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Intraspecific variation in cadmium accumulation in Arabidopsis halleri: a comparative study between a hyperaccumulator and an excluder

par An, Xinhui
Président du jury Mardulyn, Patrick
Promoteur Verbruggen, Nathalie
Co-Promoteur Corso, Massimiliano
Publication Non publié, 2023-05-17

Thèse de doctorat

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Résumé :

Arabidopsis halleri is one of the best plant models to study metal homeostasis and adaptation to extreme metallic environments. We took advantage of the existence of several non-metallicolous (NM) and metallicolous (M) populations to investigate the molecular and biochemical mechanisms underlying the large intraspecific variation of cadmium (Cd) accumulation and to contribute to a better understanding of Cd tolerance and adaptation to Cd contaminated soils. The A. halleri I16 population is considered as a Cd excluder limiting the translocation of Cd from the root to the shoot. Two genetically close A. halleri populations within the same genetic unit were compared: I30 NM population and I16 M population. The molecular mechanisms linked to the adaptation of I16 to metalliferous soil were investigated as part of my PhD project. The results supported that both alteration of cell wall (CW) composition and regulation of transporter genes played a role in limiting accumulation of metals in A. halleri I16. I16 (M) also compared to another metallicolous population from another genetic unit, the Cd hyperaccumulator PL22 (M) in a work before this PhD. Many differentially expressed genes between I16 and PL22 belonged to i) the CW category and ii) the metal transporter category, as the iron-regulated transporter (IRT1) which can transport iron (Fe), but also Cd, zinc (Zn), manganese (Mn), nickel (Ni) in A. thaliana and is believed to be a main pathway of Cd entry into the plants. Therefore, my PhD work focused on the role of CW and the role of IRT1 in the intraspecific variation of Cd accumulation between I16 and PL22. To analyse the CW part, Cd absorption capacity of CW polysaccharides, CW mono- and poly- saccharides contents and CW glycan profiles were compared between PL22 and I16. Results highlighted that pectin played a major role in the Cd adsorption in CW, and supported an indirect role for β-1,4-galactan (side chain of Rhamnogalacturonan I) in Cd translocation from the root to the shoot, possibly by a joint effect of regulating the length of Rhamnogalacturonan-I sidechains, the pectin structure and interactions between polysaccharides in the CW. In addition, GALACTAN SYNTHASE 1, BIIDXI and LEUNIG-HOMOLOG CW pectin modification-related genes were identified as new potential players involved in Zn translocation from roots to the shoots. To analyse the role of IRT1 in root Cd responses, the promoter and coding sequence of IRT1 from A. halleri PL22 and I16 A. halleri and from A. thaliana Col-0 were cloned, and their promoter activities were further studied via the GUS report in Fe deficient and/or Cd treatment conditions. The results highlighted that the IRT1 promoter sequences from A. halleri PL22 and I16 showed high similarity but were different from the IRT1 promoter of A. thaliana Col-0. Their activities were strongly induced by Fe deficient condition but sharply decreased when Cd was added to the Fe deficient medium or control medium. Moreover, a Fe/Cd competition experiment supported that Cd uptake and transport in PL22 and I16 are not affected by the Fe status. Finally, Cd tolerance and accumulation were also studied in seven (M and NM) A. halleri and A. arenosa populations. This thesis deepens our knowledge of Cd tolerance and Cd accumulation in the model species A. halleri and provides novel tools to manipulate Cd-accumulating in plants.