Cd-Induced Autophagy Responses in Pakchoi as Revealed by Transcriptome Analysis.

Cadmium (Cd) is a toxic heavy metal element, which can cause oxidative stress in plant cells and induce cell damage. Currently, the research investigating autophagy function and Cd injury in plants is still limited. In our study, we exposed Pakchoi plants to Cd chloride at different concentrations (0, 2, 4, 6, and 8 mg·L−1) for 4 consecutive weeks. The results showed that toxic damage of Pakchoi was induced by Cd exposure and its Cd injury accumulation showed a positive dose relationship with metal concentrations. When Pakchoi was exposed to Cd, it generated excessive reactive oxygen species (ROS), especially H2O2. Our data revealed that LC3 upregulation and autophagosome formation were noted in H2O2-activated root cells, indicating that Cd damage caused autophagy in Pakchoi. Under Cd stress, the antioxidant enzyme activity of peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) were decreased as Cd concentration was increased, lowest in 8 mg·L−1 treatment. Using transcriptome analysis by RNA sequencing, we identified 860 significant differentially expressed genes (DEGs) with a fold change of no less than 2 between the Cd-treated and the control groups, among which 513 genes were upregulated and 347 genes were downregulated. The DEGs were mostly enriched in functions related to the hormonal regulation of digestion and absorption, transport processes, transporter activity, and the apical plasma membrane composition. A total of 6 autophagy-related genes, including 4 AMPK genes, 1 ATG13 gene, and 1 Beclin1 gene, were found to have significantly different expression levels in the Cd groups. The expression levels of these 6 genes were significantly different between the control and Cd groups (p < 0.05) when validated by real-time quantitative PCR. Furthermore, we found the ratio of p-AMPK and AMPK increased significantly in the Cd group (p < 0.05), indicating that Cd-induced autophagy may be mediated by AMPK phosphorylation. This research provides a better understanding of the stress effect of autophagy during Cd injury. [ABSTRACT FROM AUTHOR]