Melatonin enhances cadmium tolerance in Tartary buckwheat by regulating phenylpropane biosynthesis and redox gene expression

Abstract Background Melatonin (MT) is a multifunctional molecule capable of alleviating biotic and abiotic stresses in plants including cadmium (Cd) toxicity. While studies show that MT treatment can reduce the damage caused by Cd, it remains unclear how it mitigates Cd toxicity in Tartary buckwheat. Results This study investigated the physiochemical and molecular mechanisms by which MT protects Tartary buckwheat from Cd stress. We found that Cd treatments in hydroponics (50 µM CdCl 2 ) or added to soil (100 µM µM CdCl 2 ) reduced root and shoot growth, but that the combination of these treatments with 100 or 200 µM MT, respectively, significantly reversed that inhibition of growth. The protection afforded by MT was associated with reduced Cd uptake by plants as well as lower concentrations of malondialdehyde and the reactive oxygen species superoxide anion and hydrogen peroxide. Moreover, the concentrations of glutathione and ascorbic acid in roots and shoots and the activities of superoxide dismutase and peroxidase increased with the Cd + MT treatment compared with Cd alone. The expression of glutathione S-transferase and phytochelatin synthase genes, both of which combat Cd toxicity in other species, also increased. Expression of the heavy metal transporter gene FtHMA2 was induced by Cd but unchanged in the Cd + MT treatment. A full transcriptomic analysis revealed that the Cd + MT treatment significantly altered the expression of genes involved with redox regulation, phenylpropanoid synthesis, heavy metal transport, as well as heat shock proteins (HSPs) and transcription factors from the WRKY, Dof, and AP/ERF families. Conclusion This study provides insights into the mechanisms by with MT ameliorates Cd toxicity in Tartary buckwheat. The findings could support the development of genetic or agronomic strategies for enhancing the production of this valuable crop on Cd-contaminated soils.