Objective  Our objective was to explore the molecular mechanism of cadmium stress in Populus deltoides ‘Zhonghe 1’, search for anti-cadmium genes by transcriptome analysis and provide candidate plants for phytoremediation.

  Method  The experiment used sand to cultivate the P. deltoides ‘Zhonghe 1’. Different mass concentrations (0 mg/L (ZH1C0), 10 mg/L (ZH1C1), 20 mg/L (ZH1C2)) of cadmium ionic liquor were used to stress the clones. Then RNA extracted from leaves was sequenced by the system Illumina HiSeq^TM2500.

  Result  PC1 is the principal component which can distinguish samples at different concentrations. The comparison between ZH1C0 and ZH1C2 in differential expression analysis revealed that 4 109 differential genes were detected, among which 2 741 were up-regulated and 1 368 were down-regulated. Similarly, in comparison with the ZH1C1 and ZH1C2 in differential expression analysis, 3 710 differential genes were detected with 1 969 up-regulated genes and 1 741 down-regulated ones. It was found by the annotation, which were in different databases that cadmium stress could affect the electron transport in chloroplasts and mitochondria. Transcription factor analysis showed that WRKY, MYB, ZIP, bHLH and ERF played an important role in cadmium stress.

  Conclusion  The results indicate that HIPPs play a crucial part in preventing the Cd²⁺ from entering the cell. GSH could not only promote the Cd²⁺ binding but also alleviate intracellular oxidative stress. The ABC family proteins and the MATE family proteins are the key carriers for the transfer of the Cd-PCs in the P. deltoides ‘Zhonghe 1’.