Abstract
Receptor-like kinases (RLKs) detect external and internal signals, triggering responses essential for growth and adaptation. Among internal cues, cell wall integrity (CWI) sensing plays a key role, as changes in cell wall structure activate responses critical for development and defense. While RLKs are well-studied in vascular plants, their diversity and function remain largely unknown in green algae belonging to the Chlorophyta phylum, a group that is relevant for global oxygen production and carbon cycling. Due to their varied cell wall structures, Chlorophyta offer a useful system to study the origins of CWI sensing. In this study, we used advanced bioinformatics and AI-based tools to analyze RLKs in 34 Chlorophyta species, mapping their distribution, structural features, and similarity to plant RLKs. We identified 736 putative RLKs, expanding the known repertoire in green algae. Structural analyses showed a wide range of extracellular domains, including motifs related to plant CWI sensors: domains mediating protein interactions (e.g., Leucine Rich Repeats-LRR, Plasminogen Apple Nematod e-PAN, Armadillo repeat-ARM), cell wall remodeling (e.g., glycosyl hydrolases, lyases), and mechanosensing (e.g., Leucine-Proline-X-Threonine-Glycine motifs-LPXTG, Fibronectin). This diversity suggests that mechanisms for extracellular sensing and CWI monitoring emerged early in evolution. The results provide a basis for future studies on the function of RLKs in algae and their evolutionary links to vascular plant signaling.