Thesis defended on December 10, 2024 to obtain the degree of Doctor of the Université Grenoble Alpes.
Abstract :
Iron (Fe) is an essential element for life and, for this reason, oceanic phytoplankton must adapt to inherent low Fe availability of modern oceans. Thalassiosira is a representative group among diatoms, a highly diverse and successful phytoplankton taxon that accounts for around 20% of global primary production. Two Thalassiosira species have been chosen according to their natural habitats: Fe-poor open-ocean (T oceanica) and Fe-rich coastal (T. pseudonana) waters. In these cells, Fe is mainly required for photosynthesis and respiration, the two central and interdependent bioenergetic processes occurring respectively in the chloroplasts and mitochondria. Consequently, Fe limitation imposes a deep rearrangement of both bioenergetic machineries. The PhD project aimed to understand how Fe limitation modifies the coupling between photosynthesis and respiration in these Thalassiosira species, at both the functional and the morphological level. Very likely, these modifications could be involved in a more efficient energetic management, which is arguably a major requirement under Fe limitation. Our data show that the different physiological responses to Fe limitation of T. oceanica and T. pseudonana are probably linked to a differential remodelling of plastidial compartments. This could be essential to ensure a specific stoichiometry of different cellular compartments and optimize their physical and functional interaction. If the coupling between photosynthesis and respiration seems of higher importance under Fe-limited conditions, it is likely of different natures in each species and probably requires specific architectures of both bioenergetic organelles. Overall, these results contribute to the understanding of the strategies that allow diatoms to thrive in highly different oceanic environments and to clarify the ecological traits of this essential phytoplankton taxon.
Thesis Director : Florence Courtois, Co-director: Giovanni Finazzi
Keywords :
photosynthesis,
chloroplasts, mitochondria; Thalassiosira, diatoms, FIB-SEM