P-093 - The role of the C-terminal tail of C proteins in plant immunity

Cf resistance proteins of tomato that act against fully extracellular pathogenic fungus Cladosporium fulvum are so-called trans-membrane receptor-like proteins (RLPs) that localize at the cell surface. In the resting state, Cf proteins constitutively interact with receptor-like kinase (RLK) SUPPRESSOR OF BIR1 (SOBIR1), whereas upon recognition of matching effector of C. fulvum by the Cf protein, RLK BRI1-ASSOCIATED KINASE (BAK1) is recruited. Overall structure of Cf proteins is typical for LRR-RLPs and consists of an LRR ectodomain, an extracellular juxtamembrane domain (eJM), a TM domain and a intracellular juxtamembrane (iJM) domain. Cf-4 and Cf-9 have identical iJM domains, and Cf-5 and Cf-2 are also identical for this C-terminal tail. Interestingly, Cf-5/Avr5- and Cf-2/Avr2-triggered responses are slow and activate a less strong hypersensitive response (HR) than Cf-4/Avr4- and Cf-9/Avr9-triggered response. Various domains of Cf-5 and Cf-9 were swapped and  chimeric proteins were checked for intensity of HR that they trigger upon their activation to understand role of the C-terminal tail of the Cf proteins in the intensity of the HR. The results suggest that the C-terminal tail of the Cf-proteins, and possibly all RLPs, has a specific role in determining intensity of immune response. Further studies showed that C-terminal of the Cf proteins should be functional, and full length of the C-terminal tail of Cf proteins are required for the activation of  immune signaling.