The structure of the mitochondrial DNA control region in the Relict Gull (Larus relictus) was predicted and compared with data from the National Center for Biotechnology Information (NCBI) on five other gulls. The results showed that the control regions of the six gulls comprise three domains. Sequences of CSB-1-like (domain I) and CSB-1 (domain III) in L. relictus have the highest similarity with those in the other five gulls. The insertion fragments are located in downstream domain I of L. ridibundus, L. brunnicephalus, and L. saundersi. Seven conserved sequence boxes (additional box, F-box, E-box, D-box, C-box, bird-similarity-box, and B-box) are located in domain II in all six gulls. It is suggested that the CSB-2/3 sequence, the origin of H-strand replication, and bidirectional light- and heavy-strand transcription promoters in domain III of L. relictus have some distinguishing features to those of other gulls. Some repeat units are contained in the 3' end of the control region in the five gulls; however, no repeat units are found in the sequence CAAACAACAAA in L. relictus. The distribution of nucleotide diversity analysis will provide the useful information on the selected DNA fragment within the control region for genetic analyses among gulls.
The complete mitochondrial genome sequence of Larus relictus was 16,586-bp long, containing 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA genes, and a control region. Most PCGs begin with the typical ATN start codon with the exception of COI and ND5 genes, which use GTG as the initiation codon. Stop codons AGG, TAG, TAA and AGA are present in the PCGs; exceptions are COIII and ND4, which possess incomplete termination codons (T), and ND3, in which one extra C nucleotide is found. Secondary structure prediction of the 22 tRNA genes revealed the absence of the DHU arm in tRNA(Ser)((AGN)). Seven conserved sequence box elements, as well as the origin of H-strand replication (OH) and bidirectional light- and heavy-strand transcription promoters (LSP/HSP), are found in control region.
Background
The relict gull (Larus relictus), was classified as vulnerable on the IUCN Red List and is a first-class national protected bird in China. Genomic resources for L. relictus are lacking, which limits the study of its evolution and its conservation.
Results
In this study, based on the Illumina and PacBio sequencing platforms, we successfully assembled the genome of L. relictus, one of the few known reference genomes in genus Larus. The size of the final assembled genome was 1.21 Gb, with a contig N50 of 8.11 Mb. A total of 18,454 genes were predicted from the assembly results, with 16,967 (91.94%) of these genes annotated. The genome contained 92.52 Mb of repeat sequence, accounting for 7.63% of the assembly. A phylogenetic tree was constructed using 4902 single-copy orthologous genes, which showed L. relictus had closest relative of L. smithsonianus, with divergence time of 14.7 Mya estimated between of them. PSMC analyses indicated that L. relictus had been undergoing a long-term population decline during 0.01-0.1 Mya with a small effective population size fom 8800 to 2200 individuals.
Conclusions
This genome will be a valuable genomic resource for a range of genomic and conservation studies of L. relictus and will help to establish a foundation for further studies investigating whether the breeding population is a complex population. As the species is threatened by habitat loss and fragmentation, actions to protect L. relictus are suggested to alleviate the fragmentation of breeding populations.
The complete sequence of mitochondrial genome of Larus brunnicephalus was determined using long PCR and conserved primers walking approaches. The results showed that the entire mitochondrial genome of L. brunnicephalus is 16,769 bp in length, which has been deposited in GenBank with the accession number JX155863. The mitochondrial genomic organization and gene order of L. brunnicephalus were consistent with that of Gallus gallus, which contains 13 protein coding genes (PCGs), 22 tRNA, 2 rRNA, and a control region. Except for COI gene using GTG and ND3 gene with ATT as the initiation codon, all other 11 PCGs of the mtDNA in L. brunnicephalus started with the typical ATG codon. AGG, TAG, TAA, or AGA were used in 11 PCGs as usual termination codons, except for COIII and ND4 genes with incomplete termination codon (T). The secondary structures of 22 tRNAs were predicted and it is found that the tRNASer (AGN) lacks DHU arm and tRNAPhe contains the fourth types of permutation in the TψC arm. It is predicted that the secondary structures of 12S rRNA and 16S rRNA include 4 structural domains with 47 helics and 6 domains with 60 helics, respectively. F-box, E-box, D-box, C-box, B-box, Bird similarity-box, and CSB-boxes (1-3), which were found in the control regions of other bird species were also present in L. brunnicephalus. The sequence in the starting regions of H-strand replication (OH) and the bidirectional light and heavy-strand transcription promoters (LSP/HSP) in the control region were also predicted. Result of phylogeny analysis supports that L. brunnicephalus should be categorized into the Masked gulls species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.