Origin of the angiosperm carpel. – ORANGe

This research project will address a central question in evolutionary biology: the origin of the flowering plants, or angiosperms. This group arose some 150 million years ago and rapidly diversified to form around 400 000 species alive today. The key novel structure of the angiosperms is their female reproductive organ, the carpel, which encloses the ovules. We will combine biological, biophysical, phylogenetic and bioinformatic approaches with two major objectives. Firstly, we aim to construct a molecular model of carpel development in early angiosperms, and secondly we aim to identify the molecular changes that generated the first carpels, and hence the flower and the flowering plants. Our initial approach will be based on current knowledge of the transcriptional and post-transcriptional regulators that control carpel development in the model angiosperm, Arabidopsis thaliana. We will use biophysical and bioinformatic methods to analyse, at the whole genome level, conservation in direct transcriptional and post-transcriptional mechanisms between Arabidopsis and the sister to all other living flowering plants Amborella trichopoda, whose genome has recently been sequenced. This work, which will also involve a second basal flowering plant species, Trithuria submersa, will lead to the first major deliverable of our project: a molecular model of carpel development in the last common ancestor of the living flowering plants. As the carpel is the developmental precursor to the fruit, and as fruit and grain crops are of vital importance for human nutrition, we expect the basic knowledge to be gained in this project to be of considerable strategic importance. By deriving a model of carpel development in the first angiosperms, we will be defining the genetic network that has been modified along the many different evolutionary paths leading to the tremendous biodiversity of carpel and fruit structure in nature, including all of the crop species on which human life depends. Our second major objective, to identify the molecular changes responsible for the origin of the angiosperm carpel, will be achieved in two ways. Firstly, we will perform comparative molecular analyses in gymnosperms, the angiosperms’ sister group, to define the state of the regulatory network in the last common ancestor of the living seed plants, which probably lived some 150 million years before the origin of the carpel. Secondly, we will exploit a whole genome duplication event that shortly preceded the origin of the carpel to reconstruct a selected number of ancestral regulators and identify neo-functionalization processes that may have been directly responsible for the origin of the carpel. Through these two approaches, we expect to provide a molecular explanation for the origin of the carpel and thereby contribute to an understanding of the origin of the flowering plants: the still unresolved question, famously described by Charles Darwin as “an abominable mystery”.