miRNA-seq of developing stem in Populus trichocarpa

A few plantlets of P. trichocarpa clone Nisqually-1, whose genome was sequenced early, were obtained from the Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, and vegetatively propagated in our lab using tissue culture . The plantlets were planted in humus soil and grown under 16h/8h day/night photoperiod at 25\u00b0C in the greenhouse at Northeast Forestry University for 90 days. The lengths of all internodes (IN) from the apical buds to the bases of the main stems of all trees were measured. The IN2, IN4, and IN8 internodes were PS, TS, and SS stages from primary growth to secondary growth of poplar and represent the beginning, middle, and middle and late phases of wood formation for high-throughput sequencing, respectively. Then, 63 trees were used as experimental materials for transcriptome and small RNA sequencing and qRT-PCR analysis. These materials were sampled and immediately frozen in liquid nitrogen and stored at -80\u00b0C following our previous study.