design: Total RNA was isolated from samples using TRIzol reagent according to the manufacturers protocol (Invitrogen). After confirmation of RNA quality, the samples were sequenced using a BGISEQ-500 Analyzer (BGI Genomics, Shenzhen, China). The raw reads were data-filtered to obtain high-quality clean reads by SOAPnoke, and mapped to the P. trichocarpa reference genome and reference genes using HISAT/Bowtie2