Screening of candidate gene responses to cadmium stress by RNA sequencing in oilseed rape (Brassica napus L.)

Cadmium (Cd) stress is one of the most serious threats to agriculture in the world. Oilseed rape (Brassica napus L.) is an important oil crop; however, Cd can easily accumulate in rapeseed and thus harm human health through the food chain. In the first experiment, our purpose was to measure the Cd accumulation in mature B. napus plants and its influences on fatty acid composition. The results showed that most Cd was accumulated in the root, and the seed fatty acid content was considerably different at different Cd toxicity levels. In the second experiment, 7-day-old B. napus seedlings stressed by Cd (1mM) for 0h (CK-0h), 24h (T-24h), or 72h (T-72h) were submitted to physiological and biological analyses, RNA-Seq and qRT-PCR. In total, 5469 and 6769 differentially expressed genes (DEGs) were identified in the comparisons of CK-0h vs T-24h and CK-0h vs T-72h, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the photosynthetic and glutathione (GSH) pathways were significantly enriched in response to Cd stress. Key factors in the response to Cd stress included BnPCS1, BnGSTU12, BnGSTU5, and BnHMAs. The transcription factors BnWRKY11 (BnaA03g51590D), BnWRKY28 (BnaA03g43640D), BnWRKY33 (BnaA03g17820D), and BnWRKY75 (BnaA03g04160D) were upregulated after Cd exposure. The present study revealed that upregulation of the genes encoding GST and PCS under Cd stress promoted the formation of low-molecular weight complexes (PC-Cd), and upregulation of heavy metal ATPase genes induced PC-Cd transfer to vacuoles. These findings may provide the basis for the molecular mechanism of the response of B. napus to Cd.