library_construction_protocol: RNA was extracted by Quick-DNA/RNA Miniprep kit (Zymo Research) and quality determined by TapeStation (Agilent). 1 µg of RNA was polyA-enriched and cDNA synthesis was performed with first strand random hexamer reverse transcription. Adapters were ligated to cDNA then closed to form single-stranded circular DNA and subjected to rolling circle relication for sequencing, according to the manufacturer's instructions (BGI).