MtAnnexin1 is required for the development of fully functional nodules

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Guillory, Ambre | Fournier, Joëlle | Kelner, Audrey | Auriac, Marie-Christine | Frances, Lisa | Delers, Anaïs | de Carvalho-Niebel, Fernanda

Edité par CCSD -

International audience. MtAnnexin1 (MtAnn1) encodes a Medicago truncatula calcium-and phospholipid-binding proteinof the annexin family1. Its expression is induced in response to Sinorhizobium meliloti both atearly stages in bacterial-inoculated roots and in developing nodules2,3. Notably, expression ofMtAnn1 transcription and translational protein fusions are strongly activated in outer cortical cellsat early stages after root inoculation suggesting its involvement in the reprogramming of host cellsfor rhizobia infection4. MtAnn1 has possible roles in the regulation of ion conductance5 and itscontribution might thus be connected to symbiotic calcium signalling. With this in mind, we haveinvestigated by in vivo microscopy the relationships between the spatio-temporal dynamics ofan MtAnn1-GFP fusion and calcium spiking responses, imaged using a nuclear GECO calciumsensor6 during early host cell reprogramming for rhizobial infection in WT and symbiotic mutantsimpaired for rhizobial infection. This study highlighted a close correlation between calcium spikingand MtAnn1-GFP dynamics in epidermal and outer cortex cells preparing for or undergoinginfection, and revealed new genetic determinants of this process, notably Nodule Inception (NIN),that acts as a master regulator of MtAnn1. Strikingly, mutation in MtAnn1 results in modificationof Ca+2 oscillations in root hairs, reduced levels of rhizobia infection and impaired development ofnodules.

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