DNA methylation is one of the most conserved epigenetic modifications in eukaryotes, and is involved in gene expression regulation, silencing of transposable elements, and genome stability. In plants, methylation of cytosine occurs in CG, CHG (H represents A, C, or T), and CHH three sequence contexts. In Arabidopsis, symmetric CG and CHG methylation can be maintained by METHYLTRANSFERASE 1 (MET1) and CHROMOMETHYLASE 3 (CMT3), respectively, whereas asymmetric CHH methylation is maintained by CMT2. Additionally, de novo DNA methylation of all three sequence contexts was established using DOMAINS REARRANGED METHYLASE 2 (DRM2) via the RNA-directed DNA methylation (RdDM) pathway, which is also involved in Pol IV (RNA polymerase IV), Pol V, DCLs (DICER LIKES), and several other factors. The dynamics of DNA methylation can be regulated by DNA methyltransferases and demethylases. DNA methylation can either be passive, induced by the reduced expression of methyltransferases, or active, mediated by DNA glycosylases. There are four demethylases in Arabidopsis: REPRESSOR OF SILENCING 1 (ROS1), DEMETHYLTRANSFERASE (DME), DEMETHYLTRANSFERASE LIKE 2 (DML2), and DML3. DNA methylation plays an important role in many biological processes such as seed development, fruit ripening, flowering time, hybrid vigor, and genome evolution. DNA methylation is reduced during fruit development and ripening in tomato, and exposure to the methyltransferase inhibitor 5-azacytidine prematurely ripens tomato. Flower development is one of the most complicated biological processes in angiosperms, with the need for accurate regulation of the expression of many factors, such as receptor protein kinases, transcription factors, and enzymes. Recent studies have shown that epigenetic modifications such as DNA methylation play an important role in Arabidopsis flower development. Flower color changes are mostly attributed to various pigments such as flavonoids, carotenoids, and betaines. Honeysuckle (Lonicera japonica), a member of the Caprifoliaceae family, is an important medicinal plant. It is also popular as an ornamental plant because its flower color changes from white to gold during flower development. Previous studies have shown that carotenoids are the primary pigments in honeysuckle flowers and are responsible for the flower color change from white to gold. It was also found that the accumulation of carotenoids was due to the activation of genes involved in the carotenoid biosynthetic process and inhibition of genes related to the degradation pathway. However, the role of DNA methylation in regulating carotenoid-related gene expression during honeysuckle flower development remains unclear. The honeysuckle genome has been assembled and annotated, providing an unprecedented opportunity to study DNA methylation. To investigate the regulation of honeysuckle flower development by DNA methylation, we investigated single-base resolution DNA methylation profiles by whole genome bisulfite sequencing during flower development. We observed a global decrease in DNA methylation in the late stage (golden flower) relative to that in the early stage of flower development (white bud). Moreover, reduced DNA methylation was due to increased expression of genes encoding demethylase during flower development. Combined with transcriptome data, we also observed that reduced DNA methylation was associated with the differential expression of several genes involved in carotenoid biosynthesis and degradation pathways. Collectively, our study revealed DNA methylation changes during honeysuckle flower development, which implies the epigenetic role of carotenoid metabolism in flower color change.

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Regards,
Catherine
Journal Co-Ordinator
Annals of Biological Sciences