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Resumen del póster presentado al Congreso 'At the Forefront of Plant Research', celebrado en Barcelona (España) del 6 al 8 de mayo de 2019., Plant development is influenced by multiple internal and external factors. Among these, light is of utmost importance due to its function as source of energy and also as an information signal. After the first light exposure, seedlings undergo deetiolation, whereby development switches from skotomorphogenic to photomorphogenic, characterized by the opening and expansion of the cotyledons and chloroplast development to support autotrophic growth. This process is accompanied by a massive reprogramming of the transcriptome. However, an excess of light can cause chloroplast damage, triggering a retrograde signal (RS) to the nucleus that suppresses photomorphogenesis by inhibiting the switch in gene expression that takes place during deetiolation. In this process, the chloroplast-localized protein GENOMES UNCOUPLED1 (GUN1) is a key factor mediating the RS, as gun1 mutants do not show the suppression of photomorphogenesis after chloroplast damage. However, how GUN1 mediates the RS transmitted to the nucleus remains unclear. We are performing a gain-of-function approach using the FOX (Full-length cDNA Over-eXpressing) gene hunting system (a library of about 10.000 independent cDNAs expressed under the 35S promoter) to identify suppressors of the gun1 mutant phenotype. These suppressors will potentially correspond to factors downstream of GUN1 in the RS pathway that are able to restore the communication between the chloroplast and the nucleus in the gun1 mutant.

Resumen del póster presentado al Congreso 'At the Forefront of Plant Research', celebrado en Barcelona (España) del 6 al 8 de mayo de 2019., Retrograde signaling from chloroplast to nucleus has been reported to be critical to adjust chloroplast biogenesisand modulate growth and development in Arabidopsis. GENOMES UNCOUPLED 1 (GUN1), a chloroplast-localized pentatricopeptide-repeatprotein, integrates multiple signals derived from plastid and takes an importantrole in retrograde signaling communication. Furthermore, GUN1-mediated retrograde signaling pathwaysregulate early seedling photomorphogenesis under excessive light condition by suppressing GOLDEN2-LIKE 1(GLK1) expression. In contrast, whether chloroplast retrograde signaling regulates seedling photomorphogenesis in monocotyledonsis less studied. In rice, many pentatricopeptiderepeatproteins have been found to be required for chloroplast development, seedling growth and abiotic stress response. In addition, OsGLK1 has been described to regulatechloroplast development under the control of light and phytohormones. These results suggest that GUN and GLK may regulate chloroplast development by a mechanism conserved in Oryza sativaand Arabidopsis. Our experimental system and recent data on the role of retrograde signaling in light-regulated rice developmentwill be discussed.

Resumen del póster presentado al Congreso 'At the Forefront of Plant Research', celebrado en Barcelona (España) del 6 al 8 de mayo de 2019., Besides their well-described role in photosynthesis, chloroplasts act as environmental sensors that are able to regulate nuclear gene expression in response to developmental cues and different stresses. This chloroplast-to-nucleus communication is termed retrograde signaling (RS) and it is a key component in the control of plant growth and development. Despite its essential role, the RS pathway is still poorly understood and many molecular components remain uncharacterized. Most studies on RS have been done in the model plant Arabidopsis thaliana. Here, I present the green unicellular microalga Chlamydomonas reinhardtii as a simpler and advantageous model to address fundamental aspects of RS and find novel RS molecular components. To this end, I will describe the impact of RS in Chlamydomonas physiology and present specific genetic screening strategies and transcriptomic analysis to pinpoint gene regulators of putative positive and negative retrograde signals, and study the crosstalk and timing of light and retrograde control during chloroplast biogenesis, two outstanding questions in the RS field.

Trabajo presentado al Internal Seminar of the Centre de Recerca Agrigenómica (CRAG), celebrado el 15 de noviembre de 2019.

A balance between dark and light signaling directs seedling establishment through integrating internal and environmental information.

Plants need to accurately adjust their development after germination in the underground darkness to ensure survival of the seedling, both in the dark and in the light upon reaching the soil surface. Recent studies have established that the photoreceptors phytochromes and the bHLH phytochrome interacting factors PIFs regulate seedling development to adjust it to the prevailing light environment during post-germinative growth. However, complete understanding of the downstream regulatory network implementing these developmental responses is still lacking. In a recent work, published in The Plant Cell, we report a subset of PIF3-regulated genes in dark-grown seedlings that we have named MIDAs (MISREGULATED IN DARK). Analysis of their functional relevance using mutants showed that four of them present phenotypic alterations in the dark, and that each affected a particular facet of seedling development, suggesting organ-specific branching in the signal that PIF3 relays downstream. Furthermore, our results also showed an altered response to light in seedlings with an impaired PIF3/MIDA regulatory network, indicating that these factors might also be essential to initiate and optimize the developmental adjustment of the seedling to the light environment., This work was supported by a Beatriu de Pinós fellowship from the “Comissionat per a Universitats i Recerca del Departament d’Innovació, Universitats i Empresa de la Generalitat de Catalunya” and by Marie Curie IRG PIRG06-GA-2009-256420 grant to P.L., and by grants Marie Curie IRG-046568, Spanish “Ministerio de Ciencia e Innovación” BIO2006-09254 and BIO2009-07675 and Generalitat de Catalunya 2009-SGR-206 to E.M.

En els últims trenta anys la planta angiosperma Arabidopsis thaliana ha estat l'organisme model utilitzat per milers de biòlegs. Arabidopsis s'autopol·linitza, té un genoma petit, té un cicle de vida curt, és de mida petita i té uns requisits de creixement senzills que la fan fàcil de fer créixer en condicions de laboratori. L'èxit d'Arabidopsis com a planta model es basa en la disponibilitat de mètodes genòmics i d'eines que han estimulat la recerca en la biologia de plantes i han facilitat la investigació d'un ampli ventall de preguntes biològiques. Aquest article explica alguns dels esdeveniments clau en la història d'Arabidopsis com a planta model, i en el creixement de la comunitat d'investigadors que la utilitzen per a la seva recerca. I també il·lustra com Arabidopsis ha facilitat la recerca, amb l'exemple en un camp d'especial interès en plantes: el de la percepció i resposta a la llum del seu entorn., The model plant Arabidopsis thaliana. During the past 30 years, the flowering plant Arabidopsis thaliana has been the model organism of choice for thousands of biologists. Arabidopsis is self-fertilizing, has a small genome, has a short life cycle, and the small size and simple growth requirements make it easy to grow in laboratory conditions. The extensive acceptance of Arabidopsis as a model plant is based on the genomic methods and resources that are available for it, which have greatly stimulated plant biological research and have facilitated the investigation of a range of biological questions. Here, we review some of the key events in the history of Arabidopsis as a model plant and the growth of the Arabidopsis research community. And we explain how Arabidopsis has facilitated the research in a field of particular importance in plants: the perception and response to their light environment.

l Plan de Eficiencia en el Consumo de Recursos (PECR) contempla en una de sus fases la realización de Auditorías Energéticas en las edificaciones de la UPC con el fin de establecer un panorama general del “Estado Actual” de los edificios, definiendo unos indicadores de su comportamiento energético a partir de los cuales se establecerán los objetivos de ahorro y eficiencia. Teniendo en cuenta que las normativas de ámbito europeo apuestan por la eficiencia energética, la reducción del impacto ambiental y la sostenibilidad de los edificios, este tipo de trabajo se enmarca dentro de una línea de investigación con un amplio panorama de aplicación hacia el futuro. A partir de este planteamiento se propuso crear una línea de proyectos finales de carrera para estudiantes de la Escuela Politécnica Superior de la Edificación (EPSEB) en diferentes fases en las que se realizarán las Auditorias Energéticas a los diferentes edificios de la Universidad, en función de la disponibilidad de información general de los edificios (Planos, datos de uso, acceso a instalaciones) y del consumo energético (Datos históricos, posibilidades de monitoreo, etc.)

Chloroplast biogenesis is indispensable for proper plant development and environmental acclimation. In a screen for mutants affected in photosynthesis, we identified the protein phosphatase7-like (pp7l) mutant, which displayed delayed chloroplast development in cotyledons and young leaves. PP7L, PP7, and PP7-long constitute a subfamily of phosphoprotein phosphatases. PP7 is thought to transduce a blue-light signal perceived by crys and phy a that induces expression of SIGMA FACTOR5 (SIG5). We observed that, like PP7, PP7L was predominantly localized to the nucleus in Arabidopsis (Arabidopsis thaliana), and the pp7l phenotype was similar to that of the sig6 mutant. However, SIG6 expression was unaltered in pp7l mutants. Instead, loss of PP7L compromised translation and ribosomal RNA (rRNA) maturation in chloroplasts, pointing to a distinct mechanism influencing chloroplast development. Promoters of genes deregulated in pp7l-1 were enriched in PHYTOCHROME-INTERACTING FACTOR (PIF)-binding motifs and the transcriptome of pp7l-1 resembled those of pif and CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1) signalosome complex (csn) mutants. However, pif and csn mutants, as well as cop1, cryptochromes (cry)1 cry2, and phytochromes (phy)A phyB mutants, do not share the pp7l photosynthesis phenotype. PhyB protein levels were elevated in pp7l mutants, but phyB overexpression plants did not resemble pp7l. These results indicate that PP7L operates through a different pathway and that the control of greening and photosystem biogenesis can be separated. The lack of PP7L increased susceptibility to salt and high-light stress, whereas PP7L overexpression conferred resistance to high-light stress. Strikingly, PP7L was specifically recruited to Brassicales for the regulation of chloroplast development. This study adds another player involved in chloroplast biogenesis., This work was supported by the Deutsche Forschungsgemeinschaft (project C01 no. KL 2362/1-1 to T.K. and project C05 no. TRR175 to D.L.).

Under photoperiodic conditions, Arabidopsis thaliana seedling growth is inhibited in long days (LDs), but promoted under the extended nights of short days (SDs). This behavior is partly implemented by phytochrome (phy)‐imposed oscillations in the abundance of the growth‐promoting, phy‐interacting bHLH transcription factors PHY‐INTERACTING FACTOR 1 (PIF1), PIF3, PIF4 and PIF5 (PIF quartet or PIFq). However, the observation that a pifq mutant is still stimulated to elongate when given a phy‐inactivating end‐of‐day far‐red pulse (EODFR), suggests that additional factors are involved in the phy‐mediated suppression of growth during the subsequent dark period. Here, by combining growth‐analysis of pif7 single‐ and higher‐order mutants with gene expression analysis under SD, LD, SD‐EODFR, and LD‐EODFR, we show that PIF7 promotes growth during the dark hours of SD, by regulating growth‐related gene expression. Interestingly, the relative contribution of PIF7 in promoting growth is stronger under EODFR, whereas PIF3 role is more important under SD, suggesting that PIF7 is a prominent target of phy‐suppression. Indeed, we show that phy imposes phosphorylation and inactivation of PIF7 during the light hours in SD, and prevents full dephosphorylation during the night. This repression can be lifted with an EODFR, which correlates with increased PIF7‐mediated gene expression and elongation. In addition, our results suggest that PIF7 function might involve heterodimerization with PIF3. Furthermore, our data indicate that a pifqpif7 quintuple mutant is largely insensitive to photoperiod for hypocotyl elongation. Collectively, the data suggest that PIF7, together with the PIFq, is required for the photoperiodic regulation of seasonal growth., This work was supported by Marie Curie International Reintegration Grant PIRG06‐GA‐2009‐256420 and by funds from Universitat Ramon Llull/Obra Social la Caixa (2016‐URL‐Internac‐019, 2018‐LC‐05 and 2018‐URL‐IR2nQ‐019) to P.L., by NIH (5R01GM047475‐24) and USDA ARS Current Research Information System (2030‐21000‐051‐00D) grants to P.H.Q., and by grants from the Spanish ‘Ministerio de Economía y Competitividad’ (MINECO) (BIO2012‐31672 and BIO2015‐68460‐P), by FEDER / Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación (Project Reference BIO2015‐68460‐P) and from the CERCA Programme/Generalitat de Catalunya (Project References 2014‐SGR‐1406 and 2017SGR‐718) to E.M. We acknowledge financial support by the CERCA Programme/Generalitat de Catalunya and from MINECO through the ‘Severo Ochoa Programme for Centers of Excellence in R&D’ 2016‐2019 (SEV‐2015‐0533).

[EN]: Plants perceive and integrate external (such as light and temperature) and internal (such as hormones or the circadian clock) signals to optimize growth and development in a changing environment. Light is used not only as a source of energy for plant photosynthesis, but also as a source of information to perceive the surrounding environment. Plants are armed with light sensitive proteins called photoreceptors that sense and transduce light signals to a core regulatory network that implements different facets of photomorphogenesis throughout plant life cycle. Studies in the model plant Arabidopsis thaliana have established that several transcriptional regulators such as the PHYTOCHROME INTERACTING FACTORS (PIFs) play a key role in this transcriptional network by regulating the expression of genes involved in different photomorphogenic processes such as seed germination, seedling deetiolation, diurnal and thermal growth, shade avoidance, or flowering. The downstream functions of this network and the implication of PIFs in other physiological and developmental responses remains poorly understood. The main objective of this work is to expand current understanding of the regulatory network acting downstream of PIFs during photomorphogenesis, and to define novel regulatory roles of PIFs during plant development. Previous studies had shown that MIDA9, a PIF3-regulated protein phosphatase 2C, regulates hook development during the post-germinative growth of the seedling. One of the aims of this thesis was to perform detailed genetic and phenotypic characterization of MIDA9 function, and we established that MIDA9 promotes the asymmetric growth required for the apical hook formation, possibly by altering ethylene biosynthesis. A second aim consisted in the definition of a novel role of PIFs in regulating stomata movements under diurnal conditions. We propose that PIFs accumulate at the end of the night to induce the expression of a factor that is necessary to promote stomata aperture in response to light at dawn. Moreover, light is suggested to reduce bioactive levels of ABA (Abscisic Acid) and release the repression that this hormone exerts during the night. Finally, we identified and characterized the function of KAT1 and MIDA9 as genes that modulate stomata movements downstream of the PIFs. Because regulation of stomata movements is essential to control water balance in plants, the identified regulatory components are candidate molecular targets for the development of drought resistant plants. Moreover, the described regulation of the apical hook development might contribute to the establishment and survival of the postgerminative seedling., [CA]: El desenvolupament i creixement de les plàntules està influenciat per senyals ambientals com ara la llum o la temperatura, i per senyals internes com ara les hormones o el rellotge circadià. Les plantes utilitzen la llum com a font d'energia per a realitzar la fotosíntesis i també com a font d'informació per percebre els canvis en l'entorn que les envolta. Per aquesta raó, les plantes tenen unes proteïnes sensibles a la llum anomenades fotoreceptors, que capten la llum i envien el senyal a una xarxa de regulació gènica que desencadena respostes fotomorfogèniques durant tot el seu cicle de vida. Els estudis fets en la planta model Arabidopsis thaliana han establert que els factors de transcripció anomenats Phytochrome Interacting Factors (PIFs) juguen un paper important durant aquesta resposta, regulant l'expressió de gens involucrats en processos fotomorfogènics com per exemple: la germinació, la desetiolació, el creixement diürn, la regulació del creixement a través de la temperatura, la resposta a la fugida de l'ombra i la floració. Altres processos fisiològics regulats per aquesta xarxa gènica encara estan poc estudiats. El principal objectiu d'aquest treball és ampliar el coneixement de la xarxa de regulació gènica controlada pels PIFs durant la fotomorfogènesis i definir noves funcions regulades pels PIFs durant el desenvolupament de la planta. En primer lloc, estudis previs han demostrat que MIDA9, una fosfatasa del tipus 2C, regula la formació del ganxo apical durant la postgerminació de la plàntula en foscor. Durant la tesi hem realitzat estudis genètics per caracteritzar la funció de MIDA9 i hem establert que és necessari per a promoure el creixement asimètric en l'hipocòtil, el qual és imprescindible per la formació del ganxo apical. Per altra banda, la majoria dels treballs publicats s'han focalitzat en entendre la funció dels PIFs durant el creixement de la planta. Per contra, pocs estudis s'han centrat a descobrir altres respostes fisiològiques regulades pels PIFs durant el creixement diürn. En aquest treball hem definit que l'acumulació dels PIFs al final de la nit és necessària per a regular el moviment dels estomes. Finalment, tot i que la funció de la xarxa gènica regulada pels PIFs ha estat caracteritzada durant aquests anys, en aquesta tesi hem identificat KAT1 i MIDA9 com a nous gens regulats pels PIFs, els quals participen en la modulació del moviment dels estomes. Ja que prèviament s'ha descrit que el control del moviment dels estomes és essencial per a regular el balanç hídric en plantes, aquest treball podria contribuir a la identificació de components que podrien ser dianes moleculars per a la generació de plantes resistents a la sequera. A més a més, hem contribuït a entendre millor el mecanisme involucrat en el desenvolupament del ganxo apical, un procés vital per a la supervivència de les plàntules.