The potato Rx1 protein confers resistance to most Potato Virus X strains and has proven to be a valuable model for understanding R protein functioning.
The resistance response upon recognition of the virus coat protein (CP) is fast and under normal circumstances does not require the induction of cell death to stop virus replication. Rx1 is a modular protein consisting of a CC, NB-ARC and LRR domain, which act in concert via several intramolecular interactions. Recognition of the coat protein is mediated by the C-terminal half of the LRR domain, resulting in the activation of a defense response. The N-terminal half of the LRR interacts with the NB-ARC domain in the absence of the elicitor, keeping the protein in an inactive state.
The exact role and structure of the CC-domain has not been determined, but recently two independent studies showed that it interacts with a Ran GTPase Activating Protein (RanGAP2) (Sacco et al. 2007; Tameling and Baulcombe 2007). Furthermore, it has been shown that the CC can interact with the NB-ARC-LRR and recently, we have shown that this domain accumulates in both the cytoplasm and nucleus (Slootweg et al., in prep).
In this research project, we will investigate the structure-function relationships of the CC domain of Rx1. We will study the inter- and intramolecular interactions and the predicted 3D model of the CC domain using fluorescent protein fusion constructs, which will be tested for proper functioning in trans-complementation assays on leaves of N. benthamiana. Molecular interactions will be monitored using microspectroscopic techniques like FRAP and FRET.