Multiple receptor-like kinase cDNAs from liverwort Marchantia polymorpha and two charophycean green algae, Closterium ehrenbergii and Nitella axillaris: Extensive gene duplications and gene shufflings in the early evolution of streptophytes.

Plant receptor-like kinases (RLKs) comprise a large family with more than several hundred members in vascular plants. The RLK family is thought to have diverged specifically in the plant kingdom, and no family member has been identified in other lineages except for animals and Plasmodium, both of which have RLK related families of small size. To know the time of divergence of RLK family members by gene duplications and domain shufflings, comprehensive isolations of RLK cDNAs were performed from a nonvascular plant, liverwort Marchantia polymorpha and two charophycean green algae, Closterium ehrenbergii, and Nitella axillaris, thought to be the closest relatives to land plants. We obtained twenty-nine, fourteen, and thirteen RLK related cDNAs from M. polymorpha, C. ehrenbergii, and N. axillaris, respectively. The amino acid sequences of these RLKs were compared with those of vascular plants, and phylogenetic trees were inferred by GAMT, a genetic algorithm-based maximum likelihood (ML) method that outputs multiple trees, together with best one. The inferred ML trees revealed ancient gene duplications generating subfamilies with different domain organizations, which occurred extensively at least before the divergence of vascular and nonvascular plants. Rather it remains possible that the extensive gene duplications occurred during the early evolution of streptophytes. Multicellular-specific somatic embryogenesis receptor kinase (SERK) involved in somatic embryogenesis was found in a unicellular alga C. ehrenbergii, suggesting the evolution of SERK by gene recruitment of a unicellular gene.