Identifying the evolutionary origins of the MADS-box floral quartet mechanism in seedless vascular plants

Despite its commonplace occurrence in today’s environment, the reproduction of plants via flowers and seeds is a recent evolutionary innovation arising from an ancestral seedless reproductive system similar to that still found in a subset of today’s plants (e.g. ferns, horsetails, clubmosses). How the genetic pathways that regulate seed and flower development first evolved represents a black hole in our understanding of plant evolution, and has the potential to unlock significant advances in our understanding of plant reproduction.

The characteristic structure of flowers, with concentric rings of different organ types, arises through a mechanism of co-operative protein binding between floral homeotic genes (e.g. APETALA1, PISTILLATA, AGAMOUS), which are members of the MADS-box gene superfamily of transcription factors. The ‘ABC’ or ‘floral quartet’ model(1) explains organ identity specification by these related proteins binding to form a tetramer (or quartet) with the precise combination of proteins involved activating different populations of downstream gene targets to achieve different organ identities. The evolutionary origin of this fundamental mechanism remains unknown. MADS-box genes closely related to the floral homeotic genes are found in the non-flowering sister-group to angiosperms, the gymnosperms, where it is hypothesised that a simplified version of the floral quartet regulates reproductive organ identity. Whilst MADS-box genes have been found in the closest seedless relatives to seed-bearing plants (the ferns), they do not belong to the same phylogenetic clade as the floral homeotic genes, and their functions are unknown.

This project aims to test whether the ancestral floral quartet mechanism in seed plants arose from a pre-existing similar mechanism in a seedless ancestor. The project will compare the functions and binding properties of MADS-box genes from the newly-established and genetically-tractable fern model system, Ceratopteris richardii(2,3). This will be achieved through a mix of in vivo and in vitro approaches, comparing Ceratopteris and the established angiosperm model for floral development, Arabidopsis thaliana, and investigating the functions of MADS-box genes in Ceratopteris as a proxy for their ancestral roles in plant development. Experiments will include the creation and analysis of transgenic plants in both species, combined with biochemical and bioinformatic assays to identify the protein binding partners and downstream targets of candidate genes.

Start date: October 2020.

Interested in applying? Please contact Andy Plackett ([Email Address Removed]) for further details.