Plants perceive microbial patterns by cell surface receptors that are either receptor-like kinases (RLKs) or receptor-like proteins (RLPs), usually containing extracellular leucine-rich repeats (LRRs). However, RLPs lack an intracellular kinase domain for activation of downstream signaling upon ligand perception. Recently, we showed that tomato (Solanum lycopersicum, Sl) Cf-4, an LRR-RLP mediating resistance to Avr4-expressing strains of the fungal pathogen Cladosporium fulvum, constitutively interacts with the RLK SOBIR1. Interestingly, Arabidopsis thaliana (At) SOBIR1 complements a knock-down in Nicotiana benthamiana (Nb) of NbSOBIR1 by restoring the Cf-4/Avr4-triggered hypersensitive response (HR), whereas a kinase-dead version of AtSOBIR1 does not. The Cf-4/SOBIR1 complex does not dissociate in the presence of Avr4, suggesting that the complex acts as a two-component RLK. We found that the Cf-4/SOBIR1 complex localizes at the plasma membrane, from where it is mobilised to endosomes upon activation with Avr4. Strikingly, we discovered that the Cf-4/SOBIR1 complex recruits BAK1 upon its activation by Avr4; this interaction is required for both Avr4-triggered HR and Cf-4/SOBIR1 endocytosis. Thus, the RLP Cf-4, and probably also other RLPs, indeed function like two-component PRRs in association with SOBIR1. Future studies are aimed to shed light on different aspects of SOBIR1 functioning. (1) The role of different SOBIR1 domains in the interaction with Cf-4 and recruitment of BAK1 will be studied. (2) Downstream signalling events that take place upon Avr4-mediated activation of the Cf-4/SOBIR1 complex will be examined via (co-)immunoprecipitation and mass spectrometry. (3) Possible differential phosphorylation of the SOBIR1 kinase domain before and after Avr4/Cf-4-triggered BAK1 recruitment will be explored via mutational studies and mass spectrometry.
|Title of host publication||Book of Abstracts Keystone Symposia on Molecular and Cellular Biology|
|Publication status||Published - 2015|
|Event||Keystone Symposia on Molecular and Cellular Biology 2015 - Taos, New Mexico, United States|
Duration: 8 Feb 2015 → 13 Feb 2015
|Conference||Keystone Symposia on Molecular and Cellular Biology 2015|
|City||Taos, New Mexico|
|Period||8/02/15 → 13/02/15|