Rapeseed stores lipids in the form of oil bodies. Oil bodies in the seeds of higher plants are surrounded by oleosins. Adjusting oleosin protein levels can prevent the fusion of oil bodies and maintain oil body size during seed development. However, oil contents are affected by many factors, and studies on the complex molecular regulatory mechanisms underlying the variations in seed oil contents of B. napus are limited. In this study, a total of 53 BnOLEO (B. napus oleosin) genes were identified in the genome of B. napus through a genome-wide analysis. The promoter sequences of oleosin genes consisted of various light-, hormone-, and stress-related cis-acting elements, along with transcription factor (TF) binding sites, for 25 TF families in 53 BnOLEO genes. The differentially expressed oleosin genes between two high- and two low-oil-content accessions were explored. BnOLEO3-C09, BnOLEO4-A02, BnOLEO4-A09, BnOLEO2-C04, BnOLEO1-C01, and BnOLEO7-A03 showed higher expressions in the high-oil-content accessions than in low-oil-content accessions, at 25, 35, and 45 days after pollination (DAP) in two different environments. A regional association analysis of 50 re-sequenced rapeseed accessions was used to further analyze these six BnOLEO genes, and it revealed that the nucleotide variations in the BnOLEO1-C01 and BnOLEO7-A03 gene regions were related to the phenotypic variations in seed oil content. Moreover, a co-expression network analysis revealed that the BnOLEO genes were directly linked to lipid/fatty acid metabolism, TF, lipid transport, and carbohydrate genes, thus forming a molecular network involved in seed oil accumulation. These favorable haplotypes can be utilized in molecular marker-assisted selection in order to further improve seed oil contents in rapeseed.

Histone deacetylases tuin (HDT) is a plant-specific protein subfamily of histone deacetylation enzymes (HDAC) which has a variety of functions in plant development, hormone signaling and stress response. Although the HDT family’s genes have been studied in many plant species, they have not been characterized in Brassicaceae. In this study, 14, 8 and 10 HDT genes were identified in Brassica napus, Brassica rapa and Brassica oleracea, respectively. According to phylogenetic analysis, the HDTs were divided into four groups: HDT1(HD2A), HDT2(HD2B), HDT3(HD2C) and HDT4(HD2D). There was an expansion of HDT2 orthologous genes in Brassicaceae. Most of the HDT genes were intron-rich and conserved in gene structure, and they coded for proteins with a nucleoplasmin-like (NPL) domain. Expression analysis showed that B. napus, B. rapa, and B. oleracea HDT genes were expressed in different organs at different developmental stages, while different HDT subgroups were specifically expressed in specific organs and tissues. Interestingly, most of the Bna/Br/BoHDT2 members were expressed in flowers, buds and siliques, suggesting they have an important role in the development of reproductive organs in Brassicaceae. Expression of BnaHDT was induced by various hormones, such as ABA and ethylene treatment, and some subgroups of genes were responsive to heat treatment. The expression of most HDT members was strongly induced by cold stress and freezing stress after non-cold acclimation, while it was slightly induced after cold acclimation. In this study, the HDT gene family of Brassicaceae was analyzed for the first time, which helps in understanding the function of BnaHDT in regulating plant responses to abiotic stresses, especially freezing stresses.