TOP1α regulates FLOWERING LOCUS C expression by coupling histone modification and transcription machinery

The key steps of transcription are coupled with the opens of DNA helical structure and establishment of active chromatin to facilitate the movement of the transcription machinery. Type I topoisomerase cleaves one DNA strand and relaxes supercoiled structure of transcribed templates. How TOP1-mediated DNA topological changes promote transcription and establish a permissive histone modification for transcription elongation is largely unknown. Here, we show that Topoisomerase 1α in plants regulates FLOWERING LOCUS C transcription by coupling both histone modification and transcription machinery. We demonstrate that TOP1α directly interacts with SDG8 methyltransferase to establish high levels of H3K36 methylation in downstream of FLC transcription start sites and recruits RNA polymerase II to facilitate transcription elongation. Our results provide a mechanistic framework for TOP1α control of the main steps of early transcription and demonstrate how topoisomerase couples RNA polymerase II and permissive histone modifications to initiate transcription elongation.