Cultivar- and tissue-specific transcriptomic changes induced by cadmium in Brassica parachinensis

Abstract

Background One of the main pathways for cadmium (Cd) transfer from the environment to the human body is through the consumption of leafy vegetables, and Brassica leafy crops tend to be Cd hyper-accumulators. But its response strategies to Cd still lack of systematic study. Results To investigate Brassica response strategies to Cd, we identified two cultivars with different Cd translocation efficiencies and performed mutli-transcriptomic sequencing studies under Cd treatments. Certain transporter families exhibited different temporal expression profiles in the two cultivars and may underlie the different Cd translocation efficiencies. Cd induced a drastic reduction of a 22 nt small RNA, the footprint of a pentatricopeptide repeat (PPR) protein on the chloroplast ndhB transcript and the concomitant down-regulation of the ndhB transcript. A global reduction in the expression of PPR genes was found, revealing previously unknown effects of Cd on organellar gene expression. Analyses of microRNAs (miRNAs) and their target genes by small RNA and degradome sequencing not only revealed Cd-induced changes in miRNAs but also implicated the existence of a regulatory cascade involving bra-miR156, its target gene, and bra-miR397 and bra-miR398 in Cd stress responses. Conclusions The present findings help uncover the impact of Cd stress on the transcriptome of B. parachinensis and provide candidate genes and miRNAs for further investigation.