Les séminaires ont lieu sur le Campus Montpellier InstitutAgro/INRAE
de La Gaillarde (2, place P. Viala Montpellier)

Mardi 19 septembre 2023

à 14h00 – Amphi 208 (Coeur d’école)

Jorg Kudla

Institut für Biologie und Biotechnologie der Pflanzen, Universität Münster, Münster, Germany

A bi-kinase module sensitizes and potentiates NOX activation in systemic 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 Ca2+ and H2O2 signals conferring immunity. Our work identified a Ca2+ 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 Ca2+ concentration at the infection site. Subsequently, it facilitates further signal wave proliferation with minimal amplitude requirement, triggering protective defense responses throughout the plant.
Specifically, these findings allow to deduce a model in which in the primary elicitor exposed cells, elicitor binding to PRR complexes activates the RLK BIK1. During defense signaling initiation, BIK1 in turn phosphorylates RBOHD at multiple sites including Ser343/347 resulting in NOX activation and local extracellular ROS production. Paracrine signaling by apoplastic ROS activates Ca2+ channels in neighboring cells, allowing for subtle increases in cellular Ca2+ concentration, that suffice to activate the CBL1/CIPK26/CPK5 module in the absence of PRR activation. Both kinases synergistically phosphorylate and thereby activate RBOHD for maximal ROS production already triggered through minute elevation of cytoplasmic Ca2+ concentration. This allows signal propagation to the next distal cell eventually forming an iterative paracrine cell-to-cell signaling circuit manifesting as propagating Ca2+/ROS signal. In this way, the CBL1/CIPK26/CPK5/RBOHD module concomitantly confers organ-scale signaling initially within the primary challenged leaf, but also subsequently throughout the whole plant resulting in systemic immunity.
Collectively, this 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.

Contact: Alexandre Martinière