Thesis defence – Université Montpellier

Wednesday, 17 December 2025 at 2:00 p.m. – Amphi Lamour
Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)

Timothy Mozzanino

will publicly defend his thesis entitled

Etude de la variation génétique naturelle de la réponse des plantes à l’élévation des teneurs en CO2 atmosphérique

Doctoral school : GAIA – Biodiversité, Agriculture, Alimentation, Environnement, Terre, Eau
Spéciality : BIDAP – Biologie, Interactions, Diversité Adaptative des Plantes
University : Université Montpellier
Reasearch unit : IPSiM –  Institut for Plant Sciences of Montpellier

Jury  :

Abstract :
The increase in atmospheric carbon dioxide (CO₂) is one of the main drivers of global climate change and strongly influences plant physiology, mineral nutrition, and growth. The objective of this thesis is to identify and characterize genes involved in the plant response to elevated CO₂, by combining genome-wide association studies (GWAS) with physiological analyses in Arabidopsis thaliana.
Analysis of relative changes in mineral element content in response to CO₂ led to the identification of two key genes: GATA4, involved in the regulation of nitrogen metabolism, and MIC, associated with iron (Fe) variation.
The Manhattan plot analysis for nitrogen content revealed a region on chromosome 3 containing GATA4, a transcription factor regulating genes related to nitrate assimilation (GLN2, NLP2, NLP3) and cell wall remodeling. Transcriptomic analyses (TARGETseq and RNA-seq) confirmed its role as an integrator between metabolism and growth. The gata4 mutant exhibits reduced biomass and photosynthetic activity without alteration in sucrose content, suggesting a defect in starch synthesis or degradation. Moreover, gata4 does not display the CO₂-induced root elongation observed in the wild type, indicating a disruption of cell division and auxin signaling. The interaction of GATA4 with HXK1 signaling, together with its transcriptional regulation by HY5, supports the existence of a HY5–GATA4 regulatory module coordinating light, carbon, and nitrogen signaling. These results identify GATA4 as a central integrator of the CO₂ response, adjusting metabolic and growth processes according to carbon availability.
In parallel, the analysis of relative changes in Fe content led to the characterization of a new gene, MIC, associated with the negative impact of elevated CO₂ on iron concentration. The mic mutant accumulates higher levels of Fe under elevated CO₂, suggesting a role in metal homeostasis. Annotated as a Fe³⁺–dicitrate permease, MIC may participate in intracellular iron transport, possibly at the Golgi apparatus, where it is predominantly localized. Its expression is not regulated by iron availability but its protein abundance is modulated by CO₂, indicating a post-transcriptional control. Heterologous complementation assays and high-resolution imaging approaches (CryoNanoSIMS) will help confirm its function and elucidate Fe dynamics at the subcellular level.
Together, these results reveal two distinct modes of plant response to CO₂: a transcriptional regulation through GATA4 and a post-translational regulation through MIC. CO₂ thus emerges as a complex environmental signal inducing specific molecular responses for each mineral element. To identify the genetic determinants of CO₂ perception, new GWAS combining several A. thaliana natural populations are proposed, as well as the analysis of CO₂-sensing mutants (MPK4, MPK12, CBC1).

Mots-clés : Natural genetic variation, CO2, Nutrition, Adaptation, Arabidopsis, Wheat