Poster: Plant-Pathogen Interactions

Abs # P15032: Indirect activation of the Arabidopsis NBS-LRR protein RPS5 by the Pseudomonas syringae effector AvrPphB

Presenter:	DeYoung, Brody
Authors	DeYoung, Brody  (A)   Ade, Jules  (A)   Golstein, Catherine  (B)   Innes, Roger  (C)
Affiliations:	(A): Indiana University, Biology (B): Grain Legumes Technology Transfer Platform, 12, Avenue George V, 750, (C): Indiana University, Biology (USA)

Nucleotide Binding Site-Leucine Rich Repeat (NBS-LRR) proteins mediate pathogen recognition in both mammals and plants. The molecular mechanisms by which pathogen molecules activate NBS-LRR proteins are poorly understood. In Arabidopsis, resistance to Pseudomonas syringae strains expressing AvrPphB requires RPS5, a member of the CC-NBS-LRR class of R proteins, and PBS1, a protein kinase. We have previously shown that AvrPphB proteolytically cleave PBS1, and this cleavage was required for RPS5-mediated resistance, indicating that AvrPphB is detected indirectly via its enzymatic activity. When transiently expressed in Nicotiana benthamiana leaves, full-length RPS5 protein triggered programmed cell death, but only when co-expressed with AvrPphB and PBS1. RPS5 appears to be kept in the off state by an intramolecular interaction between the NBS and LRR domains. To be activated, the N-terminal coiled-coiled domain of RPS5 must first complex with PBS1. Cleavage of PBS1 by AvrPphB appears to release the NBS domain from inhibition by the LRR domain, activating downstream responses. Mutations in the NBS site that are known to inhibit ATP binding in other NBS-LRR proteins block activation of RPS5, whereas mutations thought to inhibit ATP hyrdrolysis constitutively activate RPS5. Combined, these data suggest that ATP versus ADP binding functions as a molecular switch that is flipped by cleavage of PBS1.