Transcriptome sequencing of watermelon seedlings after Cd stress treatment

Cadmium (Cd) stress in soil seriously restricts plant growth and development, and poses a threat to human health through diets of Cd-containing foods. Watermelon is a popular fruit threatened by Cd stress worldwide, while the underlying mechanisms in response to Cd stress are poorly understood. In this study, we investigated the molecular responses to Cd stress in watermelon at physiological, transcriptomic and metabolic levels. The results showed that watermelon leaves accumulated much more Cd ions and reactive oxygen species (ROS) after Cd stress treatment. Transcriptome sequencing identified many osmotic and oxidative stress-responsive genes, such as peroxidase (POD), MYB, voltage-dependent anion channel (SLAC1), ABC transporter, etc. KEGG enrichment analysis showed that Cd stress-responsive genes were mainly enriched in the pathways of glutathione (GSH) metabolism, MAPK signaling, and biosynthesis of secondary metabolite. In the GSH metabolism pathway, many glutathione S-transferase (GST) genes were up-regulated, as well as phytochelatin synthetase (PCS) genes that catalyzed the synthesis of phytochelatin with GSH as a precursor. In MAPK signaling pathway, most genes related to ABA and ethylene signal transduction were up-regulated by Cd stress. Metabolome analysis showed that the levels of amino acids, phenolamines and esters increased under Cd stress. Overall, this study found that watermelon responded to Cd stress by activating antioxidant system, GSH metabolism pathway, MAPK signal pathway, and biosynthesis of metabolites, which provides important theoretical basis for the soil remediation of heavy metal pollution for plants.