Doctorate thesis of National Institute of Further Education in Agricultural Science

Wednesday, September 13, 2017

Control of the accumulation of toxic cations in rice by changing carriers, architecture or anatomy root: application to a culture contaminated with Cesium-137 soil

Sonia Mohamed
BPMP, “Ion transport and adaptation to environment in cereals” team
AGAP – Amélioration Génétique et Adaptation des Plantes

Jury :
Emmanuel Guiderdoni – Cadre scientifique des EPIC Cirad – Directeur de thèse
Anne-Aliénor Véry – Chargé de recherche CNRS – CoDirecteur de thèse
Nathalie Léonhardt – Chercheur CEA rang B CEA – Rapporteur
Christophe Salon – Directeur de recherche INRA – Rapporteur
Jacques Le Gouis – Directeur de recherche INRA – Examinateur
Pierre Berthomieu – Professeur SupAgro – Examinateur

Abstract
The nuclear accident in Fukushima on 11 March 2011 resulted in the release of radionuclides, mainly cesium, which was retained by clay in the first few centimeters of the ground. The objective of the thesis was to obtain ideotypes of rice limiting the entry of 137Cs by the roots, and its translocation to the aerial parts.
In order to address this problem, the identification and characterization of the genes involved in the entry of cesium into the plant was a major step. The results obtained in yeasts but also in planta confirmed the involvement of the potassium transporter OsHAK1 as the major carrier. A screening of yeast mutants for the OsHAK1 gene made it possible to generate 2 mutations which lead to a reduction in the permeability of the transporter for Cs+. An in-plant validation using Crispr / Cas9 technology would allow specific insertion of the different mutations during the double-strand break in the OsHAK1 gene by homologous recombination.
As cesium is only concentrated in the first few centimeters of the soil, root architecture represents a major stake in terms of cesium absorption. The second aspect of the study was to evaluate the influence of the modification of the root architecture of rice on its ability to capture the radio-element in the superficial soil horizons. For this we used the natural or induced diversity present in Oryza sativa L. In addition to the NIL-DRO1 line, known for its deep rooting, we chose to use an almost isogenic line affected in the gravitropism of the root system. Our results have not been able to confirm statistically that deep rooting limits the acquisition and storage of cesium in the aerial parts, but they have allowed us to improve the characterization of indica and japonica materials through an experimental device designed To mimic an artificial contamination found in Fukushima.
All the results obtained in the course of this research could have direct applications in terms of the behavior to be adopted in the event of leakage of radioactivity at the level of nuclear power plants located near agricultural crops.