Carotenoid cleavage dioxygenase 4 (CCD4) cleaves beta-carotene and interacts with IbOr in sweetpotato

Abstract

Sweetpotato (Ipomoea batatas [L.] Lam) is one of the most important food crops, as it ensures food and nutrition security in the face of climate change, given its high carbohydrate, antioxidant (carotenoid), dietary fiber, and mineral contents. The Orange protein of sweetpotato (IbOr) shows high molecular chaperone activity. Previously, we showed that transgenic sweetpotato plants overexpressing the IbOr gene exhibited strong tolerance to abiotic stresses such as high temperature (47 degrees C) and drought, owing to the increased contents of carotenoids including beta-carotene. Interestingly, the expression of the sweetpotato carotenoid cleavage dioxygenase 4 (IbCCD4) gene was also significantly up-regulated in IbOr-overexpressing sweetpotato plants. In this study, we confirmed that the IbCCD4 gene is highly expressed in carotenoid-rich leaves and storage roots of three types of sweetpotato cultivars, each with a different storage root color (pale yellow, orange, and purple). The IbCCD4 protein showed interaction with IbOr in yeast two-hybrid and pull-down assays. Additionally, in vitro, carotenoid cleavage assays indicated that beta-carotene is the major substrate of IbCCD4. Interestingly, the interaction between IbCCD4 and IbOr did not affect beta-carotene degradation. Further characterization of the IbCCD4 gene in transgenic sweetpotato plants will provide new insights into carotenoid homeostasis under severe stress conditions.