High-throughput glycan array screening reveals rhamnogalacturonan-I as a ligand for Arabidopsis leucine-rich repeat...

The plant cell wall not only serves as a physical barrier against pathogens but, when damaged, also functions as a source of cell wall-derived molecules that play crucial roles in plant immunity as damage-associated molecular patterns. While oligogalacturonides from homogalacturonan are well-studied damage-associated molecular patterns, the immune-signaling potential of other cell wall components remains largely unexplored. Conventional genetic and biochemical approaches aimed at identifying ligand-receptor pairs in plant immunity have been limited by the vast diversity of potential ligand molecules and functional redundancy of putative receptors. In this study, we developed a high-throughput screening pipeline that simultaneously examines multiple interactions between plant cell wall-derived glycans and >350 extracellular domains of receptor kinases and receptor-like proteins in Arabidopsis, resulting in the screening of >40 000 interactions. We discovered a group of leucine-rich repeat receptor kinases named ARMs (AWARENESS of RG-I MAINTENANCES) that interact with rhamnogalacturonan-I (RG-I), a major component of pectin. RG-I treatment induced pattern-triggered immunity responses with distinct kinetics compared to oligogalacturonide responses. We identified RG-I oligosaccharide structures required for interaction with ARM receptors and immune activation and found that ARM receptors function redundantly in plant immunity. Collectively, our work provides a powerful platform for discovering glycan-receptor pairs in plants, facilitating a more comprehensive understanding of cell wall surveillance mechanisms in plant immunity.