# name
Identification of suppressors of the constitutive photomorphogenic phenotype of pifq: from chloroplasts to rhythmic growth

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Universitat de Barcelona. Facultat de Biologia

# metadata.dc.description.abstract[].value
[spa]   	 Las plantas, durante todo su ciclo vital, adaptan constantemente su desarrollo y crecimiento a los cambios que se producen en el ambiente que las rodea. En periodos de oscuridad, ya sea cuando las plantas germinan bajo la superficie de la tierra o cuando crecen en condiciones diurnas (noche y día), se acumulan en el núcleo los factores de transcripción llamados Phytochrome Interacting Factors (PIFs). Estos factores de transcripción regulan la expresión de miles de genes con el fin de inducir crecimiento y reprimir el desarrollo fotomorfogénico. Tras la germinación en oscuridad, una vez las plantas alcanzan la superficie y se exponen a la luz, los fitocromos, fotoreceptores que perciben la presencia de luz roja y roja lejana, se activan y se traslocan al núcleo, donde inducen la degradación de los factores de transcripción PIFs. La degradación de estas proteínas produce amplios cambios en el transcriptoma de las plantas induciendo el desarrollo fotomorfogénico. Al inicio de la tesis, las redes transcripcionales reguladas por los PIFs habían sido descritas, sin embargo, los genes que inician la cascada transcripcional que implementan las funciones celulares que permiten a las plantas desarrollarse fotomorfogénicamente eran desconocidos. Nuestro principal objetivo ha sido determinar estos genes, para ello realizamos un cribado de supresores del fenotipo fotomorfogénico constitutivo de plantas mutantes de genes PIF. Los resultados del cribado nos han permitido identificar nuevos reguladores del desarrollo fotomorfogénico que actúan como intermediarios de la cascada de señalización iniciada por los factores de transcripción PIF. Estos resultados permiten ampliar el conocimiento de la función transcripcional de los PIFs, mostrando ejemplos específicos de genes tanto inducidos como reprimidos. Además, nuestro trabajo ha permitido determinar que la biogénesis del cloroplasto es un proceso necesario para que las plantas se desarrollen fotomorfogénicamente.

# metadata.dc.description.abstract[].value
[eng]  Plants germinated in the dark under the soil surface, undergo skotomorphogenic development. Once they emerge from the soil surface perceive light for the first time. Then, seedlings switch from skotomorphogenic to photomorphogenic development, a process that is known as seedling deetiolation. At this moment, seedlings rapidly form the photosynthetic apparatus to start to produce energy and avoid photodamage. In addition, seedlings adapt their morphology to enhance light capture for photosynthesis, inhibiting hypocotyl elongation and stimulating cotyledon separation and expansion. At the molecular level, after first exposure to light, phytochromes photoreceptors interact with a subgroup of transcription factors named PIFs (Phytochrome Interacting Factors). This light-induced interaction between the phytochromes and PIF initiates a cascade of transcriptional changes that allows plants to adjust to the new light environment. At the beginning of this thesis, the PIF-regulated transcriptional networks that operate during photomorphogenesis had been described. However, the primary target genes that implement downstream cellular functions or amplify the PIF signaling pathway had not yet been identified. Therefore the main goal of this work was to identify the downstream effector genes of the PIF transcription factors to elucidate the PIF-regulated transcriptional network that represses photomorphogenic development. In order to identify new regulators of seedling deetiolation acting downstream of PIF transcription factors, we designed a genetic screen to search for mutants that suppress the constitutive photomorphogenic phenotype of the pifq mutant. Interestingly, our genetic screen has allowed the identification of 23 genes that suppress or enhance the pifq constitutive photomorphogenic phenotype. Among them, we found a big representation of genes codifying for chloroplast proteins, then, we decided to study the interplay of chloroplast biogenesis (a PIF-regulated process) and chloroplast retrograde signaling in the regulation of seedling deetiolation. The work performed allowed us to determine that dysfunctions in chloroplast biogenesis repress photomorphogenesis, through the transcriptional repression of light induced-PIF repressed genes, in order to adjust seedling development to the photosynthetic capacity of the chloroplast. Moreover, we studied the role of CDF5, a transcription factor found in our suppressor screening, and we concluded that the transcriptional regulation of CDF5 by the circadian clock and the PIF transcription factors defines a novel mechanism of regulation of growth under diurnal conditions.

# metadata.dc.title[].value
Identification of suppressors of the constitutive photomorphogenic phenotype of pifq: from chloroplasts to rhythmic growth