Arabidopsis thaliana receptor-like protein AtRLP23 associates with the receptor-like kinase AtSOBIR1

Plants employ a large number of receptors localizing to the cell surface to sense extracellular signals. Receptor-like proteins (RLPs) form an important group of such trans-membrane receptors, containing an extracellular domain which is involved in signal perception and a short cytoplasmic domain. In contrast to receptor-like kinases (RLKs), RLPs lack a cytoplasmic kinase domain. How intracellular signaling is triggered downstream of RLPs upon perception of an extracellular signal, is therefore still poorly understood. Recently, the RLK SOBIR 1 (Suppressor Of BIR 1–1) was identified as an essential regulatory RLK of various RLPs involved in plant immunity against fungal pathogens.1 Given that SOBIR 1 appears to be a crucial component of RLP-containing complexes, we aimed to identify additional proteins interacting with SOBIR 1. Here, we report on the immunopurification of a functional Arabidopsis thaliana (At)SOBIR 1-yellow fluorescent protein (YFP) fusion protein stably expressed in Arabidopsis, followed by mass-spectrometry to identify co-purifying proteins. Interestingly, and in line with various studies showing interaction between RLPs and SOBIR 1, we discovered that AtSOBIR 1 interacts with AtRLP23, an RLP of which the function is currently unknown.