RESUMO
Thorns arise from axillary shoot apical meristems that proliferate for a time and then terminally differentiate into a sharp tip. Like other meristems, thorn meristems contain stem cells but, in the case of thorns, these stem cells undergo a programmed cessation of proliferative activity. Using Citrus, we characterize a gene network necessary for thorn development. We identify two Citrus genes, THORN IDENTITY1 (TI1) and THORN IDENTITY2 (TI2), encoding TCP transcription factors, as necessary for stem cell quiescence and thorn identity. Disruption of TI1 and TI2 function results in reactivation of stem cells and concomitant conversion of thorns to branches. Expression of WUSCHEL (WUS) defines the shoot stem cell niche in the apical meristems of many angiosperm species; we show that TI1 binds to the Citrus WUS promoter and negatively regulates its expression to terminate stem cell proliferation. We propose that shifts in the timing and function of components of this gene network can account for the evolution of Citrus thorn identity. Modulating this pathway can significantly alter plant architecture and could be leveraged to improve crop yields.
Assuntos
Diferenciação Celular/genética , Diferenciação Celular/fisiologia , Citrus/genética , Citrus/fisiologia , Redes Reguladoras de Genes/genética , Redes Reguladoras de Genes/fisiologia , Genes de Plantas/genética , Genes de Plantas/fisiologia , Meristema/genética , Meristema/fisiologia , Mutação , Fenômenos Fisiológicos Vegetais/genética , Proteínas de Plantas/genética , Proteínas de Plantas/fisiologia , Células-Tronco/fisiologia , Proliferação de Células/genética , Proliferação de Células/fisiologia , Citrus/anatomia & histologia , Citrus/citologia , Meristema/citologiaRESUMO
The WUSCHEL (WUS) gene is necessary for the maintenance of stem cells in the shoot apical meristem. Four recent reports show that cytokinin responsive type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) directly activate WUS expression, providing a long-awaited explanation for how cytokinin influences the maintenance of the stem cell niche.
