Figure 5.

SOBIR1 and BAK1 act together to signal for defence. In this model, we propose that SOBIR1 and BAK1 act together to signal for downstream defence activation. In addition to the trans‐autophosphorylation of AtSOBIR1, it is likely that AtSOBIR1 transphosphorylates BAK1. By transphosphorylating BAK1, this co‐receptor becomes activated, followed by the transphosphorylation and activation of AtSOBIR1 by activated BAK1 to enable AtSOBIR1‐induced constitutive immunity (A) and the Cf‐4/Avr4‐mediated HR (B). The arrows represent auto‐ or transphosphorylation events, and the numbers indicate the proposed order of the various phosphorylation events. The phosphorylation and activity of Solanum lycopersicum (Sl)SOBIR1 are likely to be down‐regulated by endogenous phosphatases, when not activated by Avr4 (C). PM, plasma membrane. [Colour figure can be viewed at wileyonlinelibrary.com]