The potato resistance protein Rx1 multimerizes upon activation by the Coat Protein of PVX

Nucleotide-binding Leucine Rich repeat-type immune receptors (NLRs) are intracellular proteins that sense the presence of pathogen-derived elicitors and subsequently trigger an immune response. NLR proteins have to be strictly regulated as immune responses typically result in death of affected host cells. Regulation mechanisms of NLR activation are well studied, however steps immediately following NLR activation are largely unexplained. Multimerization of NLRs is thought to be involved, although currently no unambiguous paradigm regarding the dynamics of this process exists. Some NLRs form high-molecular weight complexes before activation, others exclusively after activation, or, like Rx1, none could be detected. We investigated NLR complex formation in transgenic N. benthamiana stably expressing the potato Rx1 protein from its native promoter. Activation of the Rx1-resistance response was synchronized by dexamethasone-controlled expression of its elicitor; the Potato Virus X Coat Protein. Rx1 self-associates upon activation: Rx1 homomers are absent before dexamethasone application, a complex could be detected 1 hour after application, but surprisingly is again absent after 2 hours or later. These results show that self-association of NLR proteins upon activation can be transient, explaining the difficulties of detecting them during the normal, non-synchronized infection process as this typically involves few affected cells at any time.