RESUMO
Postembryonic development of plants depends on the activity of apical meristems established during embryogenesis. The shoot apical meristem (SAM) and the root apical meristem (RAM) have similar but distinct cellular organization. Arabidopsis FASCIATA1 (FAS1) and FAS2 genes maintain the cellular and functional organization of both SAM and RAM, and FAS gene products are subunits of the Arabidopsis counterpart of chromatin assembly factor-1 (CAF-1). fas mutants are defective in maintenance of the expression states of WUSCHEL (WUS) in SAM and SCARECROW (SCR) in RAM. We suggest that CAF-1 plays a critical role in the organization of SAM and RAM during postembryonic development by facilitating stable maintenance of gene expression states.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Proteínas Cromossômicas não Histona , Proteínas de Ligação a DNA/genética , Meristema/citologia , Proteínas de Plantas/genética , Proteínas de Saccharomyces cerevisiae , Sequência de Aminoácidos , Divisão Celular/fisiologia , Fator 1 de Modelagem da Cromatina , Replicação do DNA/fisiologia , Proteínas de Ligação a DNA/metabolismo , Proteínas Fúngicas/genética , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Genes de Plantas/fisiologia , Proteínas de Homeodomínio/genética , Meristema/embriologia , Meristema/fisiologia , Dados de Sequência Molecular , Mutação/fisiologia , Fenótipo , Proteínas de Plantas/metabolismo , Raízes de Plantas/citologia , Raízes de Plantas/embriologia , Raízes de Plantas/fisiologia , Sementes/citologia , Sementes/fisiologiaRESUMO
The steady-state level of histone mRNAs fluctuates coordinately with chromosomal DNA synthesis during the cell cycle. Such an S phase-specific expression pattern results from transcriptional activation of histone genes coupled with the onset of replication and from transcriptional repression of the genes as well as specific destabilization of histone mRNAs around the end of the S phase. Proliferation-coupled and S phase-specific expression of histone genes is primarily achieved by the activities of the proximal promoter regions, where several conserved cis-acting elements have been identified. Among them, three kinds of Oct-containing composite elements (OCEs) play a pivotal role in S phase-specific transcriptional activation. Other ones, such as Nona, solo-Oct, and CCGTC motifs, appear to modulate the functions of OCEs to enhance or repress the transcriptional level, possibly depending on the state of the cells. Here, we review the growing evidence concerning the regulatory mechanisms by which plant histone genes are expressed S phase-specifically in proliferating cells.