RESUMO
Arabidopsis (Arabidopsis thaliana) floral meristems terminate after the carpel primordia arise. This is achieved through the temporal repression of WUSCHEL (WUS), which is essential for stem cell maintenance. At floral stage 6, WUS is repressed by KNUCKLES (KNU), a repressor directly activated by AGAMOUS. KNU was suggested to repress WUS through histone deacetylation; however, how the changes in the chromatin state of WUS are initiated and maintained to terminate the floral meristem remains elusive. Here, we show that KNU integrates initial transcriptional repression with polycomb-mediated stable silencing of WUS After KNU is induced, it binds to the WUS promoter and causes eviction of SPLAYED, which is a known activator of WUS and can oppose polycomb repression. KNU also physically interacts with FERTILIZATION-INDEPENDENT ENDOSPERM, a key polycomb repressive complex2 component, and mediates the subsequent deposition of the repressive histone H3 lysine 27 trimethylation for stable silencing of WUS This multi-step silencing of WUS leads to the termination of floral stem cells, ensuring proper carpel development. Thus, our work describes a detailed mechanism for heritable floral stem cell termination in a precise spatiotemporal manner.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas de Transporte/metabolismo , Flores/genética , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Proteínas de Homeodomínio/metabolismo , Meristema/genética , Proteínas do Grupo Polycomb/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Transporte/genética , Cromatina/metabolismo , Epigênese Genética , Epistasia Genética , Proteínas de Homeodomínio/genética , Modelos Biológicos , Regiões Promotoras Genéticas/genética , Ligação Proteica , Proteínas Repressoras/metabolismo , Transcrição GênicaRESUMO
As sessile organisms, plants have evolved multiple mechanisms to respond to environmental changes to improve survival. Arabidopsis plants show accelerated flowering at increased temperatures. Here we show that Jumonji-C domain-containing protein JMJ30 directly binds to the flowering-repressor FLOWERING LOCUS C (FLC) locus and removes the repressive histone modification H3 lysine 27 trimethylation (H3K27me3). At elevated temperatures, the JMJ30 RNA and protein are stabilized, and FLC expression is maintained at high levels to prevent extreme precocious flowering. The double mutant of JMJ30 and its homologue JMJ32, grown at elevated temperatures, exhibits an early-flowering phenotype similar to the flc mutant, which is associated with increased H3K27me3 levels at the FLC locus and decreased FLC expression. Furthermore, ectopic expression of JMJ30 causes an FLC-dependent late-flowering phenotype. Taken together, JMJ30/JMJ32-mediated histone demethylation at the FLC locus constitutes a balancing mechanism in flowering control at warm temperatures to prevent premature early flowering.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Flores/crescimento & desenvolvimento , Histona Desmetilases com o Domínio Jumonji/metabolismo , Proteínas de Domínio MADS/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Flores/enzimologia , Flores/genética , Flores/metabolismo , Regulação da Expressão Gênica de Plantas , Histonas/metabolismo , Histona Desmetilases com o Domínio Jumonji/genética , Proteínas de Domínio MADS/genética , MetilaçãoRESUMO
Trimethylation of lysine 36 of histone H3 (H3K36me3) is found to be associated with various transcription events. In Arabidopsis, the H3K36me3 level peaks in the first half of coding regions, which is in contrast to the 3'-end enrichment in animals. The MRG15 family proteins function as 'reader' proteins by binding to H3K36me3 to control alternative splicing or prevent spurious intragenic transcription in animals. Here, we demonstrate that two closely related Arabidopsis homologues (MRG1 and MRG2) are localised to the euchromatin and redundantly ensure the increased transcriptional levels of two flowering time genes with opposing functions, FLOWERING LOCUS C and FLOWERING LOCUS T (FT). MRG2 directly binds to the FT locus and elevates the expression in an H3K36me3-dependent manner. MRG1/2 binds to H3K36me3 with their chromodomain and interact with the histone H4-specific acetyltransferases (HAM1 and HAM2) to achieve a high expression level through active histone acetylation at the promoter and 5' regions of target loci. Together, this study presents a mechanistic link between H3K36me3 and histone H4 acetylation. Our data also indicate that the biological functions of MRG1/2 have diversified from their animal homologues during evolution, yet they still maintain their conserved H3K36me3-binding molecular function.
Assuntos
Proteínas de Arabidopsis/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Regulação da Expressão Gênica de Plantas , Histonas/metabolismo , Acetilação , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/análise , Proteínas de Arabidopsis/genética , Proteínas Cromossômicas não Histona/análise , Proteínas Cromossômicas não Histona/genética , Eucromatina/química , Flores/genética , Histona Acetiltransferases/metabolismo , Histona-Lisina N-Metiltransferase/metabolismo , Proteínas de Domínio MADS/genética , Proteínas de Domínio MADS/metabolismo , Mutação , Fenótipo , Transcrição GênicaRESUMO
Plant floral stem cells divide a limited number of times before they stop and terminally differentiate, but the mechanisms that control this timing remain unclear. The precise temporal induction of the Arabidopsis zinc finger repressor KNUCKLES (KNU) is essential for the coordinated growth and differentiation of floral stem cells. We identify an epigenetic mechanism in which the floral homeotic protein AGAMOUS (AG) induces KNU at ~2 days of delay. AG binding sites colocalize with a Polycomb response element in the KNU upstream region. AG binding to the KNU promoter causes the eviction of the Polycomb group proteins from the locus, leading to cell division-dependent induction. These analyses demonstrate that floral stem cells measure developmental timing by a division-dependent epigenetic timer triggered by Polycomb eviction.
