Functional analysis of SOBIR1 in CLV2-mediated development and defence

Receptor-like proteins (RLPs) and receptor-like kinases (RLKs) are cell surface receptors that are essential for detecting invading pathogens and subsequent activation of plant defence responses. In contrast to RLKs, RLPs lack a cytoplasmic kinase domain to trigger downstream signalling leading to host resistance. The RLK SOBIR1 constitutively interacts with Cf-4 and is required for Cf-4-mediated resistance to Cladosporium fulvum [1]. Accumulating evidence shows that SOBIR1 is broadly required for RLP-involved resistance to fungal, oomycete and bacterial pathogens [2, 3]. CLAVATA2 (CLV2) was firstly identified as an RLP in regulating meristem homeostasis in Arabidopsis, tomato and maize [4, 5, 6]. Recent evidence shows that CLV2 also functions in plant-parasitic infection as colonisation by nematodes is reduced in Atclv2 mutants [7] and such mutants are also more resistant to the bacterial pathogen Ralstonia solanacearum [8]. In addition, a pseudo-kinase CORYNE (CRN) interacts with CLV2 and participates in all CLV2-mediated signalling pathways [7, 8, 9]. As the kinase domain of CRN is inactive, the current hypothesis is that the CLV2/CRN heterodimer likely functions together with an unknown RLK [10, 11]. Our preliminary data show that both Arabidopsis and tomato SOBIR1 interact with CLV2, indicating that SOBIR1 might be a good candidate for functionally participating in the CLV2/CRN complex. Further studies will be focused on a possible interaction between SOBIR1 and CRN and the possible involvement of SOBIR1 and the CLV2/CRN heterodimer in the same signalling pathway, including the CLV2/CRN-mediated regulation of stem cell maintenance, susceptibility to nematodes, resistance to R. solanacearum, and the requirement of SOBIR1 for resistance to different pathogens.