Development and evolution of land plant rooting systems
Résumé
The evolution of the first rooting systems some time before 400 million years was a key innovation that occurred when the first complex multicellular eukaryotic photosynthetic organisms – plants – colonized and diversified on the continental surfaces. Rooting systems are important because they facilitate the uptake of most chemical elements that are required for plant growth. The rooting systems of the earliest diverging group of extant land plants comprise unicellular tip-growing filaments called rhizoids and are morphologically similar to cells that develop at the interface between the plant and the soil in tracheophytes (vascular plants) – root hairs.
An aim of our research is use a variety of approaches to define the regulatory mechanisms that controlled the development of the first land plant root system. We describe fossils and identify genes to define the ancient control mechanism that promoted the formation of rhizoids in the extinct colonizers of the terrestrial environment. A major focus is the comparison of the genetic mechanisms that regulate rhizoid and root hair development in bryophytes and seed plants respectively. The regulatory motifs that are common to both are likely to have been inherited from the common ancestor of liverworts and seed plants – close relatives of the first plants to grow in the dry continental surfaces. Our most recent data suggest that a common mechanism controlled the development of a variety of structures – including rooting cells – that develop from the superficial layer of the common ancestor of land plants.