Genome-wide characterization of DNA methylation, small RNA expression, and histone H3 lysine nine di-methylation in Brassica rapa L.

Epigenetic gene regulation is crucial to plant life and can involve dynamic interactions between various histone modifications, DNA methylation, and small RNAs. Detailed analysis of epigenome information is anticipated to reveal how the DNA sequence of the genome is translated into the plant's phenotype. The aim of this study was to map the DNA methylation state at the whole genome level and to clarify the relationship between DNA methylation and transcription, small RNA expression, and histone H3 lysine 9 di-methylation (H3K9me2) in Brassica rapa. We performed whole genome bisulfite sequencing, small RNA sequencing, and chromatin immunoprecipitation sequencing using H3K9me2 antibody in a Chinese cabbage inbred line, RJKB-T24, and examined the impact of epigenetic states on transcription. Cytosine methylation in DNA was analysed in different sequence contexts (CG, CHG, and CHH) (where H could be A, C, or T) and position (promoter, exon, intron, terminator, interspersed repeat regions), and the H3K9me2 and 24 nucleotide small interfering RNAs (24nt-siRNA) were overlaid onto the B. rapa reference genome. The epigenome was compared with that of Arabidopsis thaliana and the relationship between the position of DNA methylation and gene expression, and the involvement of 24 nt siRNAs and H3K9me2 are discussed.