HDA6 is required for jasmonate response, senescence and flowering in Arabidopsis

Post-translational modifications of histones, including acetylation, play a key role in modulating dynamic changes in chromatin structure and gene activity. Histone acetylation is modulated through the action of histone acetyltransferases and deacetylases. HDA6 is a RPD3-type histone deacetylase in Arabidopsis. The Arabidopsis HDA6 mutant, axe1-5, and HDA6 RNA-interfering (HDA6-RNAi) plants displayed higher levels of acetylated H3 compared with wild-type, suggesting that HDA6 affects histone acetylation levels globally. The expression of the jasmonate responsive genes, PDF1.2, VSP2, JIN1, and ERF1, was down-regulated in axe1-5 and HDA6-RNAi plants. Furthermore, axe1-5 and HDA6-RNAi plants displayed increased leaf longevity compared with the wild type. The expression of the senescence-associated genes, SAG12 and SEN4, was down-regulated in the axe1-5 and HDA6-RNAi plants. In addition, axe1-5 and HDA6-RNAi plants displayed late-flowering. The expression of FLC was up-regulated and hyperacetylated in axe1-5 and HDA6-RNAi plants, suggesting that HDA6 is required to deacetylate FLC chromatin and thereby repress its expression. Our results suggest that HDA6 is involved in jasmonate response, senescence, and flowering in Arabidopsis.     

Epigenetic interplay of histone modifications and DNA methylation mediated by HDA6

One of the most fundamental questions in the control of gene expression is how epigenetic patterns of DNA methylation and histone modifications are established. Our recent studies demonstrate that histone deacetylase HDA6 integrates DNA methylation and histone modifications in gene silencing by interacting with DNA methyltransferase MET1 and histone demethylase FLD, suggesting that regulatory crosstalk between histone modifications and DNA methylation could be mediated by the interaction of various epigenetic modification proteins.     

Regulation of CYP1A2 by histone deacetylase inhibitors in mouse hepatocytes

Cytochrome P450 1A2 (CYP1A2) is constitutively expressed in the mouse liver, but the constitutive expression progressively declines to an undetectable level in isolated hepatocytes. In this study, CYP1A2 was induced in hepatocytes exposed to the histone deacetylase inhibitors trichostatin A (TSA) and sodium butyrate (SB), but only well after constitutive CYP1A2 expression was silenced. However, cotreatment with the arylhydrocarbon receptor (AhR) ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and either TSA or SB reduced the induction of CYP1A2 with the same time course as TSA or SB increased its induction. These results suggest that histone modification is involved in CYP1A2 regulation in hepatocytes through pathways that are independent of AhR.     

Pleiotropic effects of flowering time genes in the annual crucifer Arabidopsis thaliana (Brassicaceae)

Variation in flowering time of Arabidopsis thaliana was studied in an experiment with mutant lines. The pleiotropic effects of flowering time genes on morphology and reproductive yield were assessed under three levels of nutrient supply. At all nutrient levels flowering time and number of rosette leaves at flowering varied among mutant lines. The relationship between these two traits depended strongly on nutrient supply. A lower nutrient supply first led to an extension of the vegetative phase, while the mean number of leaves at flowering was hardly affected. A further reduction resulted in no further extension of the vegetative phase and, on average, plants started flowering with a lower leaf number. At low nutrients, early flowering affected the timing of production of siliques rather than the total output, whereas late flowering was favorable at high nutrients. This may explain the fact that many plant species flower at a relatively small size under poor conditions. Flowering time genes had pleiotropic effects on the leaf length, number of rosette and cauline leaves, and number of axillary flowering shoots of the main inflorescence. Silique production was positively correlated with the number of axillary shoots of the main inflorescence; the number of axillary primordia appeared to have a large impact on reproductive yield.