Studying the metabolic patterns underlying the key quality traits during the growth and development of melon is very important for the quality improvement and breeding of melon fruit. In this study, we employed transcriptomics and metabolomics to analyze the primary metabolic changes occurring in melon ('Xizhoumi 25') across five growth and development stages. We identified a total of 666 metabolites and their co-expressed genes, which were categorized into five different metabolic and gene modules. Through the analysis of these modules, the main metabolic pathways during the growth and development of melon were demonstrated from a global perspective. We also discussed the contribution of sucrose accumulation, the TCA cycle, and amino acid metabolism to the quality and flavor of melon. Enzymes related to amino acid metabolism were proposed, including Amine oxidase (AOC), aldehyde dehydrogenase (ALDH), tryptophan synthase (TRPB), etc. These results and data can provide new insights for further study on the metabolic regulation of melon quality and improve fruit quality.

Volatile flavor has prompted a great amount of influence in acceptance and view points in fruit products. Melon (Pyrus communis) is an aroma-dense fruit, thus, the evaluation of volatile flavor is crucial to melon-breeding. The volatile compounds present in nine varieties of Xinjiang muskmelons were identified and analyzed using the headspace solid-phase microextraction and gas chromatography-mass spectrometry methods. In addition, transcriptomics were used to discover the differential genes in fatty acid degradation pathways. It was found that a total of 170 volatile substances, including 52 alcohols, 41 esters, 24 aldehydes, 32 ketones, 14 acids and seven phenols, were identified in the nine melons. Results of PCA showed that 3-nonanol, 2-nonanol, bis (2-ethylhexyl) adipate, and 2-methylpropanal contributed more to the flavor of melon. It was verified that high activities of acyl-coenzyme A cholesterol acyltransferase (AAT) promoted the conversion of alcohols to esters, so that the melons have a high content of esters. Four genes of long-chain acyl-CoA synthetase were mainly responsible for the large difference in volatile substances. This practice may further undermine the primary rationale for the breeding and promotion in different cultivars of muskmelon.