CORDIS - EU research results

Origin of a cell differentiation mechanism and its evolution over 500 million years of life on land

Final Report Summary - EVO500 (Origin of a cell differentiation mechanism and its evolution over 500 million years of life on land)

During the course of EVO500 we discovered the genetic mechanism that controlled the development of the first land plant rooting structures – filamentous cells that grew from the primitive plant body into the growth substrate. Our conclusion is that RSL-related transcription factors first evolved in land plant ancestors (streptophyte algae) and then acquired a role in controlling rooting system development when plants colonised the land. Subsequently gene duplication increased the numbers of RSL genes in plants and at least one of these became the major controller of root cell growth.

The research program involved a genetic screen of unprecedented intensity in plants along with the generation of a draft genome sequence in the model early diverging land plant Marchantia polymorpha. The analysis demonstrated that a key genetic regulator – the transcription factor RSL – acts early in the development of the cells that make up the primitive rooting system. Furthermore, many other genes are required for the growth of these cells and these too are active in more derived groups of land plants where they control the development of root hairs. The shared mechanism controlling the development of rhizoids in the relatively ancestral Marchantia polymorpha rhizoids and root hairs in the relatively derived Arabidopsis thaliana, Oryza sativa and Brachypodium distachyon indicates that many components of the mechanism were derived from a common ancestor that lived soon after the colonization of the land by plants. We discovered that the final size of the rooting cell is determined by the intensity of synthesis of the RSL4 transcription factor – a novel mechanism of cell size control in plants. We also identified transcription factors related to RSL that in the algae that are most closely related to land plants. These transcription factors are not expressed in rhizoids. This suggests that these ancestral genes have a different function in algae and land plants. We propose that RSL transcription factors acquired the ability to promote the formation of rooting cells when plants colonised the land. During the course of EVO 500 we have followed the evolution of a set of transcription factors and demonstrated their role in the evolution of rooting structures, that were key innovations as plants colonised the continental surfaces, one of the key events in Earth history.