RESUMEN
The development of multicellular organisms relies on the coordinated control of cell divisions leading to proper patterning and growth. The molecular mechanisms underlying pattern formation, particularly the regulation of formative cell divisions, remain poorly understood. In Arabidopsis, formative divisions generating the root ground tissue are controlled by SHORTROOT (SHR) and SCARECROW (SCR). Here we show, using cell-type-specific transcriptional effects of SHR and SCR combined with data from chromatin immunoprecipitation-based microarray experiments, that SHR regulates the spatiotemporal activation of specific genes involved in cell division. Coincident with the onset of a specific formative division, SHR and SCR directly activate a D-type cyclin; furthermore, altering the expression of this cyclin resulted in formative division defects. Our results indicate that proper pattern formation is achieved through transcriptional regulation of specific cell-cycle genes in a cell-type- and developmental-stage-specific context. Taken together, we provide evidence for a direct link between developmental regulators, specific components of the cell-cycle machinery and organ patterning.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/genética , Tipificación del Cuerpo/genética , Tipificación del Cuerpo/fisiología , Genes cdc/fisiología , Factores de Transcripción/metabolismo , Arabidopsis/citología , Arabidopsis/embriología , Proteínas de Arabidopsis/genética , Ciclo Celular/genética , Ciclo Celular/fisiología , División Celular/genética , Ciclina D/genética , Ciclina D/metabolismo , Quinasas Ciclina-Dependientes/metabolismo , Regulación de la Expresión Génica de las Plantas , Organogénesis/genética , Organogénesis/fisiología , Raíces de Plantas/citología , Raíces de Plantas/embriología , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Factores de Tiempo , Factores de Transcripción/genéticaRESUMEN
The immature pollen grain, the microspore, under stress conditions can switch its developmental program towards proliferation and embryogenesis. The comparison between the gametophytic and sporophytic pathways followed by the microspore permitted us to analyse the nuclear changes in plant differentiating cells when switched to proliferation. The nucleus is highly dynamic, the architecture of its well organised functional domains--condensed chromatin, interchromatin region, nuclear bodies and nucleolus--changing in response to DNA replication, RNA transcription, processing and transport. In the present work, the rearrangements of the nuclear domains during the switch to proliferation have been determined by in situ molecular identification methods for the subcellular localization of chromatin at different functional states, rDNA, elements of the nuclear machinery (PCNA, splicing factors), signalling and stress proteins. The study of the changes in the nuclear domains was determined by a correlative approach at confocal and electron microscopy levels. The results showed that the switch of the developmental program and the activation of the proliferative activity affected the functional organization of the nuclear domains, which accordingly changed their architecture and functional state. A redistribution of components, among them various signalling molecules which targeted structures within the interchromatin region upon translocation from the cytoplasm, was also observed.