Utilizing the newly identified M.MedI-N377K methyltransferase, we developed a novel method of CMD-seq for the stoichiometric detection of 5mC in DNA at single-nucleotide resolution.

DNA methylation (5-methylcytosine, 5mC) represents the most prevalent modification in mammals, which is closely linked to disease pathogenesis and cancer development. Single-base resolution sequencing and quantitative analysis of 5mC are essential for elucidating its biological functions. However, current methods are still limited by resolution, sequencing bias, and false positives. In this study, we engineered a Naegleria TET-like protein (NTET), yielding a recombinant engineered NTET (eNTET), to improve both its oxidation activity and sequence compatibility for 5mC. Combined with pyridine borane reduction, we developed engineered NTET-assisted pyridine borane sequencing (eNAPS) to quantitatively detect 5mC in DNA at single-base resolution. In eNAPS, 5mC is oxidized by eNTET to 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), which are further reduced to dihydrouracil (DHU) by pyridine borane and read as thymine (T) in the subsequent sequencing. The direct conversion of 5mC-to-T allows for precise mapping of 5mC in DNA at single-base resolution. Compared with conventional bisulfite sequencing (BS-seq), eNAPS exhibits advantages such as non-destruction, enhanced sensitivity, improved accuracy, and greater efficiency. Using the eNAPS method, we achieved quantitative analysis of 5mC at single-base resolution in genomic DNA of lung tumor and tumor-adjacent normal tissues. Overall, eNAPS is a mild and bisulfite-free method with high accuracy, making it a valuable tool for investigating the dynamic interplay of 5mC in epigenetic regulation and disease pathogenesis.

Background: Small RNA, defined as RNA molecules of less than 200 nucleotides in length, play pivotal regulatory roles in plant growth, development, and environmental stress responses. However, research on modifications in plant small RNA remains limited. Methods: In this study, we developed a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the simultaneous detection of 41 RNA modifications, facilitating the systematic qualification and quantification of modifications in plant small RNA. Results: We identified a total of nine modifications, among which N⁶,N⁶-dimethyladenosine (m^6,6A) is a newly identified modification in plant small RNA. Furthermore, we conducted a quantitative analysis of these modifications in Arabidopsis thaliana during the germination process and observed significant dynamic changes in their abundance from 1 to 5 days post-germination. Notably, the trends in the contents of these modifications exhibited a strong correlation with the reported gene expression levels of the relevant modifying enzymes and demodifying enzymes, suggesting that these modifications may play essential roles during seed germination and are tightly regulated by the genes of the corresponding enzymes. Conclusions: The discovery of these modifications in plant small RNA, coupled with the dynamic changes in their levels during germination, holds great promise for a further understanding of the physiological functions of small RNA modifications and their associated regulatory mechanisms in plant seed germination.