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Longoni, Fiamma
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Longoni, Fiamma
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- PublicationAccès libreStudy of the physiological and molecular functions of ABC1K1 protein during early development of "Arabidopsis thaliana"Photosynthesis is a key bioenergetic mechanism allowing photosynthetic organisms such as plants or algae to convert sunlight energy into chemical energy to produce sugar, while releasing molecular oxygen. This process takes place in a specific cellular organelle called chloroplast. Inside the chloroplast, the components of the photosynthetic machinery required to perform the photochemical part of photosynthesis, are inserted in a highly dynamic structure, the thylakoid membrane. Plastoglobules, small lipoprotein particles (lipid droplets) associated with the thylakoid membrane, are essential for chloroplast lipid metabolism, thylakoid formation and photoprotection. These structures contain a large diversity of neutral lipids some of which have strong antioxidant properties, such as tocopherols, carotenoids or plastoquinone. Most of the plastoglobule proteins are involved in lipids metabolisms. Among them, the ABC1K proteins are involved in the regulation of neutral lipid metabolism and contribute to the maintenance of photosynthetic activity by plastoquinone homestasis. My PhD consists in the study of the physiological and molecular functions of ABC1K1 protein in the early development of Arabidopsis thaliana. In particular, we studied its role in early chloroplast biogenesis under stress-enhancing red and high light conditions. We have discovered a new signaling mechanism in which ABC1K1 promotes the degradation of EX1, a singlet oxygen trigger (1O2), though the FTSH2 protease, particularly active under red light conditions. The accumulation of EX1 in abc1k1 and ftsh2 mutant led to the arrest of chloroplast biogenesis and a greening defect. Mutation of EX1 by CRISPR/Cas9 in the abc1k1 background partially alleviated the greening defect observed in the abc1k1 mutant (Chapter 2.1). During my PhD, we also observed that abc1k1 displayed a variegated phenotype under high light conditions, similarly to the ftsh2 mutant. This result was integrated in the publication called “Plastoquinone homoeostasis by Arabidopsis proton gradient regulation 6 is essential for photosynthetic efficiency” published in the scientific journal “Communication Biology” in 2019 (Chapter 2.2). Finally, we have shown that the dark re-oxidation of the photoactive plastoquinone pool is impaired in the abc1k1 mutant suggesting a defect in the plastoquinone mobility. This defect is restored in the abc1k1/abc1k3 double mutant. This result was integrated in the publication “Mutation of the Atypical Kinase ABC1K3 Partially Rescues the PROTON GRADIENT REGULATION 6 Phenotype in Arabidopsis thaliana” published in the scientific journal “Frontiers in Plant Science” in 2020 (Chapter 2.3). This thesis provides new insight into the role of ABC1K1 and ABC1K3 proteins in theregulation of early chloroplast biogenesis and photosynthesis under stressful light conditions.
- PublicationAccès libreThylakoid Protein Phosphorylation in Chloroplasts(2021-3-26)
; Goldschmidt-Clermont, MichelBecause of their abundance and extensive phosphorylation, numerous thylakoid proteins stand out amongst the phosphoproteins of plants and algae. In particular, subunits of Light Harvesting Complex II (LHCII) and of Photosystem II (PSII) are dynamically phosphorylated and de-phosphorylated in response to light conditions and metabolic demands. These phosphorylations are controlled by evolutionarily conserved thylakoid protein kinases and counteracting protein phosphatases, which have distinct but partially overlapping substrate specificities. The best characterized are the kinases STATE TRANSITION 7 (STN7 / STT7) and STATE TRANSITION 8 (STN8), and the antagonistic phosphatases PROTEIN PHOSPHATASE 1/THYLAKOID ASSOCIATED PHOSPHATASE 38 (PPH1/TAP38) and PHOTOSYSTEM II CORE PHOSPHATASE (PBCP). The phosphorylation of LHCII is mainly governed by STN7 and PPH1/TAP38 in plants. LHCII phosphorylation is essential for state transitions, a regulatory feedback mechanism that controls allocation of this antenna to either PSII or PSI, and thus maintains the redox balance of the electron transfer chain. Phosphorylation of several core subunits of PSII, regulated mainly by STN8 and PBCP, correlates with changes in thylakoid architecture, the repair cycle of PSII after photo-damage as well as regulation of light harvesting and of alternative routes of photosynthetic electron transfer. Other kinases, such as the PLASTID CASEIN KINASE II (pCKII), also intervene in thylakoid protein phosphorylation and take part in the chloroplast kinase network. While some features of thylakoid phosphorylation were conserved through the evolution of photosynthetic eukaryotes, others have diverged in different lineages possibly as a result of their adaptation to varied environments. - PublicationAccès libreHow chloroplasts protect themselves from unfolded proteins(2019-10-15)
; A genetic screen has identified the first signaling component of the unfolded protein response in chloroplasts. - PublicationAccès libreThe kinase STATE TRANSITION 8 phosphorylates Light Harvesting Complex II and contributes to light acclimation in Arabidopsis thaliana(2019-9-19)
; - PublicationAccès librePlastoquinone homoeostasis by Arabidopsis proton gradient regulation 6 is essential for photosynthetic efficiency(2019-6-20)
; ; ; ; ; - PublicationAccès libreProduction by Tobacco Transplastomic Plants of Recombinant Fungal and Bacterial Cell-Wall Degrading Enzymes to Be Used for Cellulosic Biomass Saccharification(2015-6-2)
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