Transcriptome analysis deciphers the mechanisms of exogenous nitric oxide action on the response of melon leaves to chilling stress

Chilling stress is a major abiotic factor that limits the growth and productivity of melon (Cucumis melo L.). The application of nitric oxide (NO) can enhance plant tolerance to chilling stress; however, the underlying molecular mechanisms for this process remain poorly understood. In this study, RNA sequencing was performed on melon seedlings exposed to control conditions, chilling stress, or chilling stress in the presence of NO donor sodium nitroprusside (SNP), to identify NO-mediated transcript changes in response to chilling stress. The results identified 488, 1 012, and 1 589 differentially expressed genes (DEGs) between plants in optimum conditions (CK) and chilling stress (CS) groups, plants in the CS and chilling stress + SNP (CN) groups, and those in CK and CN groups, respectively. Through gene ontology (GO) database and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses, the DEGs were classified as predominantly involved in saccharide metabolism, biosynthesis of other secondary metabolites, lipid metabolism, amino-acid metabolism, and signal transduction pathways. In addition, 39 genes related to sugar metabolism including those encoding UDP-glucuronate-4-epimerase, beta-glucosidase, glucuronosyltransferase, alpha-1,4-galacturonosyl transferase, and hexokinase, were upregulated in the CK vs. CS comparison, and genes encoding fructose-bisphosphate aldolase and glucan-endo-1,3-beta-glucosidase were upregulated in the CS vs. CN, and CK vs. CN comparisons. A gene encoding an EREBP-like factor was upregulated in the CK vs. CS, CS vs. CN, and CK vs. CN comparisons. The expression profiles of 10 selected genes were analyzed using real-time quantitative PCR, and the candidate gene expression patterns were consistent with the DEG classification from RNA-seq. Overall, the data provide insight into the transcriptional regulation by exogenous NO in the response of melon seedlings to chilling stress. The data from this study are relevant for further research on the molecular mechanisms that underlie chilling resistance in melon plants.