The plant immune system perceives a diversity of carbohydrate ligands from plant and microbial cell walls. CBGP researchers have discovered a new family of Leucine-Rich-Repeat (LRR)-Malectin (MAL)-Receptor Kinases that percieve cellulose derived oligosaccharides and trigger immune responses.
The plant immune system perceives a diversity of carbohydrate ligands from plant and microbial cell walls through the extracellular ectodomains (ECDs) of pattern recognition receptors (PRRs), which activate pattern-triggered immunity (PTI). Among these ligands are oligosaccharides derived from mixed-linked glucans (e.g. MLG43) and cellulose (e.g. CEL3). The mechanisms behind carbohydrate perception in plants are poorly characterized except for fungal chitin oligosaccharides (e.g. CHI6), which involve several receptor kinase proteins (RKs) with LysM-ECDs. CBGP reserachers, lead by Molina group, in collaboration with the group of Julia Santiago (Lausanne University) have isolated and characterized Arabidopsis thaliana mutants impaired in glycan perception (igp) that are defective in PTI activation mediated by MLG43 and CEL3, but not by CHI6. igp1-igp4 are altered in three RKs - AT1G56145 (IGP1/CORK1), AT1G56130 (IGP2/IGP3) and AT1G56140 (IGP4) - with leucine-rich-repeat (LRR) and malectin (MAL) domains in their ECDs. igp1 harbors point mutation E906K and igp2/igp3 harbor point mutation G773E in their kinase domains, whereas igp4 is a T-DNA insertional loss-of-function mutant. Notably, isothermal titration calorimetry (ITC) assays with purified ECD-RKs of IGP1 and IGP3 showed that IGP1 binds with high affinity to CEL3 (with dissociation constant KD = 1.19 ± 0.03 μM) and cellopentaose (KD = 1.40 ± 0.01 μM), but not to MLG43, supporting its function as a novel plant PRR for cellulose-derived oligosaccharides. Published data suggest that these LRR-MAL RKs are components of a recognition mechanism for both cellulose- and MLG-derived oligosaccharides perception and downstream PTI activation in Arabidopsis. The identification of this novel type of PRRs for carbohydrates in plants, that is the second type of PRRs described so far, open the posibilility to develop cellulose and MLG-based biological products for sustainable crop protection and to replace chemical pesticides.
Martín-Dacal, M., Fernández-Calvo, P., Jiménez-Sandoval, P., López, G., Garrido-Arandía, M., Rebaque, D., del Hierro, I., Berlanga, D.J., Torres, M.Á., Kumar, V., Mélida, H., Pacios, L.F., Santiago, J., Molina, A. 2022. Arabidopsis immune responses triggered by cellulose and mixed-linked glucan oligosaccharides require a group of Leucine-Rich Repeat-Malectin Receptor Kinases. The Plant Journal. DOI: 10.1111/tpj.16088