NinaB and BCO Collaboratively Participate in the β-Carotene Catabolism in Crustaceans: A Case Study on Chinese Mitten Crab .

Carotenoid cleavage oxygenases can cleave carotenoids into a range of biologically important products. Carotenoid isomerooxygenase (NinaB) and β, β-carotene 15, 15'-monooxygenase (BCO1) are two important oxygenases. In order to understand the roles that both oxygenases exert in crustaceans, we first investigated () and () within the genome of Chinese mitten crab (). Their functions were then deciphered through an analysis of their expression patterns, an in vitro β-carotene degradation assay, and RNA interference. The results showed that both and contain an RPE65 domain and exhibit high levels of expression in the hepatopancreas. During the molting stage, exhibited significant upregulation in stage C, whereas showed significantly higher expression levels at stage AB. Moreover, dietary supplementation with β-carotene resulted in a notable increase in the expression of and in the hepatopancreas. Further functional assays showed that the expressed in underwent significant changes in its color, from orange to light; in addition, its β-carotene cleavage was higher than that of . After the knockdown of or in juvenile , the expression levels of both genes were significantly decreased in the hepatopancreas, accompanied by a notable increase in the redness () values. Furthermore, a significant increase in the β-carotene content was observed in the hepatopancreas when mRNA was suppressed, which suggests that plays an important role in carotenoid cleavage, specifically β-carotene. In conclusion, our findings suggest that and may exhibit functional co-expression and play a crucial role in carotenoid cleavage in crabs.