design: Total RNA from root samples was extracted using the RNA sample preparation kit RNeasy Mini Kit (QIAGEN) combined with TRizol reagent (Invitrogen), and genomic DNA was digested using RNase-Free DNase (Qiagen, USA). RNA integrity was evaluated by 1.0 agarose gel electrophoresis. Total RNA was quantified with a Nanodrop 2000 (Thermo scientific, Wilmington, USA) and samples were used for RNAseq library construction only when the OD 260/280 was higher than 1.8 and the OD 260/230 higher than 2.32.