Добірка наукової літератури з теми "Lhc protein"

Die pflanzliche Light-harvesting complex-Proteinfamilie besteht aus Proteinen mit vielfältigen Funktionen. Dabei ist die Funktion der Light-harvesting-like 3-Proteine (LIL3) sowie der One-helix-Proteine (OHPs) weitestgehend unbekannt. Im Rahmen dieser Arbeit wurde gezeigt, dass LIL3 nicht nur mit der Geranylgeranyl-Reduktase (CHLP), sondern auch mit der Protochlorophyllid-Oxidoreduktase (POR) interagiert. Sowohl CHLP als auch POR werden über die Interaktion zu LIL3 an die Thylakoidmembran gebunden und dadurch stabilisiert. Beide Enzyme liefern die direkten Vorstufen für den von der Chlorophyll-Synthase (CHLG) katalysierten finalen Chlorophyll-Syntheseschritt. Neben der Bestätigung der bereits früher gezeigten Chlorophyllbindung von LIL3 konnte eine Affinität zu den späten Intermediaten der Chlorophyllbiosynthese Proto IX, MgP, MgPMME und Pchlid nachgewiesen werden. Die größte Affinität bestand dabei gegenüber dem Substrat von POR, Pchlid. Basierend auf diesen Erkenntnissen wird LIL3 als Regulator der späten Chlorophyllbiosynthese-Schritte vorgeschlagen: LIL3 transportiert Substrate zwischen den Enzymen und ermöglicht durch die Bindung von CHLP und POR die Synthese der Chlorophyll-Edukte in räumlicher Nähe. Dadurch wird die Versorgung von CHLG mit dessen Edukten favorisiert. Beide OHP-Varianten (OHP1/2) bilden ausschließlich Heterodimere und binden Chlorophyll sowie Carotinoide im Verhältnis 3:1. Die Pigmentbindung basiert auf den konservierten Aminosäuren im Chlorophyllbindemotiv. An das OHP1-OHP2-Dimer bindet der PSII-Assemblierungsfaktor HCF244 und wird dadurch an der Membran verankert. HCF244 stabilisiert das OHP-Heterodimer und beide OHPs stabilisieren sich gegenseitig. Der heterotrimere OHP1-OHP2-HCF244-Komplex ist für die D1-Synthese wesentlich. Es wird vermutet, dass die OHPs an der co-translationalen Beladung von (p)D1 mit Pigmenten beteiligt sind sowie frühe Assemblierungsintermediate von PSII vor überschüssiger Anregungsenergie schützen.<br>The plant light-harvesting complex protein family comprises different members with a variety of functions. However, the function of the light-harvesting-like 3 proteins (LIL3) as well as the one-helix proteins (OHPs) is largely unknown. In this thesis, an interaction of LIL3 not only with geranylgeranyl-reductase (CHLP), but also with protochlorophyllide-oxidoreductase (POR) could be established. LIL3 tethers CHLP and POR to the thylakoid membrane, thereby conferring stability to both enzymes. Both CHLP and POR are synthesizing the direct chlorophyll precursors which are combined to chlorophyll by the subsequent chlorophyll synthase (CHLG). In addition to the chlorophyll binding ability of LIL3 reported earlier, an affinity of LIL3 towards the chlorophyll biosynthesis intermediates Proto IX, MgP, MgPMME, and Pchlide could be shown. Interestingly, the highest affinity of LIL3 was exerted towards Pchlide which is the substrate of POR. Therefore, LIL3 is postulated to shuffle the intermediates between enzymes and brings CHLP and POR in close proximity, which may help to supply CHLG with its substrates. Regarding the function of the OHPs an exclusive heterodimer formation of both the OHP1 and OHP2 variants could be shown. The OHP1-OHP2-heterodimer is able to bind chlorophyll and carotenoids in an approximate 3:1 ratio and pigment binding depends on dimer formation as well as the presence of the conserved amino acids in the chlorophyll binding motif. The PSII-assembly factor HCF244 is anchored to the thylakoid membrane by binding to both OHPs, thereby stabilizing the OHP-heterodimer. The heterotrimeric OHP1-OHP2-HCF244-complex is essential for D1 biosynthesis, although the exact molecular function of HCF244 is still unknown. It is suggested that the OHP-dimer is responsible for co-translational loading of (p)D1 with pigments as well as photoprotection of early PSII assembly intermediates.

The Large Hadron collider (LHC) is a 7\,TeV per beam proton-proton collider. The high stored beam energy of the LHC (361.6\,MJ) requires unprecedented machine protection systems. As demonstrated in September 2008, failure of any one of these systems can lead to considerable damage, and hence delays in the physics schedule. In addition to various quench protection systems and interlocks, a beam collimation system is installed to protect against regular and irregular beam loss, with the aim of protecting against superconducting magnet quenches. The high 8.33T magnetic field of the main arc bending magnets leads to a quench when exposed to beam energy leakage of $5\,\textrm{mW cm}^{-3}$. In order to ensure accurate running of this system, computer simulations must be created. A tracking code, Merlin, has been adapted to simulate the features of the collimation system. New physics models for the simulation of protons interacting in a collimator jaw have been created, and these have been fitted to all experimental scattering data for the first time. Merlin has been used to simulate beam loss in the LHC, and a comparison of the effect of these different physics models have been made. Finally, a luminosity upgrade, the High Luminosity Large Hadron Collider is to be installed in the 2020s. Merlin has also been used to simulate the collimation system for this upgrade in order to ensure reliable future operation of this upgrade.

Negli organismi eucaritici fotosintetici il sistema antenna è composto da subunità codificate dalla famiglia multigenica Light harvesting complex (Lhc). Queste proteine sono coinvolte sia nella raccolta della luce che nella fotoprotezione. In particolare, le proteine antenna del PSII, le subunità Lhcb, sembrano essere implicate nel meccanismo di dissipazione termica dell’energia di eccitazione in eccesso (NPQ, Non Photochemical Quenching). Chiarire i dettagli molecolari dell’induzione dell’NPQ nelle piante superiori si è dimostrata essere una grande sfida. Durante il mio dottorato di ricerca, ho deciso di indagare il ruolo delle subunità Lhcb nel quenching dell’energia di eccitazione utilizzando un approccio di genetica inversa: ho ottenuto mutanti privi di ciascuna delle subunità per capire il loro coinvolgimento nel meccanismo. Qui di seguito sono riassunti i principali risultati ottenuti. Sezione A. Mutanti per le subunità monomeriche Lhc e fotoprotezione È stata studiata la funzione delle proteine antenna CP26, CP24 e CP29 nella raccolta della luce e nella regolazione della fotosintesi, mediante l’isolamento di mutanti knockout (ko) di Arabidopsis thaliana che mancano completamente di una o due di queste subunità. In particolare nella sezione A.1 sono trattati i singoli mutanti koCP24, koCP26 e il doppio mutante koCP24/26. Tutte queste tre linee mostrano una ridotta efficienza di trasferimento di energia dai complessi trimerici di raccolta della luce (LHCII) al centro di reazione del fotosistema II (PSII) a causa della disconnessione fisica degli LHCII dal PSII. Abbiamo osservato che il trasporto di elettroni è diminuito nel genotipo koCP24, ma non nelle piante che mancano di CP26: koCP24 ha una diminuita velocità di trasporto elettronico, un più basso gradiente di pH transmembrana, una ridotta capacità di NPQ, e una crescita limitata. Inoltre, i complessi PSII di queste piante sono organizzati in array bidimensionali nelle membrane granali. Sorprendentemente, il doppio koCP24/26 mutante, mancante sia di CP24 che CP26, recupera la capacità di trasporto elettronico, di NPQ e il tasso di crescita ai livelli del WT. Abbiamo quindi approfondito lo studio del mutante koCP24 per comprendere le ragioni di tali alterazioni fenotipiche. L’analisi della cinetica di induzione di fluorescenza e di misure di trasporto di elettroni nei vari passaggi all’interno della catena fotosintetica hanno suggerito che la limitazione nel trasporto degli elettroni in koCP24 è dovuta alla restrizione del trasporto degli elettroni tra i siti QA e QB del PSII, ritardando la diffusione del plastoquinone. Abbiamo concluso che la mancanza di CP24 altera l’organizzazione dei PSII e limita, di conseguenza, la diffusione del plastoquinone. Tale limitazione è ripristinata in koCP24/26. Nella sezione A.2, è descritta la caratterizzazione della funzione della subunità CP29, estendendo l'analisi alle diverse isoforme CP29. A questo scopo, ho ottenuto mutanti knock-out privi di una o più isoforme CP29 ed analizzato la loro capacità fotosintetica e di fotoprotezione. La mancanza di CP29 non comporta alcuna variazione significativa del trasporto elettronico lineare/ciclico e della capacità di transizione di stato, mentre l’efficienza quantica del PSII e la capacità di NPQ risultano alterati. L’efficienza di fotoprotezione è inferiore in koCP29 rispetto sia al WT che ai mutanti che conservano una singola isoforma. È interessante notare che, mentre l’espressione di una delle isoforme CP29.1 o CP29.2 ripristina la capacità di fotoprotezione, l’espressione di solo CP29.3 non porta all’accumulo della proteina né al recupero del fenotipo fotoprotettivo. Sezione B. Riorganizzazione dinamica delle membrane: dissociazione della B4 e identificazione di due siti di quenching. Le subunità antenna sembrano essere il sito del quenching, mentre l'innesco del meccanismo è mediato da PsbS, una subunità del PSII coinvolta nella rilevazione dell’acidificazione lumenale. Abbiamo indagato il meccanismo molecolare attraverso il quale PsbS è in grado di regolare l’efficienza di raccolta della luce, studiando mutanti di Arabidopsis che mancano dei singoli Lhcbs monomerici. Nella Sezione B.1 è mostrato come PsbS è in grado di regolare l'associazione/dissociazione di un complesso membrana di cinque subunità, composto dalle due proteine monomeriche CP29 e CP24 e dal complesso trimerico LHCII-M (Band 4 Complex - B4C). Abbiamo dimostrato che la dissociazione di questo supercomplesso è indispensabile per l'attivazione dell’NPQ in luce alta. Coerentemente, abbiamo scoperto che mutanti knock-out mancanti delle due subunità componenti la B4, koCP24 e koCP29, sono fortemente influenzati nella dissipazione dell’energia. L'osservazione diretta mediante microscopia elettronica ha mostrato che la dissociazione della B4C porta alla ridistribuzione dei PSII all'interno delle membrane granali. Proponiamo che la dissociazione della B4C renda i due siti di quenching, possibilmente CP29 e CP24, disponibili per lo switch a una conformazione quenchiata. Questi cambiamenti sono reversibili e non richiedono la sintesi/degradazione proteica, consentendo in tal modo cambiamenti di dimensione dell'antenna PSII e l'adattamento a rapide variazioni delle condizioni ambientali. Nella sezione B.2 abbiamo studiato questo meccanismo di quenching mediante analisi di fluorescenza ultra-rapida. Recenti risultati sui tempi di vita di fluorescenza in vivo propongono l’attivazione di due siti indipendenti di quenching durante l’NPQ: Q1 si localizza nei complessi LHCII, funzionalmente staccati dal PSII/RC (centro di reazione) con un meccanismo che richiede PsbS ma non Zea; Q2 si trova ed è collegato al complesso PSII, e dipende dalla formazione di Zea. Questi due eventi di quenching potrebbero originarsi in ciascuno dei due domini fisici granali rivelati dall’analisi di microscopia elettronica come precedentemente riportato. Abbiamo quindi studiato la modulazione del quenching in mutanti knock out confrontando i tempi di vita di fluorescenza in condizioni di quenching e non quenching in foglie intatte: abbiamo ottenuto risultati coerenti con il modello di due siti di quenching situati, rispettivamente, nel dominio C2S2 e nel dominio arricchito in LHCII. I dati indicano che il sito Q1 manca nel koCP24 mentre il Q2 è attenuato nel koCP29. Sulla base dei risultati di questa sezione, possiamo concludere che durante l’induzione dell’NPQ in vivo il supercomplex del PSII si dissocia in due frazioni, separate in domini distinti della membrana granale e protetti ciascuno dalla sovra-eccitazione grazie all’attività di siti di quenching localizzati in CP24 e CP29. Sezione C. Trasferimento di energia di eccitazione e organizzazione della membrana: ruolo delle subunità antenna del PSII. In questa sezione è riportato lo studio del ruolo dei singoli complessi antenna fotosintetici di PSII sia nell’organizzazione di membrana che nel trasferimento dell’energia di eccitazione, utilizzando i mutanti knock out precedentemente isolati. Membrane tilacoidali wild-type e dei tre mutanti mancanti dei complessi CP24, CP26 o CP29, sono stati studiati con spettroscopia di fluorescenza rapida, utilizzando combinazioni differenti di lunghezze d'onda di eccitazione e di detection, al fine di separare le cinetiche del PSI e PSII. Tali misurazioni spettroscopiche hanno rivelato che la mancanza di CP26 non ha modificato l'organizzazione del PSII. Al contrario, l'assenza di CP29 e soprattutto di CP24 porta a cambiamenti sostanziali dell'organizzazione del PSII come evidenziato da un aumento significativo del tempo di migrazione apparente, dimostrando una cattiva connessione tra una parte significativa dell’antenna periferica e i RC. Sezione D.<br>In eukaryotes the photosynthetic antenna system is composed by subunits encoded by the light harvesting complex (Lhc) multigene family. These proteins play a key role in photosynthesis and are involved in both light harvesting and photoprotection. In particular, antenna protein of PSII, the Lhcb subunits, have been proposed to be involved in the mechanism of thermal dissipation of excitation energy in excess (NPQ, non-photochemical quenching). Elucidating the molecular details of NPQ induction in higher plants has proven to be a major challenge. In my phD work, I decided to investigate the role of Lhcbs in energy quenching by using a reverse genetic approach: I knocked out each subunit in order to understand their involvement in the mechanism. Here below the major results obtained are summarized. Section A. Mutants of monomeric Lhc and photoprotection: insights on the role of minor subunits in thermal energy dissipation. In this section I investigate the function of chlorophyll a/b binding antenna proteins, CP26, CP24 and CP29 in light harvesting and regulation of photosynthesis by isolating Arabidopsis thaliana knockout (ko) lines that completely lacked one or two of these proteins. In particular in Section A.1 I focused on single mutant koCP24, koCP26 and double mutant koCP24/26. All these three mutant lines have a decreased efficiency of energy transfer from trimeric light-harvesting complex II (LHCII) to the reaction center of photosystem II (PSII) due to the physical disconnection of LHCII from PSII. We observed that photosynthetic electron transport is affected in koCP24 plants but not in plants lacking CP26: the former mutant has decreased electron transport rates, a lower pH gradient across the grana membranes, a reduced capacity for non-photochemical quenching, and a limited growth. Furthermore, the PSII particles of these plants are organized in unusual two-dimensional arrays in the grana membranes. Surprisingly, the double mutant koCP24/26, lacking both CP24 and CP26 subunits, restores overall electron transport, non-photochemical quenching, and growth rate to wild type levels. We further analysed the koCP24 phenotype to understand the reasons for the photosynthetic defection. Fluorescence induction kinetics and electron transport measurements at selected steps of the photosynthetic chain suggested that koCP24 limitation in electron transport was due to restricted electron transport between QA and QB, which retards plastoquinone diffusion. We conclude that CP24 absence alters PSII organization and consequently limits plastoquinone diffusion. The limitation in plastoquinone diffusion is restore in koCP24/26. In Section A.2 I characterized the function of CP29 subunits, extending the analyses to the different CP29 isoforms. To this aim, I have constructed knock-out mutants lacking one or more Lhcb4 isoforms and analyzed their performance in photosynthesis and photoprotection. We found that lacks of CP29 did not result in any significant alteration in linear/cyclic electron transport rate and maximal extent of state transition, while PSII quantum efficiency and capacity for NPQ were affected. Photoprotection efficiency was lower in koCP29 plants with respect to either WT or mutants retaining a single Lhcb4 isoform. Interestingly, while deletion of either isoforms Lhcb4.1 or Lhcb4.2 get into a compensatory accumulation of the remaining subunit, photoprotection capacity in the double mutant Lhcb4.1/4.2 was not restored by Lhcb4.3 accumulation. Section B. Membrane dynamics and re-organization for the quenching events: B4 dissociation and identification of two distinct quenching sites. Antenna subunits are hypothesized to be the site of energy quenching, while the trigger of the mechanism is mediated by PsbS, a PSII subunit that is involved in detection of luminal acidification. In this section we investigate the molecular mechanism by which PsbS regulates light harvesting efficiency by studying Arabidopsis mutants specifically devoid of individual monomeric Lhcbs. In Section B.1 we showed that PsbS controls the association/dissociation of a five-subunit membrane complex, composed of two monomeric Lhcb proteins, CP29 and CP24 and the trimeric LHCII-M (namely Band 4 Complex - B4C). We demonstrated that the dissociation of this supercomplex is indispensable for the onset of non-photochemical fluorescence quenching in high light. Consistently, we found that knock-out mutants lacking the two subunits participating to the B4C, namely CP24 and CP29, are strongly affected in heat dissipation. Direct observation by electron microscopy showed that B4C dissociation leads to the redistribution of PSII within grana membranes. We interpret these results proposing that the dissociation of B4C makes quenching sites, possibly CP29 and CP24, available for the switch to an energy-quenching conformation. These changes are reversible and do not require protein synthesis/degradation, thus allowing for changes in PSII antenna size and adaptation to rapidly changing environmental conditions. In Section B.2 we studied this quenching mechanism by ultra-fast Chl fluorescence analysis. Recent results based on fluorescence lifetime analysis in vivo proposed that two independent quenching sites are activated during NPQ: Q1 is located in the major LHCII complexes, which are functionally detached from the PSII/RC (reaction centre) supercomplex with a mechanism that strictly requires PsbS but not Zea; Q2 is located in and connected to the PSII complex and is dependent on the Zea formation. These two quenching events could well originate in each of the two physical domains of grana revealed by electron microscopy analysis previously reported. We thus proceeded to investigate the modulation of energy quenching in knock out mutants by comparing the fluorescence lifetimes under quenched and unquenched conditions in intact leaves: we obtained results that are consistent with the model of two quenching sites located, respectively, in the C2S2 domain and in the LHCII-enriched domain. Data reported suggest that Q1 site is released in the koCP24 mutant while Q2 is attenuated in the koCP29 mutant. On the bases of the results of this section, we conclude that during the establishment of NPQ in vivo the PSII supercomplex dissociates into two moieties, which segregates into distinct domain of the grana membrane and are each protected from over-excitation by the activity of quenching sites probably located in CP24 and CP29. Section C. Excitation energy transfer and membrane organization: role of PSII antenna subunits. In this section we investigated the role of individual photosynthetic antenna complexes of PSII both in membrane organization and excitation energy transfer, by using the knock out mutants previously isolated. Thylakoid membranes from wild-type and three mutants lacking light harvesting complexes CP24, CP26 or CP29 respectively, were studied by ps-fluorescence spectroscopy on thylakoids, using different combination of excitation and detection wavelengths in order to separate PSI and PSII kinetics. Spectroscopic measurements revealed that absence of CP26 did not alter PSII organization. In contrast, the absence of CP29 and especially CP24 lead to substantial changes in the PSII organization as evidenced by a significant increase of the apparent migration time, demonstrating a bad connection between a significant part of the peripheral antenna and the RCs. Section D.

The purpose of this study was to establish whether curcumin protects renal proximal tubule cells against ischemic injury, determine whether this postulated cytoprotective effect is mediated through the upregulation of HSP70, and investigate whether the mechanism by which curcumin induces HSP70 expression and confers its protective effect is through activation of the Unfolded Protein Response. LLC-PK1 cells were cultured on collagen-coated filters to mimic conditions of in vivo renal proximal tubule cells and induce cell polarization. Injury with and without curcumin treatment was studied by using chemically-induced ATP-depletion which mimics renal ischemic injury. Cell injury was assessed using a TUNEL assay in order to evaluate DNA cleavage associated with ischemia-induced apoptosis and actin staining used to assess cytoskeletal disruption. Renal ischemic damage was further investigated by determining detachment of the Na-K ATPase from the basolateral membrane, which represents loss of cell polarity. Cells were incubated with curcumin in a dose- and time-response fashion and subsequent levels of HSP70 expression were assessed. Cells were then incubated with AEBSF, an inhibitor of the Unfolded Protein Response (UPR) and HSP70 and BiP/GRP78 (an ER resident chaperone that is upregulated by the UPR) expression levels were evaluated. Results demonstrated that treatment with curcumin during two hours of injury results in significantly less injury-related apoptosis and cytoskeletal disruption compared to control injured cells. It was demonstrated that curcumin induces HSP70 in both a dose- and time-response fashion. Moreover, curcumin treatment resulted in profound stabilization of Na-K ATPase on the basolateral membranes as there was significantly less Na-K ATPase detachment in cells treated with curcumin during two hours of injury compared to control injured cells. Finally, treatment with AEBSF inhibited HSP70 upregulation in curcumin-treated cells as well as inhibiting the GRP78 over-expression otherwise demonstrated in curcumin-treated cells. Protection of proximal tubule cells against renal ischemic injury by curcumin was therefore indicated to be mediated by the activation of the UPR through which HSP70 is upregulated. Curcumins activation of the UPR and induction of HSP70 explains the stabilization of Na-K ATPase on the cytoskeleton and also provides a potential mechanism explaining many of curcumins therapeutic and protective qualities.

Evolución dirigida de proteínas: La evolución dirigida es una técnica que nos permite explorar funciones enzimáticas que no son requeridas en el ambiente natural. Esta técnica, simula procesos genéticos naturales y de selección. Esta estrategia se utiliza cuando un diseño racional es muy complicado. Consiste en una repetición de ciclos de diversificación y selección que llevan a la acumulación de mutaciones benéficas. Aquí se presenta dos ejemplos de evolución dirigida con los cuales se ha trabajado directamente: la ADN polimerasa del organismo  Thermus aquaticus usada comúnmente en PCR, y la proteína LacI que regula la expresión de genes usados para el metabolismo de lactosa en E. Coli.<br>Directed evolution allows us to explore protein functionalities not required in the natural environment. It mimics natural genetic processes and selective pressures. This approach is used when the molecular basis is not completely understood and rational design is a difficult task. This approach consists of serial cycles of consecutive diversification and selection which eventually lead to the accumulation of beneficial mutations. Here are presented two cases where directed evolution is used to modify two different proteins: Taq polymerase, enzyme used for DNA extension in PCR, and the LacI repressor protein which regulates gene expression on E.coli.

Les diatomées constituent le principal groupe du phytoplancton dans les océans, contribuant à près de 20% de la production primaire globale. Dans leur environnement très variable, les diatomées sont particulièrement efficaces dans leur capacité à ajuster leur activité photosynthétique en dissipant sous forme de chaleur l’énergie lumineuse absorbée en excès, par un processus appelé le « Non-Photochemical Quenching of chlorophyll fluorescence », (NPQ). Chez la diatomée modèle, Phaeodactylum tricornutum, il a été montré que LHCX1, une protéine proche des antennes photosynthétiques, est impliquée dans le NPQ. Par des approches intrégrées de génétique, biologie moléculaire, biochimie, imagerie des cinétiques de fluorescence et spectroscopie ultrarapide, j’ai étudié le rôle de la famille des LHCX chez P. tricornutum. J’ai tout d’abord pu corréler une expression différentielle des 4 gènes LHCX de P. tricornutum avec différentes dynamiques de NPQ et activités photosynthétiques, dans différentes conditions de lumiére et nutriments. En localisant les LHCX dans les differents complexes photosynthétiques et les différents sites de dissipation d’énergie, j’ai pu proposer un modèle de régulation dynamique du NPQ impliquant à court terme principalement LHCX1 au niveau des centres réactionnels, et une autre isoforme, possiblement LHCX3, au niveau des antennes lors d’un stress lumineux prolongé. Enfin, par le criblage d’une série de mutants potentiellement dérégulés dans leur contenu en LHCXs, j’ai pu identifier des lignées avec un NPQ altéré qui pourront constituer des nouveaux outils de recherche. Dans l’ensemble ce travail de thèse a permis de mettre en évidence la diversification fonctionnelle et l’importance de la famille des LHCX dans la fine modulation des capacités de collecte de lumière et de photoprotection, expliquant sans doute en partie le succès des diatomées dans leur environnement très fluctuant<br>Diatoms dominate phytoplanktonic communities in contemporary oceans, contributing to 20% of global primary productivity. In their extremely variable environment, diatoms are especially efficient in adjusting their photosynthetic activity by dissipating as heat the light energy absorbed in excess, through a process called “Non-Photochemical Quenching of chlorophyll fluorescence”, (NPQ). In the model diatom Phaeodactylum tricornutum, it has been shown that LHCX1, a photosynthetic antenna-related gene, is involved in the NPQ process. Through integrated approaches of genetics, molecular biology, biochemistry, study of the kinetics of chlorophyll fluorescence yields and ultrafast spectroscopy, I studied the role of the LHCX family in the photoprotection activity of P. tricornutum. I first correlated a differential regulation of the 4 P. tricornutum LHCX genes with different dynamics of NPQ and photosynthetic activity, in different light and nutrient conditions. By localizing the LHCXs in fractioned photosynthetic complexes and the different sites of energy dissipation, I was able to propose a model of dynamic regulation of NPQ capacity involving mainly the LHCX1 in the reaction centers, during short-term high light responses. During prolonged high light stress, the quenching occurs mainly in the antennas, potentially mediated by the LHCX3 isoform. Finally, using photosynthetic parameters, I screened a series of transgenic lines putatively deregulated in their LHCX amount, and I identified lines with altered NPQ, which could represent novel investigation tools. Altogether, this work highlighted the functional diversification and the importance of the LHCX protein family in the fine-tuning of light harvesting and photoprotection capacity, possibly contributing to explain diatoms success in their highly fluctuating environment