Phased Telomere-to-Telomere Reference Genome and Pangenome Reveal an Expansion of Resistance Genes during Apple Domestication.

The cultivated apple (Malus domestica Borkh.) is a cross-pollinated perennial fruit tree of great economic importance. Previous versions of apple reference genomes were unphased, fragmented, and lacked comprehensive insights into the highly heterozygous genome, which impeded genetic studies and breeding programs in apple. In this study, we assembled a haplotype-resolved telomere-to-telomere reference genome for the diploid apple cultivar Golden Delicious. Subsequently, we constructed a pangenome based on twelve assemblies from wild and cultivated apples to investigate different types of resistance gene analogs (RGAs). Our results revealed the dynamics of the gene gain and loss events during apple domestication. Compared with cultivated species, more gene families in wild species were significantly enriched in oxidative phosphorylation, pentose metabolic process, responses to salt, and abscisic acid biosynthesis process. Interestingly, our analyses demonstrated a higher prevalence of RGAs in cultivated apples than their wild relatives, partially attributed to segmental and tandem duplication events in certain RGAs classes. Other types of structural variations, mainly deletions and insertions, have affected the presence and absence of TIR-NB-ARC-LRR (TNL), NB-ARC-LRR (NL), and CC-NB-ARC-LRR (CNL) genes. Additionally, hybridization/introgression from wild species has also contributed to the expansion of resistance genes in domesticated apples. Our haplotype-resolved T2T genome and pangenome provide important resources for genetic studies of apples, emphasizing the need to study the evolutionary mechanisms of resistance genes in apple breeding programs.

A Novel Gelatinase from Marine Flocculibacter collagenilyticus SM1988: Characterization and Potential Application in Collagen Oligopeptide-Rich Hydrolysate Preparation.

Although the S8 family in the MEROPS database contains many peptidases, only a few S8 peptidases have been applied in the preparation of bioactive oligopeptides. Bovine bone collagen is a good source for preparing collagen oligopeptides, but has been so far rarely applied in collagen peptide preparation. Here, we characterized a novel S8 gelatinase, Aa2_1884, from marine bacterium Flocculibacter collagenilyticus SM1988T, and evaluated its potential application in the preparation of collagen oligopeptides from bovine bone collagen. Aa2_1884 is a multimodular S8 peptidase with a distinct domain architecture from other reported peptidases. The recombinant Aa2_1884 over-expressed in Escherichia coli showed high activity toward gelatin and denatured collagens, but no activity toward natural collagens, indicating that Aa2_1884 is a gelatinase. To evaluate the potential of Aa2_1884 in the preparation of collagen oligopeptides from bovine bone collagen, three enzymatic hydrolysis parameters, hydrolysis temperature, hydrolysis time and enzyme-substrate ratio (E/S), were optimized by single factor experiments, and the optimal hydrolysis conditions were determined to be reaction at 60 ℃ for 3 h with an E/S of 400 U/g. Under these conditions, the hydrolysis efficiency of bovine bone collagen by Aa2_1884 reached 95.3%. The resultant hydrolysate contained 97.8% peptides, in which peptides with a molecular weight lower than 1000 Da and 500 Da accounted for 55.1% and 39.5%, respectively, indicating that the hydrolysate was rich in oligopeptides. These results indicate that Aa2_1884 likely has a promising potential application in the preparation of collagen oligopeptide-rich hydrolysate from bovine bone collagen, which may provide a feasible way for the high-value utilization of bovine bone collagen.

Evolutionary Genomics of Structural Variation in Asian Rice (Oryza sativa) Domestication.

Structural variants (SVs) are a largely unstudied feature of plant genome evolution, despite the fact that SVs contribute substantially to phenotypes. In this study, we discovered SVs across a population sample of 347 high-coverage, resequenced genomes of Asian rice (Oryza sativa) and its wild ancestor (O. rufipogon). In addition to this short-read data set, we also inferred SVs from whole-genome assemblies and long-read data. Comparisons among data sets revealed different features of genome variability. For example, genome alignment identified a large (∼4.3 Mb) inversion in indica rice varieties relative to japonica varieties, and long-read analyses suggest that ∼9% of genes from the outgroup (O. longistaminata) are hemizygous. We focused, however, on the resequencing sample to investigate the population genomics of SVs. Clustering analyses with SVs recapitulated the rice cultivar groups that were also inferred from SNPs. However, the site-frequency spectrum of each SV type-which included inversions, duplications, deletions, translocations, and mobile element insertions-was skewed toward lower frequency variants than synonymous SNPs, suggesting that SVs may be predominantly deleterious. Among transposable elements, SINE and mariner insertions were found at especially low frequency. We also used SVs to study domestication by contrasting between rice and O. rufipogon. Cultivated genomes contained ∼25% more derived SVs and mobile element insertions than O. rufipogon, indicating that SVs contribute to the cost of domestication in rice. Peaks of SV divergence were enriched for known domestication genes, but we also detected hundreds of genes gained and lost during domestication, some of which were enriched for traits of agronomic interest.

Genome-wide identification and analysis of membrane-bound O-acyltransferase (MBOAT) gene family in plants.

Membrane bound O-acyl transferase (MBOAT) family is composed of gene members encoding a variety of acyltransferase enzymes, which play important roles in plant acyl lipid metabolism. Here, we present the first genome-enabled identification and analysis of MBOAT gene models in plants. In total, we identified 136 plant MBOAT sequences from 14 plant species with complete genomes. Phylogenetic relationship analyses suggested the plant MBOAT gene models fell into four major groups, two of which likely encode enzymes of diacylglycerol acyltransferase 1 (DGAT1) and lysophospholipid acyltransferase (LPLAT), respectively, with one-three copies of paralogs present in each of the most plant species. A group of gene sequences, which are homologous to Saccharomyces cerevisiae glycerol uptake proteins (GUP), was identified in plants; copy numbers were conserved, with only one copy represented in each of the most plant species; analyses showed that residues essential for acyltransferases were more prone to be conserved than vertebrate orthologs. Among four groups, one was inferred to emerge in land plants and experience a rapid expansion in genomes of angiosperms, which suggested their important roles in adaptation of plants in lands. Sequence and phylogeny analyses indicated that genes in all four groups encode enzymes with acyltransferases. Comprehensive sequence identification of MBOAT family members and investigation into classification provide a complete picture of the MBOAT gene family in plants, and could shed light into enzymatic functions of different MBOAT genes in plants.

Metabolomic analysis reveals key metabolites and metabolic pathways in Suaeda salsa under salt and drought stress.

Suaeda salsa is an important salt- and drought-tolerant plant with important ecological restoration roles. However, little is known about its underlying molecular regulatory mechanisms. Therefore, understanding the response mechanisms of plants to salt and drought stress is of great importance. In this study, metabolomics analysis was performed to evaluate the effects of salt and drought stress on S. salsa . The experiment consisted of three treatments: (1) control (CK); (2) salt stress (Ps); and (3) drought stress (Pd). The results showed that compared with the control group, S. salsa showed significant differences in phenotypes under salt and drought stress conditions. First, a total of 207 and 292 differential metabolites were identified in the Ps/CK and Pd/CK groups, respectively. Second, some soluble sugars and amino acids, such as raffinose, maltopentoses, D -altro-beptulose, D -proline, valine-proline, proline, tryptophan and glycine-L -leucine, showed increased activity under salt and drought stress conditions, suggesting that these metabolites may be responsible for salt and drought resistance in S. salsa . Third, the flavonoid biosynthetic and phenylalanine metabolic pathways were significantly enriched under both salt and drought stress conditions, indicating that these two metabolic pathways play important roles in salt and drought stress resistance in S. salsa . The findings of this study provide new insights into the salt and drought tolerance mechanisms of S. salsa .

Assembly and comparative analysis of the complete mitochondrial genome of Isopyrum anemonoides (Ranunculaceae).

Ranunculaceae is a large family of angiosperms comprising 2500 known species-a few with medicinal and ornamental values. Despite this, only two mitochondrial genomes (mitogenomes) of the family have been released in GenBank. Isopyrum anemonoides is a medicinal plant belonging to the family Ranunculaceae, and its chloroplast genome has recently been reported; however, its mitogenome remains unexplored. In this study, we assembled and analyzed the complete mitochondrial genome of I. anemonoides and performed a comparative analysis against different Ranunculaceae species, reconstructing the phylogenetic framework of Isopyrum. The circular mitogenome of I. anemonoides has a length of 206,722 bp, with a nucleotide composition of A (26.4%), T (26.4%), C (23.6%), and G (23.6%), and contains 62 genes, comprising 37 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, and three ribosomal RNA (rRNA) genes. Abundantly interspersed repetitive and simple sequence repeat (SSR) loci were detected in the I. anemonoides mitogenome, with tetranucleotide repeats accounting for the highest proportion of SSRs. By detecting gene migration, we observed gene exchange between the chloroplast and mitogenome in I. anemonoides, including six intact tRNA genes, six PCG fragments, and fragments from two rRNA genes. Comparative mitogenome analysis of three Ranunculaceae species indicated that the PCG contents were conserved and the GC contents were similar. Selective pressure analysis revealed that only two genes (nad1 and rpl5) were under positive selection during their evolution in Ranunculales, and two specific RNA editing sites (atp6 and mttB) were detected in the I. anemonoides mitogenome. Moreover, a phylogenetic analysis based on the mitogenomes of I. anemonoides and the other 15 taxa accurately reflected the evolutionary and taxonomic status of I. anemonoides. Overall, this study provides new insights into the genetics, systematics, and evolution of mitochondrial evolution in Ranunculaceae, particularly I. anemonoides.

Transcriptomic study of Suaeda salsa in response to salt and drought stress.

Drought and salinity are the main factors limiting agricultural production. Improving crop resistance to relieve land stress is a major challenge in agriculture. The salt-tolerant species Suaeda salsa is a typical indicator of saline soil. It has a strong drought tolerance and can be used as a model plant to study salt and drought tolerance in plants. In this study, transcriptome sequencing and bioinformatic analysis were performed to study gene expression changes in S. salsa under salt and drought stresses, and to screen out differentially expressed genes. The genetic changes were most abundant in cellular processes, metabolic processes, ion binding, signalling, post-translational modifications, protein conversion, and molecular chaperones, suggesting that the above methods may play a significant role in the response of S. salsa to external salt and drought stress. Enrichment analysis showed that carbohydrate metabolic processes, oxidoreductase activity, transmembrane transport, kinase activity, cellular protein modification processes, and ion-binding pathways are involved in the stress response of S. salsa .

[Characteristics of the chloroplast genome of Isopyrum anemonoides].

In order to characterize the chloroplast genome and phylogenetic relationships of Isopyrum anemonoides, we performed Illumina Hiseq high-throughput sequencing to sequence the complete chloroplast genome of this plant and constructed a whole-genome map based on contig assembly and annotation. The chloroplast genome of I. anemonoides is 161 034 bp in length and has a typical tetrad structure, comprising 85 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The genome also contains a total of 44 dispersed repeat sequences and 47 simple sequence repeats. Among the genome's 53 678 codons, the largest proportion are leucine-encoding codons (5 251), whereas the smallest proportion encode tryptophan (712). Colinear analysis revealed an absence of inversions and rearrangements between I. anemonoides and related species at the chloroplast genome level. Whereas phylogenetic analysis indicated that I. anemonoides did not cluster in a clade with I. manshuricum, it did show a very close phylogenetic relationship with Paraquilegia microphylla. The findings of this study provide basic data that will contribute to further species identification and phylogenetic study of the genus Isopyrum.

Comparative analyses of chloroplast genomes in 'Red Fuji' apples: low rate of chloroplast genome mutations.

BACKGROUND: Fuji is a vital apple cultivar, and has been propagated clonally for nearly a century. The chloroplast genome variation of Fuji apples in China has not been investigated. METHODS: This study used next-generation high-throughput sequencing and bioinformatics to compare and analyze the chloroplast genome of 24 Red Fuji varieties from nine regions in China. RESULTS: The results showed that the 24 chloroplast genomes were highly conserved in genome size, structure, and organization. The length of the genomes ranged from 160,063 to 160,070 bp, and the GC content was 36.6%. Each of the 24 chloroplast genomes encoded 131 genes, including 84 protein-coding genes, 37 tRNA genes, and eight rRNA genes. The results of repeat sequence detection were consistent; the most common sequence was forward repeats (53.1%), and the least common sequence was complementary repeats (4.1%). The chloroplast genome sequence of Red Fuji was highly conserved. Two indels were detected, but the PI value was 0, and there were no SNP loci. The chloroplast genome variation rate of Red Fuji was low.

Complete chloroplast genome studies of different apple varieties indicated the origin of modern cultivated apples from Malus sieversii and Malus sylvestris.

Background: Apple is one of the most important temperate deciduous fruit trees worldwide, with a wide range of cultivation. In this study, we assessed the variations and phylogenetic relationships between the complete chloroplast genomes of wild and cultivated apples (Malus spp.). Method: We obtained the complete chloroplast genomes of 24 apple varieties using next-generation sequencing technology and compared them with genomes of (downloaded from NCBI) the wild species. Result: The chloroplast genome of Malus is highly conserved, with a genome length of 160,067-160,290 bp, and all have a double-stranded circular tetrad structure. The gene content and sequences of genomes of wild species and cultivated apple were almost the same, but several mutation hotspot regions (psbI-atpA, psbM-psbD, and ndhC-atpE) were detected in these genomes. These regions can provide valuable information for solving specific molecular markers in taxonomic research. Phylogenetic analysis revealed that Malus formed a new clade and four cultivated varieties clustered into a branch with M. sylvestris and M. sieversii, which indicated that M. sylvestris and M. sieversii were the ancestor species of the cultivated apple.

Diet-induced microbial adaptation process of red deer (Cervus elaphus) under different introduced periods.

Insufficient prey density is a major factor hindering the recovery of the Amur tiger (Panthera tigris altaica), and to effectively restore the Amur tiger, red deer (Cervus elaphus) was released into the Huangnihe National Nature Reserve of Northeast China as the main reinforcement. Differences in feeding and synergistic changes caused by the intestinal microbial communities could impact the adaptation of wildlife following reintroductions into field environments. We analyzed the foraging changes in shaping the intestinal microbial community of the red deer after being released to the Huangnihe National Nature Reserve and screened the key microbial flora of the red deer when processing complex food resources. The feeding and intestinal microbial communities of the red deer were analyzed by plant Deoxyribonucleic acid (DNA) barcoding sequencing and 16S rRNA high-throughput sequencing, respectively. The results showed that there were significant differences in food composition between wild and released groups [released in 2019 (R2): n = 5; released in 2021 (R0): n = 6]; the wild group fed mainly on Acer (31.8%) and Abies (25.6%), R2 fed mainly on Betula (44.6%), R0 had not formed a clear preferred feeding pattern but had certain abilities to process and adapt to natural foods. Firmicutes (77.47%) and Bacteroides (14.16%) constituted the main bacterial phylum of red deer, of which, the phylum Firmicutes was the key species of the introduced red deer for processing complex food resources (p < 0.05). The wild release process significantly changed the intestinal microbial structure of the red deer, making it integrate into the wild red deer. The period since release into the wild may be a key factor in reshaping the structure of the microbial community. This study suggested that the intestinal microbial structure of red deer was significantly different depending on how long since captive deer has been translocated. Individuals that have lived in similar environments for a long time will have similar gut microbes. This is the adaption process of the wildlife to natural environment after wild release, taking into account the gut microbes, and the feeding changes in shaping microbial communities can help introduced red deer match complex food resources and novel field environments.

Phylogeography and Population Genetics Analyses Reveal Evolutionary History of the Desert Resource Plant Lycium ruthenicum (Solanaceae).

Climactic oscillations during the Quaternary played a significant role in the formation of genetic diversity and historical demography of numerous plant species in northwestern China. In this study, we used 11 simple sequence repeats derived from expressed sequence tag (EST-SSR), two chloroplast DNA (cpDNA) fragments, and ecological niche modeling (ENM) to investigate the population structure and the phylogeographic history of Lycium ruthenicum, a plant species adapted to the climate in northwestern China. We identified 20 chloroplast haplotypes of which two were dominant and widely distributed in almost all populations. The species has high haplotype diversity and low nucleotide diversity based on the cpDNA data. The EST-SSR results showed a high percentage of total genetic variation within populations. Both the cpDNA and EST-SSR results indicated no significant differentiation among populations. By combining the evidence from ENM and demographic analysis, we confirmed that both the last interglacial (LIG) and late-glacial maximum (LGM) climatic fluctuations, aridification might have substantially narrowed the distribution range of this desert species, the southern parts of the Junggar Basin, the Tarim Basin, and the eastern Pamir Plateau were the potential glacial refugia for L. ruthenicum during the late middle Pleistocene to late Pleistocene Period. During the early Holocene, the warm, and humid climate promoted its demographic expansion in northwestern China. This work may provide new insights into the mechanism of formation of plant diversity in this arid region.

On the origin of the woody buckwheat Fagopyrum tibeticum (=Parapteropyrum tibeticum) in the Qinghai-Tibetan Plateau.

Here we tested whether 'insular woodiness', a striking evolutionary pattern that commonly occurs on islands, has also appeared in QTP continental endemics. Parapteropyrum, a monotypic shrubby genus occurring in the central QTP, has been previously placed in the tribe Atraphaxideae of the family Polygonaceae, while all the other woody species of this tribe mainly occur in western and central Asia. We studied sequence variations of nuclear ITS (internal transcribed spacer) and cp (chloroplast) DNA (rbcL and accD) of this genus and the other ten genera. The constructed phylogenies based on ITS, cpDNA or a combination of both datasets, suggest that the woody Parapteropyrum is nested within and most likely evolved from the herbaceous Fagopyrum. We propose that the large-scale uplift of the QTP not only promoted continental species radiation, but also the secondary feature of woodiness in a few herbaceous lineages in response to strong selection pressures, similar to those acting on island flora. In addition, the confirmation of Parapteropyrum within Fagopyrum highlights its potential use as a new, perennial source of buckwheat.

Taxonomic and Enzymatic Characterization of Flocculibacter collagenilyticus gen. nov., sp. nov., a Novel Gammaproteobacterium With High Collagenase Production.

Collagens from marine animals are an important component of marine organic nitrogen. Collagenase-producing bacteria and their collagenases play important roles in collagen degradation and organic nitrogen recycling in the ocean. However, only a few collagenase-producing marine bacteria have been so far discovered. Here, we reported the isolation and characterization of a collagenase-secreting bacterium, designated strain SM1988T, isolated from a green alga Codium fragile sample. Strain SM1988T is a Gram-negative, aerobic, oxidase-, and catalase-positive, unipolar flagellated, and rod-shaped bacterium capable of hydrolyzing casein, gelatin and collagens. Phylogenetic analysis revealed that strain SM1988T formed a distinct phylogenetic lineage along with known genera within the family Pseudoalteromonadaceae, with 16S rRNA gene sequence similarity being less than 93.3% to all known species in the family. Based on the phylogenetic, genomic, chemotaxonomic and phenotypic data, strain SM1988T was considered to represent a novel species in a novel genus in the family Pseudoalteromonadaceae, for which the name Flocculibacter collagenilyticus gen. nov., sp. nov. is proposed, with the type strain being SM1988T (= MCCC 1K04279T = KCTC 72761T). Strain SM1988T showed a high production of extracellular collagenases, which had high activity against both bovine collagen and codfish collagen. Biochemical tests combined with genome and secretome analyses indicated that the collagenases secreted by strain SM1988T are serine proteases from the MEROPS S8 family. These data suggest that strain SM1988T acts as an important player in marine collagen degradation and recycling and may have a promising potential in collagen resource utilization.

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A total of 64 haplotypes were obtained from the complete Cytochrome b gene (Cyt b) of 77 Sorex isodon collected from three populations (Daxing'anling, Xiaoxing'anling, and Changbai Mountains) in Northeast China. The haplotype diversity was 0.9920 and the nucleotide diversity was 0.0105, indicating high genetic diversity. The genetic diversity of Changbai Mountains population was significantly higher than that of Daxing'anling and Xiaoxing'anling populations. The F-statistics, the number of migrants per generation and the genetic distance results showed that the genetic distances among the populations and among the sampling sites were generally consistent with geographical distance. Analysis of molecular variance showed that the differentiation among populations, among sampling sites, and within sampling site accounted for 33.4%, 10.2% and 56.4% of total variation, respectively. The analysis of population history showed that S. isodon in Northeast China experienced no population expansion. The reported complete sequence of Cyt b gene of S. isodon (GenBank) of Europe and other parts of Asia was downloaded to examine the genetic structure of S. isodon. The phylogenetic tree was divided into two large branches. One branch consisted mainly of Daxing'anling and Xiaoxing'anling samples. The other branch was departed into two sub-branches. Median-joining network analysis showed that there were three lineages: one lineage mainly consisted of haplotypes from Daxing'anling and Xiaoxing'anling, and also four haplotypes of Changbai Mountains, while the other lineage included a few haplotypes of three populations in Northeast China, and those from Baikal Lake, Russia and Finland. The last lineage was entirely composed of haplotypes from Changbai Mountains. The results of genetic diversity, phylogenetic tree and median-joining network all suggested that the Changbai Mountains was the refuge for S. isodon during last glacial.

Complete chloroplast genome of an endangered endemic tree, handeliodendron bodinieri (levl.) rehder (sapindaceae) from karst forests of southwest China.

Handeliodendron bodinieri (Sapindaceae) is an endangered monotypic species endemic to the karst forests in southwest China whose populations are now fragmented and the total number of individuals evidently decreased. In this research, we characterized the chloroplast (cp) genome of H. bodinieri using genome skimming. The whole cp genome was 155,291 bp long and comprised 137 genes, including 8 unique rRNAs, 40 tRNAs, and 89 protein-coding genes. The overall guanine-cytosine content of H. bodinieri cp genome was 37.8%. The phylogenetic analysis suggested that H. bodinieri is closely related to the genus Mangifera. This study will be useful for future studies on conservation genetics of this economically important endemic plant.

Complete chloroplast genome of Erythropsis kwangsiensis (Sterculiaceae), an endemic wild tree from South China.

Erythropsis kwangsiensis (Sterculiaceae), a wild endangered tree that grows in South China, is an economically important species. There is scant information available on the chloroplast (cp) genome of this species. The present study is the first to analyze the cp genome of E. kwangsiensis using genome skimming. The whole cp genome is 160,836 bp long with 131 genes, including 84 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. The GC content is 37.0%. Phylogenetic analysis revealed a close relationship to Firmiana colorata. This data will be useful for future investigations of conservation genetics and potential applications in breeding new varieties of this endangered and economically important tree.

Euphorbia Section Hainanensis (Euphorbiaceae), a New Section Endemic to the Hainan Island of China From Biogeographical, Karyological, and Phenotypical Evidence.

Euphorbia hainanensis is an endangered species endemic to the tropical Hainan Island in southern China and of historical importance for Chinese medicine. It is currently the only unplaced species of the genus Euphorbia (Euphorbiaceae) due to its isolated island distribution and debated placement by a previous molecular phylogenetic study. We sequenced nuclear ITS and chloroplast rbcL and ndhF for newly collected accessions of E. hainanensis and additional Euphorbia species found in Hainan, and analyzed the sequences in the context of the entire genus together with published data. All gene regions highly supported that E. hainanensis occupied an isolated phylogenetic position, showing no close affinity with any known Euphorbia sections suggesting it was a new section. ITS placed E. hainanensis sister to sect. Crossadenia (subgenus Chamaesyce) from Brazil with an estimated divergence time of 9.3-30.6 Mya while the chloroplast markers placed E. hainanensis at a position sister to the entire New World clade of Euphorbia subgenus Chamaesyce. In addition, our karyological results suggested a close affinity between E. hainanensis and the New World species of Euphorbia subg. Chamaesyce, with which shared the same chromosome number 2n = 28 and basic chromosome number x = 7. Phenotypically, E. hainanensis is unique with no close resemblance to other species in Euphorbia subg. Chamaesyce. Based on its isolated biogeographical, karyological, and phenotypical position, we propose a new section E. subgenus Chamaesyce section Hainanensis that might origin from long distance dispersal events because collective evidences showed a close affinity between the species from the Old World with those from the New World.

The complete chloroplast genome of Atraphaxis jrtyschensis (polygonaceae), an endemic and endangered desert shrub to Xinjiang, China.

Atraphaxis jrtyschensis (Polygonacae) is an endangered desert shrub endemic to China in Xinjiang province with great ecological importance for sand fixation. However, its genomic resources are still very limited. Here, we generated the first chloroplast (cp) genome of A. jrtyschensis using genome skimming sequencing. The whole cp genome is 164,192 bp and comprises 130 genes, including 83 protein-coding genes, 37 tRNA genes, 8 rRNA genes, and 2 pseudogenes (rpl23). The overall GC content of A. jrtyschensis cp genome is 37.5%. The phylogenic analysis placed A. jrtyschensis at the base of Trib Rumiceae, which contained the genera Rheum and Oxyria. This study will be useful for future researches to investigate the conservation genetics and potential applications in sand fixation of the endangered desert shrub.

Expression Divergence of Duplicate Genes in the Protein Kinase Superfamily in Pacific Oyster.

Gene duplication has been proposed to serve as the engine of evolutionary innovation. It is well recognized that eukaryotic genomes contain a large number of duplicated genes that evolve new functions or expression patterns. However, in mollusks, the evolutionary mechanisms underlying the divergence and the functional maintenance of duplicate genes remain little understood. In the present study, we performed a comprehensive analysis of duplicate genes in the protein kinase superfamily using whole genome and transcriptome data for the Pacific oyster. A total of 64 duplicated gene pairs were identified based on a phylogenetic approach and the reciprocal best BLAST method. By analyzing gene expression from RNA-seq data from 69 different developmental and stimuli-induced conditions (nine tissues, 38 developmental stages, eight dry treatments, seven heat treatments, and seven salty treatments), we found that expression patterns were significantly correlated for a number of duplicate gene pairs, suggesting the conservation of regulatory mechanisms following divergence. Our analysis also identified a subset of duplicate gene pairs with very high expression divergence, indicating that these gene pairs may have been subjected to transcriptional subfunctionalization or neofunctionalization after the initial duplication events. Further analysis revealed a significant correlation between expression and sequence divergence (as revealed by synonymous or nonsynonymous substitution rates) under certain conditions. Taken together, these results provide evidence for duplicate gene sequence and expression divergence in the Pacific oyster, accompanying its adaptation to harsh environments. Our results provide new insights into the evolution of duplicate genes and their expression levels in the Pacific oyster.