High-Throughput Glycan Array Screening Reveals Rhamnogalacturonan-I as a Ligand for Arabidopsis Leucine-Rich Repeat Receptor Kinases

The plant cell wall not only serves as a physical barrier against pathogens but also functions as a source of cell wall-derived molecules that play crucial roles in plant immunity as damage-associated molecular patterns (DAMPs). While oligogalacturonides from homogalacturonan are well-studied DAMPs, the immune-signaling potential of other cell wall components remains largely unexplored. However, conventional genetic approaches to identify ligand-receptor pairs in plant immunity have been limited by vast diversity of potential ligand molecules and receptor functional redundancy. Here, we developed a high-throughput screening pipeline that simultaneously examines multiple interactions between plant cell wall-derived glycans and extracellular domains of Arabidopsis receptor kinases. Through this approach, we discovered a group of leucine-rich repeat receptor kinases termed ARMs (AWARENESS of RG-I MAINTENANCES) that interact with rhamnogalacturonan-I (RG-I), a major pectin component. Treatment with RG-I induced pattern-triggered immunity responses, including MAPK activation and extensive transcriptional reprogramming, albeit with distinct kinetics compared to oligogalacturonide responses. We identified minimal RG-I oligosaccharide structures required for immune activation and specific interactions with ARM receptors, and that ARM receptors involved in plant immunity through complex, redundant mechanisms. Thus, our approach can provide a powerful platform for discovering novel ligand-receptor pairs in plant immunity.