title: Knowing your friends and foes--plant receptor-like kinases as initiators of symbiosis or defence.
abstract: The decision between defence and symbiosis signalling in plants involves alternative and modular plasma membrane-localized receptor complexes. A critical step in their activation is ligand-induced homo- or hetero-oligomerization of leucine-rich repeat (LRR)- and/or lysin motif (LysM) receptor-like kinases (RLKs). In defence signalling, receptor complexes form upon binding of pathogen-associated molecular patterns (PAMPs), including the bacterial flagellin-derived peptide flg22, or chitin. Similar mechanisms are likely to operate during the perception of microbial symbiont-derived (lipo)-chitooligosaccharides. The structurally related chitin-oligomer ligands chitooctaose and chitotetraose trigger defence and symbiosis signalling, respectively, and their discrimination involves closely related, if not identical, LysM-RLKs. This illustrates the demand for and the challenges imposed on decision mechanisms that ensure appropriate signal initiation. Appropriate signalling critically depends on abundance and localization of RLKs at the cell surface. This is regulated by internalization, which also provides a mechanism for the removal of activated signalling RLKs. Abundance of the malectin-like domain (MLD)-LRR-RLK Symbiosis Receptor-like Kinase (SYMRK) is additionally controlled by cleavage of its modular ectodomain, which generates a truncated and rapidly degraded RLK fragment. This review explores LRR- and LysM-mediated signalling, the involvement of MLD-LRR-RLKs in symbiosis and defence, and the role of endocytosis in RLK function.
authors.affiliation: Faculty of Biology, Genetics, University of Munich (LMU), 82152, Martinsried, Germany.
authors.forename: Meritxell
authors.initials: M
authors.lastname: Antolín-Llovera
authors.forename: Elena Kristin
authors.initials: EK
authors.lastname: Petutsching
authors.forename: Martina Katharina
authors.initials: MK
authors.lastname: Ried
authors.forename: Volker
authors.initials: V
authors.lastname: Lipka
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nürnberger
authors.forename: Silke
authors.initials: S
authors.lastname: Robatzek
authors.forename: Martin
authors.initials: M
authors.lastname: Parniske
mesh_terms: D020816:Amino Acid Motifs; D029681:Arabidopsis Proteins / Q000378:metabolism; D002686:Chitin / Q000378:metabolism; D004705:Endocytosis; D054884:Host-Pathogen Interactions / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism* / Q000382:microbiology*; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D012231:Rhizobium; D013559:Symbiosis / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D002686:Chitin; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases
keywords: PAMP-triggered immunity (PTI); RLK turnover; leucine-rich repeat (LRR); lysin motif (LysM); pathogen-associated molecular pattern (PAMP); plant immunity; receptor-like kinase (RLK); symbiosis