateral symmetry, whorled or spiral phyllotaxis, dramatic variations in the colour, arrangement, number or size of floral organs, or even evolution of extra floral organs, such as, for example, in the genus Aquilegia. In recognition of the recent advances in our understanding of the mechanisms involved in the evolution of floral phenotypes, this issue gathers together eleven articles contributing to the field of ‘flower evo-devo’, which represent diverse approaches ranging from morphological and developmental comparative studies, to phylogenetic analyses of important developmental regulators, and gene function analysis in non-model plants.