RESUMEN
The barley gene HvS40, encoding a putative regulator of leaf senescence, is strongly induced during leaf senescence. As shown by chromatin immunoprecipitation, euchromatic histone modification H3K9ac is added at promoter close to ATG and coding sequence of HvS40 after onset of senescence. In parallel, level of heterochromatic H3K9me2 decreases at this gene. Bisulfite sequencing revealed no DNA-methylation in this region, but a heavily methylated DNA-island, starting 664 bp upstream from translational start site in both, mature and senescent leaves. A decrease in DNA methylation in senescing leaves could be shown at one specific CpG motif at the end of this methylation island. In addition, global changes in chromatin structure during senescence were analyzed via immunocytology, revealing senescence-associated changes in spatial distribution of heterochromatic H3K9me2 patterns in the nuclei. Our results prove a senescence-specific mechanism, altering histone modification marks at distinct sequences of the senescence-associated gene HvS40 and altering distribution of heterochromatic areas in the nuclei.
Asunto(s)
Envejecimiento/genética , Genes de Plantas/genética , Código de Histonas/genética , Hordeum/genética , Envejecimiento/fisiología , Clorofila/análisis , Metilación de ADN , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Genes de Plantas/fisiología , Heterocromatina/genética , Heterocromatina/fisiología , Código de Histonas/fisiología , Hordeum/fisiología , Hojas de la Planta/química , Hojas de la Planta/fisiología , Reacción en Cadena en Tiempo Real de la PolimerasaRESUMEN
Senescence processes are part of the plant developmental programme. They involve reprogramming of gene expression and are under the control of a complex regulatory network closely linked to other developmental and stress-responsive pathways. Recent evidence indicates that leaf senescence is regulated via epigenetic mechanisms. In the present review, the epigenetic control of plant senescence is discussed in the broader context of environment-sensitive plant development. The review outlines the concept of epigenetic control of interconnected regulatory pathways steering stress responses and plant development. Besides giving an overview of techniques used in the field, it summarizes recent findings on global alterations in chromatin structure, histone and DNA modifications, and ATP-dependent chromatin remodelling during plant senescence and linked processes.
Asunto(s)
Desarrollo de la Planta/genética , Cromatina/metabolismo , Epigénesis Genética , Regulación de la Expresión Génica de las Plantas , Redes Reguladoras de Genes/genética , Estrés Fisiológico/genéticaRESUMEN
Leaf senescence, the final step of leaf development, involves extensive reprogramming of gene expression. Here, we show that these processes include discrete changes of epigenetic indexing, as well as global alterations in chromatin organization. During leaf senescence, the interphase nuclei show a decondensation of chromocenter heterochromatin, and changes in the nuclear distribution of the H3K4me2, H3K4me3, and the H3K27me2 and H3K27me3 histone modification marks that index active and inactive chromatin, respectively. Locus-specific epigenetic indexing was studied at the WRKY53 key regulator of leaf senescence. During senescence, when the locus becomes activated, H3K4me2 and H3K4me3 are significantly increased at the 5' end and at coding regions. Impairment of these processes is observed in plants overexpressing the SUVH2 histone methyltransferase, which causes ectopic heterochromatization. In these plants the transcriptional initiation of WRKY53 and of the senescence-associated genes SIRK, SAG101, ANAC083, SAG12 and SAG24 is inhibited, resulting in a delay of leaf senescence. In SUVH2 overexpression plants, significant levels of H3K27me2 and H3K27me3 are detected at the 5'-end region of WRKY53, resulting in its transcriptional repression. Furthermore, SUVH2 overexpression inhibits senescence-associated global changes in chromatin organization. Our data suggest that complex epigenetic processes control the senescence-specific gene expression pattern.