Nucleosome loss and histone modifications are important mechanisms for transcriptional regulation. Concomitant changes in chromatin structures of two peanut (Arachis hypogaea L.) oleosin genes, AhOleo17.8 and AhOleo18.5, were examined in relation to transcriptional activity. Spatial and temporal expression analyses showed that both AhOleo17.8 and AhOleo18.5 promoters can adopt three conformational states, an inactive state (in vegetative tissues), a basal activated state (in early maturation embryos), and a fully activated state (in late maturation embryos). Chromatin immunoprecipitation assays revealed an increase of histone H3 acetylation levels at the proximal promoters and coding regions of AhOleo17.8 and AhOleo18.5 associated with basal transcription in early maturation embryos. Meanwhile, a decrease of histone H3K9 dimethylation levels at coding regions of oleosins was observed in early maturation embryos. However, a dramatic decrease in the histone acetylation signal was observed at the core promoters and the coding regions of the two oleosins in the fully activated condition in late maturation embryos. Although a small decrease of histone H3 levels of oleosins chromatin was detected in early maturation embryos, a significant loss of histone H3 levels occurred in late maturation embryos. These analyses indicate that the histone eviction from the proximal promoters and coding regions is associated with the high expression of oleosin genes during late embryos maturation. Moreover, the basal expression of oleosins in early maturation embryos is accompanied by the increase of histone H3 acetylation and decrease of histone H3K9me2.

Peanut (Arachis hypogaea) allergy is one of the most serious food allergies. Peanut seed protein, Ara h 3, is considered to be one of the most important peanut allergens. Little is known about the temporal and spatial regulation mechanism of Ara h 3 during seed development. In this study, chromatin structure of the Ara h 3 promoter was analyzed to examine its transcriptional regulation. Analysis of transgenic plants of Arabidopsis thaliana expressing Arah3: GUS showed that the Ara h 3 promoter could efficiently direct the seed-specific expression of the GUS reporter gene. Chromatin immunoprecipitation revealed that nucleosomes were depleted at the core promoter of the Ara h 3 upon full activation in the late stage of embryo maturation, which was accompanied by a dramatic decrease of histone acetylation. However, in the early stage of embryo maturation, histone H3 hyperacetylation at the core promoter of Ara h 3 was detected. A decrease of histone H3-K9 dimethylation levels at core promoter of Ara h 3 was also observed with concomitant repression of Ara h 3 in the vegetative tissues. Our results suggest that the histone modification status of Ara h 3 undergoes targeted changes including the increase of histone H3 acetylation and decrease of histone H3-K9 dimethylation in early maturation embryos. In addition, the loss of histone H3 from the proximal promoter of Ara h 3 is associated with its high expression during late embryo maturation.