====== Photinus pyralis ======


{{ ::photinus.jpg?200|}}



    Class          : Insecta
    Infraclass     : Neoptera
    Order          : Coleoptera
    Suborder       : Polyphaga
    Superfamily    : Elateroidea
    Family         : Lampyridae

//Common name//: firefly

NCBI:txid[[https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=7054|7054]]

Annotation from assembly GCA_008802855.1, WGS project VVIM01 and TSA GEZM01 and GEOW01. 

201 sequences including an alternatively spliced gene (CYP305R1_v1a and _v1b) and 8 pseudogenes as well as 20 pairs of recent duplicates that are either identical or differ by as little as 2 amino acids. These are marked as a and b  (e.g. CYP6MW4a and CYP6MW4b). This high number of duplicates reflects the number of duplicates at the genome level: [[https://a3cat.unil.ch|BUSCO]] score arthropoda duplicated 9.5%.

A FASTA format file of this CYPome can be downloaded {{ ::photinus_pyralis.fasta |here}}

The distribution of genes by CYP clan is tabulated [[CYPfam_by_clan|here]]

The //Photinus pyralis// CYPome is remarkable for the bloom in [[cyp2_clan|CYP303 genes]]. The CYP303A1 gene is usually a single ortholog in insects, but the firefly has a cluster of CYP303 genes as noted by[[https://doi.org/10.7554/eLife.36495|Fallon et al.]], 2018. 
The cluster annotated here on chromosome 9 has 16 CYP303 genes and two CYP303 pseudogenes, with CYP15A1 and two CYP305 genes in the middle. 

Fallon et al. suggested that the CYP303 genes might be involved in the biosynthesis of the defensive lucibufagin  because related fireflies that do not make lucibufagins have only a single CYP303 gene. Making these polyhydroxylated sterols from cholesterol may require 6-7 P450 reactions (see figure 6A from Fallon et al. below). While the enzymatic details of lucibufagin biosynthesis are unknown, the firefly case suggests that the original CYP303A1 is already able to metabolize a sterol or terpenoid structure.

{{ ::lucibufagins.jpg?800 |}}



The cluster of six [[cyp4g|CYP4G genes]] in Photinus pyralis, all of the CYP4G15 type, is also remarkable.  

Major CYP4G duplication events are seen in Elateroidea (see discussion and references in [[https://doi.org/10.1016/j.ympev.2019.106695|Feyereisen ]]2020): In fireflies and click beetles (Lampyridae and Elateridae), the CYP4G15type gene was repeatedly duplicated to three clustered genes in //Aquatica lateralis//, five in //Ignelater luminosus//,  ten genes in //Pyrocoelis pectoralis// and six in //Photinus pyralis//. Duplications of the CYP4G15 gene started to occur over 125MYA. If bioluminescence evolved independently in click beetles and in fireflies (Fallon et al., 2018), then the expansion of CYP4G15 genes predated the emergence of bioluminescence. Whether it is related at all to bioluminescence remains conjectural, but several observations would justify a closer examination. The firefly lanterns of //P. pyralis// and //A.lateralis// highly and differentially express the same CYP4G gene (Fig.5 of Fallon et al., 2018) one of only 26 genes in this class.  Photogenic tissues of //Phrixothrix hirtus// and //Aspisoma lineatum// also highly express CYP4G genes (Amaral et al., 2017).

Significantly, luciferase has evolved from fatty acid acyl-CoA synthase, an enzyme highly enriched in oenocytes (e.g. Gutierrez et al., 2007), as are the CYP4G enzymes. Although the origin of photocytes and lanterns is often ascribed to fat body cells, it is possible that the fat body cells located close to abdominal epidermis were misidentified, being in fact oenocytes. At least in //Phengodes// and //Phrixothrix// lanterns are reported to be of oenocyte origin (Buck, 1948; Viviani, 2002). The high oxygen consumption of luciferase is accomodated by the unusually rich tracheolization of light organs (Buck, 1948; Smith, 1963). One attractive hypothesis would be that the CYP4G enzymes are providing the hydrocarbons needed to coat the inner epicuticle of tracheal tubes (Moussian, 2010), and thus play an important role in oxygen supply for light flashing (Tsai et al., 2014). Two other and unrelated close associations between CYP4G-derived cuticular hydrocarbons and specialized trachae are found around the subgenual organ in Gasteruptiid wasps (Mikó et al., 2019), and possibly close to the tympanal membranes of tree weta “ears” (Lomas et al., 2012) as well.