Chromosome-level genome assembly and annotation of the loquat (Eriobotrya japonica) genome.

The loquat (Eriobotrya japonica) is a species of flowering plant in the family Rosaceae that is widely cultivated in Asian, European, and African countries. It blossoms in the winter and ripens in the early summer. The genome of loquat has to date not been published, which limits the study of molecular biology in this cultivated species. Here, we used the third-generation sequencing technology of Nanopore and Hi-C technology to sequence the genome of Eriobotrya. We generated 100.10 Gb of long reads using Oxford Nanopore sequencing technologies. Three types of Illumina high-throughput sequencing data, including genome short reads (47.42 Gb), transcriptome short reads (11.06 Gb), and Hi-C short reads (67.25 Gb), were also generated to help construct the loquat genome. All data were assembled into a 760.1-Mb genome assembly. The contigs were mapped to chromosomes by using Hi-C technology based on the contacts between contigs, and then a genome was assembled exhibiting 17 chromosomes and a scaffold N50 length of 39.7 Mb. A total of 45,743 protein-coding genes were annotated in the Eriobotrya genome, and we investigated the phylogenetic relationships between the Eriobotrya and 6 other Rosaceae species. Eriobotrya shows a close relationship with Malus and Pyrus, with the divergence time of Eriobotrya and Malus being 6.76 million years ago. Furthermore, chromosome rearrangement was found in Eriobotrya and Malus. We constructed the first high-quality chromosome-level Eriobotrya genome using Illumina, Nanopore, and Hi-C technologies. This work provides a valuable reference genome for molecular studies of the loquat and provides new insight into chromosome evolution in this species.

Jiang S ，An H ，Xu F ，Zhang X ... -  《GigaScience》

Chromosomal-level assembly of Juglans sigillata genome using Nanopore, BioNano, and Hi-C analysis.

Juglans sigillata, or iron walnut, belonging to the order Juglandales, is an economically important tree species in Asia, especially in the Yunnan province of China. However, little research has been conducted on J. sigillata at the molecular level, which hinders understanding of its evolution, speciation, and synthesis of secondary metabolites, as well as its wide adaptability to its plateau environment. To address these issues, a high-quality reference genome of J. sigillata would be useful. To construct a high-quality reference genome for J. sigillata, we first generated 38.0 Gb short reads and 66.31 Gb long reads using Illumina and Nanopore sequencing platforms, respectively. The sequencing data were assembled into a 536.50-Mb genome assembly with a contig N50 length of 4.31 Mb. Additionally, we applied BioNano technology to identify contacts among contigs, which were then used to assemble contigs into scaffolds, resulting in a genome assembly with scaffold N50 length of 16.43 Mb and contig N50 length of 4.34 Mb. To obtain a chromosome-level genome assembly, we constructed 1 Hi-C library and sequenced 79.97 Gb raw reads using the Illumina HiSeq platform. We anchored ∼93% of the scaffold sequences into 16 chromosomes and evaluated the quality of our assembly using the high contact frequency heat map. Repetitive elements account for 50.06% of the genome, and 30,387 protein-coding genes were predicted from the genome, of which 99.8% have been functionally annotated. The genome-wide phylogenetic tree indicated an estimated divergence time between J. sigillata and Juglans regia of 49 million years ago on the basis of single-copy orthologous genes. We provide the first chromosome-level genome for J. sigillata. It will lay a valuable foundation for future research on the genetic improvement of J. sigillata.

Ning DL ，Wu T ，Xiao LJ ，Ma T ，Fang WL ，Dong RQ ，Cao FL ... -  《GigaScience》

Chromosome-level genome assembly of a cyprinid fish Onychostoma macrolepis by integration of nanopore sequencing, Bionano and Hi-C technology.

Onychostoma macrolepis is an emerging commercial cyprinid fish species. It is a model system for studies of sexual dimorphism and genome evolution. Here, we report the chromosome-level assembly of the O.macrolepis genome obtained from the integration of nanopore long-read sequencing with physical maps produced using Bionano and Hi-C technology. A total of 87.9 Gb of nanopore sequence provided approximately 100-fold coverage of the genome. The preliminary genome assembly was 883.2 Mb in size with a contig N50 size of 11.2 Mb. The 969 corrected contigs obtained from Bionano optical mapping were assembled into 853 scaffolds and produced an assembly of 886.5 Mb with a scaffold N50 of 16.5 Mb. Finally, using the Hi-C data, 881.3 Mb (99.4% of genome) in 526 scaffolds were anchored and oriented in 25 chromosomes ranging in size from 25.27 to 56.49 Mb. In total, 24,770 protein-coding genes were predicted in the genome, and ~96.85% of the genes were functionally annotated. The annotated assembly contains 93.3% complete genes from the BUSCO reference set. In addition, we identified 409 Mb (46.23% of the genome) of repetitive sequence, and 11,213 non-coding RNAs, in the genome. Evolutionary analysis revealed that O. macrolepis diverged from common carp approximately 24.25 million years ago. The chromosomes of O. macrolepis showed an unambiguous correspondence to the chromosomes of zebrafish. The high-quality genome assembled in this work provides a valuable genomic resource for further biological and evolutionary studies of O. macrolepis.

Sun L ，Gao T ，Wang F ，Qin Z ，Yan L ，Tao W ，Li M ，Jin C ，Ma L ，Kocher TD ，Wang D ... -  《-》

De novo assembly of a chromosome-level reference genome of red-spotted grouper (Epinephelus akaara) using nanopore sequencing and Hi-C.

The red-spotted grouper Epinephelus akaara (E. akaara) is one of the most economically important marine fish in China, Japan and South-East Asia and is a threatened species. The species is also considered a good model for studies of sex inversion, development, genetic diversity and immunity. Despite its importance, molecular resources for E. akaara remain limited and no reference genome has been published to date. In this study, we constructed a chromosome-level reference genome of E. akaara by taking advantage of long-read single-molecule sequencing and de novo assembly by Oxford Nanopore Technology (ONT) and Hi-C. A red-spotted grouper genome of 1.135 Gb was assembled from a total of 106.29 Gb polished Nanopore sequence (GridION, ONT), equivalent to 96-fold genome coverage. The assembled genome represents 96.8% completeness (BUSCO) with a contig N50 length of 5.25 Mb and a longest contig of 25.75 Mb. The contigs were clustered and ordered onto 24 pseudochromosomes covering approximately 95.55% of the genome assembly with Hi-C data, with a scaffold N50 length of 46.03 Mb. The genome contained 43.02% repeat sequences and 5,480 noncoding RNAs. Furthermore, combined with several RNA-seq data sets, 23,808 (99.5%) genes were functionally annotated from a total of 23,923 predicted protein-coding sequences. The high-quality chromosome-level reference genome of E. akaara was assembled for the first time and will be a valuable resource for molecular breeding and functional genomics studies of red-spotted grouper in the future.

Ge H ，Lin K ，Shen M ，Wu S ，Wang Y ，Zhang Z ，Wang Z ，Zhang Y ，Huang Z ，Zhou C ，Lin Q ，Wu J ，Liu L ，Hu J ，Huang Z ，Zheng L ... -  《-》

Chromosome-level assembly of the mustache toad genome using third-generation DNA sequencing and Hi-C analysis.

The mustache toad, Vibrissaphora ailaonica, is endemic to China and belongs to the Megophryidae family. Like other mustache toad species, V. ailaonica males temporarily develop keratinized nuptial spines on their upper jaw during each breeding season, which fall off at the end of the breeding season. This feature is likely result of the reversal of sexual dimorphism in body size, with males being larger than females. A high-quality reference genome for the mustache toad would be invaluable to investigate the genetic mechanism underlying these repeatedly developing keratinized spines. To construct the mustache toad genome, we generated 225 Gb of short reads and 277 Gb of long reads using Illumina and Pacific Biosciences (PacBio) sequencing technologies, respectively. Sequencing data were assembled into a 3.53-Gb genome assembly, with a contig N50 length of 821 kb. We also used high-throughput chromosome conformation capture (Hi-C) technology to identify contacts between contigs, then assembled contigs into scaffolds and assembled a genome with 13 chromosomes and a scaffold N50 length of 412.42 Mb. Based on the 26,227 protein-coding genes annotated in the genome, we analyzed phylogenetic relationships between the mustache toad and other chordate species. The mustache toad has a relatively higher evolutionary rate and separated from a common ancestor of the marine toad, bullfrog, and Tibetan frog 206.1 million years ago. Furthermore, we identified 201 expanded gene families in the mustache toad, which were mainly enriched in immune pathway, keratin filament, and metabolic processes. Using Illumina, PacBio, and Hi-C technologies, we constructed the first high-quality chromosome-level mustache toad genome. This work not only offers a valuable reference genome for functional studies of mustache toad traits but also provides important chromosomal information for wider genome comparisons.

Li Y ，Ren Y ，Zhang D ，Jiang H ，Wang Z ，Li X ，Rao D ... -  《GigaScience》