Etude de systèmes protéolytiques et anti-protéolytiques impliqués dans la remobilisation de l'azote au cours de la sénescence chez les Brassicacées (Arabidopsis thaliana L., Brassica napus L)

Abstract : Rapeseed (Brassica napus L.) is a field crop plant that is particularly requiring nitrogen (N) and characterized by a low Nitrogen Use Efficiency (NUE), mainly due to a poor Nitrogen Remobilization Efficiency (NRE) during foliar senescence. The optimization of NRE is therefore a major challenge to improve the agro-environmental balance of this crop. Since protein degradation is one of the key processes in the remobilization of N associated with senescence, the objective of this work is to identify and characterize the main actors of proteolysis during natural or induced by N limitation senescence. In the plant model Arabidopsis thaliana grown under high N conditions (HN), we have shown that SAG12 is a major protease during leaf senescence to ensure the remobilization of N essential for yield and seed N filling. Indeed, our work shows that the role of SAG12 is pivotal and that in the absence of its activity, other proteases belonging to the CPs but also to other classes (aspartate proteases; APs) are requested to support the remobilization of foliar N. In this context, AED1 (a CND41-like APs) is particularly interesting since it seems to collaborate closely with SAG12. In addition, this study shows for the first time a root localization of SAG12. In this organ, the role of SAG12 is crucial, in particular to remobilize N from the roots to sustain yield and N content of the seeds when plants face an N limitation. Another aspect of this work was to study other ways of regulating proteolytic activity, focusing in particular on anti-proteolytic systems. This study suggests that a Water Soluble Chlorophyll binding Protein (WSCP), the WSCP1 protein, has effectively a dual function of chlorophyll protection and serine proteases inhibition, which make it a potential candidate to extend leaf lifespan and thus, reduce asynchronism between leaf emptying time and the N seed filling time.Altogether, these results allow to suggest new relevant candidates for the selection of rapeseed varieties with an efficient N remobilization in a context of nitrogen input limitation.
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Maxence James. Etude de systèmes protéolytiques et anti-protéolytiques impliqués dans la remobilisation de l'azote au cours de la sénescence chez les Brassicacées (Arabidopsis thaliana L., Brassica napus L). Agronomie. Normandie Université, 2018. Français. ⟨NNT : 2018NORMC275⟩. ⟨tel-02163516⟩

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