Metabolic engineering of rice endosperm for crocin biosynthesis

Crocins, the main active ingredients in Crocus sativus, have anti-inflammatory, antioxidant, hypolipidemic, hypoglycemic, and antitumor properties. Due to the harsh growing conditions and the limited yield of C. sativus, sustainable alternative methods for crocin production need to be explored. In this study, a new rice germplasm resource, "crocin rice", was developed by expressing eight genes of the crocin synthesis pathway in rice endosperm. The content of crocins in rice seeds was up to 9.25 μg/g dry weight, and it was also rich in a variety of carotenoids, including α-carotene, lutein, and violaxanthin. The expression of exogenous genes did not affect normal growth or the major nutritional structure of rice. Feeding experiments on mice showed that crocin rice could effectively reduce lipopolysaccharide-induced liver injury. With the adjuvant therapeutic benefits, crocin rice could be used to improve human nutrition and health. In addition, rice callus also showed the ability to synthesize crocins, which could serve as a potential substitute for C. sativus to alleviate resource shortage.