[ES] Las flores se producen por la actividad del meristemo inflorescente tras la transición floral. En plantas con inflorescencias indeterminadas, como Arabidopsis, el número final de flores producidas por el meristemo inflorescente va a depender de dos factores principales: la tasa de producción de flores del meristemo y la duración de la fase de actividad del meristemo inflorescente. El final de la floración, entendido como el momento en el que la inflorescencia detiene la producción de nuevas flores, está asociado a la parada de la proliferación del meristemo. En este punto, el meristemo deja de iniciar nuevos primordios florales y las flores sin polinizar ya formadas detienen su desarrollo. Ya hace tiempo que se conoce que la producción de frutos y semillas induce la parada del meristemo, pero no se conocen tanto los mecanismos que controlan este proceso. Durante los últimos años, la regulación del final de la floración ha empezado a elucidarse en Arabidopsis. La parada del meristemo al final de la floración está controlada a nivel genético por la ruta FRUITFULL-APETALA2 (FUL-AP2), que modula la capacidad proliferativa del meristemo y el cese de su actividad. También se ha demostrado que la parada proliferativa está controlada a nivel hormonal. Se ha propuesto que las auxinas pueden mediar la señalización entre los frutos y semillas y el meristemo. La regulación y respuesta a citoquininas también se ha propuesto como un factor importante controlando la actividad del meristemo al final de la floración. Finalmente, se ha descrito que los meristemos parados al final de la floración se asemejan a meristemos en dormancia a nivel transcriptómico. En este trabajo nos propusimos ampliar el conocimiento sobre la ruta FUL-AP2, identificando nuevos elementos tanto aguas arriba como aguas abajo. Aguas arriba caracterizamos los genes de la familia SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL), una familia de genes cuyo papel se relaciona con el cambio de fase del meristemo de vegetativo a reproductivo. Nos centramos en parte de aquellos genes SPL que no están regulados por el miR156: SPL1, SPL12, SPL14, SPL16 y su relación con FUL. Observamos que se tratan de represores de FUL y que puedan estar relacionados con la parada de la floración a través de múltiples vías, incluyendo a FLOWERING LOCUS T (FT) y la ruta de respuesta a ácido abscísico (ABA). Aguas abajo, nos centramos en la caracterización funcional de factores de transcripción HOMEOBOX PROTEIN (HB), centrándonos en los genes HB21, HB40 y HB53, genes relacionados con el establecimiento de la dormancia de los meristemos axilares. En este trabajo observamos que estos genes se acumulan al final de la floración y actúan de manera redundante en esta parada de la floración, probablemente a través de un incremento de la respuesta a ABA. Con este trabajo, hemos ampliado el conocimiento sobre la red reguladora de la parada de la floración, caracterizando el papel de elementos adicionales de la misma y aportando evidencias sobre el papel de la señalización por ABA en el control de la parada del meristemo inflorescente. / [CA] Les flors es produeixen per l'activitat del meristem inflorescent rere la transició floral. En plantes amb inflorescències indeterminades, com Arabidopsis, el número final de flors produïdes pel meristem inflorescent dependrà de dos factors principals: la taxa de producció de flors del meristem i la duració de la fase d'activitat del meristem inflorescent. El final de la floració, és a dir, el moment en el que la inflorescència deté la producció de noves flors, està associat a la parada de la proliferació del meristem. En aquest punt, el meristem deixa d'iniciar nous primordis florals i les flors sense pol·linitzar ja formades detenen el seu desenvolupament. Ja fa temps que se sap que la producció de fruits i llavors indueix la parada del meristem, però no es coneixen tant els mecanismes que controlen aquest procés. Durant els últims anys, la regulació del final de la floració ha començat a elucidar-se en Arabidopsis. La parada del meristem al final de la floració està controlada a nivell genètic per la ruta FRUITFULL-APETALA2 (FUL-AP2), que modula la capacitat proliferativa del meristem i el cessament de la seua activitat. També s'ha demostrat que la parada proliferativa està controlada a nivell hormonal. S'ha proposat que les auxines poden mediar la senyalització entre els fruits i llavors i el meristem. La regulació i resposta a citoquinines també s'ha proposat com un factor important controlant l'activitat del meristem al final de la floració. Finalment, s'ha descrit que els meristems aturats al final de la floració s'assemblen a meristems en dormància a nivell transcriptómic. En aquest treball ens vam proposar ampliar el coneixement sobre la ruta FUL-AP2, identificant nous elements tant aigües amunt com aigües avall. Aigües amunt caracteritzem els gens de la família SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL), una família de gens relacionada amb el canvi de fase del meristem de vegetatiu a reproductiu. Ens centrem en part d'aquells gens SPL que no estan regulats pel miR156: SPL1, SPL12, SPL14, SPL16 i la seua relació amb FUL. Observem que es tracten de repressors de FUL i que poden estar relacionats amb la parada de la floració a través de múltiples vies, incloent a FLOWERING LOCUS T (FT) i la ruta de resposta a àcid abscísic (ABA). Aigües avall, ens centrem en la caracterització funcional de factors de transcripció HOMEOBOX PROTEIN (HB), centrant-nos en els gens HB21, HB40 i HB53, gens relacionats amb l'establiment de la dormància dels meristems axil·lars. Observem que aquests gens s'acumulen al final de la floració i actuen de manera redundant en aquesta parada de la floració, probablement a través d'un increment de la resposta a ABA. Amb aquest treball, hem ampliat el coneixement sobre la xarxa reguladora de la parada de la floració, caracteritzant el paper d'elements addicionals de la mateixa i aportant evidències sobre el paper de la senyalització per ABA en el control de la parada del meristem inflorescent. / [EN] Flowers are produced by the activity of the inflorescence meristem after the floral transition. In plants with indeterminate inflorescences, such as Arabidopsis, the final number of flowers produced by the inflorescence meristem depends on two main factors: the rate of flower production by the meristem and the duration of the phase of inflorescence meristem activity. The end of flowering, understood as the moment when the inflorescence stops the production of new flowers, is associated with the meristem proliferative arrest. At this time point, the meristem ceases to initiate new floral primordia and the unpollinated flowers already formed arrest their development. It is well stablished that fruit/seed production induces inflorescence meristem arrest, but the mechanisms controlling this process have remained elusive. During the last years, the regulation of the end of flowering has started to be elucidated in Arabidopsis. The meristem arrest at the end of flowering is controlled at the genetic level by the FRUITFULL-APETALA2 (FUL-AP2) pathway, that modulates meristem proliferative capacity and the cessation of its activity. The meristem arrest has been also shown to be controlled at the hormonal level. Auxins have been proposed to mediate the fruit/seed signal to the meristem. Cytokinins regulation and response have been also proposed as important factors controlling the meristem activity at the end of flowering. Finally, it has been also described that arrested meristems at the end of flowering resemble dormant meristems at the transcriptomic level. In this work we aim to enlarge the existing knowledge about the FUL-AP2 pathway, identifying new elements both upstream and downstream. Upstream, we characterized the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family of transcription factors, a family of genes linked to the phase change of the meristem from vegetative to reproductive. We focus on part of those SPL genes that are not regulated by miR156(SPL1, SPL12, SPL14, SPL16) and their relationship with FUL. We observed that they are FUL repressors and that they may be related to flowering arrest through multiple pathways, including FLOWERING LOCUS T (FT) and the abscisic acid (ABA) response pathway. Downstream, we focus on the HOMEOBOX PROTEIN (HB) family of transcription factors, and more specifically on the HB21, HB40 and HB53 genes, all of them related to the establishment of dormancy of the axillary meristems. In this work we observed that these genes accumulate at the end of flowering and act redundantly at this flowering arrest, probably through an increase in the response to ABA. With this work we have expanded the existing knowledge about the proliferative arrest regulatory network, characterizing novel involved elements and providing evidence on the role of ABA signaling in the inflorescent meristem arrest control. / Sánchez Gerschon, V. (2023). El control del final de la floración: identificación de nuevos reguladores de la parada proliferativa [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/196875

Toxoplasma gondii is an obligate intracellular protozoan parasite of animals and man. The asexual life cycle of Toxoplasma involves three very distinct, but tightly coordinated developmental stages. In nature, the sporozoite (contained within an oocyst) and bradyzoite (contained within a tissue cyst) initiate infection of the intermediate host, followed by rapid differentiation into the actively replicating tachyzoite. When countered by an effective host response, the tachyzoite differentiates back into the latent bradyzoite and this unique ability of Toxoplasma to interconvert between the replicating tachyzoite and the latent bradyzoite within a single host is the cause of life long infection. The transcriptional mechanisms controlling tachyzoite to bradyzoite differentiation and inter-conversion are largely unknown, however, a linkage between the parasite cell cycle and differentiation may underlie these developmental mechanisms. The recent discovery of a family of DNA binding proteins in Apicomplexa (ApiAP2) that are distantly related to the APETALA-2 (AP2) class of plant transcription factors has uncovered an important set of proteins (ApiAP2 factors) that have critical roles in regulating growth and developmental gene expression. Five Toxoplasma ApiAP2s were studied in this thesis project: AP2IX-9, AP2Ib-1, AP2IV-3 (Chapter 2); AP2IV-4 (Chapter 3); and AP2VI-1 (Chapter 4). A major conclusion of this work highlights a novel paradigm in our understanding of the cellular mechanisms regulating stage conversion in Toxoplasma. The study of AP2IX-9 and AP2IV-4 indicate development of the bradyzoite is governed by transcriptional repressors acting at two independent levels, one late in the cell cycle and a second governing the transition from the tachyzoite to the end-stage bradyzoite tissue cyst. The use of repressors to regulate development provides flexibility for the parasite to immediately respond to changing host conditions and modulate the competing needs of expansion and persistence. In addition, the study of AP2VI-1 demonstrates that Toxoplasma employs ApiAP2s that bind chromosome heterochromatin to establish a state of developmental competency AP2IX-9 (Chapter 2) has a unique transient expression profile restricted to early bradyzoite differentiation, and absent form both the tachyzoite and terminal tissue cyst. Disruption of the AP2IX-9 locus resulted in increased tissue cyst formation in vitro while conditional overexpression of AP2IX-9 significantly reduced tissue cyst formation, indicating AP2IX-9 operates as a repressor of bradyzoite development. Consistent with a role as a repressor, AP2IX-9 specifically inhibited the expression of bradyzoite mRNAs including BAG1, B-NTPase and LDH2, common markers for bradyzoite development. Two other ApiAP2s, AP2Ib-1 and AP2IV-3 have similar expression profiles as AP2IX-9 and are candidates for expanding our understanding of this repressor mechanisms regulating development. A number of mRNAs encoding ApiAP2 proteins are dynamically regulated during the tachyzoite cell cycle that also show unique profiles during bradyzoite development. AP2IV-4 (Chapter 3) and AP2VI-1 (Chapter 4) represent two of several cell cycle AP2s whose expression is associated with specific S-phase and mitotic transitions but illustrate divergent roles in regulating growth and development. The expression of AP2IV-4 is exclusive to the tachyzoite stage of development and peak expression coincides with mitosis of the cell cycle. Interestingly, deletion of AP2IV-4 results in the up-regulation of tissue cyst wall and bradyzoite surface antigens in the tachyzoite. The mis-expression of bradyzoite proteins in the tachyzoite indicate AP2IV-4, much like AP2IX-9, is stage specific transcriptional repressor active only late in the tachyzoite cell cycle, likely promoting continued replication of the tachyzoite stage. For AP2VI-1 (Chapter 4), an S phase exclusive factor, we have verified S phase expression using an HA fusion protein at the endogenous locus, determined its DNA binding specificity by EMSA, and developed a genetic model of conditional expression based on the small molecule, Shield-1. Attempts to genetically delete this factor were successful only in laboratory adapted strains of Toxoplasma, indicating AP2VI-1 has an essential function in the bradyzoite developmental pathway. Genome-wide binding (chromatin immunoprecipitation and microarray analysis (ChIP-chip)) regions of AP2VI-1 are indistinguishable from the recently published CenH3 regions (centromere marker) and similarly fall within the H3K9me2 and H3K9me3 methylation patterns (heterochromatin markers) that mark the centromere boundaries. AP2VI-1 was also detected in mature bradyzoites from in vitro or animal tissue cysts. This dual expression profile for AP2VI-1 may suggest this factor has a unique role in chromosome maintenance or stability during developmental transitions.

Clathrin-mediated endocytosis is the process whereby specific cargoes are internalized into coated vesicles from the plasma membrane. Numerous clathrin adaptors facilitate this process by linking the coat protein clathrin to the plasma membrane by associating with PI(4,5)P2 and binding to membrane-bound cargo. Here, I investigated the role of two clathrin adaptors, APβ1/2 and Hip1r, in clathrin-mediated endocytosis. I found that Dictyostelium APβ1/2 functions in both the AP1 and AP2 complexes, unlike vertebrates, which have distinct β subunits for each AP complex. I found that APβ1/2 function is required for several clathrin-dependent processes, including cytokinesis, development and osmoregulation. I also uncovered a role for APβ1/2 in the stability other subunits of the AP1 and AP2 complexes. Finally, phenotypic comparisons of APβ1/2 mutant cells with cells missing subunits that are specific to the AP1 or AP2 complex allowed me to distinguish between endocytic defects and endosomal trafficking defects in clathrin mutants. My investigation of Hip1r centered on the known requirement for Hip1r in actin dynamics during endocytosis and a possible role for Hip1r phosphorylation in regulating actin. To determine how phosphorylation contributes to Hip1r function, I identified a specific serine residue that serves as a Hip1r phosphorylation site. I also identified a novel role for the kinase PKB in Hip1r phosphorylation. I determined that phosphorylation is not required for Hip1r localization to the plasma membrane. Similar to Hip1r, PKB is required for proper actin dynamics during endocytosis. My results support a model in which epsin recruits Hip1r to the plasma membrane during formation of clathrin-coated vesicles. Here, Hip1r functions as both a clathrin adaptor and a negative regulator of actin polymerization. I propose that phosphorylation of Hip1r by PKB triggers a reduction in the affinity of Hip1r for clathrin, which may stimulate actin polymerization and tethering of clathrin-coated vesicles with the actin cytoskeleton. / text

AP2 complex protein is an essential clathrin adaptor protein during clathrin mediated endocytosis. However, this view has been challenged in simple organisms. To gain insight into this conflict, the role of AP2 in clathrin localization and other clathrin related processes were assessed in Dictyostelium discoideum. In Dictyostelium, deleting function AP2 caused mild phenotypes in clathrin membrane localization, cytokinesis, osmoregulation and cell development. This supported the idea that AP2 have significant roles in multicellular organisms but not in unicellular system. Clathrin mediated processes carries important function not only on the plasma membrane but also on some internal organelles. But clathrin coated vesicles on internal organelles are not as well studied as on the plasma membrane. To understand more of the clathrin coated vesicles on internal organelles, the clathrin coated vesicles on Dictyostelium discoideum contractile vacuole were studied. Contractile vacuole associated clathrin coated vesicles contained clathrin adaptor proteins AP2, AP180, and epsin but not Hip1r. The absence of AP180 or AP2 produced abnormal large vacuoles, but the absence of epsin did not cause any detectable contractile vacuole abnormality. The enlarged contractile vacuoles in AP180 minus cells were caused by excessive homotypic fusion among contractile vacuoles. Using both GST-pull down and immunostaining AP180 was identified as the possible adaptor protein for a contractile vacuole-associated SNARE protein, Vamp7B. Therefore recycling Vamp7B from contractile vacuole by AP180 through clathrin coated vesicles could be an efficient way to prevent excessive homotypic fusions among contractile vacuoles. Dictyostelium contractile vacuoles offer a valuable system to study clathrin coated vesicles on cell internal organelles. / text

No description available.

Abiotic stress is one of the major factors that affect food production worldwide and, therefore understanding stress responsive proteins and engineering plants for abiotic stress tolerance is very important. In the present study, the biological role of pea pathogenesis-related 10.4 (PR-10.4; also known as abscisic acid responsive 17; ABR17) in abiotic stress tolerance has been investigated. Our investigation on ribonuclease (RNase) activity of ABR17 suggested that highly conserved histidine-69 and glutamic acid-148 are important for RNase activity. In order to further investigate the biological role(s) of ABR17, transcriptional profiling of pea ABR17-mediated gene expression changes in ABR17-transgenic Arabidopsis thaliana plants was carried out using microarrays. Our results indicated that pea ABR17 modulates many plant growth/development genes most of which are cytokinin (CK) responsive. These results agree very well with previously reported enhanced endogenous CKs in these transgenic plants. However, no significant changes in transcript abundance of CK biosynthetic genes were observed between transgenic and wild-type plants, suggesting an alternate source of CK in ABR17-transgenic plants. It is speculated that ABR17 may act as either a CK reservoir (through its reported CK binding property) or may be responsible for isopentenylated-tRNA degradation (through its demonstrated RNase activity) thereby increasing endogenous CK pools. Furthermore, microarray analysis of salinity stressed ABR17-Arabidopsis indicated that ABR17 modulates many stress responsive genes that included four putative AP2 family genes (RAP2.6-At1g43160, RAP2.6L-At5g13330, DREB26-At1g21910 and DREB19-At2g38340). Functional characterization of these genes suggested that they are transcription factors and they play very important roles in abiotic stress response in addition to growth and development. Moreover, overexpression of RAP2.6L and DREB19 genes enhanced salinity and drought tolerance in Arabidopsis. Taken together, our results suggest that pea ABR17 proteins are important in abiotic stress responses as they may act as source of enhanced CKs and they may also modulate expression of stress responsive genes to enhance stress tolerance in plants. However, additional research aimed at deciphering the links between ABR17 and CK biosynthesis as well as the mechanism of ABR17-mediated gene expression changes should be conducted in order to get more insights into the biological roles of PR10 proteins in planta. / Plant Science

WRINKLED 1(WRI1), a member of AP2/EREBP class of transcription factors regulates carbon allocation between glycolytic and fatty acid biosynthetic pathway. Additionally, among the four WRI1 paralogs in arabidopsis, WRI3 and 4 but not WRI2, are also able to increase fatty acid content in different tissues. While the role of WRI1 is well established in seeds, the potential or WRI1 or its paralogs as master regulators in oil-rich nonseed tissues is poorly understood. Recent transcriptome studies of avocado (Persea americana) mesocarp revealed that the ortholog of WRI2, along with WRI1 and WRI3 was highly expressed during oil accumulation. Through transient expression assays, we further demonstrated that both PaWRI1 and PaWRI2 can accumulate oil in tobacco leaves. We conducted a comprehensive and comparative in silico analysis of WRI paralogs from a dicot, monocot and a basal angiosperm to identify distinct features associated with function. These data provide insights into the possible evolutionary changes in WRI1 homologs and allow for identification of new targets to enhance oil biosynthesis in diverse tissues.

Vers une analyse fonctionnelle du TALome des souches Africaines de Xanthomonas oryzae pv. oryzae : identification d’une nouvelle stratégie de virulence. Les bactéries du genre Xanthomonas injectent à l’intérieure de la cellule hôte des effecteurs de type TAL (Transcription Activator-Like) qui agissent comme des facteurs de transcription spécifiques à l’aide d’un nouveau domaine de liaison à l’ADN qui est programmable. La bactérie pathogène du riz Xanthomonas oryzae pv. oryzae (Xoo) contient un nombre important de gènes TAL (de 9 à 16) dans leur génome. Tandis que un ou deux de ces gènes codent des facteurs de virulence majeurs, la contribution relative de chacun des autres gènes TALs à la pathogénie de Xoo reste encore obscure. Afin d’élucider cela, le génome complet de trois souches Africaines de Xoo a été analysé à l’aide de la technologie de séquençage PacBio. Une analyse phylogénétique des trois TALomes combinée à des prédictions de cibles des TAL in silico montre que les TALomes Africains sont très conservés et génétiquement distants des correspondants asiatiques. Les gènes TAL individuels des souches Africaines de Xoo MAI1 et BAI3 ont été sous-clonés via une nouvelle méthode d’analyse à moyen débit dans un vecteur d’expression compatible avec des tests de pathogénie. Un test systématique de « gain de virulence » de la fonction de chacun des 11 haplotypes TAL a été réalisé en les introduisant dans la souche de Xoo X11-5A qui est peu virulente et ne contient naturellement pas de TALs, révélant Tal2 comme un nouveau facteur de virulence majeur dans les souches Africaines de Xoo. La prédiction in-silico des cibles de Tal2 dans le promoterome de riz associée à des expériences de QRT-PCR ont mis en évidence deux cibles de virulence candidates de Tal2, OsTFX1 qui code un facteur de transcription de type bZIP déjà rapporté comme gène de sensibilité S commun à différentes souches Asiatiques de Xoo, et Os09g39810 (aussi appelé ici OsERF#123), qui code pour un facteur de transcription de la famille des protéines de type « ethylene response factor ». Des test de pathogénie ont confirmé l’induction spécifique de ce dernier obtenue à l’aide de TAL artificiels confère une sensibilité accrue du riz aux souches africaines de Xoo. Des expériences de type 5’-RACE ont montré que Tal2 induisait l’expression d’un transcrit alternatif caractérisé par une séquence « leader » plus longue. Nous faisons l’hypothèse que l’accumulation de ce transcrit alternatif spécifique de Tal2 interfère avec la fonction endogène de ce facteur de transcription de type ERF, dont nous montrons qu’elle est potentiellement impliquée dans l’induction des réponses de défense de la plante.Un autre axe de recherche de cette thèse a été d’initier la caractérisation des bactérioses du riz au Vietnam, qui est l’un des plus grands exportateurs de riz au monde. Tandis que la bactériose vasculaire due à Xoo a été rapportée plusieurs fois dans ce pays, une description formelle de la bactériose à stries foliaires causée par X. oryzae pv. oryzicola faisait défaut. Ici, nous avons confirmé l’occurrence de la BLS au Nord du Vietnam à l’aide d’une PCR-multiplexée. L’échantillonnage a également montré que les deux pathovars étaient présents dans cette région et parfois retrouvés sur la même feuille. Des analyses de la dynamique des populations de Xo et l’analyse fonctionnelle des TALomes serviront de base pour établir de nouvelles stratégies de lutte contre les xanthomonads infectant le riz au Vietnam. / Towards a functional analysis of African Xanthomonas oryzae pv. oryzae TALomes : identification of a novel virulence strategy Bacterial plant-pathogenic Xanthomonas translocate Transcription Activator-Like (TAL) effectors into plant cells to function as specific plant transcription factors via a novel programmable DNA-binding domain. Rice-pathogenic Xanthomonas oryzae pv. oryzae (Xoo) strains contain multiple TAL genes (from 9 to 16) in their genome. While one or two act as major virulence factors, the relative contribution of each of the other members to Xoo pathogenicity remains unclear. To address that question, three African Xoo TALome have been analyzed using whole genome PacBio sequencing data. A phylogenetic analysis of the three TALomes combined to TAL targets in-silico predictions showed that African TALomes are highly conserved and genetically distant from Asian ones.Individual TAL genes from African Xoo strains MAI1 and BAI3 were directly sub-cloned via a self-developing medium-throughput approach into an expression vector suitable for pathogenicity analysis. A systematic “gain-of-virulence” analysis of the function of each of the 11 TAL effector clusters was assessed in Xoo strain X11-5A which has low virulence and is naturally devoid of TAL genes, revealing Tal2 as a novel major virulence factor in African Xoo. In-silico prediction for Tal2 binding sites in the rice promoterome and qRT-PCR analysis highlighted two virulence targets for Tal2, i.e. OsTFX1, which encodes a bZIP transcription factor previously known as a common susceptibility S gene targeted by Asian Xoo, and Os09g39810 (also referred to as OsERF#123), which encodes a putative transcription factor of the ethylene response factor family. Pathogenicity assays further confirmed that designer TALE-mediated specific induction of Os09g39810 confers higher susceptibility of rice to African strains of Xoo. 5’-RACE experiments showed that Tal2 induces the transcription of an alternative Os09g39810 transcript characterized by a longer leader sequence. We hypothesize that accumulation of this Tal2-specific transcript interferes with the endogenous function of this ERF-encoding gene, which is potentially involved with the induction of defense responses. Another project was to initiate the characterization of bacterial diseases of rice in Vietnam, one of the biggest rice exporting country over the world. While the occurrence of bacterial blight which is due to Xoo, was documented in several reports in this country, there was no formal description of bacterial leaf streak which is due to X. oryzae pv. oryzicola. Here, we attempted to confirm the presence of BLS in North Vietnam by using multiplex-PCR assay. The survey also indicated that both pathovars appear in this area and eventually in the same leaf samples. Further analysis of Xo populations dynamic and functional analysis of TALomes will be useful to infer novel strategies to control rice-pathogenic Xanthomonads in this country in the future.

The prevention and treatment of obesity is a major problem of health care systems in affluent societies. Metabolism of adipose tissue belongs to the therapeutical targets, since accumulation of adipose tissue is the basis of obesity development. Experiments using transgenic mice with ectopic expression of brown- fat uncoupling protein 1 (UCP1) in white adipose tissue (WAT), verified a concept that obesity could be ameliorated by increasing energy expenditure in WAT. The goal of the experiments of this PhD Thesis was to characterize in detail the phenotype of this unique animal model of obesity resistance. We have shown that mitochondrial uncoupling in WAT resulted in increased oxidation of fatty acids (FA), in face of decreased lipogenesis and induced mitochondrial biogenesis in this tissue. In further studies, we aimed to modulate propensity to obesity be increasing FA oxidation in WAT in response to physiological stimuli. This could be accomplished in response to the combination treatment using n-3 polyunsaturated fatty acids (n-3 PUFA) and mild calorie restriction in mice fed high-fat diet. Synergistic induction of mitochondrial oxidative capacity and lipid catabolism in epididymal WAT was associated with suppression of low-grade inflammation of WAT, which is typical for obesity. The improvement of lipid...

Value at Risk (VaR) approach has been extensively used by investment and commercial banks since its development by JP Morgan in 1990s. As time passes, it has become interesting to investigate whether VaR could be used also by other financial intermediaries like pension funds and insurance companies. The aim of this paper is to outline Value at Risk (VaR) methodology by giving more emphasis on parametric approach which is used for empirical section and to investigate the applicability and usefulness of VaR in pension funds. After providing theoretical framework for VaR approach, the paper continues with pension fund systems in general and especially highlights AP funds of Swedish National pension fund system by trying to show why VaR could be an invaluable risk management tool for these funds together with other traditional risk measures used. Based on this given theoretical frame, a practical application of VaR –parametric or covariance/variance method- is executed on 50 biggest investments in the fixed income and equity portfolios of three selected Swedish national pension funds – AP1, AP2 and AP3. Results of one day VaR (DEAR) estimations on 30/12/2005 for each fund have been presented and it is aimed to show the additional information that could be obtained by using VaR and which is not always apparent from other risk measures employed by funds. According to the two traditional risk measures which are active risk and Sharpe ratio; AP2 and AP3 lie in the same risk level for 2005 which can create a contradiction by considering their different returns. On the other hand, obtained DEAR estimates show their different risk exposures even with the 50 biggest investments employed. The results give a matching relationship between return of funds and DEAR estimates meaning that; the fund with the highest return has the highest DEAR value and the fund with the lowest return has the lowest DEAR value; which is consistent with the main rule- “higher risk, higher return”. Thus, we can conclude that VaR could be applied additionally to get a better picture about real risk exposures and also to get valuable information on expected possible loss together with other traditional risk measures used. Key words: Value at Risk, DEAR, Pension funds, Risk management, Swedish pension plan, AP1, AP2, AP3