The complete mitochondrial genome of soft coral Sarcophyton trocheliophorum (Cnidaria: Anthozoa) using next-generation sequencing

Abstract The complete mitochondrial genome of Sarcophyton trocheliophorum was completed using next-generation sequencing (NGS) method. The mitochondrial genome is a circular molecule of 18,508 bp in length, containing 14 protein-coding genes, two ribosomal RNA genes and one transfer RNA gene (Met-tRNA). The base composition is 30.45% A, 16.03% C, 19.13% G, and 34.40% T, with an A + T content of 64.85%. A phylogenetic analysis of Alcyoniidae showed that genus Sarcophyton had the closest relationship with Sinularia.

Species of soft coral genus Sarcophyton are widespread, from Polynesia in the east to the Red Sea in the west. Usually, they habitat in marine environment from the intertidal zone to depths up to 15 m. Colonies of Sarcophyton are characteristically fleshy and soft, mainly mushroom shape with yellow, beige, brown or green colour (Feussner and Waqa 2013).
Incomplete mitogenome of Sarcophyton glaucum is the only sequence in genus Sarcophyton, contains 11,715 bp (Beaton et al. 1998). In this study, we submitted and analyzed the first complete mitogenome of Sarcophyton, Sarcophyton trocheliophorum (GenBank: MK994517).
The complete mitogenome of S. trocheliophorum was 18,508 in length, with a nucleotide composition of 30.45% A, 16.03% C, 19.13% G and 34.40% T.
The structure of S. trocheliophorum mitogenome was significantly different from classic metazoan mitogenomes, which contain 13 PCGs, 2 rRNAs and 22tRNAs.
The gene content and gene order in present mitogenome are the same as in the other Alcyoniidae, which include 14 PCGs, 2 rRNAs and 1 tRNA. Twelve genes (cox1, 12S, nad1, cytb, nad6, nad3, nad4L, mutS, 16S, nad2, nad5, and nad4) were located on the heavy strand and the other five genes (tRNA-Met, cox3, atp6, atp8 and cox2) were encoded on the light strand. All PCGs were detected to start with the ATG codon. Seven genes (nad1, nad6, nad3, nad2, nad5, cox3 and cox2) appeared to use TAG as stop codon, whereas six genes (cytb, nad4L, mutS, nad4, atp6, and atp8) use the stop codon TAA, and cox1 use no premature stop codon T. We found that there was only one tRNA (Met-tRNA) that can be folded into typical clover-leaf secondary structures. There were a total of 15 gaps between coding genes, the length of which ranged from 3 nucleotides to 112 nucleotides. A 13 nucleotide overlap existed between nad2 and nad5, which was the same as Sinularia peculiaris. The whole mitogenome possessed strong A þ T content bias. A þ T content of the overall mitogenome was 64.85%, and A þ T content of PCGs, rRNAs, and tRNA was 66.26, 58.7, and 56.34%, respectively.

Disclosure statement
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the manuscript.