ELR interacts with sobir1 to mount defense responses against phytophthora infestans in potato

Late blight, caused by the oomycete Phytophthora infestans, is the most threatening disease of potato. So far, plant breeding for late blight resistance has been focused on the introduction of cytoplasmic NLR resistance (R) genes. However, any introduced R-gene has been defeated by the pathogen rather quickly, indicating that alternative resistance mechanisms should be studied. Recently, the receptor-like protein ELR was identified in a wild potato species, Solanum microdontum (Sm). ELR confers response to elicitins, a highly conserved family of secreted effectors of Phytophthora and Pythium. It has been shown that upon INF1 elicitation, ELR forms an inducible complex with the receptor-like kinase (RLK) SERK3. In order to study whether ELR associates with potato SOBIR1, another RLK involved in immunity, co-immunoprecipitation studies were performed. We found that ELR is indeed forming a constitutive complex with SmSOBIR1. Moreover, SmSOBIR1 seems to have a stabilizing effect on ELR, leading to a higher accumulation of the receptor. Virus-induced gene silencing (VIGS) studies of SOBIR1 homologues in Nicotiana benthamiana resulted in a compromised response to INF1 of P. infestans. This response could be complemented by expressing a synthetic version of SmSOBIR1 that is not targeted by VIGS. Additionally, the same NbSOBIR1-silenced plants were more susceptible to a number of P. infestans isolates. This indicates that SOBIR1 plays an important role in plant defense against P. infestans, as shown for other pathogens. Further studies aim to demonstrate whether ELR physically associates with INF1 in a direct or indirect fashion.