Function of the LEAFY floral regulator before flowers – BEFLORE

A major goal of developmental and evolutionary biology is to elucidate the genetic changes underpinning morphological innovations. Plant architecture is determined by the activity of meristems, groups of proliferating cells responsible for the construction of all organs, including leaves, branches and flowers. Identifying the molecular mechanisms controlling meristem formation and identity is critical to determine how plant architecture is established. While these mechanisms are well studied in flowering plants, how meristems form in other plant groups and have acquired new identities during evolution remains largely unknown.
In this project, we will address this fundamental question by studying the evolution of the floral regulator LEAFY. LEAFY is a transcription factor well known for its role in floral meristem identity in flowering plants. However, this protein originated in the common ancestor of charophyte algae and land plants, and thus before the emergence of flowers. Various studies and our preliminary results indicate that LEAFY is always expressed in meristems, regardless of their morphology and function. Notably, it is needed for meristem formation in the moss Physcomitrium and the fern Ceratopteris in both the haploid gametophytic and diploid sporophytic phases of life of these plants. Furthermore, various observations indicate that LEAFY has retained this ability to promote meristem formation in flowering plants even though this role is less obvious. For instance, LEAFY controls thallus formation in rice, compound leaf development in legumes and shoot apical meristem function in cucumber, and it is also involved in the initial steps of floral meristem formation in Arabidopsis.
It is therefore likely that LEAFY had an ancestral role in the formation of meristems in both phases of the plant life cycle and was co-opted later in evolution to confer a floral fate to meristems in flowering plants.
In this project, we propose to :
i) elucidate the developmental and molecular function of LEAFY in bryophytes,
ii) reconstruct the evolutionary trajectory of the LEAFY gene regulatory network in land plants
iii) determine the cis-regulatory code that maintained LEAFY expression in shoot meristems during land plant diversification.
This project is unique for the magnitude of the evolutionary distance it encompasses and the importance of the process in plant development. It combines the expertise of two complementary teams (bryophyte genetics, meristem biology, genomic and bioinformatics analyses, extensive knowledge of the LEAFY protein). Fundamental results on plant evolution are expected, which will serve as a basis for high-impact publications and wide scientific dissemination to different audiences.