In most organisms, the maturation of nascent RNAs is coupled to transcription. In plants, unlike in animals, the RNA polymerase II (RNAPII) transcribes microRNA genes (MIRNAs) as long and structurally variable pri-miRNAs. Current evidence suggests that the miRNA biogenesis complex assembly initiates early during the transcription of pri-miRNAs in plants. However, it is unknown whether miRNA processing occurs in plants co-transcriptionally. The authors used native elongating transcript sequencing data and imaging techniques to demonstrate that plant miRNA biogenesis occurs coupled to transcription. They found that the entire biogenesis occurs co-transcriptionally for pri-miRNAs processed from the loop of the hairpin, but requires a second nucleoplasmic step for those processed from the base. Furthermore, the article demonstrates that co- and post-transcriptional miRNA processing mechanisms co-exist for most miRNAs in a dynamic balance. Notably, the authors discovered that R-loops, special RNA/DNA structures, formed near the transcription start site region of MIRNAs, promote co-transcriptional pri-miRNA processing.
Advance online publication:
Lucia Gonzalo, Ileana Tossolini, Tomasz Gulanicz, Damian A. Cambiagno, Anna Kasprowicz-Maluski, Dariusz Jan Smolinski, María Florencia Mammarella, Federico D. Ariel, Sebastian Marquardt, Zofia Szweykowska-Kulinska, Artur Jarmolowski & Pablo A. Manavella. https://www.nature.com/articles/s41477-022-01125-x