Evolution of the WOX gene family and the stem cell niche

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Robust phylogenetic reconstructions imply a monophyletic origin of the WOX homeobox gene family in green algae and successive gene amplifications from basal land plants over gymnosperms to basal angiosperms. Members of the ancient WOX13 lineage are still present in extant higher plant species, but their genealogy and functional relation to modern family members is unclear. The modern WUSCHEL and WOX5 genes promote stem cell fate in the shoot or root meristem of Arabidopsis thaliana and represent an angiosperm-specific duplication from a common gymnosperm WUS/WOX5 ancestor. This project aims to analyse the origin of the WUS or WOX5 functions in the stem cell niches of seed plant and their relation to the ancient WOX13 gene lineage. It uses homologous recombination in Physcomitrella patens, available Arabidopsis T-DNA insertion lines and asks for functional equivalence of WUS and WOX5 orthologues in basal angiosperms (Nymphaea jamesoniana) or their Ginkgo, Gnetum or Pinus ancestors. Evolutionary information highlighted by conserved polypeptide motifs in WUS or WOX5 orthologues from basal angiosperms or gymnosperm ancestors will guide wus-1 rescue experiments in Arabidopsis thaliana.