Identification of signaling components downstream of Avr4/Cf-4/SOBIR1 cell surface receptor complex

As we know, tomato leaf mold is a severely fungal disease caused by Cladosporium fulvum that results in significant economic losses in the world. So it is meaningful to focus on the study of the relationship between tomato and Cladosporium fulvum. Plants can deploy numerous cell surface-localized immune receptors to perceive microbe-derived effectors. The Cf protein Cf-4 and its co-receptor SOBIR1 constitutively interact at the plasma-membrane and this Cf-4/SOBIR1 complex acts like a two-component receptor-like kinase (RLK). When the effector Avr4 from invading C. fulvum comes in, the co-receptor BAK1 is recruited to the Cf-4/SOBIR1 complex. Avr4 might directly bind to the extracellular domain of Cf-4 and might act as a “bridge” for BAK1 binding. Trans-phosphorylation events have been shown to take place between the kinase domains of BAK1 and SOBIR1, and probably various downstream RLCKs will be phosphorylated too. Subsequently, these activated RLCKs are probably released from the complex, and in their turn phosphorylate the RBOH enzyme, thereby activating it and inducing ROS production. The defence signal is amplified through a MAP kinase cascade and possibly also by the activation of so-called calcium-dependent protein kinases (CDPKs) that is caused by a strong Ca2+ influx, which then activates hypersensitive cell death. The schematic Model shows in the following Figure1. It is clear that RLCKs and MAP kinases play very important roles in plant immunity, but it is not known which MAPKs and RLCKs are actually involved and how they perform downstream signalling. In this project, we are aim to elucidate this problem.