Receptor Kinases Mediating Early Symbiotic Signalling

Abstract

The intimate intercellular relation between plant and bacteria in root nodule symbiosis is established after specific recognition of the microsymbiont. This delicate process involves various cellular components including at least three receptor kinases in the model legume Lotus japonicus. Whereas the exact role of the SYMRK receptor is still unclear, the lipochitin-oligosaccharide receptors NFR1 and NFR5 have been shown to be major determinants in host recognition and the role of the extracellular LysM domains have been analysed. Biochemical analyses of the cytoplasmic domain of NFR5 reveal that NFR5 is a pseudokinase that lacks detectable kinase activity. However, recent data show that NFR1 can interact with and phosphorylate NFR5. The signalling mechanism of NFR1 and NFR5 therefore differs from that of previously described plant RLKs. Interestingly, NFR1 and the Arabidopsis chitin receptor CERK1 are highly similar and minor differences in the cytoplasmic domain determines the signalling potential.