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 and HO signals conferring immunity. Here, we identify a Ca sensing bi-kinase module as becoming super-activated through mutual phosphorylation and as 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 concentration. Subsequently, it facilitates further signal wave proliferation with minimal Ca 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.