Resequencing of durian genomes reveals large genetic variations among different cultivars.

Durian (Durio zibethinus), which yields the fruit known as the "King of Fruits," is an important economic crop in Southeast Asia. Several durian cultivars have been developed in this region. In this study, we resequenced the genomes of three popular durian cultivars in Thailand, including Kradumthong (KD), Monthong (MT), and Puangmanee (PM) to investigate genetic diversities of cultivated durians. KD, MT, and PM genome assemblies were 832.7, 762.6, and 821.6 Mb, and their annotations covered 95.7, 92.4, and 92.7% of the embryophyta core proteins, respectively. We constructed the draft durian pangenome and analyzed comparative genomes with related species in Malvales. Long terminal repeat (LTR) sequences and protein families in durian genomes had slower evolution rates than that in cotton genomes. However, protein families with transcriptional regulation function and protein phosphorylation function involved in abiotic and biotic stress responses appeared to evolve faster in durians. The analyses of phylogenetic relationships, copy number variations (CNVs), and presence/absence variations (PAVs) suggested that the genome evolution of Thai durians was different from that of the Malaysian durian, Musang King (MK). Among the three newly sequenced genomes, the PAV and CNV profiles of disease resistance genes and the expressions of methylesterase inhibitor domain containing genes involved in flowering and fruit maturation in MT were different from those in KD and PM. These genome assemblies and their analyses provide valuable resources to gain a better understanding of the genetic diversity of cultivated durians, which may be useful for the future development of new durian cultivars.

The complete chloroplast genome sequence of Intsia bijuga (Colebr.) Kuntze (Fabaceae: Detaroideae: Afzelieae).

Intsia bijuga (Colebr.) Kuntze. (1891) is a threatened mangrove species, belonging to the Fabaceae family and is native to the western Pacific coast and Southeast Asia. Here, we applied short-read Illumina technology to sequence and assemble its chloroplast genome. The complete chloroplast genome is 158,363 bp in length, composed of one large single-copy (LSC) region of 87,489 bp, one small single-copy (SSC) region of 19,438 bp, and a pair of inverted repeats (IRs) of 25,719 bp. A total of 129 unique genes were annotated, comprising 84 protein-coding genes, eight rRNA genes, and 37 tRNA genes. Our phylogenetic analysis showed the placement of I. bijuga (OL699920.1) with Afzelia species within Fabaceae family.

Assessment of the Genetic Diversity and Population Structure of Rhizophora apiculata Blume (Rhizophoraceae) in Thailand.

Rhizophora apiculata is one of the most widespread and economically important mangrove trees in the Indo-West Pacific region. Knowledge of the genetic variation of R. apiculata in Thailand is limited. Here, we generated a whole-genome sequence of R. apiculata using the 10× Genomics technology. R. apiculata genome assembly was 230.47 Mb. Based on its genome, 2640 loci of high-quality biallelic SNPs were identified from 82 R. apiculata accessions collected from 17 natural mangrove forests in Thailand to assess the genetic diversity and population structure among them. A moderate level of genetic diversity of R. apiculata was observed. The average observed heterozygosity (Ho = 0.48) was higher than the average expected heterozygosity (He = 0.36). Two subpopulations were observed and confirmed from three approaches: population structure, PCA, and phylogenetic analyses. They corresponded to the Gulf of Thailand and the Andaman Sea separated by the Malay Peninsula. AMOVA analyses indicated that genetic variation was attributable to 76.22% within populations and 23.78% among populations. A high level of genetic differentiation between the two subpopulations (FST = 0.24, p < 0.001) was observed. This study evaluated the genetic diversity and population structure of R. apiculata, providing useful information for sustainable mangrove management in Thailand.

The complete mitochondrial genome sequence of the karst-dwelling crab, Terrapotamon thungwa (Crustacea: Brachyura: Potamidae).

Terrapotamon thungwa is a new species of terrestrial long-legged crab discovered in a karst landscape of southern Thailand. Here, we report the first complete mitochondrial genome of this crab species. The mitochondrial genome size is 16,156 base-pairs (bp), including 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA), and two ribosomal RNA (rRNA) genes. The AT and GC content of the mitochondrial genome sequence is 73.2% and 26.8%, respectively. Phylogenetic analysis with 26 crustacean species, based on 13 mitochondrial conserve genes, showed that T. thungwa was closely related to other freshwater crab species in the family Potamidae.

Chromosome-level genome assembly of Indian mangrove (Ceriops tagal) revealed a genome-wide duplication event predating the divergence of Rhizophoraceae mangrove species.

Mangrove ecosystems are unique, highly diverse, provide benefits to humans, and aid in coastal protection. The Indian mangrove, or spurred mangrove, [Ceriops tagal (Perr.) C. B. Rob.] is a member of the Rhizophoraceae family and is commonly found along the intertidal zones in tropical regions in Southeast Asia, southern Asia, and Africa. Here, we present the first high-quality reference genome assembly of the Ceriops species. A preliminary draft assembly, generated from the 10× Genomics linked-read library, was scaffolded using the proximity ligation chromatin contact mapping technique (Hi-C) to obtain a chromosome-scale assembly of 231,919,005 bases with an N50 length of 11,408,429 bases. The benchmarking universal single-copy orthologs (BUSCO) analysis revealed that C. tagal gene predictions recovered 95.8% of the highly conserved orthologs. Phylogenetic analyses suggested that C. tagal diverged from the last common ancestor of flat-leaf spurred mangrove [C. decandra (Griff.) Ding Hou] and C. zippeliana Blume ∼10.4 million yr ago (MYA), and the last common ancestor of genera Ceriops, Kandelia, and Rhizophora diverged from that of genus Bruguiera ∼49.4 MYA. In addition, our analysis of the transversion rate at fourfold-degenerate sites from orthologous gene pairs provided evidence supporting a recent whole-genome duplication in C. tagal. The STRUCTURE and principal component analyses illustrated that C. tagal individuals investigated in this study were the admixture of two subpopulations, the genetic background of which was influenced primarily by location. The availability of genomic and transcriptomic resources and biodiversity data reported in this work will be useful for future studies that may shed light on adaptive evolutions of mangrove species.

Complete chloroplast genome sequences of five Bruguiera species (Rhizophoraceae): comparative analysis and phylogenetic relationships.

Bruguiera is a genus of true mangroves that are mostly distributed in the Indo-West Pacific region. However, the number of published whole chloroplast genome sequences of Bruguiera species are limited. Here, the complete chloroplast sequences of five Bruguiera species were sequenced and assembled using Illumina data. The chloroplast genomes of B. gymnorhiza, B. hainesii, B. cylindrica, B. parviflora and B. sexangula were assembled into 161,195, 164,295, 164,297, 163,228 and 164,170 bp, respectively. All chloroplast genomes contain 37 tRNA and eight rRNA genes, with either 84 or 85 protein-coding genes. A comparative analysis of these genomes revealed high similarity in gene structure, gene order and boundary position of the LSC, SSC and two IR regions. Interestingly, B. gymnorhiza lost a rpl32 gene in the SSC region. In addition, a ndhF gene in B. parviflora straddles both the SSC and IRB boundary regions. These genes reveal differences in chloroplast evolution among Bruguiera species. Repeats and SSRs in the chloroplast genome sequences were found to be highly conserved between B. cylindrica and B. hainesii as well as B. gymnorhiza and B. sexangula indicating close genetic relationships based on maternal inheritance. Notably, B. hainesii, which is considered a hybrid between B. gymnorhiza and B. cylindrica, appears to have inherited the chloroplast from B. cylindrica. Investigating the effects of selection events on shared protein-coding genes showed a positive selection in rps7 and rpl36 genes in all species compared to land-plant species. A phylogenetic analysis, based on 59 conserved chloroplast protein-coding genes, showed strong support that all Bruguiera species are in the clade Rhizophoraceae. This study provides valuable genetic information for the study of evolutionary relationships and population genetics in Bruguiera and other mangrove species.

Transcriptome sequencing revealed the influence of blue light on the expression levels of light-stress response genes in Centella asiatica.

Centella asiatica is rich in medical and cosmetic properties. While physiological responses of C. asiatica to light have been widely reported, the knowledge of the effects of light on its gene expression is sparse. In this study, we used RNA sequencing (RNA-seq) to investigate the expression of the C. asiatica genes in response to monochromatic red and blue light. Most of the differentially expressed genes (DEGs) under blue light were up-regulated but those under red light were down-regulated. The DEGs encoded for CRY-DASH and UVR3 were among up-regulated genes that play significant roles in responses under blue light. The DEGs involved in the response to photosystem II photodamages and in the biosynthesis of photoprotective xanthophylls were also up-regulated. The expression of flavonoid biosynthetic DEGs under blue light was up-regulated but that under red light was down-regulated. Correspondingly, total flavonoid content under blue light was higher than that under red light. The ABI5, MYB4, and HYH transcription factors appeared as hub nodes in the protein-protein interaction network of the DEGs under blue light while ERF38 was a hub node among the DEGs under red light. In summary, stress-responsive genes were predominantly up-regulated under blue light to respond to stresses that could be induced under high energy light. The information obtained from this study can be useful to better understand the responses of C. asiatica to different light qualities.

The Genome and Transcriptome Analysis of the Vigna mungo Chloroplast.

Vigna mungo is cultivated in approximately 5 million hectares worldwide. The chloroplast genome of this species has not been previously reported. In this study, we sequenced the genome and transcriptome of the V. mungo chloroplast. We identified many positively selected genes in the photosynthetic pathway (e.g., rbcL, ndhF, and atpF) and RNA polymerase genes (e.g., rpoC2) from the comparison of the chloroplast genome of V. mungo, temperate legume species, and tropical legume species. Our transcriptome data from PacBio isoform sequencing showed that the 51-kb DNA inversion could affect the transcriptional regulation of accD polycistronic. Using Illumina deep RNA sequencing, we found RNA editing of clpP in the leaf, shoot, flower, fruit, and root tissues of V. mungo. We also found three G-to-A RNA editing events that change guanine to adenine in the transcripts transcribed from the adenine-rich regions of the ycf4 gene. The edited guanine bases were found particularly in the chloroplast genome of the Vigna species. These G-to-A RNA editing events were likely to provide a mechanism for correcting DNA base mutations. The V. mungo chloroplast genome sequence and the analysis results obtained in this study can apply to phylogenetic studies and chloroplast genome engineering.

The complete mitochondrial genome of Luffa acutangula.

Based on PacBio de novo assembly, we report the first complete mitochondrial genome of Luffa acutangula (460,333 bp) containing nine large chloroplast-derived sequences (1.9-17.3 kb) across the mitogenome. The base composition of the mitogenome in descending order is A: 28.02%, C: 22.04%, G: 21.83% and T: 28.10%, and the G + C content is 43.87%. There are 63 mitochondrial genes including 40 protein-coding genes, 3 rRNA genes and 20 tRNA genes. Additionally, a total of 288 repeats ranging from 31 to 5,301 bp were identified, accounting for 5.7% of the mitogenome. Two large direct repeats (5,301 and 405 bp) within the mitogenome were found for the formation of four subgenomic molecules. A phylogenetic analysis showed that L. acutangula was closely related to other species in Cucurbiaceae. This mitogenome provides useful genetic information for evolutionary studies.