RESUMO
Meristems are centers of cell proliferation with a defined internal structure that is dynamically perpetuated throughout a plant's life although its constituent cells constantly change. When progressing from stem cell state towards differentiation, individual cells adopt developmental programs according to their current position within the meristem provided by signals from neighboring cells. In recent years, progress has been made in the identification of signaling pathways and their integration into mechanistic networks.
Assuntos
Arabidopsis/fisiologia , Flores/fisiologia , Meristema/fisiologia , Brotos de Planta/fisiologia , Transdução de Sinais/fisiologia , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Flores/genética , Flores/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Ácidos Indolacéticos/metabolismo , Luz , Meristema/genética , Meristema/metabolismo , MicroRNAs/genética , MicroRNAs/metabolismo , Brotos de Planta/genética , Brotos de Planta/metabolismo , Transdução de Sinais/genética , Transdução de Sinais/efeitos da radiaçãoRESUMO
A long-standing question in plants and animals is how spatial patterns are maintained within stem cell niches despite ongoing cell divisions. Here we address how, during shoot meristem formation in Arabidopsis thaliana, the three apical cell layers acquire stem cell identity. Using a sensitized mutant screen, we identified miR394 as a mobile signal produced by the surface cell layer (the protoderm) that confers stem cell competence to the distal meristem by repressing the F box protein LEAF CURLING RESPONSIVENESS. This repression is required to potentiate signaling from underneath the stem cells by the transcription factor WUSCHEL, maintaining stem cell pluripotency. The interaction of two opposing signaling centers provides a mechanistic framework of how stem cells are localized at the tip of the meristem. Although the constituent cells change, the surface layer provides a stable point of reference in the self-organizing meristem.