Cassava storage roots under the postharvest physiological deterioration (PPD) produce a large number of colored coumarin compounds through the shikimic acid pathway, resulting in the occurrence of PPD symptoms. During the process, polyphenol oxidase (PPO) is formed into difluoride through oxygen-dependent oxidation of monophenols or diphenols, and eventually produces colored compounds such as scopolin and scopoletin, resulting in browning of cassava storage roots.  Our research group, in collaboration with Professor Ling erjun, jointly developed a new technology to inhibit the enzymatic activity of polyphenol oxidase by expressing the hen egg-white lysozyme (HEWL) in cassava, significantly delaying the occurrence of PPD, and providing new ideas and new technologies for postharvest preservation of cassava.

Recent studies have found that lysozyme can inhibit the activity of insect prophenoloxidase, which in turn mediates the immune defense response of the insect body.  Based on this finding, the HEWL protein was expressed in cassava driven by the vascular bundle-specific promoter p54 and it was found that the growth of the transgenic plant was not affected, and the storage roots were evaluated according to the method of the International Center for Tropical Agriculture (CIAT) after harvest. The results showed that the PPD process of the HEWL transgenic cassava was found to be significantly delayed, showing after two weeks their severity of PPD symptoms could be reached as that of wildtype 4 days postharvest. Further analysis found that the activity of PPO was significantly inhibited after 48 h, and the content of scopolin and scopoletin was significantly lower than that of the wild type, indicating that HEWL inhibited the activity of polyphenol oxidase, which in turn affected the progress of PPD. The antioxidant capacity of the transgenic plants is greatly improved. Therefore, this study provides a new means for genetically regulating the occurrence of physiological deterioration of cassava after harvest, prolongs the shelf life of storage roots, and is of great significance to the industrialization of cassava. The technology has been granted a patent by the State Intellectual Property Office and was recently published in a paper entitled "Lysozyme inhibits postharvest physiological deterioration of cassava" published online in JIPB (https://doi.org/10.1111/jipb.13219).