A bi-kinase module sensitizes and potentiates plant immune signaling

Systemic signaling is an essential hallmark of multicellular life. Pathogen encounter occurs locally but triggers organ-scale and organismic immune responses. In plants, elicitor perception provokes systemically expanding Ca 2+ and H 2 O 2 signals conferring immunity. Here, we identify a Ca 2+ sensing bi-kinase module as becoming super-activated through mutual trans-phosphorylation and imposing synergistically enhanced NADPH oxidase activation. A combined two-layer bi-kinase/substrate phospho-code allows for sensitized signaling initiation already by near-resting elevations of Ca 2+ concentration at the infection site. Subsequently, it facilitates further signal wave proliferation with minimal amplitude requirement, triggering protective defense responses throughout the plant. Our study reveals how plants build and perpetuate trans-cellular immune signal proliferation while avoiding disturbance of ongoing cellular signaling along the path of response dissemination. One sentence summary Mutual trans-activation of a Ca 2+ sensing bi-kinase module potentiates NADPH oxidase activation to facilitate systemic immunity.