Thèse les Mécanismes de la Régulation de l'Homéostasie du Nickel chez les Plantes - Vers la Construction d'Un Hyperaccumulateur Synthétique. H/F - Doctorat.Gouv.Fr

Établissement : Université de Toulouse École doctorale : SEVAB - Sciences Ecologiques, Vétérinaires, Agronomiques et Bioingenieries Laboratoire de recherche : LRSV - Laboratoire de Recherche en Sciences Végétales Direction de la thèse : Sylvain MERLOT ORCID 0000000293521184 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-06-01T23:59:59 Malgré son rôle essentiel dans la physiologie végétale, les mécanismes moléculaires impliqués dans l'homéostasie du nickel sont encore mal compris. L'utilisation de la plante modèle Arabidopsis thaliana, qui est très sensible au nickel, n'a pas facilité jusqu'à présent l'analyse de ces mécanismes. Il est intéressant de noter que certaines espèces, telles que Noccaea caerulescens (famille des Brassicacées), sont capables d'accumuler et de tolérer des concentrations élevées de nickel dans leurs feuilles. Ces espèces hyperaccumulatrices de nickel offrent une opportunité originale pour identifier de nouveaux facteurs impliqués dans la régulation de l'homéostasie du nickel.
Ce projet de thèse vise à exploiter les connaissances génomiques récentes acquises sur N. caerulescens afin d'identifier de nouveaux gènes candidats impliqués dans la régulation de l'homéostasie du nickel. Le rôle des gènes candidats identifiés par des analyses de génomique comparative, de transcriptomique, de protéomique et de métabolomique sera étudié par des études fonctionnelles et cellulaires. De plus, des approches transgéniques seront développées chez N. caerulescens et A. thaliana afin de fournir des preuves génétiques confirmant le rôle de ces gènes dans l'accumulation et la tolérance au nickel.
Ces résultats apporteront de nouvelles connaissances fondamentales sur la régulation de l'homéostasie du nickel chez les plantes et sur l'évolution de l'hyperaccumulation de nickel chez N. caerulescens. L'identification des gènes clés impliqués dans ce processus est essentielle pour développer des phytotechnologies permettant d'extraire et de recycler le nickel des sols contaminés.
Transition metals, such as iron, zinc and nickel, are essential for living organisms, including plants. However, high concentrations of these metals can be toxic, triggering oxidative and genotoxic stresses, as well as nutritional imbalances that affect photosynthesis. Therefore, all plant species must regulate metal homeostasis according to their needs and the metal concentration available in the soil. This process depends on a complex network of proteins involved in metal transport (metal transporters) and binding (chaperones), metalloenzymes, and proteins involved in sensing and signaling pathways, as well as a myriad of small molecules that can bind and chelate metals (Krämer 2024). Compared to iron, zinc or manganese, the mechanisms involved in nickel homeostasis regulation are poorly understood, essentially (Merlot 2020). This is primarily because most plants, including the model plant Arabidopsis thaliana, require only trace amounts of nickel and are highly sensitive to it. In contrast, the Brassicaceae species Noccaea caerulescens can accumulate and tolerate a tremendous amount of nickel in its leaves. The mechanisms involved in metal hyperaccumulation likely evolved from an amplification of metal homeostasis mechanisms (Manara et al. 2020). Thus, nickel hyperaccumulator species therefore represent an excellent opportunity to discover novel mechanisms involved in nickel homeostasis regulation.
Over the past few years, our team has used N. caerulescens as a model species to study the mechanisms of nickel homeostasis and hyperaccumulation. Specifically, we developed genomic and transcriptomic resources that enabled us to identify two metal transporters, NcIRT1 and NcIREG2, which are involved in nickel uptake and vacuolar storage, respectively (García de la Torre et al. 2021; Belloeil et al. 2026). Recently, we obtained high-quality genomic assemblies from ten accessions of N. caerulescens originating from different edaphic conditions and displaying distinct metal accumulation capacities. This new information enable us to initiate comparative studies to identify candidate loci associated with nickel hyperaccumulation (Maria Kuzmik & Ophélie Courtin, unpublished). Building on these resources, we developed the HOMONIME project, which aims to use Noccaea caerulescens to discover of new actors of nickel homeostasis in plants by combining of genomic, proteomic and metabolomic approaches (https://anr.fr/Projet-ANR-25-CE20-4366). This project will bring together three partner laboratories with complementary expertise in the biology of metals in plants: the LRSV (Toulouse), the LPCV (Grenoble) and the IPREM (Pau)
More specifically, the first part of the proposed Ph.D. project, in collaboration with the three partners of the project, will aim to identify new candidate genes involved in nickel homeostasis, such as metal transporters, nickel-binding proteins, and metabolomic pathways involved in the synthesis of nickel chelators, using comparative transcriptomics, genomics, proteomics, and metabolomics analysis. These data will be used to create a database of genes involved in nickel homeostasis and accumulation.
The second part of the project will aim to study the activity and role of candidate nickel membrane transporters using heterologous expression in yeast, as well as expression in N. caerulescens hairy roots and in transgenic A. thaliana (Belloeil et al. 2026).
The third part of the project will aim to demonstrate the role of the candidate genes in nickel hyperaccumulation. The strategy will be to induce specific mutations in the candidate genes using CRISPR/Cas9-based methods in N. caerulescens. Since stable transformation of N. caerulescens is still under development, we propose, in parallel, to continue building of a synthetic nickel hyperaccumulator from A. thaliana through successive expression of N. caerulescens candidate genes involved in nickel accumulation. Evaluating nickel tolerance, accumulation and localization at each step of the transformation will reveal the role of the candidate genes in nickel tolerance and accumulation.
This project aims to enhance our fundamental understanding of the molecular mechanisms underlying nickel homeostasis and hyperaccumulation in plants. This knowledge is essential for developing sustainable phytotechnologies that use metal-hyperaccumulating crops to extract and recycle metals from contaminated soils (Rylott and van der Ent 2025). Identifying the loci involved in nickel hyperaccumulation is also important for studying the evolution of this remarkable trait in Brassicaceae and other plant families.

Nous recherchons un candidat titulaire d'un Master 2 ou d'un diplôme équivalent, fortement motivé par l'étude des mécanismes d'adaptation des plantes aux métaux. Des compétences en biologie moléculaire, en biochimie des protéines, en biologie végétale et en évolution seront particulièrement appréciées.