library_construction_protocol: Root were cut, flash frozen on liquid nitrogen, and total RNA was isolated using a RNeasy Mini Kit (TIANGEN Biotech). First strand cDNA was generated using reverse transcriptase and random primers. The constructed cDNA libraries was qualified and quantified with Agilent 2100 Bioanaylzer and ABI StepOnePlus Real_Time PCR System, and then sequenced via Illumina HiSeqTM 2000 or other sequencer when necessary at the Beijing Genomics Institute, Shenzhen, China.