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A nuclear-targeted cameleon demonstrates intranuclear Ca2+ spiking in Medicago truncatula root hairs in response to rhizobial nodulation factors.

Abstract : Lipochitooligosaccharide nodulation factors (NFs) secreted by endosymbiotic nitrogen-fixing rhizobia trigger Ca(2+) spiking in the cytoplasmic perinuclear region of host legume root hairs. To determine whether NFs also elicit Ca(2+) responses within the plant cell nucleus we have made use of a nucleoplasmin-tagged cameleon (NupYC2.1). Confocal microscopy using this nuclear-specific calcium reporter has revealed sustained and regular Ca(2+) spiking within the nuclear compartment of Medicago truncatula root hairs treated with Sinorhizobium meliloti NFs. Since the activation of Ca(2+) oscillations is blocked in M. truncatula nfp, dmi1, and dmi2 mutants, and unaltered in a dmi3 background, it is likely that intranuclear spiking lies on the established NF-dependent signal transduction pathway, leading to cytoplasmic calcium spiking. A semiautomated mathematical procedure has been developed to identify and analyze nuclear Ca(2+) spiking profiles, and has revealed high cell-to-cell variability in terms of both periodicity and spike duration. Time-lapse imaging of the cameleon Förster resonance energy transfer-based ratio has allowed us to visualize the nuclear spiking variability in situ and to demonstrate the absence of spiking synchrony between adjacent growing root hairs. Finally, spatio-temporal analysis of the asymmetric nuclear spike suggests that the initial rapid increase in Ca(2+) concentration occurs principally in the vicinity of the nuclear envelope. The discovery that rhizobial NF perception leads to the activation of cell-autonomous Ca(2+) oscillations on both sides of the nuclear envelope raises major questions about the respective roles of the cytoplasmic and nuclear compartments in transducing this key endosymbiotic signal.
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Submitted on : Saturday, May 30, 2020 - 7:18:44 PM
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Björn J Sieberer, Mireille Chabaud, Antonius C Timmers, André Monin, Joëlle Fournier, et al.. A nuclear-targeted cameleon demonstrates intranuclear Ca2+ spiking in Medicago truncatula root hairs in response to rhizobial nodulation factors.. Plant Physiology, Oxford University Press ; American Society of Plant Biologists, 2009, 151 (3), pp.1197-206. ⟨10.1104/pp.109.142851⟩. ⟨hal-02659817⟩

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