library_construction_protocol: The total RNA was extracted according to the instruction manual of the TRlzol Reagent (Life technologies, California, USA). Qualified RNA were processed for library construction. The procedures are described as follow: (1) mRNA was isolated by Oligo(dT)-attached magnetic beads. (2) mRNA was then randomly fragmented in fragmentation buffer. (3) First-strand cDNA was synthesized with fragmented mRNA as template and random hexamers as primers, followed by second-strand synthesis with addition of PCR buffer, dNTPs, RNase H and DNA polymerase I. Purification of cDNA was processed with AMPure XP beads. (4) Double-strand cDNA was subjected to end repair. Adenosine was added to the end and ligated to adapters. AMPure XP beads were applied here to select fragments within size range of 300-400 bp. (5) cDNA library was obtained by certain rounds of PCR on cDNA fragments generated from step 4.