A DNA-Binding Bromodomain-Containing Protein Interacts with and Reduces Rx1-Mediated Immune Response to Potato Virus X.

Plant NLR proteins enable the immune system to recognize 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 DBCP, a bromodomain-containing chromatin-interacting protein. DBCP accumulates in the nucleoplasm and nucleolus, interacts with chromatin, and redistributes Rx1 to the nucleolus in a subpopulation of imaged cells. Rx1 overexpression reduces the interaction between DBCP and chromatin. DBCP 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, Glk1. Rx1 and DBCP act synergistically to reduce Glk1 DNA binding, suggesting a mode of action for DBCP's inhibitory effect on immunity. This study provides new mechanistic insight into the mechanism by which a chromatin-localized NLR complex co-ordinates immune signaling after pathogen perception.