Control del reloj circadiano por la señal fotoperiódica en plantas

Los organismos fotosintéticos son muy eficientes en la adaptación de su desarrollo a las condiciones ambientales. Para conseguir esta adaptación monitorizan continuamente los estímulos externos que les llegan del ambiente y promueven cambios fisiológicos, como ocurre con las modificaciones del transcriptoma. La luz solar es esencial para la supervivencia de los organismos fotosintéticos, ya que constituye su principal fuente de energía y controla múltiples aspectos de su fisiología. En la percepción de la luz en plantas y algas participan un conjunto de receptores y factores de transcripción que conectan las señales procedentes de la luz con cambios específicos en la expresión génica. La existencia de eventos externos cíclicos muy predecibles como la sucesión de días/noches o de las estaciones, permite coordinar y anticipar de manera muy robusta los procesos biológicos. Esta medida del tiempo es llevada a cabo por un oscilador interno denominado reloj circadiano. Por otra parte, la señalización de la vía fotoperiódica permite a los organismos vegetales medir la longitud del día y así obtener información estacional para controlar complejos procesos que son clave para su supervivencia como la floración. Uno de los genes centrales en esta vía es CONSTANS, que está regulado a nivel transcripcional y postraduccional por el reloj circadiano y por señales luminosas. En esta tesis doctoral se ha seguido un enfoque de Biología Molecular de Sistemas para entender cómo han evolucionado estos procesos a lo largo del linaje verde, se han generado herramientas para su estudio y finalmente se ha descrito una nueva conexión entre el reloj circadiano y la vía fotoperiódica en la planta modelo Arabidopsis thaliana. En una primera aproximación investigamos la evolución de la expresión génica diaria en el linaje vegetal, empleando las microalgas Ostreococcus tauri y Chlamydomonas reinhardtii y la planta superior Arabidopsis thaliana. Inicialmente, realizamos un estudio de ortología que ha revelado por una parte la aparición de genes específicos en Chamydomonas y Arabidopsis y por otra parte la amplificación y diversificación de familias génicas. Además, hemos investigado cómo ha cambiado la influencia de los ciclos día/noche sobre el transcriptoma a lo largo de la evolución vegetal mediante la construcción de redes de co-expresión en ciclos de luz/oscuridad. Nuestros resultados indican una mayor dependencia de los ciclos diurnos en microalgas que en plantas. En cuanto a la evolución de los patrones de expresión, hemos observado un alto nivel de conservación en genes que se expresan en las transiciones luz/oscuridad a pesar de la gran distancia evolutiva entre algas y plantas. Estos resultados pueden ser explorados en la herramienta CircadiaNet. En segundo lugar, construimos la red transcripcional ATTRACTOR que integra datos transcriptómicos y datos de ChIP-seq de factores de transcripción involucrados en el reloj circadiano y en la señalización por luz. De esta forma, el estudio de la red permite investigar la regulación coordinada del reloj circadiano y la señalización lumínica sobre la expresión génica en Arabidopsis. Mediante el análisis topológico de ATTRACTOR hemos descrito que estos programas transcripcionales poseen la característica conocida como “robusto pero frágil”, es decir, son robustos frente a ataques aleatorios y frágiles frente a ataques dirigidos a genes altamente conectados. Por otra parte, se ha demostrado que los genes cuya regulación es más dependiente del reloj circadiano se expresan durante las primeras horas de la mañana, modulando procesos concretos como respuesta inmune, respuesta a hormonas o crecimiento. Además, se ha descrito que algunos motivos de red compuestos por varios factores de transcripción pueden explicar la regulación de determinados aspectos del desarrollo, dando lugar a propiedades emergentes. Por ejemplo, el motivo formado por CCA1, PIF y PRR5 participa en la respuesta a sequía y frío. Para este fin, se ha desarrollado una aplicación web para su exploración por parte de la comunidad científica. Por último, utilizando estas herramientas, hemos demostrado un nuevo papel para CO en la regulación del reloj circadiano en Arabidopsis. CO formaría parte de una señalización retrógrada desde la vía fotoperiódica hacia el oscilador central, proporcionando información estacional al reloj. En condiciones de día largo, CO se une a genes centrales del reloj circadiano para alterar su perfil de expresión. Uno de estos genes es el PSEUDO RESPONSE REGULATOR 5 (PRR5), con el que además comparte sitios de unión en el genoma. Por ello, CO y PRR5 establecen un motivo de doble retroalimentación con salida múltiple regulando genes diana en común. Además, hemos encontrado que CO se une a motivos de DNA G-box en estos promotores, probablemente a través del factor de transcripción bZIP LONG HYPOCOTIL 5 (HY5).Photosynthetic organisms are highly efficient in the adaptation of their development to environmental conditions. To achieve this, they continuosly track the external stimuli and promote physiological changes, which can be readily checked by transcriptome modifications. Sunlight is essential for plant survival as it is the main energy source and controls multiple aspects of their physiology. In plants and algae, light perception is carried out by several receptors and transcription factors that connect light signals with specific changes in gene expression. The existence of highly predictable cyclical external events, such as the succession of days/nights or seasons, allows them to coordinate and anticipate biological processes in a robust way. This daily time measurement is performed by an internal oscillator called circadian clock. Alternatively, the photoperiodic regulatory pathway allows plants and algae to measure the day length and obtain seasonal information to control complex processes that are key to their survival, such as flowering. One of the key genes in this pathway is CONSTANS, which is regulated at transcriptional and posttranslational levels by the circadian clock and by light signals. In this doctoral thesis, a Molecular Systems Biology approach was chosen to try to understand how these processes have evolved along the green lineage. Several tools have been generated for their study and a new connection between the circadian clock and the photoperiodic pathway has been described in the model plant Arabidopsis thaliana. Firstly, we studied the diurnal gene expression evolution along the plant lineage, using the microalgae Ostreococcus tauri and Chlamydomonas reinhardtii and the spermatophyte Arabidopsis thaliana. Initially, we have carried out an orthology analysis that has revealed, on the one hand, the emergence of specific genes in Chamydomonas and Arabidopsis and, on the other hand, the amplification and diversification of gene families between plants and algae. In addition, we have investigated the influence raised by day/night cycles on the transcriptome throughout evolution by constructing gene networks of light/dark samples. Our results indicate a greater dependence on diurnal cycles in microalgae than in plants. Regarding the evolution of expression patterns, we have observed a high level of conservation in genes that are expressed in light/dark transitions despite the great evolutionary distance between algae and plants. These results can be explored in the CircadiaNet web. Second, the ATTRACTOR transcriptional network allows to elucidate the coordinated regulation of circadian clock and light signalling on Arabidopsis gene expression. Through the topological analysis of the network, we have shown that these transcriptional programs have the property known as “robust but fragile”, meaning that they are robust against random failures and fragile against attacks directed at highly connected genes. Furthermore, we have shown that those genes whose regulation is more dependent on the circadian clock are expressed during the first hours of the morning, modulating specific processes such as the plant pathogen interaction, response to hormones or growth. In addition, it has been described that network motifs constituted by several transcription factors may help to explain the regulation of certain aspects of development, giving rise to emergent properties. For example, the CCA1/PIF5/PRR5 network motif participates in the response to drought and cold. For this reason, a web application has been developed and is available for the scientific community. Finally, using these tools, we have demonstrated a new role for CO in the regulation of the circadian clock in Arabidopsis. CO would participate in a retrograde signaling from the photoperiodic pathway to the central oscillator, providing seasonal information to the system. Under long-day conditions, CO could bind the promoter of core genes of the circadian clock to alter its expression profile. One of these genes is the PSEUDO RESPONSE REGULATOR 5 (PRR5), which also shares CO binding sites in the genome. Therefore, CO and PRR5 establish a double feedback motif with multiple output regulating common target genes. Furthermore, we have found that CO binds to G-box DNA motifs in these promoters, probably through a bZIP transcription factor, such as LONG HYPOCOTIL 5 (HY5)

Characterization of the sucrose phosphate phosphatase (SPP) isoforms from Arabidopsis thaliana and role of the S6PPc domain in dimerization

Sucrose-phosphate phosphatase (SPP) catalyses the final step in the sucrose biosynthesis pathway. Arabidopsis thaliana genome codifies four SPP isoforms. In this study, the four Arabidopsis thaliana genes coding for SPP isoforms have been cloned, expressed in Escherichia coli and the kinetic and regulatory properties of the purified enzymes analysed. SPP2 is the isoform showing the highest activity, with SPP3b and SPP3a showing lower activity levels. No activity was detected for SPP1. We propose that this lack of activity is probably due to the absence of an essential amino acid participating in catalysis and/or in the binding of the substrate, sucrose-6-phosphate (Suc6P). The expression patterns of Arabidopsis SPP genes indicate that SPP2 and SPP3b are the main isoforms expressed in different tissues and organs, although the non-catalytic SPP1 is the main isoform expressed in roots. Thus, SPP1 could have acquired new unknown functions. We also show that the three catalytically active SPPs from Arabidopsis are dimers. By generating a chimeric SPP composed of the monomeric cyanobacterial SPP fused to the higher plant non-catalytic S6PPc domain (from SPP2), we show that the S6PPc domain is responsible for SPP dimerization. This is the first experimental study on the functionality and gene expression pattern of all the SPPs from a single plant species.Ministerio de Economía y Competitividad TRANSPLANTA Consolider 28317Junta de Andalucía P08-AGR-03582 y CVI-28

Exergy analysis of solar central receivers

A high-resolution method to analyse the exergy of the SPT external tubular receivers is presented, examining the different heat transfer process involved individually. This sheds light on the role that each irreversibility source plays in the outcome, aiding in the receiver design and the facility location selection. The exergy efficiency is around 32% in the base configuration. Besides the exergy loss in the heliostat field, over 40%, it is found that the biggest exergy destruction cause are the radiation emissions and absorptions in the tube outer surface, around 17%. From the remaining ones, the greatest are the exergy destructed in the HTF and the one escaping to the ambient (over 4% each). Then, the exergy balance for a variety of strategies and ambient conditions is performed: optical properties of the tubes coating, peak and flat aiming strategies, DNI and ambient temperature. The heliostat field exergy loss rate only varies when changing the aiming. However, the emission and absorption losses and the ones in the HTF suffer the greater modifications with all the parameters studied. The impact of the optical properties degradation, 1% descent in the efficiency per 5% degradation, would advise repainting works in order to avoid greater exergy destruction. The surroundings temperature modification impacts considerably the exergy efficiency, showing the suitability of locations with low ambient temperature and a moderate DNI: descends of over 0.35% occur every 5 °C increase of the temperature for a fixed DNI.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario"; (FPU-02361) awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the fellowship"Ayuda a la investigación en energía y medio ambiente" of the Iberdrola España Foundation, the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I+D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

Assessment of the time resolution used to estimate the central solar receiver lifetime

This study assesses the impact of the time resolution and design day on the estimated lifetime of the molten-salt external tubular receiver of a solar power tower, one of the most damaged components of these facilities, considering operation under clear conditions. A global analysis is performed by first determining the heliostat field aiming strategy; the receiver operation limits are set to keep a low enough film temperature and to avoid the stress reset. The former prevents excessive corrosion rates of the tubes while the latter assures the global stress relaxation, which significantly reduces their damage during the receiver cyclic operation. Time steps of 60, 30, 15, 5 and 1 min are tested considering the spring equinox design day, as well as only solar noon conditions. The latter significantly underpredicts the receiver lifetime with respect to the 1-min case, being early discarded. The lifetime in the most damaged panel is underestimated over 18% and 16% using the 60- and 30-minute time steps, dropping to 2.57% using the 5-min time step at a reasonable computational cost. Finer resolutions enable more precise aiming strategy selection, decreasing the receiver peak fluxes. Lastly, a set of 8 representative days for the year, equally spaced in solar height, is more accurate than using the spring equinox alone, which results in an underestimate of the receiver lifetime that may be overly conservative. The summer solstice is the least-damaging day, with the lifetime decreasing as approaching the winter one, as long as the storage tank is filled.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario" (FPU-02361) awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I + D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the projects RETOrenovable-CM-UC3M and ZEROGASPAIN-CM-UC3M, funded on the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

Material selection for solar central receiver tubes

The severe operation conditions and great capital investment of solar power tower central receivers motivate the lifetime analysis of a molten-salt external-cylindrical-tubular receiver, considering five alloy alternatives for its tubes manufacturing: Haynes 230, alloy 316H, Inconel 625, 740H and 800H. An analytical low-computational cost methodology is employed, considering the temperature dependence of tube material properties, elastic-plastic stresses/strains and stress relaxation. Thus, creep and fatigue experimental data available in the literature for these alloys are compiled in this work, providing the coefficients required for the methodology followed. A great alloys operation limitation is the film temperature to avoid corrosion issues; the most permissive are H230, 740H and 800H (650 °C), followed by Inconel 625 (630 °C) and 316H (600 °C). This, and the twice the yield strength, is regarded to set the heliostat field aiming strategy as equatorial as possible for each alloy, resulting in great power production divergences: 24% and 65% less for 625 and alloy 316H receivers with respect to the 740H receiver. Then, the lifetime analysis for a clear design day operation, representative of the receiver during ideal operation, is performed. The stress relaxation regard becomes critical for the accurate damage prediction; alloys 316H and 800H show stress reset during operation, not benefitting from a global stress relaxation. Thus, 800H exhibits a poor endurance. For the clear-day assumption, 740H shows the best lifetime and costs/power performance; the levelized cost of alloy of H230, 625 and alloy 316H is 0.01, 0.09 and over 0.25, respectively, with respect to 740H.This research is partially funded by the scholarship "Ayudas para la formación del profesorado universitario" [grant number FPU-02361] awarded by the Spanish Ministerio de Educación, Cultura y Deporte (MECD), the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE) and the call "Programa de apoyo a la realización de proyectos interdisciplinares de I+D para jóvenes investigadores de la Universidad Carlos III de Madrid 2019-2020", under the projects RETOrenovable-CM-UC3M [grant number 2020/00034/001] and ZEROGASPAIN-CM-UC3M [grant number 2020/00033/001], funded on the frame of the Convenio Plurianual Comunidad de Madrid- Universidad Carlos III de Madrid

ALGAEFUN with MARACAS, microALGAE FUNctional enrichment tool for MicroAlgae RnA-seq and Chip-seq AnalysiS

Background Microalgae are emerging as promising sustainable sources for biofuels, biostimulants in agriculture, soil bioremediation, feed and human nutrients. Nonetheless, the molecular mechanisms underpinning microalgae physiology and the biosynthesis of compounds of biotechnological interest are largely uncharacterized. This hinders the development of microalgae full potential as cell-factories. The recent application of omics technologies into microalgae research aims at unraveling these systems. Nevertheless, the lack of specific tools for analysing omics raw data generated from microalgae to provide biological meaningful information are hampering the impact of these technologies. The purpose of ALGAEFUN with MARACAS consists in providing researchers in microalgae with an enabling tool that will allow them to exploit transcriptomic and cistromic high-throughput sequencing data. Results ALGAEFUN with MARACAS consists of two different tools. First, MARACAS (MicroAlgae RnA-seq and Chip-seq AnalysiS) implements a fully automatic computational pipeline receiving as input RNA-seq (RNA sequencing) or ChIP-seq (chromatin immunoprecipitation sequencing) raw data from microalgae studies. MARACAS generates sets of differentially expressed genes or lists of genomic loci for RNA-seq and ChIP-seq analysis respectively. Second, ALGAEFUN (microALGAE FUNctional enrichment tool) is a web-based application where gene sets generated from RNA-seq analysis as well as lists of genomic loci from ChIP-seq analysis can be used as input. On the one hand, it can be used to perform Gene Ontology and biological pathways enrichment analysis over gene sets. On the other hand, using the results of ChIP-seq data analysis, it identifies a set of potential target genes and analyses the distribution of the loci over gene features. Graphical representation of the results as well as tables with gene annotations are generated and can be downloaded for further analysis. Conclusions ALGAEFUN with MARACAS provides an integrated environment for the microalgae research community that facilitates the process of obtaining relevant biological information from raw RNA-seq and ChIP-seq data. These applications are designed to assist researchers in the interpretation of gene lists and genomic loci based on functional enrichment analysis. ALGAEFUN with MARACAS is publicly available on https://greennetwork.us.es/AlgaeFUN/.España Ministerio de Ciencia e Innovación project MINOTAUR (BIO2017-84066-R

Thermodynamic and economic assessment of a new generation of subcritical and supercritical solar power towers

The feasibility of using more efficient Rankine power blocks in solar power towers (SPTs) with molten salt as the heat transfer fluid has been studied as a method for increasing the global efficiency of these power plants. The temperature and pressure of the main steam and the reheating pressure affect the temperature of the molten salt in the receiver; for temperature increase decreasing the receiver efficiency and increasing the power block efficiency. Therefore, a detailed study of these SPTs has been conducted to determine whether the proposed changes increase the global efficiency of the SPTs. A total of eight different subcritical and supercritical SPTs have been investigated. To set the most important cost of the SPT, the same heliostat field has been used. The receiver geometry has been optimised for each SPT to maximise the heliostat-receiver efficiency, fulfilling the material limitations. It has been observed that the pressure at the inlet of the turbine increases the SPT efficiency even more than the temperature. However, special attention has to be paid to the reheating pressure, which is the most influential factor on the SPT efficiency. A high reheating pressure considerably decreases the SPT efficiency. Therefore, the best efficiencies have been obtained for the supercritical SPTs with a low reheating pressure and high temperature. It is closely followed by subcritical SPTs at high pressure and temperature. The investment cost of the different SPTs also increases with the pressure and the temperature of the PB, with subcritical SPTs being less expensive than supercritical SPTs. However, the cost increase is balanced by the increase in the efficiency. The same cost per kWe is found in subcritical SPTs working at 16 MPa and in supercritical SPTs with low reheating pressure

CONSTANS–FKBP12 interaction contributes to modulation of photoperiodic flowering in Arabidopsis

Flowering time is a key process in plant development. Photoperiodic signals play a crucial role in the floral transition in Arabidopsis thaliana, and the protein CONSTANS (CO) has a central regulatory function that is tightly regulated at the transcriptional and post-translational levels. The stability of CO protein depends on a light-driven proteasome process that optimizes its accumulation in the evening to promote the production of the florigen FLOWERING LOCUS T (FT) and induce seasonal flowering. To further investigate the post-translational regulation of CO protein we have dissected its interactome network employing in vivo and in vitro assays and molecular genetics approaches. The immunophilin FKBP12 has been identified in Arabidopsis as a CO interactor that regulates its accumulation and activity. FKBP12 and CO interact through the CCT domain, affecting the stability and function of CO. fkbp12 insertion mutants show a delay in flowering time, while FKBP12 overexpression accelerates flowering, and these phenotypes can be directly related to a change in accumulation of FT protein. The interaction is conserved between the Chlamydomonas algal orthologs CrCO–CrFKBP12, revealing an ancient regulatory step in photoperiod regulation of plant development.Ministerio de Ciencia BIO2014-52425-P, BIO2017-83629-RJunta de Andalucía P08-AGR-03582, BIO-281European Union GA83831

H2AK121ub in Arabidopsis associates with a less accessible chromatin state at transcriptional regulation hotspots

Although it is well established that the Polycomb Group (PcG) complexes maintain gene repression through the incorporation of H2AK121ub and H3K27me3, little is known about the effect of these modifications on chromatin accessibility, which is fundamental to understand PcG function. Here, by integrating chromatin accessibility, histone marks and expression analyses in different Arabidopsis PcG mutants, we show that PcG function regulates chromatin accessibility. We find that H2AK121ub is associated with a less accessible but still permissive chromatin at transcriptional regulation hotspots. Accessibility is further reduced by EMF1 acting in collaboration with PRC2 activity. Consequently, H2AK121ub/H3K27me3 marks are linked to inaccessible although responsive chromatin. In contrast, only-H3K27me3-marked chromatin is less responsive, indicating that H2AK121ub-marked hotspots are required for transcriptional responses. Nevertheless, despite the loss of PcG activities leads to increased chromatin accessibility, this is not necessarily accompanied by transcriptional activation, indicating that accessible chromatin is not always predictive of gene expression.National Natural Science Foundation of China 31970532Ministerio de Ciencia e Innovación BIO2016-76457-P, PID2019-106664GB-I00, BIO2017-84066-

The Spanish Infrared Camera onboard the EUSO-BALLOON (CNES) flight on August 24, 2014

The EUSO-Balloon (CNES) campaign was held during Summer 2014 with a launch on August 24. In the gondola, next to the Photo Detector Module (PDM), a completely isolated Infrared camera was allocated. Also, a helicopter which shooted flashers flew below the balloon. We have retrieved the Cloud Top Height (CTH) with the IR camera, and also the optical depth of the nonclear atmosphere have been inferred with two approaches: The first one is with the comparison of the brightness temperature of the cloud and the real temperature obtained after the pertinent corrections. The second one is by measuring the detected signal from the helicopter flashers by the IR Camera, considering the energy of the flashers and the location of the helicopter