Cytoplasmic male sterility (CMS) is widely exploited in hybrid seed production. Kenaf is an important fiber crop with high heterosis. The molecular mechanism of kenaf CMS remains unclear, particularly in terms of DNA methylation. Here, using the anthers of a kenaf CMS line (P3A) and its maintainer line (P3B), comparative physiological, DNA methylation, and transcriptome analyses were performed. The results showed that P3A had considerably lower levels of IAA, ABA, photosynthetic products and ATP contents than P3B. DNA methylome analysis revealed 650 differentially methylated genes (DMGs) with 313 up- and 337 down methylated, and transcriptome analysis revealed 1788 differentially expressed genes (DEGs) with 558 up- and 1230 downregulated genes in P3A compared with P3B. Moreover, 45 genes were characterized as both DEGs and DMGs, including AUX,CYP, BGL3B, SUS6, AGL30 and MYB21. Many DEGs may be regulated by related DMGs based on methylome and transcriptome studies. These DEGs were involved in carbon metabolism, plant hormone signal transduction, the TCA cycle and the MAPK signaling pathway and were shown to be important for CMS in kenaf. These results provide new insights into the epigenetic mechanism of CMS in kenaf and other crops.

Background: F. hirta vahl is a famous Chinese medicinal plant. The root is the main organ accumulating bioactive compounds, and its development is directly related to the yield and quality of the harvested F. hirta. However, the molecular mechanisms underlying the bioactive compound biosynthesis occurring during the root development of F. hirta are unknown. Method: Transcriptome and widely targeted metabolome analyses were performed to investigate gene expression and metabolite variation during the development of F. hirta taproots. Results: A total of 3792 differentially expressed genes (DEGs) were identified between the one- and three-year-old F. hirta taproots; they are related to circadian rhythm–plant, phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant–pathogen interaction pathways. In total, 119 differentially accumulated metabolites (DAMs) were identified between the one- and three-year-old F. hirta taproots, including flavonols, phenolic acids, and coumarins compounds. Integrative transcriptome and metabolome analyses revealed a significant correlation between 172 DEGs and 21 DAMs; they were predominantly enriched for processes associated with phenylpropanoid biosynthesis, flavonoid biosynthesis, plant hormone signal transduction, and stilbenoid, diarylheptanoid, and ginerol biosynthesis. In addition, 26 DEGs were identified to be significantly correlated with the DAMs that accumulated in the phenylpropanoid biosynthesis pathway, and these DEGs may be the key genes for the biosynthesis of F. hirta active compounds. Conclusions: The phenylpropanoid biosynthesis pathway plays a dual role in both development and bioactive compound synthesis in F. hirta taproots. These findings provide a molecular regulatory network in the relationships between F. hirta taproot development and the accumulation of secondary metabolites. The identification of candidate genes and pathways provides a genetic resource for quality control and future molecular breeding in F. hirta.

Cadmium (Cd) is a highly toxic heavy metal that impairs plant growth, metabolism, and the accumulation of bioactive compounds. To investigate methylation-associated Cd responses in the medicinal plant Sophora tonkinensis, we integrated whole-genome bisulfite sequencing (WGBS) and transcriptome sequencing under three Cd treatments (T0, T2, and T4). Cd stress induced extensive transcriptional reprogramming and widespread DNA methylation changes, with CHH methylcytosines accounting for the largest proportion of methylated sites, whereas CG sites showed the highest average methylation level. Differentially methylated regions (DMRs) were predominantly detected in the CHH context and were frequently located in promoter and flanking regions. Integrated analysis identified 6547 and 6204 differentially methylated genes in T2 vs. T0 and T4 vs. T0, respectively, and 420 and 612 genes, respectively, showing concurrent changes in DNA methylation and transcript abundance. Genes with hypermethylation and reduced expression were more frequent than hypomethylated/upregulated genes and were mainly associated with photosynthesis, carbon fixation, fatty acid metabolism, sulfur-related metabolism, and secondary metabolic pathways potentially related to medicinal quality. Among the hypomethylated/upregulated genes, the hormone-related candidate gene StGH3.1 was selected for functional validation, and heterologous overexpression of StGH3.1 enhanced Cd tolerance in transgenic Nicotiana benthamiana. These results indicate that Cd stress is accompanied by coordinated methylome and transcriptome remodeling in S. tonkinensis and provide methylation-associated candidate genes for further investigation of Cd-responsive adaptation.