The complete mitochondrial genome of Korean endemic species, Timarete posteria (Polychaeta, Cirratulidae)

Abstract

The mitogenome sequence of a typical multi-tentaculate cirratulid species, Timarete posteria (Terebellida, Cirratulidae), was determined first in the genus Timarete. The complete mitogenome is 15,497 bp in length, containing 13 protein coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 23 transfer RNAs (tRNAs), and gene order and structure are identical to those of other cirratulid species. Mitogenome consists of 30.4% A, 25.2% C, 12.8% G, 31.6% T, revealing high content of A + T, similar to the other cirratulid polychaetes. Results will be valuable for inferring phylogenetic relationships among members of Cirratulidae within the Terebellids.

Keywords:

• Complete mitogenome
• Timarete posteria
• Cirratulidae
• Polychaeta

The genus Timarete Kinberg, 1866 is assigned to a multi-tentaculate cirratulid polychaete (Blake 1996). Recently, some Timarete species have been taxonomically re-evaluated with genetic analysis, based on barcoded regions of mitochondrial cytochrome c oxidase subunit I and 16S ribosomal RNA (Magalhães et al. 2014, 2017; Seixas et al. 2017; Choi et al. 2018). Among them, Choi et al. (2018) suggested that Timarete is not monophyletic and closely related to Cirriformia Hartman, 1936 in the phylogenetic relationship using COI and 16S, but they pointed out that further study with more detailed molecular data is needed to verify the reality of the phylogenetic relationship of multi-tentaculate cirratulid genera. In Korean waters, Choi et al. (2018) defined an endemic Timarete species, T. posteria (Choi et al. 2018) and Timarete is represented by T. posteria only from this region. In this study, we determined complete mitochondrial genome (mitogenome) of Korean endemic species, Timarete posteria, and it will be valuable information in further study for the phylogeny of multi-tentaculate cirratulids.

Samples were collected from intertidal rocky bottoms in East Sea (Sea of Japan) of South Korea. The voucher specimen was deposited in National Marine Biodiversity Institute of Korea (MABIKNA00146235). Genomic DNA was isolated from muscle tissue and mitogenome sequences were analyzed by application of Illumina HiSeq2000 sequencing platform (Macrogen, Seoul, Korea). Sequences were assembled and annotated, in comparison with previously reported mitogenome sequences of cirratulid species (Choi et al. 2017) using Geneious 9.1.8 (Biomatters Ltd, Auckland, New Zealand) (Kearse et al. 2012). Additionally, we used the mitochondrial genome annotation server (Bernt et al. 2013) and tRNAscan-SE server (Lowe and Chan 2016) for annotation.

The complete mitogenome of Timarete posteria (GenBank accession number MK105766) is 15,497 bp in length, containing 13 protein coding genes (PCGs), 2 ribosomal RNAs (rRNAs), and 23 transfer RNAs (tRNAs). Overall base composition of Timarete posteria is 30.4% A, 25.2% C, 12.8% G, 31.6% T, revealing high A + T content (62%) similar to the other Cirratulid polychaetes. All PCGs except COI gene use typical ATG and COI use ATT as an initiation codon. Eleven PCGs (cox1, cox2, atp8, cox3, cytb, nad4l, nad4, nad1, nad3, nad2 and nad6) had TAA and one (atp6) had TAG as the stop codon, while one (nad5) had an incomplete stop codon, T. Lengths of tRNA genes range from 61 to 68 bp and all tRNAs have the typical clover leaf structure except tRNA^Ser_UCN. The one tRNAs have a reduced DHU arm.

A maximum-likelihood tree was constructed to investigate molecular taxonomic position of these species using GTR + G model in MEGA6 (Tamura et al. 2013), and dataset used were nucleotide sequences of 13 PCGs from mitogenomes of the other three species in the order Terebellida. T. posteria was grouped within cirratulid speceis previously anounced from GenBank, with high bootstrap values of 100%. Genus Timarete is sister taxon relationships with genus Cirriformia, as well as support for previously published COI gene trees (Figure 1) (Weidhase et al. 2016).

Figure 1. Maximum-likelihood (ML) tree based on the protein coding genes (PCGs) of Timarete posteria with family Cirratulidae and other polychaetes under order Terebellida. Riftia pachyptila was used as outgroup for tree rooting. Numbers above the branches indicate ML bootstrap values from 1,000 replications.

Disclosure statement

The authors declare that they do not have any conflict of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by the grants of National Marine Biodiversity Institute of Korea [2018M00200].