Comparative transcriptomic analysis reveals the roles of ROS scavenging genes in response to cadmium in two pak choi cultivars

To identify key regulatory genes involved in ROS scavenging in response to cadmium (Cd) exposure in pak choi, eight cDNA libraries from Cd-treated and Cd-free roots of two cultivars, Baiyewuyueman (high Cd accumulator) and Kuishan'aijiaoheiye (low Cd accumulator), were firstly performed by RNA-sequencing. Totally 0.443 billion clean reads and 244,190 unigenes were obtained from eight transcriptome. About 797 and 1167 unigenes encoding ROS related proteins and transcription factors were identified. Of them, 11 and 16 ROS scavenging system related DEGs, and 29 and 15 transcription factors related DEGs were found in Baiyewuyueman and Kuishan'aijiaoheiye, respectively. Ten ROS-scavenging genes (Cu/Zn-SOD, GST1, PODs, TrxR2, PrxR, FER3 and NDPK) showed higher expression levels in Cd-exposed seedings of Baiyewuyueman than those of Kuishan'aijiaoheiye. Four genes (GPX, APX, GRX and GST3) specifically expressed in Cd-free roots of Kuishan'aijiaoheiye. For transcription factors, ERF12/13/22 and WRKY31 was up-regulated by Cd in Baiyewuyueman, while in Kuishan'aijiaoheiye, Cd induced down-regulations of bZIP, NAC and ZFP families. The results indicate that the two cultivars differed in the mechanism of ROS scavenging in response to Cd stress. Fe SOD1, POD A2/44/54/62 and GST1 may be responsible for the difference of Cd tolerance between Baiyewuyueman and Kuishan'aijiaoheiye.