Transcriptome analyses of Acer Truncatum Bunge seeds to delineate the genes involved in fatty acid metabolism.

BACKGROUND: Acer truncatum Bunge is an economic, ecological, oil, and medicinal tree, and its kernel oil is rich in nervonic acid. It is crucial to explore the transcriptional expression patterns of genes affecting fatty acid synthesis to improve the quality of Acer truncatum oil. RESULTS: This study used the seeds from high fatty acid strain YQC and those from low fatty acid strain Y38 as the test materials. Specifically, we performed a comparative transcriptome analysis of Y38 seeds and YQC to identify differentially expressed genes (DEGs) at two time points (seeds 30 days after the blooming period and 90 days after the blooming period). Compared with YQC_1 (YQC seeds at 30 days after the blooming period), a total of 3,618 DEGs were identified, including 2,333 up-regulated and 1,285 downregulated DEGs in Y38_1 (Y38 seeds at 30 days after blooming period). In the Y38_2 (Y38 seeds at 90 days after the blooming period) versus YQC_2 (YQC seeds at 90 days after the blooming period) comparison group, 9,340 genes were differentially expressed, including 5,422 up-regulated and 3,918 down-regulated genes. The number of DEGs in Y38 compared to YQC was significantly higher in the late stages of seed development. Gene functional enrichment analyses showed that the DEGs were mainly involved in the fatty acid biosynthesis pathway. And two fatty acid synthesis-related genes and seven nervonic acid synthesis-related genes were validated by qRT-PCR. CONCLUSIONS: This study provides a basis for further research on biosynthesizing fatty acids and nervonic acidnervonic acids in A. truncatum seeds.

Testing plastomes and nuclear ribosomal DNA sequences as the next-generation DNA barcodes for species identification and phylogenetic analysis in Acer.

BACKGROUND: Acer is a taxonomically intractable and speciose genus that contains over 150 species. It is challenging to distinguish Acer species only by morphological method due to their abundant variations. Plastome and nuclear ribosomal DNA (nrDNA) sequences are recommended as powerful next-generation DNA barcodes for species discrimination. However, their efficacies were still poorly studied. The current study will evaluate the application of plastome and nrDNA in species identification and perform phylogenetic analyses for Acer. RESULT: Based on a collection of 83 individuals representing 55 species (c. 55% of Chinese species) from 13 sections, our barcoding analyses demonstrated that plastomes exhibited the highest (90.47%) species discriminatory power among all plastid DNA markers, such as the standard plastid barcodes matK + rbcL + trnH-psbA (61.90%) and ycf1 (76.19%). And the nrDNA (80.95%) revealed higher species resolution than ITS (71.43%). Acer plastomes show abundant interspecific variations, however, species identification failure may be due to the incomplete lineage sorting (ILS) and chloroplast capture resulting from hybridization. We found that the usage of nrDNA contributed to identifying those species that were unidentified by plastomes, implying its capability to some extent to mitigate the impact of hybridization and ILS on species discrimination. However, combining plastome and nrDNA is not recommended given the cytonuclear conflict caused by potential hybridization. Our phylogenetic analysis covering 19 sections (95% sections of Acer) and 128 species (over 80% species of this genus) revealed pervasive inter- and intra-section cytonuclear discordances, hinting that hybridization has played an important role in the evolution of Acer. CONCLUSION: Plastomes and nrDNA can significantly improve the species resolution in Acer. Our phylogenetic analysis uncovered the scope and depth of cytonuclear conflict in Acer, providing important insights into its evolution.

Integrated analysis of metabolome, transcriptome, and bioclimatic factors of Acer truncatum seeds reveals key candidate genes related to unsaturated fatty acid biosynthesis, and potentially optimal production area.

BACKGROUND: Lipids found in plant seeds are essential for controlling seed dormancy, dispersal, and defenses against biotic and abiotic stress. Additionally, these lipids provide nutrition and energy and are therefore important to the human diet as edible oils. Acer truncatum, which belongs to the Aceaceae family, is widely cultivated around the world for its ornamental value. Further because its seed oil is rich in unsaturated fatty acids (UFAs)- i.e. α-linolenic acid (ALA) and nervonic acid (NA)- and because it has been validated as a new food resource in China, the importance of A. truncatum has greatly risen. However, it remains unknown how UFAs are biosynthesized during the growth season, to what extent environmental factors impact their content, and what areas are potentially optimal for their production. RESULTS: In this study, transcriptome and metabolome of A. truncatum seeds at three representative developmental stages was used to find the accumulation patterns of all major FAs. Cumulatively, 966 metabolites and 87,343 unigenes were detected; the differential expressed unigenes and metabolites were compared between stages as follows: stage 1 vs. 2, stage 1 vs. 3, and stage 2 vs. 3 seeds, respectively. Moreover, 13 fatty acid desaturases (FADs) and 20 ß-ketoacyl-CoA synthases (KCSs) were identified, among which the expression level of FAD3 (Cluster-7222.41455) and KCS20 (Cluster-7222.40643) were consistent with the metabolic results of ALA and NA, respectively. Upon analysis of the geographical origin-affected diversity from 17 various locations, we found significant variation in phenotypes and UFA content. Notably, in this study we found that 7 bioclimatic variables showed considerable influence on FAs contents in A. truncatum seeds oil, suggesting their significance as critical environmental parameters. Ultimately, we developed a model for potentially ecological suitable regions in China. CONCLUSION: This study provides a comprehensive understanding of the relationship between metabolome and transcriptome in A. truncatum at various developmental stages of seeds and a new strategy to enhance seed FA content, especially ALA and NA. This is particularly significant in meeting the increasing demands for high-quality edible oil for human consumption. The study offers a scientific basis for A. truncatum's novel utilization as a woody vegetable oil rather than an ornamental plant, potentially expanding its cultivation worldwide.

High-quality maple genome reveals duplication-facilitated leaf color diversity.

Acer truncatum is a horticultural tree species with individuals that display either yellow or red leaves in autumn, giving it high ornamental and economic value. 'Lihong' of A. truncatum is an excellent cultivar due to its characteristic of having autumn leaves that turn a bright and beautiful shade of red, while its closely related cultivar 'Bunge' does not. However, the molecular mechanism underlying the color change in the cultivar 'Lihong' is still unclear. Here, we assembled a high-quality genome sequence of Acer truncatum 'Lihong' (genome size = 688 Mb, scaffold N50 = 9.14 Mb) with 28,438 protein-coding genes predicted. Through comparative genomic analysis, we found that 'Lihong' had experienced more tandem duplication events although it's a high degree of collinearity with 'Bunge'. Especially, the expansion of key enzymes in the anthocyanin synthesis pathway was significantly uneven between the two varieties, with 'Lihong' genome containing a significantly higher number of tandem/dispersed duplication key genes. Further transcriptomic, metabolomic, and molecular functional analyses demonstrated that several UFGT genes, mainly resulting from tandem/dispersed duplication, followed by the promoter sequence variation, may contribute greatly to the leaf color phenotype, which provides new insights into the mechanism of divergent anthocyanin accumulation process in the 'Lihong' and 'Bunge' with yellow leaves in autumn. Further, constitutive expression of two UFGT genes, which showed higher expression in 'Lihong', elevated the anthocyanin content. We proposed that the small-scale duplication events could contribute to phenotype innovation.

Ribosome footprint profiling enables elucidating the systemic regulation of fatty acid accumulation in Acer truncatum.

BACKGROUND: The accumulation of fatty acids in plants covers a wide range of functions in plant physiology and thereby affects adaptations and characteristics of species. As the famous woody oilseed crop, Acer truncatum accumulates unsaturated fatty acids and could serve as the model to understand the regulation and trait formation in oil-accumulation crops. Here, we performed Ribosome footprint profiling combing with a multi-omics strategy towards vital time points during seed development, and finally constructed systematic profiling from transcription to proteomes. Additionally, we characterized the small open reading frames (ORFs) and revealed that the translational efficiencies of focused genes were highly influenced by their sequence features. RESULTS: The comprehensive multi-omics analysis of lipid metabolism was conducted in A. truncatum. We applied the Ribo-seq and RNA-seq techniques, and the analyses of transcriptional and translational profiles of seeds collected at 85 and 115 DAF were compared. Key members of biosynthesis-related structural genes (LACS, FAD2, FAD3, and KCS) were characterized fully. More meaningfully, the regulators (MYB, ABI, bZIP, and Dof) were identified and revealed to affect lipid biosynthesis via post-translational regulations. The translational features results showed that translation efficiency tended to be lower for the genes with a translated uORF than for the genes with a non-translated uORF. They provide new insights into the global mechanisms underlying the developmental regulation of lipid metabolism. CONCLUSIONS: We performed Ribosome footprint profiling combing with a multi-omics strategy in A. truncatum seed development, which provides an example of the use of Ribosome footprint profiling in deciphering the complex regulation network and will be useful for elucidating the metabolism of A. truncatum seed oil and the regulatory mechanisms.

Identification and Analysis of the CBF Gene Family in Three Species of Acer under Cold Stress.

The C-Repeat Binding Factor (CBF) gene family has been identified and characterized in multiple plant species, and it plays a crucial role in responding to low temperatures. Presently, only a few studies on tree species demonstrate the mechanisms and potential functions of CBFs associated with cold resistance, while our study is a novel report on the multi-aspect differences of CBFs among three tree species, compared to previous studies. In this study, genome-wide identification and analysis of the CBF gene family in Acer truncatum, Acer pseudosieboldianum, and Acer yangbiense were performed. The results revealed that 16 CBF genes (five ApseCBFs, four AcyanCBFs, and seven AtruCBFs) were unevenly distributed across the chromosomes, and most CBF genes were mapped on chromosome 2 (Chr2) and chromosome 11 (Chr11). The analysis of phylogenetic relationships, gene structure, and conserved motif showed that 16 CBF genes could be clustered into three subgroups; they all contained Motif 1 and Motif 5, and most of them only spanned one exon. The cis-acting elements analysis showed that some CBF genes might be involved in hormone and abiotic stress responsiveness. In addition, CBF genes exhibited tissue expression specificity. High expressions of ApseCBF1, ApseCBF3, AtruCBF1, AtruCBF4, AtruCBF6, AtruCBF7, and ApseCBF3, ApseCBF4, ApseCBF5 were detected on exposure to low temperature for 3 h and 24 h. Low expressions of AtruCBF2, AtruCBF6, AtruCBF7 were detected under cold stress for 24 h, and AtruCBF3 and AtruCBF5 were always down-regulated under cold conditions. Taken together, comprehensive analysis will enhance our understanding of the potential functions of the CBF genes on cold resistance, thereby providing a reference for the introduction of Acer species in our country.

Integrating Single-Cell Methylome and Transcriptome Data with MAPLE.

As a mechanism of epigenetic gene regulation, DNA methylation has crucial roles in developmental and differentiation programs. Thanks to the recently introduced bisulfite-sequencing-based methods, it is possible to profile the entire methylome at single-cell resolution. However, analysis of single-cell methylome data is challenging due to data sparsity and moderate correlation with transcript level. Our recently developed computational framework, MAPLE, addresses these challenges using supervised learning models. Using both genomic sequence and methylation information as the input, MAPLE predicts activity for each gene, which can be used to integrate with transcriptome data from the same cell types. Here, we provide an overview of our method and detailed guidance on how to use it for the integration of methylome and transcriptome data.

Chromosomal-level genome and multi-omics dataset provides new insights into leaf pigmentation in Acer palmatum.

Acer palmatum (A. palmatum), a deciduous shrub or small arbour which belongs to Acer of Aceraceae, is an excellent greening species as well as a beautiful ornamental plant. In this study, a high-quality chromosome-level reference genome for A. palmatum was constructed using Oxford Nanopore sequencing and Hi-C technology. The assembly genome was ∼745.78 Mb long with a contig N50 length of 3.20 Mb, and 95.30 % (710.71 Mb) of the assembly was anchored into 13 pseudochromosomes. A total of 28,559 protein-coding genes were obtained, ∼90.02 % (25,710) of which could be functionally annotated. The genomic evolutionary analysis revealed that A. palmatum is most closely related to A. yangbiense and A. truncatum, and underwent only an ancient gamma whole-genome duplication event. Despite lacking a recent independent WGD, 25,795 (90.32 %) genes of A. palmatum were duplicated, and the unique/expanded gene families were linked with genes involved in plant-pathogen interaction and several metabolic pathways, which might underpin adaptability. A combined genomic, transcriptomic, and metabolomic analysis related to the biosynthesis of anthocyanin in leaves during the different season were characterized. The results indicate that the dark-purple colouration of the leaves in spring was caused by a high amount of anthocyanins, especially delphinidin and its derivatives; and the red colouration of the leaves in autumn by a high amount of cyanidin 3-O-glucoside. In conclusion, these valuable multi-omic resources offer important foundations to explore the molecular regulation mechanism in leaf colouration and also provide a platform for the scientific and efficient utilization of A. palmatum.

Transcriptomics Profiling of Acer pseudosieboldianum Molecular Mechanism against Freezing Stress.

Low temperature is an important environmental factor that affects the growth and development of trees and leads to the introduction of failure in the genetic improvement of trees. Acer pseudosieboldianum is a tree species that is well-known for its bright red autumn leaf color. These trees are widely used in landscaping in northeast China. However, due to their poor cold resistance, introduced A. pseudosieboldianum trees suffer severe freezing injury in many introduced environments. To elucidate the physiological indicators and molecular mechanisms associated with freezing damage, we analyzed the physiological indicators and transcriptome of A. pseudosieboldianum, using kits and RNA-Seq technology. The mechanism of A. pseudosieboldianum in response to freezing stress is an important scientific question. In this study, we used the shoots of four-year-old A. pseudosieboldianum twig seedlings, and the physiological index and the transcriptome of A. pseudosieboldianum under low temperature stress were investigated. The results showed that more than 20,000 genes were detected in A. pseudosieboldianum under low temperature (4 °C) and freezing temperatures (-10 °C, -20 °C, -30 °C, and -40 °C). There were 2505, 6021, 5125, and 3191 differential genes (DEGs) between -10 °C, -20°C, -30°C, -40 °C, and CK (4 °C), respectively. Among these differential genes, 48 genes are involved in the MAPK pathway and 533 genes are involved in the glucose metabolism pathway. In addition, the important transcription factors (MYB, AP2/ERF, and WRKY) involved in freezing stress were activated under different degrees of freezing stress. A total of 10 sets of physiological indicators of A. pseudosieboldianum were examined, including the activities of five enzymes and the accumulation of five hormones. All of the physiological indicators except SOD and GSH-Px reached their maximum values at -30 °C. The enzyme activity of SOD was highest at -10 °C, and that of GSH-Px was highest at -20 °C. Our study is the first to provide a more comprehensive understanding of the differential genes (DEGs) involved in A. pseudosieboldianum under freezing stress at different temperatures at the transcriptome level. These results may help to clarify the molecular mechanism of cold tolerance of A. pseudosieboldianum and provide new insights and candidate genes for the genetic improvement of the freezing tolerance of A. pseudosieboldianum.

Transcriptomic and metabolomic analyses reveal how girdling promotes leaf color expression in Acer rubrum L.

BACKGROUND: Acer rubrum L. (red maple) is a popular tree with attractive colored leaves, strong physiological adaptability, and a high ornamental value. Changes in leaf color can be an adaptive response to changes in environmental factors, and also a stress response to external disturbances. In this study, we evaluated the effect of girdling on the color expression of A. rubrum leaves. We studied the phenotypic characteristics, physiological and biochemical characteristics, and the transcriptomic and metabolomic profiles of leaves on girdled and non-girdled branches of A. rubrum. RESULTS: Phenotypic studies showed that girdling resulted in earlier formation of red leaves, and a more intense red color in the leaves. Compared with the control branches, the girdled branches produced leaves with significantly different color parameters a*. Physiological and biochemical studies showed that girdling of branches resulted in uneven accumulation of chlorophyll, carotenoids, anthocyanins, and other pigments in leaves above the band. In the transcriptomic and metabolomic analyses, 28,432 unigenes including 1095 up-regulated genes and 708 down-regulated genes were identified, and the differentially expressed genes were mapped to various KEGG (kyoto encyclopedia of genes and genomes) pathways. Six genes encoding key transcription factors related to anthocyanin metabolism were among differentially expressed genes between leaves on girdled and non-girdled branches. CONCLUSIONS: Girdling significantly affected the growth and photosynthesis of red maple, and affected the metabolic pathways, biosynthesis of secondary metabolites, and carbon metabolisms in the leaves. This resulted in pigment accumulation in the leaves above the girdling site, leading to marked red color expression in those leaves. A transcriptome analysis revealed six genes encoding anthocyanin-related transcription factors that were up-regulated in the leaves above the girdling site. These transcription factors are known to be involved in the regulation of phenylpropanoid biosynthesis, anthocyanin biosynthesis, and flavonoid biosynthesis. These results suggest that leaf reddening is a complex environmental adaptation strategy to maintain normal metabolism in response to environmental changes. Overall, the results of these comprehensive phenotype, physiological, biochemical, transcriptomic, and metabolomic analyses provide a deeper and more reliable understanding of the coevolution of red maple leaves in response to environmental changes.

Genetic structure and trait variation within a maple hybrid zone underscore North China as an overlooked diversity hotspot.

Tertiary relict flora in East Asia can be divided into northern and southern regions. North China is a diversity hotspot because it can be the secondary contact zone of ancient lineages from the two regions. To test the extent of ancient lineages hybridization and distinguish between the putative species pair Acer pictum subsp. mono and Acer truncatum, we conducted genetic and ecological studies within a maple hybrid zone in North China. Our results suggest that the two lineages of Acer coexist in the hybrid zone and that adult and offspring populations show typical bimodal genetic patterns. Hybrid individuals are established at intermediate altitudes between the two parental lineages. Flowering phenology is divergent between lineages, whereas the complex sexual system of Acer may ensure pollination among lineages. Leaf and fruit morphologies are different between the northern and southern origin lineages, corresponding to A. pictum subsp. mono and A. truncatum, respectively. Reduced gene flow between lineages suggests that they should be considered as two species. However, large morphological variations within each species and the existence of hybrids offer low reliability of species identification based solely on morphological traits. Our study underscores North China as an overlooked diversity hotspot that requires further study in the future.

The chromosome-scale genome provides insights into pigmentation in Acer rubrum.

Acer rubrum L. is one of the most prevalent ornamental species of the genus Acer, due to its straight and tall stems and beautiful leaf colors. For this study, the Oxford Nanopore platform and Hi-C technology were employed to obtain a chromosome-scale genome for A. rubrum. The genome size of A. rubrum was 1.69 Gb with an N50 of 549.44 Kb, and a total of 39 pseudochromosomes were generated with a 99.61% genome. The A. rubrum genome was predicted to have 64644 genes, of which 97.34% were functionally annotated. Genome annotation identified 67.14% as the transposable element (TE) repeat sequence, with long terminal repeats (LTR) being the richest (55.68%). Genome evolution analysis indicated that A. rubrum diverged from A. yangbiense ∼6.34 million years ago. We identified 13 genes related to pigment synthesis in A. rubrum leaves, where the expressions of four ArF3'H genes were consistent with the synthesis of cyanidin (a key pigment) in red leaves. Correlation analysis verified that the pigmentation of A. rubrum leaves was under the coordinated regulation of non-structural carbohydrates and hormones. The genomic sequence of A. rubrum will facilitate genomic breeding research for this species, while providing the valuable utilization of Aceraceae resources.

De novo transcriptome revealed genes involved in anthocyanin biosynthesis, transport, and regulation in a mutant of Acer pseudosieboldianum.

BACKGROUND: Acer pseudosieboldianum is a kind of excellent color-leafed plants, and well known for its red leaves in autumn. At the same time, A. pseudosieboldianum is one of the native tree species in the northeast of China, and it plays an important role in improving the lack of color-leafed plants in the north. In previous study, we found a mutant of the A. pseudosieboldianum that leaves intersect red and green in spring and summer. However, it is unclear which genes cause the color change of mutant leaves. RESULTS: In order to study the molecular mechanism of leaf color formation, we analyzed the leaves of the mutant group and the control group from A. pseudosieboldianum by RNA deep sequencing in this study. Using an Illumina sequencing platform, we obtained approximately 276,071,634 clean reads. After the sequences were filtered and assembled, the transcriptome data generated a total of 70,014 transcripts and 54,776 unigenes, of which 34,486 (62.96%) were successfully annotated in seven public databases. There were 8,609 significant DEGs identified between the control and mutant groups, including 4,897 upregulated and 3,712 downregulated genes. We identified 13 genes of DEGs for leaf color synthesis that was involved in the flavonoid pathway, 26 genes that encoded transcription factors, and eight genes associated with flavonoid transport. CONCLUSION: Our results provided comprehensive gene expression information about A. pseudosieboldianum transcriptome, and directed the further study of accumulation of anthocyanin in A. pseudosieboldianum, aiming to provide insights into leaf coloring of it through transcriptome sequencing and analysis.

Key regulatory pathways, microRNAs, and target genes participate in adventitious root formation of Acer rubrum L.

Red maple (Acer rubrum L.) is a type of colorful ornamental tree with great economic value. Because this tree is difficult to root under natural conditions and the seedling survival rate is low, vegetative propagation methods are often used. Because the formation of adventitious roots (ARs) is essential for the asexual propagation of A. rubrum, it is necessary to investigate the molecular regulatory mechanisms of AR formation in A. rubrum. To address this knowledge gap, we sequenced the transcriptome and small RNAs (sRNAs) of the A. rubrum variety 'Autumn Fantasy' using high-throughput sequencing and explored changes in gene and microRNA (miRNA) expression in response to exogenous auxin treatment. We identified 82,468 differentially expressed genes (DEGs) between the treated and untreated ARs, as well as 48 known and 95 novel miRNAs. We also identified 172 target genes of the known miRNAs using degradome sequencing. Two key regulatory pathways (ubiquitin mediated proteolysis and plant hormone signal transduction), Ar-miR160a and the target gene auxin response factor 10 (ArARF10) were selected based on KEGG pathway and cluster analyses. We further investigated the expression patterns and regulatory roles of ArARF10 through subcellular localization, transcriptional activation, plant transformation, qRT-PCR analysis, and GUS staining. Experiments overexpressing ArARF10 and Ar-miR160a, indicated that ArARF10 promoted AR formation, while Ar-miR160a inhibited AR formation. Transcription factors (TFs) and miRNAs related to auxin regulation that promote AR formation in A. rubrum were identified. Differential expression patterns indicated the Ar-miR160a-ArARF10 interaction might play a significant role in the regulation of AR formation in A. rubrum. Our study provided new insights into mechanisms underlying the regulation of AR formation in A. rubrum.

Transcriptome Sequencing and Screening of Anthocyanin-Related Genes in the Leaves of Acer truncatum Bunge.

Acer truncatum Bunge is generally used as an ornamental tree because of its autumn leaves, although the viewing period is short-approximately 7-15 days. Color improvement of ornamental trees has consistently been an important research topic because color partially determines the value of the commodity; however, a lack of genomic data have limited the progress of molecular breeding research in this area. The purposes of this study were to obtain a transcriptome database for A. truncatum, screen anthocyanin biosynthesis-related genes, and reveal the mechanisms underlying leaf color transformation to provide a basis for increasing the viewing period or breeding cultivars that display red leaves throughout the growing season via gene regulation. In this study, although the use of an Illumina HiSeq 2000 platform and systematic bioinformatics analysis using both young and mature leaves as experimental materials, 233,912,882 clean reads were generated and 121,287 unique transcripts were retrieved. We selected 16 color-related genes (from the transcriptome results) for qRT-PCR to validate the results, and the expression trends of the selected genes were largely consistent with the transcriptome analysis results, with a consistency of 0.875. According to the results of the transcriptome analysis, the validation, and previous studies, we obtained sequences of genes related to anthocyanins, including CHS, CHI, ANS, UFGT, UGT75c1, DFR, BZ1, F3H, F3'H, LAR, ANR, FLS, and those of several transcription factors, including MYB1, BHLH, and WD40. Verifying specific regulation by one or several of these genes in the control of leaf color requires further research. The acquisition of transcriptomic information, especially information concerning anthocyanin biosynthesis-related genes and their base sequences, can provide a theoretical basis for the study of the molecular mechanisms determining changes in leaf color in Acer and is of great importance to the breeding of new cultivars.

Oxidative damage and DNA repair in desiccated recalcitrant embryonic axes of Acer pseudoplatanus L.

BACKGROUND: Most plants encounter water stress at one or more different stages of their life cycle. The maintenance of genetic stability is the integral component of desiccation tolerance that defines the storage ability and long-term survival of seeds. Embryonic axes of desiccation-sensitive recalcitrant seeds of Acer pseudoplatnus L. were used to investigate the genotoxic effect of desiccation. Alkaline single-cell gel electrophoresis (comet assay) methodology was optimized and used to provide unique insights into the onset and repair of DNA strand breaks and 8-oxo-7,8-dihydroguanine (8-oxoG) formation during progressive steps of desiccation and rehydration. RESULTS: The loss of DNA integrity and impairment of damage repair were significant predictors of the viability of embryonic axes. In contrast to the comet assay, automated electrophoresis failed to detect changes in DNA integrity resulting from desiccation. Notably, no significant correlation was observed between hydroxyl radical (Ù OH) production and 8-oxoG formation, although the former is regarded to play a major role in guanine oxidation. CONCLUSIONS: The high-throughput comet assay represents a sensitive tool for monitoring discrete changes in DNA integrity and assessing the viability status in plant germplasm processed for long-term storage.

Assembly and comparative analysis of the first complete mitochondrial genome of Acer truncatum Bunge: a woody oil-tree species producing nervonic acid.

BACKGROUND: Acer truncatum (purpleblow maple) is a woody tree species that produces seeds with high levels of valuable fatty acids (especially nervonic acid). The species is admired as a landscape plant with high developmental prospects and scientific research value. The A. truncatum chloroplast genome has recently been reported; however, the mitochondrial genome (mitogenome) is still unexplored. RESULTS: We characterized the A. truncatum mitogenome, which was assembled using reads from PacBio and Illumina sequencing platforms, performed a comparative analysis against different species of Acer. The circular mitogenome of A. truncatum has a length of 791,052 bp, with a base composition of 27.11% A, 27.21% T, 22.79% G, and 22.89% C. The A. truncatum mitogenome contains 62 genes, including 35 protein-coding genes, 23 tRNA genes and 4 rRNA genes. We also examined codon usage, sequence repeats, RNA editing and selective pressure in the A. truncatum mitogenome. To determine the evolutionary and taxonomic status of A. truncatum, we conducted a phylogenetic analysis based on the mitogenomes of A. truncatum and 25 other taxa. In addition, the gene migration from chloroplast and nuclear genomes to the mitogenome were analyzed. Finally, we developed a novel NAD1 intron indel marker for distinguishing several Acer species. CONCLUSIONS: In this study, we assembled and annotated the mitogenome of A. truncatum, a woody oil-tree species producing nervonic acid. The results of our analyses provide comprehensive information on the A. truncatum mitogenome, which would facilitate evolutionary research and molecular barcoding in Acer.

Genetic variation of the relict maple Acer miyabei: uncovering its history of disjunct occurrence and the role of mountain refugia in shaping genetic diversity.

PREMISE: Relict species provide valuable insights into the origin and formation of extant vegetation. Here, we aimed to elucidate the genetic structure and diversity of a riparian relic, Acer miyabei, in Japan. Once widely distributed, it now occurs in three isolated regions. The most northern regional group is located at low elevation on Hokkaido Island, whereas the southernmost group in central Honshu Island is at high elevation in a mountainous landscape. This contrastive distribution enables us to examine the effects of climate oscillations on genetic diversity in relation to topographic variation. METHODS: We collected 604 individuals of A. miyabei from 43 sites. Their genetic structure and diversity were analyzed using 12 microsatellite markers and cpDNA sequences. RESULTS: According to structure analyses, ∆K was lowest at K = 2; the clustering essentially separated many of the individuals in the most northern regional group from the others. In contrast, the two southern groups were not clearly differentiated from each other, despite their geographic discontinuity. The proportion of private alleles was high in populations from the mountain terrain in the southern group although the number of extant populations is limited. CONCLUSIONS: Genetic clustering of A. miyabei is not perfectly congruent with the current patterns of geographic distribution. We infer that disjunction of the two southern groups occurred more recently than that between these groups and the northern group. The mountainous landscape in the most southern region likely provided multiple refugia and contributed to the retention of distinctive genetic variation.

Demographic history and identification of threats revealed by population genomic analysis provide insights into conservation for an endangered maple.

Recent advancements in whole genome sequencing techniques capable of covering nearly all the nucleotide variations of a genome would make it possible to set up a conservation framework for threatened plants at the genomic level. Here we applied a whole genome resequencing approach to obtain genome-wide data from 105 individuals sampled from the 10 currently known extant populations of Acer yangbiense, an endangered species with fragmented habitats and restricted distribution in Yunnan, China. To inform meaningful conservation action, we investigated what factors might have contributed to the formation of its extremely small population sizes and what threats it currently suffers at a genomic level. Our results revealed that A. yangbiense has low genetic diversity and comprises different numbers of genetic groups based on neutral (seven) and selected loci (13), with frequent gene flow between populations. Repeated bottleneck events, particularly the most recent one occurring within ~10,000 years before present, which decreased its effective population size (Ne ) < 200, and severe habitat fragmentation resulting from anthropogenic activities as well as a biased gender ratio of mature individuals in its natural habitat, might have together contributed to the currently fragmented and endangered status of A. yangbiense. The species has suffered from inbreeding and deleterious mutation load, both of which varied among populations but had similar patterns; that is, populations with higher FROH (frequency of runs of homozygosity) always carried a larger number of deleterious mutations in the homozygous state than in populations with lower FROH. In addition, based on our genetic differentiation results, and the distribution patterns of homozygous deleterious mutations in individuals, we recommend certain conservation actions regarding the genetic rescue of A. yangbiense. Overall, our study provides meaningful insights into the conservation genetics and a framework for the further conservation for the endangered A. yangbiense.