P-218 - Calcium-dependent protein kinases in the regulation of an intrinsically disordered transcription factor in systemic plant immunity

Triggered by a local pathogen attack, plants relay the signal to distal leaf tissue manifesting the systemic immune response, also known as Systemic Acquired Resistance (SAR). Through SAR, distal tissues are primed for possible subsequent pathogen attacks and display enhanced immunity. The manifestation of SAR requires different transcriptional activation and reprogramming events, which are dependent on the key transcriptional regulator SAR DEFICIENT 1 (SARD1). Loss of this transcription factor leads to the loss of SAR, rendering plants unable to establish their immune memory. Understanding the underlying molecular mechanisms behind SAR may help to protect valuable crop plants and yields in the future. Using Phosphoproteomics, our group identified a novel in vivo phospho-site within the N-terminal intrinsically disordered region (IDR) of SARD1, which is targeted by a Calcium-dependent Protein Kinase (CDPK). Using cross-linking MS, we aim to elucidate effects on SARD1 structure and implications on protein-protein/-DNA interaction. Through biochemical and molecular characterization our data indicates a positive influence of SARD1 phosphorylation on both transactivation activity and enhanced resistance of plants against the phytopathogen Pseudomonas syringae pv. tomata DC3000. Altogether, our studies indicate an integration of Ca²⁺-regulated networks and transcriptional activation via the key transcriptional regulator SARD1 to enable and modulate systemic plant immunity.