Abstract: In order to gain further insights into the mechanism of action of trypsin in fruit preservation, the synergistic mechanisms of trypsin and antioxidant enzymes were evaluated in pitaya (Hylocereus undatus). Reactive oxygen species (ROS) and antioxidant enzyme-related genes were selected based on the RNA-seq data of H. undatus regulated by trypsin. The results of protein-protein interaction (PPI) networks suggested that the entire ROS network could be a true biological scale-free network. Analysis using the Molecular Complex Detection (MCODE) plugin in Cytoscape showed that most antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPXs), were gathered in the cluster 2 of the ROS network. The differentially expressed antioxidant enzymes were further analyzed, revealing that peroxidase 5 (POD5) and CAT as the hub proteins were regulated by trypsin. In addition, all 22 saturated fatty acids identified based on targeted metabolomic data were down-regulated. Seven of the saturated lysophosphatidylethanolamine (LysoPC) and lysophosphatidylcholine (LysoPE) were the major metabolites. To sum up, trypsin can regulate the antioxidant system and inhibit the levels of saturated fatty acids to preserve pitaya. This finding may provide a new strategy for fruit preservation.

Key words: Hylocereus undatus; protein-protein interaction; antioxidant enzyme; omics; trypsin