Doctorate thesis of Montpellier 2 University

Thursday, December 12th, 2013


Nitrate signaling depending on the NRT1.1 “transceptor” in Arabidopsis thaliana

Eléonore Bouguyon
BPMP, “Integration of Nutritional Functions” team


Jury :
M. Christian MEYER, IJBP INRA Versailles, Rapporteur
M. Sébastien THOMINE, ISV CNRS Gif-sur-Yvette, Rapporteur
M. Philippe NACRY, BPMP, IBIP, INRA-Supagro Montpellier, Directeur de thèse
M. Bruno TOURAINE, Université de Montpellier II, Examinateur
M. Alain GOJON, BPMP, IBIP, INRA-Supagro Montpellier, Invité
M. Téva VERNOUX, RDP, ENS Lyon, Invité


Abstract :
Plants are able to sense the external availability of nitrate (NO3), a major macro-nutrient. In Arabidopsis thaliana, the NO3 transporter NRT1.1 acts as a sensor that triggers many different adaptive responses, including the regulation of gene expression and lateral root development. In the latter case, a transduction mechanism that involves a NO3-inhibited auxin transport activity dependent of NRT1 has been proposed. However, the molecular mechanism(s) allowing NRT1.1 to control such a large palette of NO3 responses is still largely unknown. Thus the aim of this work was to better understand and characterize the NRT1.1-dependent NO3 signaling pathway(s). Using mutants and transgenic lines expressing point mutated forms of NRT1.1, we uncoupled several of the NRT1.1-dependent responses and thus demonstrated that NR1.1 can sense/transduce NO3 signal through at least three distinct mechanisms at the protein level. This work also largely confirmed the hypothesis that NRT1.1 directly controls lateral root development through its auxin transport activity regardless of the other auxin transporters expressed in lateral root primordia. Finally, we showed that, besides the already well characterized transcriptional NO3-dependent regulation of NRT1.1, this gene is also subjected to complex post-transcriptional regulations. Indeed, on the one hand, NRT1.1 mRNA is stabilized by NO3 in roots whereas, on the other hand, protein accumulation is specifically repressed by NO3 in lateral root primordia. Altogether, these results allowed us to build a comprehensive model of the complex NRT1.1 signaling and open many perspectives to understand how plant “transceptors” (transporter/sensor) can monitor a large variety of adaptive responses to environmental factors.