Function Conservation of Plant Cell-Surface Co-Regulatory Receptors Across 400 Million Years of Evolution of the Land Plants

Abstract

Plants possess a variety of cell surface receptors that perceive endogenous and exogenous signals to regulate plant growth, development, and immunity. These receptors include receptor-like kinase (RLKs) and receptor-like protein (RLPs) that possess different extracellular domains perceiving distinct ligands and leading to the activation of downstream signaling. The signaling pathways mediated by RLKs and RLPs converge at a small group of co-receptors called somatic embryogenesis receptor kinases (SERK). These co-receptors modulate both immunity and plant development and growth. Although their homologous sequences are widespread across various plant species, it remains unknown if SERKs redundant and distinct functions are also conserved across plant kingdom. To shed light on the functional conservation of SERKs, three homologous genes were retrieved from the moss Physcomitrella patens, a bryophyte representative of early land plants. Their ability to complement Arabidopsis serk mutant deficiencies in terms of brassinosteroid responses and immunity was analyzed. Furthermore, to enlighten the physiological functions of PpSERKs in Physcomitrella, knockout lines of PpSERKs were generated via homologous recombination and their growth, development, and responses to Botrytis cinerea were assessed. In this work, we showed that SERKs homologs are present in the moss Physcomitrella and possess conserved function in immunity activation and brassinosteroid-mediated growth and development.