Genome-wide association study reveals genomic loci of sex differentiation and gonadal development in Plectropomus leopardus.

Introduction: Plectropomus leopardus, a commercially significant marine fish, is primarily found in the Western Pacific regions and along the coast of Southeast Asia. A thorough analysis of the molecular mechanisms involved in sex differentiation is crucial for gaining a comprehensive understanding of gonadal development and improving sex control breeding. However, the relevant fundamental studies of P. leopardus are relatively lacking. Methods: In this study, a genome-wide association study (GWAS) was conducted to investigate the genetic basis mechanism of sex differentiation and gonadal developmental traits in P. leopardus utilizing about 6,850,000 high-quality single-nucleotide polymorphisms (SNPs) derived from 168 individuals (including 126 females and 42 males) by the genome-wide efficient mixed-model association (GEMMA) algorithm. Results: The results of these single-trait GWASs showed that 46 SNP loci (-log10 p > 7) significantly associated with sex differentiation, and gonadal development traits were distributed in multiple different chromosomes, which suggested the analyzed traits were all complex traits under multi-locus control. A total of 1,838 potential candidate genes were obtained by considering a less-stringent threshold (-log10 p > 6) and ±100 kb regions surrounding the significant genomic loci. Moreover, 31 candidate genes were identified through a comprehensive analysis of significant GWAS peaks, gene ontology (GO) annotations, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, including taf7, ddx6, apoeb, sgk1, a2m, usf1, hsd3b7, dll4, xbp1, tet3, esr1, and gli3. These trait-associated genes have been shown to be involved in germline development, male sex differentiation, gonad morphogenesis, hormone receptor binding, oocyte development, male gonad development, steroidogenesis, estrogen-synthetic pathway, etc. Discussion: In the present study, multiple genomic loci of P. leopardus associated with sex differentiation and gonadal development traits were identified for the first time by using GWAS, providing a valuable resource for further research on the molecular genetic mechanism and sex control in P. leopardus. Our results also can contribute to understanding the genetic basis of the sex differentiation mechanism and gonadal development process in grouper fish.

The complete mitochondrial genome of Apolemichthys trimaculatus (Perciformes, Chaetodontidae).

Three-spot angelfish (Apolemichthys trimaculatus) is one of the most widespread angelfish that belongs to Pomacanthidae. However, there are few reports of the systemically classification and evolutionary analysis for A. trimaculatus so far. In this study, the complete mitochondrial genome of the A. trimaculatus is described. The full length of the mitogenome is 16,548 bp, consisting of 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs genes, and a non-coding control region. The overall base composition is 28.4% for A, 25.6% for T, 29.5% for C, and 16.5% for G, with a slight AT bias (54.0%). The mitogenome of A. trimaculatus provided essential and valuable DNA molecular information for further phylogeny and management of angelfish species.

Characterization of the complete mitochondrial genome of Congrogadus subducens (Richardson, 1843).

The complete mitochondrial genome of Congrogadus subducens is first presented in this study. The whole mitogenome is a closed circular molecule of 16,881 bp in size, including 13 protein-coding, 22 transfer RNA, 2 ribosomal RNA genes and a non-coding control region. The overall base composition of the mitochondrial DNA is 30.2% for A, 28.6% for T, 26.4% for C and 14.8% for G. The phylogenetic analysis conducted using 18 protein-coding genes showed that C. subducens was most closely related to the Pseudochromidae. This work will be useful for further research on species identification and evolutionary relationships within related species.

The complete mitochondrial genome of Slender Giant Moray Strophidon sathete (Hamilton, 1822).

The whole mitochondrial genome of the Slender Giant Moray Strophidon sathete (Hamilton, 1822) from the Hainan island was characterized using next-generation sequencing for the first time. The circular mitogenome of S. sathete is 16,568 bp, with 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes, and a D-loop region. The base composition is little biased (A, G, T, and C was 30.95%, 16.73%, 27.09%, and 25.23%, respectively) with A + T contents of 58.04%. Among 13 PCGs, 12 PCGs use a normal ATG as the start codon except COX1 use GTG; four of them end with TAA or TAG, others terminate with an unusual stop codon. The phylogenetic tree showed that S. sathete was first clustered with Rhinomuraena quaesita and Gymnothorax minor, which further clarify the phylogenetic and evolution position of the genus Strophidon in the family Muraenidae.

Complete chloroplast genome of red seaweed Halymenia maculata (J. Agardh, 1885).

In this study, we first assembled and characterized the complete chloroplast genome of red seaweed Halymenia maculata. It is 190,431 bp in length, with an AT content of 70.56%. In total, 122 genes were identified, and they consisted of 87 protein-coding genes, 33 tRNA genes, and two rRNA genes. The chloroplast genome of H. maculata did not show an obvious quadripartite structure. A total of five microsatellites (SSRs) were identified in the genome using MISA. Phylogenetic analysis revealed that H. maculata was first clustered with Grateloupia filicina and Grateloupia taiwanensis in a monophyletic clade that provides useful data for the phylogeny and taxonomy of Rhodymeniophycidae.

Complete chloroplast genome of green alga Caulerpa serrulata (Forsskål) J.Agardh, 1837.

The complete chloroplast genome of Caulerpa serrulata from South China Sea has been assembled and characterized for the first time. The circular chloroplast genome was 177,848 bp in length, with a GC content of 33.80%. It contained 117 genes, which included 78 protein-coding genes, 37 tRNA genes, and 2 ribosomal RNA genes. Like other species in Caulerpa, the chloroplast genome of C. serrulata did not demonstrate a typical quadripartite structure. A total of 35 microsatellites (SSRs) were identified in the genome using MISA. Phylogenetic analysis showed that C. serrulata was closer to Caulerpa cupressoides, which further clarified the phylogenetic relationships of species in Caulerpa.

Complete chloroplast genome of green alga Caulerpa sertularioides f. longipes (J.Agardh) Collins, 1909.

The complete chloroplast (cp) genome of Caulerpa sertularioides f. longipes was first assembled and characterized using Illumina pair-end sequencing from the South China Sea. It is 133,626 bp long, with a GC content of 32.94%. In total, 92 genes were identified in the genome, and they consisted 60 protein-coding genes (PCGs), 30 tRNA genes, and 2 rRNA genes. Like other species in Caulerpa, the whole cp genome of C. sertularioides f. longipes did not demonstrate an obvious quadripartite structure. A total of 31 microsatellites (SSRs) were identified in the cp genome using MISA. A phylogenetic tree revealed that C. sertularioides f. longipes was closer to Caulerpa cupressoides, which further clarified the phylogenetic relationships of species in Caulerpa.