Ionomics, transcriptomics and untargeted metabolomics analyses provide new insights into the Cd response and accumulation mechanisms of mulberry

Recently, the phytoremediation and safe utilization of cadmium (Cd) polluted soil by mulberry planting and sericulture have attracted researchers' attention. However, the understandings of related molecular mechanisms of mulberry response to Cd are still limited. Meanwhile, there are few reports on the diversity of the Cd tolerance and accumulation ability of different mulberry cultivars. Here, we obtained two mulberry cultivars with significant differences in Cd accumulation: high Cd accumulation cultivar FC and low Cd accumulation cultivar G12. Ionomics analysis showed that the distribution pattern of Na is the most similar to that of Cd in both G12 and FC. In transcriptomics analysis, the results of GO and KEGG enrichment analyses showed that cell wall organization-related genes were significantly affected by Cd stress, while cell division-related genes were significantly down-regulated. The expression levels of several Cd-chelation and transporter genes (AGT2, MT2, HIPP26, MTP9 and DTX43/44) were higher in all groups of G12 than those of FC, while the expression level of PCR2 and ABCC2 were higher in all groups of FC than those of G12. In untargeted metabolomics analysis, compared with FC, the metabolites of G12 were less affected by Cd stress in phenylpropanoid, flavonoid and isoflavonoid biosynthesis pathways. Notably, the content of rutin in FC was significantly lower than that of G12. These results provide theoretical support and candidate cultivars for mulberry application in Cd polluted soil, and candidate genes for mulberry genetic modification and molecular breeding in the future.