The DNA Binding Activity of the Potato NBLRR protein Rx1

Abstract

Plant NBLRR proteins are immune receptors named for their characteristic domains. Their mode of action is currently undetermined. The potato NBLRR protein Rx1 has been shown to possess a DNA binding activity in vitro. This thesis presents evidence that Rx1 binds DNA in response to its cognate elicitor CP106 in fixed N. benthamiana leaf material using a novel FRET-FLIM assay. The Rx1 CC and NBARC domains were both shown to possess this DNA binding activity. A nucleocytoplasmic distribution of Rx1 was shown to be required for DNA binding. Potential regulators of Rx1 DNA binding activity were identified using a yeast 2-hybrid screen against the CC domain of Rx1 and their effects on Rx1 DNA binding and Rx1 mediated immunity characterised. The transcription factor NbGLK1 was identified and characterised as a promoter of Rx1 DNA binding using FRET-FLIM and a promotor of Rx1 mediated extreme resistance to PVX. However, NbGLK1 was not found to affect Rx1 mediated HR. The protein NbMLHP was also identified in the yeast 2-hybrid screen. This protein was not found to impact Rx1 DNA binding in FRET-FLIM assays. It was, however, identified as a suppressor of Rx1 mediated extreme resistance to PVX (but not HR), and Rx1 did inhibit NbMLHP DNA binding.