Combined transcriptomic, proteomic and biochemical approaches to identify the cadmium hyper-tolerance mechanism of turnip seedling leaves.

Cadmium (Cd) pollution is a prominent environment problem, and great interests have been developed towards the molecular mechanism of Cd accumulation in plants. In this study, we conducted combined transcriptomic, proteomic and biochemical approaches to explore the detoxification of a Cd-hyperaccumulating turnip landrace exposed to 5 μM (T5) and 25 μM (T25) Cd treatments. A total of 1090 and 2111 differentially expressed genes (DEGs) and 161 and 303 differentially expressed proteins (DEPs) were identified in turnips under T5 and T25, respectively. However, poor correlations were observed in expression changes between mRNA and protein levels. The enriched KEGG pathways of DEGs with a high proportion (> 80%) of upregulated genes were focused on the flavonoid biosynthesis, sulphur metabolism and glucosinolate biosynthesis pathways, whereas those of DEPs were enriched on the glutathione metabolism pathway. This result suggests that these pathways contribute to Cd detoxification in turnips. Furthermore, induced antioxidant enzymes, heat stock proteins and stimulated protein acetylation modification seemed to play important roles in Cd tolerance in turnips. In addition, several metal transporters were found responsible for the Cd accumulation capacity of turnips. This study may serve as a basis for breeding low-Cd-accumulating vegetables for foodstuff or high-Cd-abstracting plants for phytoremediation.