Description du projet
Sur la piste d’une évolution endosymbiotique potentielle
Les plastes, y compris les chloroplastes, sont des organites photosynthétiques présents dans les organismes eucaryotes. Les chloroplastes étaient à l’origine des cyanobactéries qui ont été internalisées par des eucaryotes dans le cadre d’une relation symbiotique (endosymbiose). Avec le soutien du programme Actions Marie Skłodowska-Curie, le projet UCYN2PLAST étudiera l’hypothèse selon laquelle nous assistons aux préparatifs évolutifs d’une internalisation similaire. Cette fois, le photosynthétiseur, une algue eucaryote unicellulaire, pourrait être l’internalisateur, absorbant la cyanobactérie fixatrice d’azote qui lui fournit l’azote dont il a tant besoin en échange de la matière organique de l’algue. Le projet évaluera cette hypothèse en recourant à l’analyse métatranscriptomique et à la microscopie électronique combinées à des sondes moléculaires et à des techniques isotopiques quantitatives appliquées à des échantillons marins et à des expériences d’incubation en eau de mer.
Objectif
Symbioses are evident sources of innovation in nature, critical for the evolution of plastids and the success of eukaryotes on Earth. The mechanisms promoting such relationships, however, are difficult to identify, especially between single-celled organisms, and remain largely unknown. A widespread symbiosis was recently discovered in the ocean between an unicellular cyanobacterium (UCYN-A) and single-celled eukaryotic algae (prymnesiophyte). UCYN-A lacks typical cyanobacterial features such as the capacity to perform oxygenic photosynthesis, CO2 fixation or the tricarboxylic acid cycle, and must thus rely on the supply of organic matter from the algal host. In turn, UCYN-A shows a dramatic genome reduction with a high specialization in nitrogen fixation, providing fixed nitrogen to the alga. Given the importance of nitrogen for the algal productivity, it has been hypothesized that UCYN-A could eventually give rise to a nitrogen-fixing plastid in a process analogous to the origin of chloroplasts. This project aims to study the UCYN-A symbiosis both from an evolutionary and a functional point of view: First, the identification and characterization of new associations from marine samples at a global scale through molecular techniques will allow a deep comparison of closely-related symbiotic lineages that will help to understand the evolutionary underpinnings of this symbiosis. Second, nutrient incubation experiments of seawater samples over diel cycles will be performed to identify potential factors regulating the carbon and nitrogen exchange between partners to gain knowledge on the host-symbiont coupling mechanisms. For this purpose, metatranscriptomic analysis and electron microscopy combined with molecular probes and quantitative isotopic techniques (FISH-nanoSIMS) will be applied. Elucidating the mechanisms underlying this unusual nitrogen fixing symbiosis will provide valuable insight into previously unknown processes explaining the evolution of plastids
Champ scientifique
- natural sciencesbiological sciencesmicrobiologyphycology
- natural sciencesphysical sciencesopticsmicroscopyelectron microscopy
- natural sciencesbiological sciencesbiological behavioural sciencesethologybiological interactions
- natural sciencesbiological sciencesgeneticsgenomes
- natural sciencesbiological sciencesbotany
Mots‑clés
Programme(s)
Régime de financement
MSCA-IF - Marie Skłodowska-Curie Individual Fellowships (IF)Coordinateur
75006 Paris
France