Evolutionary history of Mo25 gene in plants, a component of RAM/MOR signaling network

Change in cell morphogenesis is an important feature for proper development of eukaryotes. It is necessary for cell polarity and asymmetry and is essential for asymmetric cell division. RAM/MOR is a conserved signaling network that coordinates cell polarity determinants important for asymmetric cell division and cell polarity establishment. Mo25 is a scaffold protein that acts as a master regulator of the germinal center kinase (GCK) which triggers the downstream signaling of this network. Little is known about RAM/MOR network or Mo25 protein homologs in plants. Here, we provide a glimpse of the evolutionary gene history of Mo25 in green plants. Our data showed that a duplication of Mo25 occurred at the basis of land plants (Embryophyta), forming the groups Mo25A and Mo25B. Further duplication events occurred in other plant lineages and one subgroup of sequences seemed to be rapidly diverging. This subgroup contained an A. thaliana paralog (AtMo25-1) which lacks intron and is expressed in a similar fashion of retrogenes (i.e. low expression levels and narrow expression breadth), suggesting that this paralog was duplicated by retroposition. We also showed that all AtMo25 proteins are structurally similar to each other and to the human homolog, although differences in residues in the interface between human Mo25 and MST3 are observed in the A. thaliana homologs. Expression profile of AtMo25 homologs suggest that they are required at different developmental contexts, possibly interacting with different partners. Finally, we discuss whether Mo25 duplication in Embryophyta could be an evolutionary novelty important for the terrestrial environment conquest and whether the duplicated paralogs are undergoing neo- or subfunctionalization.