Comparative transcriptomic analysis reveals bioluminescence-related genes in firely Pyrocoelia pectoralis

Bioluminescence in fireflies is dependent on luciferin metabolism in luminous organs. Our study applied RNA-seq to compare the transcriptome profiles between the luminous and non-luminous tissues from the larvae of the firely Pyrocoelia pectoralis. Genes that were differentially expressed between the two tissue samples were screened to identify candidate genes involved in luciferin metabolism. Among which, cystathionine gamma-lyase, 4-hydroxyphenylpyruvate dioxygenase, and β-glucosidase 2 were upregulated, whereas cysteine dioxygenase type 1 was downregulated in the luminous group compared to that in the non-luminous group, suggesting that these genes may participate in the synthesis of luciferin precursors including L-cysteine and 1, 4-benzoquinone. Several genes encoding 4-coumarate: CoA ligases were upregulated in the luminous organs compared to that in the non-luminous organs, indicating that they may be involved in the formation of 2-S-cysteinylhydroquinone, an intermediate in the luciferin biosynthesis pathway. A sterol carrier protein 2 (Scp2) gene (58 kDa) was speculated to play a role similar to that of ScpXs, which are involved in β-oxidation in peroxisomes of P. pectoralis. Moreover, the expression levels of genes encoding acyl-CoA thioesterases, alpha-methylacyl-CoA racemase, bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase 1, and luciferin sulfotransferase were higher in the luminous tissues than those in the non-luminous tissues, suggesting their possible roles in the biosynthesis and storage of D-luciferin. Overall, the results of this study may serve as a theoretical basis for further elucidation of the bioluminescence-related mechanisms in P. pectoralis.