PhD position: Description by spectrometric and spectroscopic analyses of the chemical forms of nickel in (hyper)accumulator plants. M/F

Job Description

Thesis Subject

Nickel is an essential metal for plants, but is toxic when present in excess, affecting photosynthesis and inducing genotoxic and oxidative stress. All plants must therefore finely regulate nickel homeostasis according to the nickel available in the soil and their needs. The mechanisms involved in regulating nickel homeostasis in plants are still poorly understood. Some rare species, known as hyperaccumulators,
accumulate extremely large quantities of nickel in their leaves without showing any signs of toxicity, and it is now accepted that this property results from an exacerbation of the mechanisms involved in nickel
homeostasis.
The objective of this PhD thesis is to progress in the understanding of the mechanisms involved in nickel homeostasis and hyperaccumulation, particularly in targeting new players (transporters, chelators, nickel-binding proteins). The approach will be based on state-of-the-art analytical techniques for metal speciation and imaging, and the work will be conducted in collaboration with plant biologists expert in transcriptomics and metalloproteomics. It will focus on the hyperaccumulator plant Noccea caerulescens as well as the model plant Arabidopsis thaliana, which will be used to construct a synthetic nickel hyperaccumulator by sequential genetic transformation to overexpress the genes involved in nickel homeostasis in specific tissues. This knowledge could support the development of phytotechnologies aimed at extracting and recycling nickel present in some contaminated soils and, more broadly, to understand the mechanisms involved in metal accumulation in plants.
More specifically, the PhD work will rely on analytical techniques based on elemental mass spectrometry (ICP-MS) and molecular mass spectrometry (LC-ESI-Orbitrap-MS), as well as imaging techniques (X-ray microfluorescence) and speciation techniques (X-ray absorption spectroscopy) from synchrotron radiation.

Some soils contain high concentrations of nickel (Ni) due to specific geological conditions (e.g. ultramafic soils) or human activity. This contamination is an issue in terms of environmental and human health. A few plants known as hyperaccumulators, such as the species Noccaea caerulescens (Brassicaceae), tolerate high concentrations of Ni in the soil and are able to accumulate very large amounts of the metal in their aerial parts. Although known for a long time, the mechanisms involved in this hyperaccumulation are still poorly understood, and it is now known that nickel hyperaccumulation results from an exacerbation of the mechanisms involved in the homeostatic regulation of the metal (Deng et al., 2018; Manara et al., 2020; Merlot et al., 2021). These mechanisms include a variety of membrane transporters, small organic molecules, and metalloproteins involved in metal transport and complexation. For instance, it has been shown that organic acids (e.g., malate and citrate), histidine, and nicotianamine can complex nickel in the xylem of N. caerulescens (Mari et al., 2006; Ouerdane et al., 2006), enabling significant translocation of the metal. However, it is difficult to study these regulatory mechanisms in the model species Arabidopsis thaliana due to its high sensitivity to nickel. It may therefore be appropriate to take advantage of the unique physiology of the hyperaccumulator N. caerulescens to study these mechanisms. Ni-hyperaccumulating species also offer the opportunity to develop phytotechnology strategies (phytomining, agromining) to extract metals from soils.

The global objective of this PhD thesis is to better understand the mechanisms involved in nickel homeostasis and hyperaccumulation in plants, with a particular focus on the speciation and localization of the metal. Specifically, the objectives are 1) to set-up appropriate mass spectrometry techniques to identify and quantify molecules, potentially new ones, involved in metal binding, and 2) to implement micro-X-ray fluorescence imaging and X-ray absorption spectroscopy techniques using synchrotron radiation to determine, respectively, the localization of nickel at the tissue and cellular levels and to identify its ligands, 3) to determine the role of certain transporters and genes in nickel accumulation through the use of specific accessions and mutants.
The thesis is based on an interdisciplinary approach using chromatography and mass spectrometry tools (Ouerdane et al., 2006; Flis et al., 2016) as well as imaging techniques (synchrotron-based micro-X-ray fluorescence, µXRF, Huguet et al., 2015; Isaure et al., 2015) and speciation techniques (X-ray absorption spectroscopies, XANES/EXAFS, Huguet et al., 2015; Isaure et al., 2015).
The work, based in Pau, will be conducted in collaboration with the LRSV and the LPCV. The Ph.D. student will be involved in all stages of the project, from setting up the cultures to performing the analyses.

The candidate should hold a master degree in environmental chemistry, analytical chemistry, physico-chemistry or equivalent. He/she should have strong interest in performing experimental and analytical work in the laboratory. He/she will be able to work autonomously and rigorously. He/she has strong interest for work in collaboration and will work occasionnaly in partners' lab (Toulouse, synchrotron missions...). Driving licence will be a plus. Skills in writing. English required and French speaking is a plus.

Your Work Environment

IPREM institute is a joint research unit (UMR 5254) CNRS and Université de Pau et des Pays de l'Adour (UPPA). Research activities focus on the development of fundamental knowledge in physical chemistry, analytical chemistry and microbiology, in relation to environment and materials. IPREM is composed of three scientific Teams. The CME Team (Environmental Chemistry and Microbiology) focuses on contaminants and trace elements in the environment, and the CAPT Team (Analytical, Physical and Theoretical Chemistry) focuses on the development of analytical chemistry methods. To study chemical species, their transformations and their interactions with living organisms, our laboratory uses various analytical chemistry techniques (hyphenated techniques based on mass spectrometry, isotopes, etc…), as well as imaging and speciation techniques based on synchrotron radiation (XRF, XAS). The institute hosts state-of-the art Platform for Mass Spectrometry instruments (Platform Mass Spectrometry) dedicated to metal-speciation analysis (elemental, molecular and isotopic).
The PhD student will be enrolled in the Doctoral School 'Sciences Exactes et leurs Applications' of UPPA (https://ed-sea.univ-pau.fr/fr/index.html).

Constraints and risks

Assignments in Toulouse and the synchrotron

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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