ISRH-seq: a sensitive and robust methodology for R-loop profiling

R-loops serve as key modulators in various biological processes in humans and plants.Current high-throughput methodologies for R-loop profiling have their own intrinsic pros and cons. Therefore, any robust, sensitive, and amenable methods, complementary and/or advantageous to existing methodologies, are much needed for advancing R-loop biology. We here present an RNase H based cleavage combined with DNA polymerase-mediated in situ biotin-dATP/dCTP labeling of newly synthesized DNA for sequencing, termed ISRH-seq, an antibody-independent approach for strand-specific mapping of R-loops. After conducting a parallel comparison with DRIP-seq, we found that ISRH-seq can identify more R-loop peaks with the same sequencing depth. Moreover, ISRH- and DRIP-specific R-loops had distinct genomic and epigenetic features, exhibited distinct relationships with expression of overlapping genes, and functional divergence. Importantly, we found that ISRH-seq can be scalable down to 250-100ng DNA input, indicative of a robust and sensitive high-throughput methodology. In addition, it can be applied for R-loop profiling under stress conditions. Thus, our study provides a valuable orthogonal methodology for comprehensive profiling of R-loops in plants. It could be easily adapted to other non-plant systems, especially for these biologically important tissues or cell types with limited cell numbers, thereby advancing understanding of R-loop biology. Overall design: ISRH-seq