Total RNA was isolated using TRIzol reagent according to the manufacturer's instructions. The isolated RNA was treated with RNase-free DNase I (Sangon, Shanghai, China) to eliminate possible genomic DNA contamination. Equal quantities of total RNA from three replicate samples were mixed to prepare the pooled RNA sample for RNA-Seq. RNA purity was checked using the Nano Photometer® spectrophotometer (IMPLEN, CA, USA) and RNA concentration was measured using Qubit® RNA Assay Kit in Qubit® 2.0 Fluorometer (Life Technologies, CA, USA). RNA integrity was determined using the RNA Nano 6000 Assay Kit of the Bioanalyzer 2100 system (Agilent Technologies, CA, USA).