Tomato grafting onto Torubamu (Solanum melongena): miR166a and miR395b reduce scion Cd accumulation by regulating sulfur transport

Abstract

This study aims to understand the mechanism by which grafting tomato (Solanum lycopersicum) onto Torubamu (Solanum melongena) reduces cadmium (Cd) accumulation in tomato. Tomato plants were grafted onto Torubamu rootstocks, and both the un-grafted and grafted tomato plants were grown in the control soil and soil that contained 2.0 or 5.0 mg•kg−1 Cd for 30 d. Grafting onto Torubamu rootstock markedly reduced the accumulation of both Cd and total sulfur in the leaves of tomato plants to 4.1–11.7% and 25.0–36.7% of the values in the un-grafted tomato plants, respectively. Moreover, the expression of miR166a and miR395b markedly increased in tomato scions. Tobacco dual-luciferase (LUC) assays and Agrobacterium-mediated tomato genetic transformation verified that miR166a and miR395b targeted Phavoluta (PHV), Revolute (REV), Class III Homeodomain Leucine Zipper (HD-ZIP), Sulfate transporter 2;1 (SULTR2;1), ATP sulfurylase (APS) (APS1/3), and High-affinity sulfate transporter (HAST) genes, which are directly or indirectly responsible for sulfate transport. Based on the correlations between the Cd and sulfur accumulation in the tomato scions (r2 = 0.91) and in the miR166a/395b-transformed tomato scions (r2 = 0.96–0.98) grown in the soil with 2.0 mg•kg−1 Cd, we conclude that tomato grafting onto Torubamu rootstock can reduce Cd accumulation because of the sulfate transport regulatory ability of miR166a and miR395b. Understanding this mechanism can be of great benefit for Cd tolerance breeding.