We previously described BT2, a BTB/POZ domain containing protein, as an activator of telomerase in Arabidopsis thaliana. In the current study, I present evidence of its interesting roles in mediating multiple hormone, stress and metabolic responses in plants. Steady-state expression of BT2 mRNA was regulated diurnally and was under the control of circadian clock, with a maximum expression in the dark. BT2 mRNA was responsive to nutrient status and to multiple biotic and abiotic stress signals. Using bt2 loss-of-function and BT2 over-expressing lines, I show that BT2 suppresses sugar and ABA-mediated responses during germination. BT2 is also essential for transcriptional gene activation mediated by CaMV 35S enhancers in Arabidopsis. Loss of BT2 in several well-characterized 35S enhancer activation-tagged lines such as yucca1d, pap1d, jaw1d etc., resulted in suppression of the activation phenotypes. The suppression of the phenotypes was due to decreased transcription of the activation-tagged genes. I further demonstrate that BT2 genetically interacts with CULLIN3. I propose that BT2 and CULLIN3 are components of a ubiquitin ligase complex. Together with associated proteins BET9 and BET10, the BT2 complex is required for CaMV 35S enhancer-mediated activation of gene expression and may regulate expression of target genes involved in multiple responses to fluctuating biotic and abiotic conditions. I also found that BT2 protein levels are tightly regulated in plants. BT2 protein was primarily localized in the nucleus and was developmentally regulated. BT2 turn-over was regulated in part by the 26S-proteosome, and rare codons present in its open reading frame affected BT2 protein accumulation. In addition to BT2, its orthologs, BT1, BT3, BT4 and BT5, also responded to light, clock and nutrients, with some differences. Moreover, BT1, BT3 and BT4 were also required for 35S enhancer-mediated activation of gene expression. I propose that BT family proteins assemble into multi-protein complexes to mediate multiple responses to changing environmental and nutritional conditions.

No description available.

We investigated the gestational expression of androgen receptor (AR) and defined its regulation and that of its co-repressors, PSF and p54nrb, by steroid hormones and myometrial stretch in vivo in pregnant and non-pregnant rats. Our data demonstrate that, 1) myometrial AR expression decreases prior to term; 2) AR expression is up-regulated by MPA treatment and down-regulated by mechanical stretch; (3) myometrial PSF protein expression is down-regulated by estrogen signaling and by mechanical stretch, and up-regulated by androgen signaling; (4) while myometrial PSF mRNA expression is also down-regulated by stretch, the regulation by estrogen and P4 on PSF mRNA appear to be opposite to the effects on PSF protein. We conclude that the decreased androgen signaling in late pregnancy (as a result of decreased AR and PSF expression mediated by hormonal and mechanical signals) may contribute to the mechanisms leading to labor initiation.

We investigated the gestational expression of androgen receptor (AR) and defined its regulation and that of its co-repressors, PSF and p54nrb, by steroid hormones and myometrial stretch in vivo in pregnant and non-pregnant rats. Our data demonstrate that, 1) myometrial AR expression decreases prior to term; 2) AR expression is up-regulated by MPA treatment and down-regulated by mechanical stretch; (3) myometrial PSF protein expression is down-regulated by estrogen signaling and by mechanical stretch, and up-regulated by androgen signaling; (4) while myometrial PSF mRNA expression is also down-regulated by stretch, the regulation by estrogen and P4 on PSF mRNA appear to be opposite to the effects on PSF protein. We conclude that the decreased androgen signaling in late pregnancy (as a result of decreased AR and PSF expression mediated by hormonal and mechanical signals) may contribute to the mechanisms leading to labor initiation.

Les derniers acteurs de la voie de signalisation à l’éthylène sont des facteurs de transcription appelés ERF (Ethylene Response Factors). La connaissance de leur rôle spécifique dans la régulation des processus développementaux dépendant de l’éthylène reste limitée. Les travaux présentés dans la thèse concernent la caractérisation fonctionnelle du gène Sl-ERF.B3, un membre de cette grande famille de régulateurs transcriptonnels dans la tomate (Solanum lycopersicum). Utilisant une stratégie répresseur dominant ; il est montré en particulier que ce gène intervient dans la mise en place de la réponse à l’éthylène et dans le contrôle de la maturation du fruit. L’expression d’une construction ERF.B3-SRDX, une version chimérique de Sl-ERF.B3 fusionné à un domaine répresseur de type EAR, entraine des phénotypes pléotropiques aussi bien dans la signalisation de l’éthylène que dans le développement des parties végétatives et des organes reproducteurs. Ainsi, une altération de la triple réponse à l’éthylène est constatée chez les lignées transgéniques et au stade adulte, les plantes présentent des phénotypes d’épinastie des feuilles, de sénescence prématurée des fleurs et d’abscission accélérée des fruits. L’ensemble de ces observations est corrélée avec une modification de l’expression de gènes impliqués dans la biosynthèse et la réponse à l’éthylène. Ces données suggèrent que ERF.B3 intervient dans un mécanisme de rétro-control de la réponse à l’éthylène en agissant à la fois sur les gènes de biosynthèse et de signalisation de l’hormone. Au niveau du fruit, la sur-expression d’ERF.B3-SRDX entraine une modification du processus de maturation avec un retard notable de l’avènement de l’acquisition de la compétence à murir. Cependant, une fois la maturation initiée, elle s’accompagne d’une forte production d’éthylène et d’une accélération du ramollissement du fruit. A l’inverse, l’accumulation de pigment est inhibée par altération de la voie de biosynthèse des caroténoïdes. Ces données phénotypiques sont corrélées avec le niveau d’expression des gènes clés impliqués dans ces processus. Les résultats indiquent que dans les lignées transgéniques, il y a découplage de certaines caractéristiques de la maturation du fruit et permettent de mettre en lumière le rôle d’ERF.B3 dans la régulation des processus de développement dépendant de l’éthylène chez la tomate. / Ethylene Response Factors (ERFs) are known to be the last transcription factors of the ethylene transduction pathway. Their specific role in ethylene-dependent developmental processes remains poorly understood. This work demonstrated a specific role of Sl- ERF.B3, a member of the ERF gene family in tomato (Solanum lycopersicum), in mediating ethylene response and fruit ripening through a dominant repressor strategy. ERF.B3-SRDX dominant repressor etiolated seedlings displayed partial constitutive ethylene-response in the absence of ethylene and adult plants exhibited typical ethylenerelated alterations such as leaf epinasty, premature flower senescence and accelerated fruit abscission. The multiple symptoms related to enhanced ethylene sensitivity correlate with the altered expression of ethylene biosynthesis and signaling genes, suggesting the involvement of Sl-ERF.B3 in a feedback mechanism regulating components of ethylene production and response. In addition, over-expression of ERF.B3-SRDX in tomato results in alterations in both fruit morphology and ripening process. The attainment of competence to ripen is dramatically delayed in ERF.B3-SRDX fruits but once ripening proceeds it is associated with high climacteric ethylene production and enhanced fruit softening while pigment accumulation is strongly reduced. Moreover, a number of genes involved in the fruit ripening process showed expression pattern deviating from that of wild type. These data suggest a putative role of Sl-ERF.B3 in the transcriptional network underlying the ripening process and uncover a mean for uncoupling some of the main features of fruit ripening such as fruit softening and pigment accumulation. Overall, the study highlighted the importance of an ERF gene in ethylene-mediated developmental processes such as plant growth and fruit ripening.

[ES] Las plantas necesitan acomodar su crecimiento a las condiciones ambientales. Con el objetivo de ajustar su desarrollo a las señales externas, usan una serie de mecanismos moleculares. Uno de estos son las rutas de señalización hormonal, que participan en integrar la información externa con programas de desarrollo propios. Una de las hormonas más relevantes en la biología vegetal son las giberelinas (GAs). La señalización por GAs se inicia con la percepción de la hormona a través del receptor GID1, y continúa por la degradación de las reguladoras transcripcionales DELLA. Sin embargo, solo las plantas vasculares tienen un sistema de percepción de GAs completo. Entender la relevancia de la señalización por GAs requiere estudiar cómo se ensambló la ruta y qué funciones atribuidas a las GAs estaban ya codificadas en las proteínas DELLA ancestrales. Aquí mostramos mediante análisis filogenéticos y bioquímicos que las proteínas DELLA emergieron inequívocamente en un ancestro común de las plantas terrestres, y que el reclutamiento de las DELLAs al módulo de percepción de GAs depende de la presencia de un dominio de transactivación conservado que fue co-optado por el receptor GID1 ancestral para actuar como un degrón dependiente de GAs. Este dominio de transactivación parece regular la co-activación transcripcional de genes concretos por las DELLAs en todas las plantas terrestres mediante el reclutamiento de complejos Mediator a través de su subunidad MED15. Por último, nos hemos centrado en entender las funciones de las proteínas DELLA en briófitas, un clado sin señalización por GAs. Hemos descubierto el rol de la DELLA de Marchantia polymorpha como coordinadora entre las respuestas de crecimiento y estrés, sugiriendo que dicha función estaba ya codificada en proteínas DELLA del ancestro común de plantas terrestres y se ha mantenido durante más de 450 millones de años. / [CA] Les plantes necessiten acomodar el seu creixement a les condicions ambientals. Amb l'objectiu d'ajustar el seu desenvolupament als senyals externs, usen una sèrie de mecanismes moleculars. Un d'aquests són les rutes de senyalització hormonal, que participen en integrar la informació externa amb programes de desenvolupament propis. Una de les hormones més rellevants en la biologia vegetal són les giberel·lines (GAs). La senyalització per GAs s'inicia amb la percepció de l'hormona a través del receptor GID1, i continua per la degradació de les reguladores transcripcionals DELLA. No obstant això, només les plantes vasculars tenen un sistema complet de percepció de GAs. Entendre la rellevància de la senyalització per GAs requereix estudiar com es va assemblar la ruta i quines funcions atribuïdes a les GAs estaven ja codificades en les proteïnes DELLA ancestrals. Ací mostrem mitjançant anàlisis filogenètiques i bioquímiques que les proteïnes DELLA van emergir inequívocament en un ancestre comú de les plantes terrestres, i que el reclutament de les DELLAs al mòdul de percepció de GAs depén de la presència d'un domini de transactivació conservat que va ser co-optat pel receptor GID1 ancestral per a actuar com un degró dependent de GAs. Aquest domini de transactivació sembla regular la co-activació transcripcional de gens concrets per les DELLAs en totes les plantes terrestres mitjançant el reclutament de complexos Mediator a través de la seua subunitat MED15. Finalment, ens hem centrat en entendre les funcions de les proteïnes DELLA en briòfites, un clade sense senyalització per GAs. Hem descobert el rol de la DELLA de Marchantia polymorpha com a coordinadora entre les respostes de creixement i estrés, suggerint que aquesta funció estava ja codificada en proteïnes DELLA de l'ancestre comú de plantes terrestres i s'ha mantingut durant més de 450 milions d'anys. / [EN] Plants need to accommodate their growth habits to environmental conditions. For this aim, several mechanisms are used to adjust developmental responses to exogenous signals. Among them, hormonal signalling pathways participate by integrating external information with endogenous programs. One of the most relevant hormones in plant biology are gibberellins (GAs). GA signalling involves perception of the hormone by the GA receptor GID1 and subsequent degradation of the DELLA transcriptional regulators. However, only vascular plants possess a full GA perception system. Understanding the relevance of GA signalling requires elucidating how this pathway was assembled and which of the functions attributed to GAs were encoded in the ancestral DELLA proteins. Here we show by phylogenetic and biochemical analyses that DELLA proteins emerged unequivocally in a land plant common ancestor and that their recruitment into the GA-perception module relies in the presence of a conserved transactivation domain co-opted by an ancestral GID1 receptor to act as a GA-dependent degron. Moreover, this transactivation domain seems to regulate DELLA-dependent transcriptional co-activation of selected target genes by recruitment of Mediator complexes through the MED15 subunit in all land plants. Finally, we have focused on understanding the functions of DELLA proteins in bryophytes, a clade with no GA signalling. We have uncovered the role of Marchantia polymorpha DELLA protein as a coordinator between growth and stress responses, suggesting that this function was already present in the DELLA protein of a land plant common ancestor and has been maintained for over 450 millions of years. / La realización de esta tesis doctoral ha sido posible gracias a una ayuda para contratos predoctorales FPU (FPU15/01756), dos Ayudas para Estancias Breves FPU (EST17/00237, IPS2, París; EST18/00400, WUR, Wageningen), una ayuda EMBO Short-Term (ASTF 8239, WUR, Wageningen), y la financiación MSCA H2020 RISE para desplazamientos en el contexto del proyecto SIGNAT (RISE Action 644435, PUC, Santiago). Así mismo, el grueso del trabajo experimental incluido ha sido financiado por el proyecto HUBFUN del MINECO (BFU2016-80621-P) / Hernández García, J. (2021). Ancestral Functions of DELLA Proteins [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/169370 / TESIS