A reduction in cadmium accumulation and sulphur containing compounds resulting from grafting in eggplants (Solanum melogena) is associated with DNA methylation

Grafting is an effective strategy to reduce the accumulation of cadmium (Cd) from the soil to the aerial plant parts. However, few studies have investigated the mechanisms involved. DNA methylation and high-throughput sequencing were used to explore the mechanism of the Cd reduction in grafted eggplants (Solanum melongena) on Torubamu (Solanum torvum) as a rootstock. Compared to un-grafted eggplants, grafting significantly reduced Cd accumulation in the leaves and fruits by 65.21% and 81.48%, respectively, of grafted eggplants cultivated in 3 mg kg−1 Cd-contaminated soil. In addition, the total methylation levels of CG, CHG, and CHH were reduced in grafted eggplants, leading to lower total cytosine methylation level than in un-grafted eggplants. The most significant change occurred in CHH methylation in the repeat elements. Furthermore, there were 55 hypomethylated and 23 hypermethylated genes in the leaves of grafted eggplants, most of which were involved in S metabolism, correlating with a decrease in S compounds. Grafting using S. torvum as a rootstock could impact S compounds regulation by altering DNA methylation levels, and thereby, reducing Cd accumulation in scions of grafted eggplants.