PhD proposal 2023-2026

Context

The Esteban study conducted by Santé Publique France recently showed that the urinary concentration of the toxic trace metal element (ETM) cadmium (Cd) was higher than the toxicological critical value for 48% of the individuals tested (Oleko et al., 2021 ). Studies on French diets (Total Diet Study, EAT) confirm an increase over time in dietary exposure to Cd, with wheat-derived products being a major contributor (ANSES, 2011). Consequently, the European regulation for food contaminants (EC1881/2006) has become stricter and the limit for the Cd content of wheat has been lowered from 0.2 mg Cd/kg to 0.1 mg Cd/kg for bread wheat and 0.18 mg Cd/kg for durum wheat (EC1323/2021). The Esteban and EAT studies also revealed possible health risks for nickel (Ni), lead (Pb) and arsenic (As), indicating the need to reduce these harmful ETMs in food products. On the other hand, it has been observed that the selection of high-yielding wheat varieties during the green revolution was accompanied by a drop in their concentration of iron (Fe) and zinc (Zn) in the grains. This is an issue for people whose diet is mainly or exclusively based on plant products because the risk of deficiency for these trace elements is significant.

Thesis objectives and hypotheses

The proposed thesis work aims to study the allocation of ETMs to grain wheat in order to be able to identify ecophysiological traits useful for the selection of wheats accumulating little toxic ETMs (As, Cd, Ni, Pb) while maintaining or even increasing their Fe and Zn contents. According to the work reported in the literature and those conducted by Ispa, several founding hypotheses are made:

1. There is an exploitable intraspecific variability for some ecophysiological traits associated to the ETM content of grains: size and architecture of the root system which determine the acquisition of ETM TM from the soil, distribution of biomass between organs which conditions the relationships between the source and sink organs for ETM, structure of conductive tissues that transport ETM, ecophysiology of the plant (rhizospheric activity, phenology, etc.).

2. The intraspecific variability of the ecophysiological traits has a significant effect on the ETM content of the grain and it is possible to identify the favourable traits.

3. It is possible to lower the contaminant content of the grains without impacting that of Fe and Zn.

4. The ecophysiological traits of interest do not harm other major agronomic performances, in particular yield.

5. The ecophysiological traits of interest are stable enough in different environments to be of value for varietal selection.

The thesis work will therefore focus on understanding the source-sink relationships between organs for ETM in order to identify and test the ecophysiological traits of interest. This approach will be conducted in parallel with a quantitative genetic approach (GWAS: genome wide association study) conducted elsewhere (outside thesis) and which aims to identify the chromosomal regions (QTL: quantitative traits loci) and genes of interest for reducing the content of contaminants in the grains while preserving the nutritional qualities for Fe and Zn.

Provisional program

The thesis work has two parts and potentially a third if the progress of the work allows it:

1. Study of the intraspecific variability of the ecophysiological traits described above and identification of the most interesting. 40 genotypes of bread wheat and 20 of durum wheat will be grown in the field on two sites with distinct environmental conditions. The detailed study of the root system will be carried out under controlled conditions.

2. Study of the functioning of the allocation of ETMs to and within the spike. The aim is to study the role played by the last node of the stem in the sequestration/distribution of ETMs to the ear and to understand the relationships between the allocation of carbonaceous assimilates and that of ETMs to the different grains of the ear. This work will be carried out on a bread wheat genotype and a durum wheat genotype under controlled conditions.

3. Test of ecophysiological traits of interest in different environments to assess their stability. The bread wheat and durum wheat genotypes presenting the selected ecophysiological traits will be evaluated by agronomic trials conducted on 4 contrasting geographical sites.

The thesis work will implement: experiments/observations in the fields (collaborations Florimond-Desprez, RAGT, Arvalis Institut du Végétal), laboratory experiment to manipulate plant growth (modification of transpiration, of the allocation of assimilates by destruction of the phloem, collaboration with Inrae GDEC, Clermont-Ferrand), elementary chemical analyzes (ICP-MS and OES, collaboration Urave, Inrae Bordeaux) including imaging for the localization and speciation of ETMs in tissues (X-ray microfluorescence , Xanes, tomography: collaboration with Iprem, Univ. de Pau), statistical data processing and modelling.

The thesis is part of the ANR BSWheat project (2023-2027) which provides the funding for the entire thesis including salary and operating costs. The project website can be consulted for more details (https://bswheat.hub.inrae.fr/). The thesis will be conducted in close collaboration with the project partners, and more particularly with the UMR GDEC.

Candidate profile

Strong motivation for scientific research. Experience in plant biology or ecophysiology or agronomy, skills and motivation for data analysis and modelling, strong ability to work collaboratively in project mode (including interpersonal skills and organizational skills), autonomy, initiative and motivation are particularly expected. The work includes a significant experimental field part with associated travel of 2-3 hours.

Application and recruitment workflow

The candidate will have to validate his application by taking the competitive examination for the Environmental Science doctoral school at the University of Bordeaux where he will be registered (end of June, beginning of July 2023). Funding is secured.

Start of the thesis: September 01, 2023 for a period of 3 years

Unit of attachment: UMR ISPA, Inrae, Villenvae d'Ornon

Thesis supervisor: Christophe NGUYEN (Inrae Research Director)

Partners:

1. Inrae, GDEC, Clermond Ferrand, Ecophysiology and genetics of wheat

2. Inrae Urave, plant analysis laboratory, Villenave d'Ornon

3. Iprem-UPPV, in situ imaging and speciation of ETMs

4. Florimond-Desprez and RAGT2N, private wheat breeders

5. Arvalis Plant Institute, Technical Institute, genetics of durum wheat, transfer to the profession

To apply, send a cover letter and a curriculum vitae to christophe.nguyen@inrae.fr