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DELLA proteins are negative regulators of the gibberellin response pathway in angiosperms, acting as central hubs that interact with hundreds of transcription factors (TFs) and regulators to modulate their activities. While the mechanism of TF sequestration by DELLAs to prevent DNA binding to downstream targets has been extensively documented, the mechanism that allows them to act as coactivators remains to be understood. Here, we demonstrate that DELLAs directly recruit the Mediator complex to specific loci in Arabidopsis, facilitating transcription. This recruitment involves DELLA amino-terminal domain and the conserved MED15 KIX domain. Accordingly, partial loss of MED15 function mainly disrupted processes known to rely on DELLA coactivation capacity, including cytokinin-dependent regulation of meristem function and skotomorphogenic response, gibberellin metabolism feedback, and flavonol production. We have also found that the single DELLA protein in the liverwort Marchantia polymorpha is capable of recruiting MpMED15 subunits, contributing to transcriptional coactivation. The conservation of Mediator-dependent transcriptional coactivation by DELLA between Arabidopsis and Marchantia implies that this mechanism is intrinsic to the emergence of DELLA in the last common ancestor of land plants.

DELLA proteins are negative regulators of the gibberellin response pathway in angiosperms, acting as central hubs that interact with hundreds of transcription factors and regulators to modulate their activities. While the mechanism of transcription factor sequestration by DELLAs to prevent DNA binding to downstream targets has been extensively documented, the mechanism that allows them to act as co-activators remains to be understood. Here, we demonstrate that DELLAs directly recruit the Mediator complex to specific loci in Arabidopsis, facilitating transcription. This recruitment involves DELLA amino-terminal domain and the conserved MED15 KIX domain. Accordingly, partial loss of MED15 function mainly disrupted processes known to rely on DELLA co-activation capacity; including cytokinin-dependent regulation of meristem function and skotomorphogenic response, gibberellin metabolism feedback, and flavonol production. We have also found that the single DELLA protein in the liverwort Marchantia polymorpha is capable of recruiting MpMED15 subunits, contributing to transcriptional co-activation. The conservation of Mediator-dependent transcriptional co-activation by DELLA between Arabidopsis and Marchantia implies that this mechanism is intrinsic to the emergence of DELLA in the last common ancestor of land plants.

The prefoldin complex (PFDc) was identified in humans as a co-chaperone of the cytosolic chaperonin T-COMPLEX PROTEIN RING COMPLEX (TRiC)/CHAPERONIN CONTAINING TCP-1 (CCT). PFDc is conserved in eukaryotes and is composed of subunits PFD1–6, and PFDc-TRiC/CCT folds actin and tubulins. PFDs also participate in a wide range of cellular processes, both in the cytoplasm and in the nucleus, and their malfunction causes developmental alterations and disease in animals and altered growth and environmental responses in yeast and plants. Genetic analyses in yeast indicate that not all of their functions require the canonical complex. The lack of systematic genetic analyses in plants and animals, however, makes it difficult to discern whether PFDs participate in a process as the canonical complex or in alternative configurations, which is necessary to understand their mode of action. To tackle this question, and on the premise that the canonical complex cannot be formed if one subunit is missing, we generated an Arabidopsis (Arabidopsis thaliana) mutant deficient in the six PFDs and compared various growth and environmental responses with those of the individual mutants. In this way, we demonstrate that the PFDc is required for seed germination, to delay flowering, or to respond to high salt stress or low temperature, whereas at least two PFDs redundantly attenuate the response to osmotic stress. A coexpression analysis of differentially expressed genes in the sextuple mutant identified several transcription factors, including ABA INSENSITIVE 5 (ABI5) and PHYTOCHROME-INTERACTING FACTOR 4, acting downstream of PFDs. Furthermore, the transcriptomic analysis allowed assigning additional roles for PFDs, for instance, in response to higher temperature.

[ES] Debido a su naturaleza sésil, las plantas han de enfrentarse "in situ" a variaciones ambientales que pueden comprometer su supervivencia y éxito reproductivo. Para ello las plantas han desarrollado mecanismos con los que monitorizar constantemente el ambiente (intensidad y calidad de la luz, temperatura, disponibilidad de agua y nutrientes, etc.) y reajustar su desarrollo en consecuencia. Por ejemplo, cuando las condiciones ambientales son adversas (estrés abiótico), las plantas frenan el crecimiento y simultáneamente activan los mecanismos de defensa. Las proteínas DELLA juegan un papel central en esta respuesta coordinada gracias a su capacidad de interaccionar con más de 300 proteínas, principalmente factores de transcripción (TFs), que regulan procesos tan diversos como la división celular, la elongación celular o la biosíntesis de compuestos antioxidantes. En concreto, las DELLA reprimen el crecimiento mediante la interacción con TFs de las familias TCP, PIF y BES1/BZR principalmente mientras que desencadenan las respuestas defensivas mediante la interacción con proteínas de la familia JAZ entre otras. Aunque se ha argumentado que el freno del crecimiento es imprescindible para la redistribución de recursos energéticos en la planta, estudios más recientes indican que esto no es así, sino que la percepción del estrés provoca la acumulación de DELLAs por su papel positivo en defensa y esta acumulación es la que causa la represión colateral del crecimiento. En este trabajo se propone la generación y caracterización de alelos arísticos DELLA (del inglés `edgetic alleles"), es decir, versiones de las proteínas DELLA que pierdan específicamente la capacidad de interaccionar con factores promotores del crecimiento pero que mantengan la capacidad de interaccionar con proteínas con efecto positivo en defensa. Por tanto, nuestro objetivo último es utilizar las DELLA como herramienta biotecnológica para obtener plantas cuyo crecimiento no se vea penalizado en condici, [EN] In a stressful situation, plants slow down their growth and simultaneously activate their defense mechanisms. defense mechanisms. The DELLA proteins play a central role in this coordinated coordinated response through their interaction with more than 300 proteins, mainly transcription factors (TFs). transcription factors (TFs). Specifically, DELLAs repress growth by interacting with TFs of the through interaction with TFs from the TCP, PIF and BES1/BZR and ARR families mainly, while they promote defensive responses by interacting with proteins of the JAZR and interaction with JAZ family proteins. The aim of this master thesis has been to functionally characterize the activity of potential alleles of GAI, variants of this DELLA that have selectively lost certain functions. functions. Previous work in the group identified several GAI clones that did not interact with PIF but did interact with PIF but did interact with ARR1 and JAZ in yeast assays. The phenotypic phenotypic analysis performed in this TFM shows that the GAI aristatic alleles complemented root root development (DELLA-ARR1 interaction-dependent) and defense gene activation (DELLA-ARR1-dependent) and (DELLA-JAZ interaction-dependent) in loss-of-function dellaKO mutants. dellaKO loss-of-function mutants. However, these alleles did not complement the development of the development (DELLA-PIF interaction-dependent). Thus, it is concluded that a strategy has been the development of a strategy to uncouple different DELLA activities in plants. DELLA activities.

[ES] Uno de los retos principales de los biotecnólogos del siglo XXI es el desarrollo de cultivos más productivos y resistentes a condiciones ambientales adversas. Ante una situación de estrés las plantas desarrollan estrategias de defensa que van ligadas a una reducción del crecimiento. Las proteínas DELLA son reguladores clave de esta respuesta coordinada y, por tanto, han constituido desde su descubrimiento en una herramienta con la que mejorar diversos aspectos agronómicos. Sin embargo, modificar la actividad DELLA también puede provocar efectos secundarios no deseados en los cultivos como un descenso en la productividad o en la tolerancia al ataque por patógenos. Uno de los objetivos de nuestro grupo es generar nuevos alelos DELLA que mejoren específicamente caracteres de interés biotecnológico pero minimizando los efectos no deseados. En este TFM se han establecido ensayos con los que evaluar la tolerancia a estrés del mutante procera (pro) tomate, con pérdida de función DELLA. Estos ensayos son esenciales para poder evaluar en el futuro la actividad en un cultivo de los nuevos alelos DELLA generados. En concreto, se han optimizado ensayos de estrés salino moderado y de tratamiento con metil-jasmónico, como simulación de estrés biótico. Sorprendentemente, nuestro estudio indica que pro no es más sensible al estrés salino que el silvestre. Al contrario, la activación de respuestas defensivas dependientes de MeJA sí está afectada en pro, lo que apoya una menor tolerancia a estrés biótico., [EN] One of the main challenges for biotechnologists in the 21st century is the development of crops that are more productive and resistant to adverse environmental conditions. Under stress, plants develop defense strategies linked to a reduction in growth. DELLA proteins are critical regulators of this coordinated response and have been a tool to improve various agronomic aspects since their discovery. However, modifying DELLA activity can also lead to undesirable side effects in crops, such as decreased productivity or tolerance to pathogen attack. One of the objectives of our group is to generate new DELLA alleles that specifically improve traits of biotechnological interest while minimizing undesirable effects. In this Master¿s thesis, we have established assays to evaluate the stress tolerance of the procera (pro) tomato mutant with loss of DELLA function. These assays are essential to assess the activity of the new DELLA alleles generated in a crop. Specifically, moderate salt stress and methyl jasmonate treatment assays have been optimized to simulate biotic stress. Excitingly, our study indicates that pro tomato plants are not more sensitive to salt stress than wild-type. However, activation of MeJA-dependent defensive responses is impaired in pro plants, suggesting a lower tolerance to biotic stress

[ES] Ante una situación de estrés, las plantas frenan el crecimiento y simultáneamente activan los mecanismos de defensa. Esta respuesta está coordinada por diferentes rutas de señalización hormonal entre las que destaca la establecida por las giberelinas (GAs), un grupo de hormonas vegetales que promueven el crecimiento cuando las condiciones ambientales son óptimas, y sus reguladores negativos, las proteínas DELLA. Por tanto, las GAs y los inhibidores de su biosíntesis son una herramienta biotecnológica de interés para mejorar determinados aspectos agronómicos; por ejemplo, la aplicación de GAs sincroniza la fructificación. Sin embargo, el uso de estos compuestos provoca otros efectos secundarios no deseados como hipersensibilidad frente a estrés biótico y abiótico. Este trabajo de final de máster (TFM) forma parte del proyecto Prometeo TECNODELLA cuyo objetivo es modificar la ruta de señalización GAs-DELLA para desacoplar en plantas de tomate (Solanum lycopersicum) el freno del crecimiento de la activación de respuestas defensivas. Es decir, buscamos plantas donde las GAs puedan seguir ejerciendo su papel positivo en procesos de interés biotecnológico sin penalizar la tolerancia de las mismas al estrés. El objetivo particular de este TFM ha sido optimizar ensayos de estrés por salinidad en líneas de tomate, cultivar MicroTom, en las que la ruta de señalización por GAs está activada constitutivamente. Estas líneas se han cultivado en condiciones óptimas de crecimiento (condiciones control) y bajo concentraciones crecientes de sal en el suelo. La respuesta de las mismas a estas condiciones se ha evaluado mediante una serie de abordajes complementarios: (1) caracterización fenotípica del desarrollo vegetativo y reproductivo en presencia y ausencia de sal, (2) cuantificación de los niveles de diferentes hormonas que regulan el crecimiento y la defensa y (3) análisis de la expresión de genes que protegen a la planta del estrés salino., [EN] Upon stress, plants restrain growth and simultaneously activate defense mechanisms. This response is coordinated by different hormone signaling pathways, including the one established by gibberellins (GAs), a group of plant hormones that promote growth when environmental conditions are optimal, and their negative regulators, the DELLA proteins. Therefore, GAs and their biosynthesis inhibitors are biotechnological tools of interest to improve certain agronomic traits; for instance, GAs application synchronizes fruit set. However, the use of these compounds causes other undesired side effects such as hypersensitivity to biotic and abiotic stress. This master's final project (TFM) is part of the Prometeo tecnodella project, whose objective is to modify the GAs-DELLA signaling pathway to uncouple the growth brake from the activation of defensive responses in tomato plants (Solanum Lycopersicum). In other words, we are looking for plants where GAs can continue to exercise their positive role in processes of biotechnological interest without penalizing their tolerance to stress. The particular objective of this TFM has been to optimize salinity stress assays in tomato lines, cultivar MicroTom, with constitutively activated GA signaling. These lines have been cultivated under optimal growing conditions (control conditions) and under increasing concentrations of salt in soil. Their response to these conditions has been evaluated through a series of complementary approaches: (1) phenotypic characterization of vegetative and reproductive development in the presence and absence of salt, (2) quantification of the levels of different hormones that regulate growth and defense and (3) analysis of the expression of genes that protect the plant from salt stress., [CA] Davant una situació d'estrés, les plantes frenen el creixement i simultàniament activen els mecanismes de defensa. Aquesta resposta està coordinada per diferents rutes de senyalització hormonal entre les quals destaca l'establida per les giberelines (GAs), un grup d'hormones vegetals que promouen el creixement quan les condicions ambientals són òptimes, i els seus reguladors negatius, les proteïnes DELLA. Per tant, les GAs i els inhibidors de la seua biosíntesi són una eina biotecnològica d'interés per a millorar determinats aspectes agronòmics; per exemple, l'aplicació de GAs sincronitza la fructificació. No obstant això, l'ús d'aquests compostos provoca altres efectes secundaris no desitjats com a hipersensibilitat enfront d'estrés biòtic i abiòtic. Aquest treball de final de màster (TFM) forma part del projecte Prometeu TECNODELLA l'objectiu del qual modificar la ruta de senyalització GAs-DELLA per a desacoblar en plantes de tomaca (Solanum lycopersicum) el fre del creixement de l'activació de respostes defensives. És a dir, busquem plantes on les GAs puguen continuar exercint el seu paper positiu en processos d'interés biotecnològic sense penalitzar la tolerància de les mateixes a l'estrés. L'objectiu particular d'aquest TFM ha sigut optimitzar assajos d'estrés per salinitat en línies de tomaca (Solanum lycopersicum), cultivar MicroTom, on s'ha modificat la senyalització per GAs. Aquestes línies s'han cultivat en condicions òptimes de creixement (condiciones control) i sota concentracions creixents de sal al sòl. La resposta de les mateixes a aquestes condicions s'ha avaluat mitjançant una sèrie d'abordatges complementaris: (1) caracterització fenotípica del desenvolupament vegetatiu i reproductiu en presència i absència de sal, (2) quantificació dels nivells de diferents hormones que regulen el creixement i la defensa i (3) anàlisi de l'expressió de gens que protegeixen la planta de l'estrés salí.

[EN] The prefoldin complex (PFDc) was identified in humans as a co-chaperone of the cytosolic chaperonin T-COMPLEX PROTEIN RING COMPLEX (TRiC)/CHAPERONIN CONTAINING TCP-1 (CCT). PFDc is conserved in eukaryotes and is composed of subunits PFD1-6, and PFDc-TRiC/CCT folds actin and tubulins. PFDs also participate in a wide range of cellular processes, both in the cytoplasm and in the nucleus, and their malfunction causes developmental alterations and disease in animals and altered growth and environmental responses in yeast and plants. Genetic analyses in yeast indicate that not all of their functions require the canonical complex. The lack of systematic genetic analyses in plants and animals, however, makes it difficult to discern whether PFDs participate in a process as the canonical complex or in alternative configurations, which is necessary to understand their mode of action. To tackle this question, and on the premise that the canonical complex cannot be formed if one subunit is missing, we generated an Arabidopsis (Arabidopsis thaliana) mutant deficient in the six PFDs and compared various growth and environmental responses with those of the individual mutants. In this way, we demonstrate that the PFDc is required for seed germination, to delay flowering, or to respond to high salt stress or low temperature, whereas at least two PFDs redundantly attenuate the response to osmotic stress. A coexpression analysis of differentially expressed genes in the sextuple mutant identified several transcription factors, including ABA INSENSITIVE 5 (ABI5) and PHYTOCHROME-INTERACTING FACTOR 4, acting downstream of PFDs. Furthermore, the transcriptomic analysis allowed assigning additional roles for PFDs, for instance, in response to higher temperature.

[EN] Throughout development, plant meristems regularly produce organs in defined spiral, opposite, or whorl patterns. Cauliflowers present an unusual organ arrangement with a multitude of spirals nested over a wide range of scales. How such a fractal, self-similar organization emerges from developmental mechanisms has remained elusive. Combining experimental analyses in an Arabidopsis thaliana cauliflower-like mutant with modeling, we found that curd self-similarity arises because the meristems fail to form flowers but keep the "memory" of their transient passage in a floral state. Additional mutations affecting meristem growth can induce the production of conical structures reminiscent of the conspicuous fractal Romanesco shape. This study reveals how fractal-like forms may emerge from the combination of key, defined perturbations of floral developmental programs and growth dynamics.

The arrangement of plant organs, called phyllotaxis, produce remarkable spiral or whorled patterns. Cauliflowers present a unique phyllotaxis with a multitude of spirals over a wide range of scales. How such a self-similar fractal organization emerges from developmental mechanisms has remained elusive. Combining experimental assays with modeling, we found that cauliflowers arise due to the hysteresis of the bistable floral network that generates inflorescences imprinted by a transient floral state. We further show how additional mutations affecting meristem growth dynamics can induce the production of conical phyllotactic structures reminiscent of the conspicuous fractal Romanesco shape. This study reveals how the spectacular morphological modification of the inflorescences in cauliflower and Romanesco shape arises from the hysteresis of the genetic programs controlling inflorescence development.

Plant survival depends on the optimal use of resources under variable environmental conditions. Among the mechanisms that mediate the balance between growth, differentiation and stress responses, the regulation of transcriptional activity by DELLA proteins stands out. In angiosperms, DELLA accumulation promotes defense against biotic and abiotic stress and represses cell division and expansion, while loss of DELLA function is associated with increased plant size and sensitivity towards stress1. Given that DELLA protein stability is dependent on gibberellin (GA) levels2, and GA metabolism is influenced by the environment3, this pathway is proposed to relay environmental information to the transcriptional programs that regulate growth and stress responses in angiosperms4,5. However, DELLA genes are also found in bryophytes, whereas canonical GA receptors appeared only in vascular plants6–10. Thus, it is not clear whether these regulatory functions of DELLA predated or emerged with typical GA signaling. Here we show that, as in vascular plants, the only DELLA in the liverwort Marchantia polymorpha also participates in the regulation of growth and key developmental processes, and promotes the tolerance towards oxidative stress. Moreover, part of these effects is likely caused by the conserved physical interaction with the MpPIF transcription factor. Therefore, we suggest that the role in the coordination of growth and stress responses was already encoded in DELLA from the common ancestor of land plants, and the importance of this function is justified by its conservation over the past 450 M years.

Plant survival depends on the optimal use of resources under variable environmental conditions. Among the mechanisms that mediate the balance between growth, differentiation, and stress responses, the regulation of transcriptional activity by DELLA proteins stands out. In angiosperms, DELLA accumulation promotes defense against biotic and abiotic stress and represses cell division and expansion, while the loss of DELLA function is associated with increased plant size and sensitivity toward stress.1 Given that DELLA protein stability is dependent on gibberellin (GA) levels2 and GA metabolism is influenced by the environment,3 this pathway is proposed to relay environmental information to the transcriptional programs that regulate growth and stress responses in angiosperms.4,5 However, DELLA genes are also found in bryophytes, whereas canonical GA receptors have been identified only in vascular plants.6, 7, 8, 9, 10 Thus, it is not clear whether these regulatory functions of DELLA predated or emerged with typical GA signaling. Here, we show that, as in vascular plants, the only DELLA in the liverwort Marchantia polymorpha also participates in the regulation of growth and key developmental processes and promotes oxidative stress tolerance. Moreover, part of these effects is likely caused by the conserved physical interaction with the MpPIF transcription factor. Therefore, we suggest that the role in the coordination of growth and stress responses was already encoded in the DELLA protein of the common ancestor of land plants, and the importance of this function is underscored by its conservation over the past 450 million years.

[EN] DELLA proteins are the negative regulators of the gibberellin (GA) signaling pathway. GAs have a pervasive effect on plant physiology, influencing processes that span the entire life cycle of the plant. All the information encoded by GAs, either environmental or developmental in origin, is canalized through DELLAs, which modulate the activity of many transcription factors and transcriptional regulators. GAs unlock the signaling pathway by triggering DELLA polyubiquitination and degradation by the 26S proteasome. Recent reports indicate, however, that there are other pathways that trigger DELLA polyubiquitination and degradation independently of GAs. Moreover, results gathered during recent years indicate that other post-translational modifications (PTMs), namely phosphorylation, SUMOylation and glycosylation, modulate DELLA function. The convergence of several PTMs in DELLA therefore highlights the strict regulation to which these proteins are subject. In this review, we summarize these discoveries and discuss DELLA PTMs from an evolutionary perspective and examine the possibilities these and other post-translational regulations offer to improve DELLA-dependent agronomic traits.

[EN] Plants are sessile organisms that need to constantly adapt to changing environmental conditions. In the presence of a stress, plants promote the defensive responses at the expense of reducing growth, a process that is known as the growth-defense trade-off. The signaling pathway established by the phytohormone gibberellins (GA) and DELLA proteins is central for the regulation of this trade-off. GA levels respond to environmental and endogenous signals and transmit this information through the degradation of DELLA proteins. DELLAs interact with many other proteins, mainly transcription factors, to inhibit cell growth and division and to activate the defense mechanisms. An ambitious objective of biotechnological interest is to break the balance between growth and defense, that is to obtain plants able to activate an efficient defensive response without compromising growth. We have explored this possibility through the analysis of the interaction between DELLA proteins and SMR1, a negative regulator of cell cycle progression. We first confirmed previous work in the group, showing that DELLA proteins bind to genomic regions close to the SMR1 gene. We also show that DELLAs repress inflorescence growth through the upregulation of SMR1 expression. Thus, the smr1-1 loss-of-function restores flowering-time and partially suppresses dwarfism in gai-1D mutants. Finally, we have optimized protocols and generated the tools necessary to evaluate if the defensive response of gai-1D mutants is affected by enhanced shoot growth in gai-1D;smr1-1 plants., [ES] Para contrarrestar su incapacidad de movimiento, las plantas han desarrollado una estrategia muy eficiente: monitorizar de manera continua las condiciones ambientales y utilizar esta información para optimizar el uso de su maquinaria celular. Un ejemplo claro es que las plantas sometidas a algún tipo de estrés (sequía, alta concentración de sal, temperaturas extremas...) frenan su crecimiento y simultáneamente activan el programa de defensa. Esta respuesta doble está coordinada por las proteínas DELLA que, mediante la interacción con factores de transcripción, inhiben el ciclo celular y activan respuestas que protegen frente al estrés. Con este proyecto querríamos contestar varias preguntas: (1) ¿cómo regulan las DELLA el ciclo celular? (2) ¿se pueden desacoplar las dos respuestas coordinadas por las DELLA? (3) El freno del crecimiento ¿supone por sí mismo una respuesta protectora frente a estrés? Para ello nos centraremos en el desarrollo de la inflorescencia, la región de la planta donde se producen los frutos y que, por tanto, tiene un elevado interés biotecnológico. En el trabajo reciente del laboratorio con la planta modelo Arabidopsis thaliana, hemos encontrado que una mutación en el gen SMR1 (un regulador negativo del ciclo celular) suprime muchos de los defectos en el crecimiento de los mutantes semi-enanos gai-1D (ganancia de función de DELLA). Sin embargo, la respuesta defensiva de las plantas gai-1D smr1-1 apenas parece verse afectada. Estas observaciones sugieren que es posible desacoplar las diferentes funciones DELLA. El proyecto que proponemos profundizará en este análisis a través de 2 objetivos principales: (1) caracterizar SMR1 como una diana directa de las proteínas DELLA y (2) caracterizar el mutante doble gai-1D;smr1-1 como una herramienta para desacoplar el balance entre crecimiento y defensa mediado por las DELLA.

DELLA proteins are the negative regulators of the gibberellin (GA) signaling pathway. GAs have a pervasive effect on plant physiology, influencing processes that span the entire life cycle of the plant. All the information encoded by GAs, either environmental or developmental in origin, is canalized through DELLAs, which modulate the activity of many transcription factors and transcriptional regulators. GAs unlock the signaling pathway by triggering DELLA polyubiquitination and degradation by the 26S proteasome. Recent reports indicate, however, that there are other pathways that trigger DELLA polyubiquitination and degradation independently of GAs. Moreover, results gathered during recent years indicate that other post-translational modifications (PTMs), namely phosphorylation, SUMOylation and glycosylation, modulate DELLA function. The convergence of several PTMs in DELLA therefore highlights the strict regulation to which these proteins are subject. In this review, we summarize these discoveries and discuss DELLA PTMs from an evolutionary perspective and examine the possibilities these and other post-translational regulations offer to improve DELLA-dependent agronomic traits.

[ES] Las plantas son organismos sésiles que necesitan monitorizar constantemente las condiciones ambientales y, en consecuencia, ajustar el uso de su maquinaria celular para sobrevivir y lograr el éxito reproductivo. De ahí que las plantas sometidas a diferentes tipos de estrés abiótico, como la sequía, restrinjan el crecimiento y promuevan los mecanismos de defensa. Esta doble respuesta está controlada por las proteínas DELLA que, a través de la interacción con factores de transcripción, inhiben la progresión del ciclo celular a la vez que activan las respuestas a estrés. Este proyecto ha explorado la posibilidad de separar estas funciones de las proteínas DELLA en crecimiento y defensa. Datos preliminares en el grupo no publicados muestran que la pérdida de función en el gen SMR1, un regulador negativo del ciclo celular, suprime parcialmente el defecto en la elongación del tallo de los mutantes semienanos gai-1D. Por lo tanto, hemos caracterizado con detalle el crecimiento de la inflorescencia en las plantas gai-1D; smr1-1 y RGAp:GFP-rga¿17;smr1-1, y analizado su respuesta a condiciones extremas de estrés por sequía. Además, hemos generado un conjunto de líneas testigo SMR1 para examinar el patrón de expresión de SMR1 en el tallo de la inflorescencia y para estudiar cómo está regulado por las proteínas DELLA., [EN] Plants are sessile organisms that need to continuously monitor the environmental conditions and accordingly adjust the use of their cellular machinery in order to survive and achieve reproductive success. Hence plants subjected to different types of abiotic stress, such as drought, restrict growth and promote defence mechanisms. This dual response is controlled by DELLA proteins that, through the interaction with transcription factors, inhibit cell cycle progression and simultaneously activate stress responses. This project has explored the possibility of separating these DELLA functions in growth and defence. Preliminary unpublished data in the group shows that loss-of-function in the SMR1 gene, a negative regulator of the cell cycle, partially suppresses the defect in stem elongation of gai-1D semi-dwarf mutants. We have characterized with detail inflorescence growth in gai-1D;smr1-1 and RGAp:GFP- rga¿17;smr1-1 plants and analyzed their response to extreme drought stress conditions. In addition, we have generated a set of SMR1 reporter lines to examine SMR1 expression pattern in the inflorescence stem and to study how it is regulated by DELLA proteins.

[EN] The thickening of plant organs is supported by secondary growth, a process by which new vascular tissues (xylem and phloem) are produced. Xylem is composed of several cell types, including xylary fibers, parenchyma and vessel elements. In Arabidopsis, it has been shown that fibers are promoted by the class-I KNOX gene KNAT1 and the plant hormones gibberellins, and are repressed by a small set of receptor-like kinases; however, we lack a mechanistic framework to integrate their relative contributions. Here, we show that DELLAs, negative elements of the gibberellin signaling pathway, physically interact with KNAT1 and impair its binding to KNAT1-binding sites. Our analysis also indicates that at least 37% of the transcriptome mobilized by KNAT1 is potentially dependent on this interaction, and includes genes involved in secondary cell wall modifications and phenylpropanoid biosynthesis. Moreover, the promotion by constitutive overexpression of KNAT1 of fiber formation and the expression of genes required for fiber differentiation were still reverted by DELLA accumulation, in agreement with post-translational regulation of KNAT1 by DELLA proteins. These results suggest that gibberellins enhance fiber development by promoting KNAT1 activity.

The thickening of plant organs is supported by secondary growth, a process by which new vascular tissues (xylem and phloem) are produced. Xylem is composed of several cell types, including xylary fibers, parenchyma and vessel elements. In Arabidopsis, it has been shown that fibers are promoted by the class-I KNOX gene KNAT1 and the plant hormones gibberellins, and repressed by a small set of receptor-like kinases, but we lack a mechanistic framework to integrate their relative contributions. Here we show that DELLAs, negative elements of the gibberellin signaling pathway, physically interact with KNAT1 and impair its binding to KNAT1 binding sites. Our analysis also indicates that at least 37% of the transcriptome mobilized by KNAT1 is potentially dependent on this interaction, and includes genes involved in secondary cell wall modifications and phenylpropanoid biosynthesis. Moreover, the promotion by constitutive overexpression of KNAT1 of fiber formation and the expression of genes required for fiber differentiation were still reverted by DELLA accumulation, in agreement with post-translational regulation of KNAT1 by DELLA proteins. These results suggest that gibberellins enhance fiber development by promoting KNAT1 activity.

"This is an Accepted Manuscript of an article published by Taylor & Francis in Plant Signaling and Behaviour on 21-09-2017, available online: https://www.tandfonline.com/doi/full/10.1080/15592324.2017.1370164.", [EN] The gene regulatory network comprised of LEAFY (LFY), APETALA1 (AP1), the AP1 paralog CAULIFLOWER (CAL), and TERMINAL FLOWER1 (TFL1) is a major determinant of the flowering process in Arabidopsis thaliana. TFL1 activity in the shoot apical meristem provides inflorescence identity while the transcription factors LFY and AP1/CAL confer floral identity to emerging floral primordia. It has been thought that LFY and AP1/CAL control the onset of flowering in part by repressing TFL1 expression in flowers. However, in the June issue of Plant Physiology, we reported that LFY and AP1 act antagonistically in the regulation of several key flowering regulators, including TFL1. Specifically, TFL1 transcription was suppressed by AP1 but promoted by LFY. Here, we present additional evidence for the role of LFY as an activator of TFL1 and propose that this regulatory activity is pivotal for the indeterminate growth of the SAM during the reproductive phase of development.

[EN] The transcription factors LEAFY (LFY) and APETALA1 (AP1), together with the AP1 paralog CAULIFLOWER (CAL), control the onset of flower development in a partially redundant manner. This redundancy is thought to be mediated, at least in part, through the regulation of a shared set of target genes. However, whether these genes are independently or cooperatively regulated by LFY and AP1/CAL is currently unknown. To better understand the regulatory relationship between LFY and AP1/CAL and to obtain deeper insights into the control of floral initiation, we monitored the activity of LFY in the absence of AP1/CAL function. We found that the regulation of several known LFY target genes is unaffected by AP1/CAL perturbation, while others appear to require AP1/CAL activity. Furthermore, we obtained evidence that LFY and AP1/CAL control the expression of some genes in an antagonistic manner. Notably, these include key regulators of floral initiation such as TERMINAL FLOWER1 (TFL1), which had been previously reported to be directly repressed by both LFY and AP1. We show here that TFL1 expression is suppressed by AP1 but promoted by LFY. We further demonstrate that LFY has an inhibitory effect on flower formation in the absence of AP1/CAL activity. We propose that LFY and AP1/CAL act as part of an incoherent feed-forward loop, a network motif where two interconnected pathways or transcription factors act in opposite directions on a target gene, to control the establishment of a stable developmental program for the formation of flowers.

The gene regulatory network comprised of LEAFY (LFY), APETALA1 (AP1), the AP1 paralog CAULIFLOWER (CAL), and TERMINAL FLOWER1 (TFL1) is a major determinant of the flowering process in Arabidopsis thaliana. TFL1 activity in the shoot apical meristem provides inflorescence identity while the transcription factors LFY and AP1/CAL confer floral identity to emerging floral primordia. It has been thought that LFY and AP1/CAL control the onset of flowering in part by repressing TFL1 expression in flowers. However, in the June issue of Plant Physiology, we reported that LFY and AP1 act antagonistically in the regulation of several key flowering regulators, including TFL1. Specifically, TFL1 transcription was suppressed by AP1 but promoted by LFY. Here, we present additional evidence for the role of LFY as an activator of TFL1 and propose that this regulatory activity is pivotal for the indeterminate growth of the SAM during the reproductive phase of development.

TERMINAL FLOWER 1 (TFL1) is a key regulator of Arabidopsis plant architecture that responds to developmental and environmental signals to control flowering time and the fate of shoot meristems. TFL1 expression is dynamic, being found in all shoot meristems, but not in floral meristems, with the level and distribution changing throughout development. Using a variety of experimental approaches we have analysed the TFL1 promoter to elucidate its functional structure. TFL1 expression is based on distinct cis-regulatory regions, the most important being located 3' of the coding sequence. Our results indicate that TFL1 expression in the shoot apical versus lateral inflorescence meristems is controlled through distinct cis-regulatory elements, suggesting that different signals control expression in these meristem types. Moreover, we identified a cis-regulatory region necessary for TFL1 expression in the vegetative shoot and required for a wild-type flowering time, supporting that TFL1 expression in the vegetative meristem controls flowering time. Our study provides a model for the functional organisation of TFL1 cis-regulatory regions, contributing to our understanding of how developmental pathways are integrated at the genomic level of a key regulator to control plant architecture.