A DNA-binding bromodomain-containing protein interacts with and reduces Rx1-mediated immune response to Potato Virus X

Abstract

Plant NLR proteins enable the immune system to recognise and respond to pathogen attack. An early consequence of immune activation is transcriptional reprogramming. Some NLRs have been shown to act in the nucleus and interact with transcription factors. The Rx1 NLR protein of potato binds and distorts double-stranded DNA. However, the components of the chromatin localized Rx1-complex are largely unknown. Here we report a physical and functional interaction between Rx1 and NbDBCP, a bromodomain-containing chromatin-interacting protein. NbDBCP accumulates in the nucleolus, interacts with chromatin and redistributes Rx1 to the nucleolus in a subpopulation of imaged cells. Rx1 over-expression reduces NbDBCP interactions with chromatin. NbDBCP is a negative regulator of Rx1-mediated immune responses to potato virus X (PVX) and this activity requires an intact bromodomain. Previously, Rx1 has been shown to regulate the DNA-binding activity of a Golden2-like transcription factor, NbGlk1. Rx1 and NbDBCP act synergistically to reduce NbGlk1 DNA-binding suggesting a mode of action for NbDBCP’s inhibitory effect on immunity. This study provides new mechanistic insight into how a chromatin localised NLR complex co-ordinates immune signalling following pathogen perception.