Comparative transcriptome analysis of cadmium responses in Solanum nigrum and Solanum torvum

Solanum nigrum is a cadmium (Cd) accumulator, whereas Solanum torvum is a low Cd-accumulating plant. The molecular mechanisms that are responsible for differential cadmium (Cd) accumulation in the two Solanum species are poorly understood. Here, grafting experiments confirmed that increased Cd loading into the root xylem was responsible for the differential Cd accumulation in the two Solanum species. An iron (Fe) supply assay indicated that low Fe accumulation in S. torvum leaves is related to its Cd sensitivity. Transcriptome analyses revealed higher expression of the genes that encode several metal transporters as well as antioxidant-related genes, and several organic and amino acid biosynthesis/metabolism-related genes in Cd-treated S. nigrum. Our data also indicated that the different responsive mechanisms of the transporter genes to Fe deficiency might be responsible for differential uptake and redistribution of metals in the two Solanum species These results form a basis upon which to further explore the molecular mechanisms of Cd accumulation and tolerance, and provide an insight into novel strategies that can be used for phytoremediation and food safety.