Generation of high purity capsanthin and capsorubin through synthetic metabolic engineering in carrot germplasm

Capsanthin and capsorubin are red κ-xanthophylls exclusively found in a handful of other plant species. Currently, capsanthin and capsorubin are extracted from red pepper (Capsicum annuum L.). Here, high purity production of capsanthin and capsorubin was achieved in carrot (Daucus carota L.) taproot by a synthetic metabolic engineering strategy. Expression of a capsanthin-capsorubin synthase gene (CaCCS) from pepper resulted in dominant production of capsanthin, whereas expression of a LiCCS gene from tiger lily (Lilium lancifolium Thunb.) resulted in production of both capsanthin and capsorubin in carrot taproot. The highest content of capsanthin and capsorubin was obtained in LiC-1 carrot taproot hosting the LiCCS gene. Co-expression of DcBCH1 with CCS could improve the purity of capsanthin and capsorubin by eliminating the non-target carotenoids (e.g. α-carotene and β-carotene). The highest purity of capsanthin and capsorubin was obtained in BLiC-1 carrot taproot hosting DcBCH1+LiCCS genes, 91.10% of total carotenoids. The non-native pigments were esterified partially and stored in the globular chromoplast of carrot taproot. Our results demonstrated the use of carrot taproot as green factories for high purity production of capsanthin and capsorubin. The capsanthin/capsorubin carrot germplasms are also valuable materials for breeding colorful carrots cultivars.