Unearthing the origin of root stem cells in a relative of the first root bearing plants

470 million years ago, the first land plants emerged from the water dwelling charophyte algae. The subsequent evolution of roots, including the establishment of a new stem cell niche, was one of the innovations that allowed plant life to thrive in this new terrestrial environment. The first root bearing plants belonged to lycophytes, the sister clade of euphyllophytes (ferns and seed plants). As such, lycophytes could be instrumental in understanding the origin of root stem cells. Research in the lycophyte Selaginella moellendorffii by the Root Development group of Prof. Tom Beeckman (Ghent University) identified two WOX transcription factors with putative roles in the Selaginella root meristem. Also in seed plants, despite evolutionary and structural divergence, WOX genes are well-known regulators of root stem cell formation. We aim to gain insight in the evolution of the WOX pathway by employing the new model plant, Selaginella moellendorffii. Despite the absence of molecular tools in this plant, we can use original and innovative methods, including TARGET, a method that employs transient transfection in protoplasts to identify direct targets of transcription factors, and I yeast-one-hybrid assays. Finally, interspecies experiments, between Selaginella, the moss Physcomitrella patents and the seed plant Arabidopsis thaliana, aim to identify conserved parts and shed light on the evolution of the pathway.