Genome-wide identification and expression profile of Elovl genes in threadfin fish Eleutheronema

Long-chain polyunsaturated fatty acids (LC-PUFA), including eicosapentaenoic acid and docosahexaenoic acid, are the essential fatty acids for organs to maintain various biological functions and processes. The threadfin fish Eleutheronema, with its rich nutritional value especially the high fatty acid contents, has become one of the promising aquaculture species in China and the potential food source of fatty acids for human consumption. However, the molecular basis underlying the biosynthesis of fatty acids in Eleutheronema species is still unknown. The elongation of the very long-chain fatty acids (Elovl) gene family in fish plays several critical roles in LC-PUFA synthesis. Therefore, in the present study, we performed genome-wide identification of the Elovl gene family to study their evolutionary relationships and expression profiles in two threadfin fish species Eleutheronema tetradactylum and Eleutheronema rhadinum, the first representatives from the family Eleutheronema. Phylogenetic analysis revealed that the Elovl genes in Eleutheronema were classified into six subfamilies (elovl1a/1b, elovl4a/4b, elovl5, elovl6/6 l, elovl7a, elovl8b). Phylogenetic, gene structure, motif, and conserved domain analysis indicated that the Elovl genes were highly conserved within the same subfamily in Eleutheronema. In addition, the Elovl genes were distributed in 7/26 chromosomes, while the duplicated gene pair, elovl4a and elovl4b, showed collinear relationships. The predicted secondary structure patterns and the 3D models revealed the highly similar functions and evolutionary conserved structure of Elovl proteins in Eleutheronema. The selection pressure analysis revealed that Elovl genes underwent strong purifying selection during evolution, suggesting that their functions might be evolutionarily conserved in Eleutheronema. Additionally, the expression patterns of Elovl genes in different tissues and species were distinct, indicating the possible functional divergence during evolution in the Eleutheronema genus. Collectively, we provided the first comprehensive genomic information on Elovl genes in threadfin fish Eleutheronema. This study enhanced the understanding of the underlying mechanisms of fatty acids biosynthesis in Eleutheronema, and provided new insights on breeding new varieties of fatty acids-enriched fish with potential benefits to farmers and the health of consumers.