Immune signaling: receptor-like proteins make the difference

Both LRR-RLKs and LRR-RLP/SOBIR1 complexes recruit the co-receptor BAK1 to initiate downstream signaling. However, BAK1 association occurs by different mechanisms.BAK1 is merely an activator of primary receptor kinase that perceives the corresponding ligand. Therefore, the specificity of downstream signaling is determined by the kinase domain of the primary receptor, being the kinase domain of SOBIR1 for all LRR-RLPs involved in immunity and, for example, the kinase domain of FLS2.Some receptor-like cytoplasmic kinases (RLCKs) play opposite roles, either as positive or negative regulators downstream of LRR-RLP/SOBIR1 complexes and of LRR-RLKs.LRR-RLP/SOBIR1 complexes employ different downstream signaling components in arabidopsis (Arabidopsis thaliana), when compared with the solanaceous plant Nicotiana benthamiana.There is (negative) crosstalk between signaling by LRR-RLKs and LRR-RLP/SOBIR1. To resist biotic attacks, plants have evolved a sophisticated, receptor-based immune system. Cell-surface immune receptors, which are either receptor-like kinases (RLKs) or receptor-like proteins (RLPs), form the front line of the plant defense machinery. RLPs lack a cytoplasmic kinase domain for downstream immune signaling, and leucine-rich repeat (LRR)-containing RLPs constitutively associate with the RLK SOBIR1. The RLP/SOBIR1 complex was proposed to be the bimolecular equivalent of genuine RLKs. However, it appears that the molecular mechanisms by which RLP/SOBIR1 complexes and RLKs mount immunity show some striking differences. Here, we summarize the differences between RLP/SOBIR1 and RLK signaling, focusing on the way these receptors recruit the BAK1 co-receptor and elaborating on the negative crosstalk taking place between the two signaling networks. To resist biotic attacks, plants have evolved a sophisticated, receptor-based immune system. Cell-surface immune receptors, which are either receptor-like kinases (RLKs) or receptor-like proteins (RLPs), form the front line of the plant defense machinery. RLPs lack a cytoplasmic kinase domain for downstream immune signaling, and leucine-rich repeat (LRR)-containing RLPs constitutively associate with the RLK SOBIR1. The RLP/SOBIR1 complex was proposed to be the bimolecular equivalent of genuine RLKs. However, it appears that the molecular mechanisms by which RLP/SOBIR1 complexes and RLKs mount immunity show some striking differences. Here, we summarize the differences between RLP/SOBIR1 and RLK signaling, focusing