Astaxanthin is not indispensable for crustaceans: Carotenoid differences and metabolic mechanisms of crayfish (Procambarus clarkii) with different carapace colors

Qing Liu^1*Zhihui He¹Lirong Yang¹Xiangyu Li¹Huili Zhai¹Lele Zhao¹Guojun Guo²Yu Liu¹Liang Xiao³Jing Song¹Shaozhen Liu¹Weiwei Wang¹Xianzong Wang¹

• ¹Shanxi Agricultural University, Jinzhong, China
• ²Henan University of Animal Husbandry and Economy, Zhengzhou, China
• ³Faculty of Naval Medicine, Naval Medical University Shanghai, Shanghai, China

Procambarus clarkii is an important economic aquatic species, and body color is an important economic trait. However, studies on the regulation of body color in crayfish remains limited. Therefore, we conducted an integrated transcriptomic and metabolomic investigation of the hepatopancreas (H) and endothelia (P) of four color variations of crayfish (N = normal, W = white, R = red-orange, and B = blue) to clarify body-color regulation mechanisms. A total of eight carotenoids were detected in the targeted metabolome; however, the types and concentrations varied considerably among the four color phenotypes or between tissues. The highest carotenoid concentrations were found in NP and NH and the lowest in WP and WH. Of the identified carotenoid types, zeaxanthin was not detected in WP. Notably, astaxanthin and canthaxanthin were found in the endothelium and hepatopancreas, whereas β-cryptoxanthin was only detected in the hepatopancreas of crayfish. For transcriptome analysis, we selected genes related to body-color regulation (crustacyanin-A2 subunit-like [CRCN-A2], crustacyanin-C1 subunit-like [CRCN-C1], beta,beta-carotene 15,15' -dioxygenase-like β-carotene oxygenase 1 [BCO1], xanthine dehydrogenase/oxidase-like [XDH], ABC transporter G family member 9-like [ABCG21], Solute Carrier Family Member [SLC2A3], and microphthalmia-associated transcription factor [mitf]), and analyzed the mechanism of body color formation by combining the gene expression pattern with carotenoid composition. In addition, there were four carotenoid metabolism-related pathways in the endodermis and hepatopancreas of Procambarus clarkii using non-targeted metabolomics techniques. In the integrated transcriptomic and metabolomic KEGG analysis, several metabolic pathways such as vitamin digestion and absorption, retinol digestion and absorption, and purine metabolism impact the changes in differential genes such as Sbcar1, NinaB, and XDH, as well as differential metabolites such as xanthine, retinol, and β-carotene. These findings are crucial to the regulation mechanism of body color in crayfish.