library_construction_protocol: Total RNA was extracted from 2-week-old seedlings using RNAiso Plus reagent (Takara, 9109). Small RNAs were enriched with 5% PEG8000 (Sigma, P5413) and 0.5 M NaCl (Sigma, S3014). Small RNAs (20 μg) were resolved on a 15% Urea-PAGE gel. RNAs that are 16–26 nt were excised and purified. Small RNA libraries were constructed using NEBNext Multiplex Small RNA Library Prep system (NEB, E7300L) essentially according to the manufacturer's instructions. The libraries were paired-end sequenced in 150 bp on an Illumina HiSeqX-Ten platform.