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Abstract The sugar and organic acid content significantly impacts the flavor quality of star fruit, and it undergoes dynamic changes during development. However, the metabolic network and molecular mechanisms governing the formation of sugar and organic acid in star fruit remain unclear. In this study, 23 of 743 components were detected by metabonomic analysis. The highest metabolites contents were organic acids and derivatives. The highest sugar content in the fruit was fructose and glucose, followed by sucrose, which proved that A. carambola is a hexose accumulation type fruit. Genome identification preliminarily screened 141 genes related to glucose metabolism and 67 genes related to acid metabolism. A total of 7,881 unigenes were found in transcriptome data, 6,124 differentially expressed genes were screened, with more up-regulated than down-regulated genes. Transcriptome and metabolome association analysis screened seven core candidate genes related to glucose metabolism and 17 core genes highly related to organic acid pathway, and eight differentially expressed sugar and acid genes were selected for qRT-PCR verification. In addition, 29 bHLHs and eight bZIPs transcription factors were predicted in the glucose metabolism pathway, and 23 MYBs, nine C2H2s transcription factors and one GRAS transcription factor was predicted in the acid metabolism pathway, and transcription factors have both positive and negative regulatory effects on sugar and acid structure genes. This study increased our understanding of A. carambola fruit flavor and provided basic information for further exploring the ornamental and edible values of star fruit.

Abstract Background C. Oleifera is among the world’s largest four woody plants known for their edible oil production, yet the contribution rate of improved varieties is less than 20%. The species traditional breeding is lengthy cycle (20–30 years), occupation of land resources, high labor cost, and low accuracy and efficiency, which can be enhanced by molecular marker-assisted selection. However, the lack of high-quality molecular markers hinders the species genetic analysis and molecular breeding. Results Through quantitative traits characterization, genetic diversity assessment, and association studies, we generated a selection population with wide genetic diversity, and identified five excellent high-yield parental combinations associated with four reliable high-yield ISSR markers. Early selection criteria were determined based on kernel fresh weight and cultivated 1-year seedling height, aided by the identification of these 4 ISSR markers. Specific assignment of selected individuals as paternal and maternal parents was made to capitalize on their unique attributes. Conclusions Our results indicated that molecular markers-assisted breeding can effectively shorten, enhance selection accuracy and efficiency and facilitate the development of a new breeding system for C. oleifera.

Abstract Background Drought stress severely impedes plant growth, and only a limited number of species exhibit long-term resistance to such conditions. Pinus sylvestris var. mongolica, a dominant tree species in arid and semi-arid regions of China, exhibits strong drought resistance and plays a crucial role in the local ecosystem. However, the molecular mechanisms underlying this resistance remain poorly understood. Results Here, we conducted transcriptome sequence and physiological indicators analysis of needle samples during drought treatment and rehydration stages. De-novo assembly yielded approximately 114,152 unigenes with an N50 length of 1,363 bp. We identified 6,506 differentially expressed genes (DEGs), with the majority being concentrated in the heavy drought stage (4,529 DEGs). Functional annotation revealed enrichment of drought-related GO terms such as response to water (GO:0009415: enriched 108 genes) and response to water deprivation (GO:0009414: enriched 106 genes), as well as KEGG categories including MAPK signaling pathway (K04733: enriched 35 genes) and monoterpenoid biosynthesis (K21374: enriched 27 genes). Multiple transcription factor families and functional protein families were differentially expressed during drought treatment. Co-expression network analysis identified a potential drought regulatory network between cytochrome P450 genes (Unigene4122_c1_g1) and a core regulatory transcription factor Unigene9098_c3_g1 (PsNAC1) with highly significant expression differences. We validated PsNAC1 overexpression in Arabidopsis and demonstrated enhanced drought resistance. Conclusions These findings provide insight into the molecular basis of drought resistance in P. sylvestris var. mongolica and lay the foundation for further exploration of its regulatory network.

Summary: Range-limited endemic species, often labeled as endangered due to their low adaptability to climate change, exhibit unclear evolutionary mechanisms influencing their distribution. This study explores the relationship between leaf length, maximum height, and seed diameter and their linkage to phylogeny and climate in the macroecology of 1,370 woody endemics. Using Bayesian analytical method that allows partitioning phylogenetic and environmental variances and covariance, we revealed moderate to high phylogenetic signals in these traits, indicating evolutionary constraints potentially impacting climate change adaptability. The study uncovered a phylogenetically conserved coordination between height and leaf length which showed to be independent of macroecological patterns of temperature and precipitation. These findings emphasize the role of phylogenetic ancestry in shaping the distribution of woody endemics, highlighting the need for prioritized in-situ conservation and providing insights for ex situ conservation strategies.

The genus Rhododendron exhibits an immense diversity of flower colors and represents one of the largest groups of woody plants, which is of great importance for ornamental plant research. This review summarizes recent progress in deciphering the genetic basis for flower coloration in Rhododendron. We describe advances in phylogenetic reconstruction and genome sequencing of Rhododendron species. The metabolic pathways of flower color are outlined, focusing on key structural and regulatory genes involved in pigment synthesis. Gene duplications and losses associated with color diversification are discussed. In addition, the application of multi-omics approaches and analysis of gene co-expression networks to elucidate complex gene regulatory mechanisms is emphasized. This synthesis of current knowledge provides a foundation for future research on the evolution of flower color diversity within the Rhododendron lineage. Ultimately, these discoveries will support breeding endeavors aimed at harnessing the genetics of flower coloration and developing novel cultivars that exhibit desired floral traits.

Abstract Background Most of Camellia oleifera forests have low fruit yield and poor oil quality that are largely associated with soil fertility. Soil physical and chemical properties interact with each other affecting soil fertility and C. oleifera growing under different soil conditions produced different yield and oil composition. Three main soil types were studied, and redundancy, correlation, and double-screening stepwise regression analysis were used for exploring the relationships between C. oleifera nutrients uptake and soil physical and chemical properties, shedding light on the transport law of nutrient elements from root, leaves, and kernel, and affecting the regulation of fruit yield and oil composition. Results In the present study, available soil elements content of C. oleifera forest were mainly regulated by water content, pH value, and total N, P and Fe contents. Seven elements (N, P, K, Mg, Cu, Mn and C) were key for kernel’s growth and development, with N, P, K, Cu and Mn contents determining 74.0% the yield traits. The transport characteristics of these nutrients from root, leaves to the kernel had synergistic and antagonistic effects. Increasing oil production and unsaturated fatty acid content can be accomplished in two ways: one through increasing N, P, Mg, and Zn contents of leaves by applying corresponding N, P, Mg, Zn foliar fertilizers, while the other through maintaining proper soil moisture content by applying Zn fertilizer in the surface layer and Mg and Ca fertilizer in deep gully. Conclusion Soil type controlled nutrient absorption by soil pH, water content and total N, P and Fe content. There were synergistic and antagonistic effects on the inter-organ transport of nutrient elements, ultimately affecting N, P, K, Cu and Mn contents in kernel, which determined the yield and oil composition of C. oleifera.

Abstract Background Pinus is the largest genus of Pinaceae and the most primitive group of modern genera. Pines have become the focus of many molecular evolution studies because of their wide use and ecological significance. However, due to the lack of complete chloroplast genome data, the evolutionary relationship and classification of pines are still controversial. With the development of new generation sequencing technology, sequence data of pines are becoming abundant. Here, we systematically analyzed and summarized the chloroplast genomes of 33 published pine species. Results Generally, pines chloroplast genome structure showed strong conservation and high similarity. The chloroplast genome length ranged from 114,082 to 121,530 bp with similar positions and arrangements of all genes, while the GC content ranged from 38.45 to 39.00%. Reverse repeats showed a shrinking evolutionary trend, with IRa/IRb length ranging from 267 to 495 bp. A total of 3,205 microsatellite sequences and 5,436 repeats were detected in the studied species chloroplasts. Additionally, two hypervariable regions were assessed, providing potential molecular markers for future phylogenetic studies and population genetics. Through the phylogenetic analysis of complete chloroplast genomes, we offered novel opinions on the genus traditional evolutionary theory and classification. Conclusion We compared and analyzed the chloroplast genomes of 33 pine species, verified the traditional evolutionary theory and classification, and reclassified some controversial species classification. This study is helpful in analyzing the evolution, genetic structure, and the development of chloroplast DNA markers in Pinus.

Abstract Coriaria nepalensis Wall. (Coriariaceae) is a nitrogen-fixing shrub which forms root nodules with the actinomycete Frankia. Oils and extracts of C. nepalensis have been reported to be bacteriostatic and insecticidal, and C. nepalensis bark provides a valuable tannin resource. Here, by combining PacBio HiFi sequencing and Hi-C scaffolding techniques, we generated a haplotype-resolved chromosome-scale genome assembly for C. nepalensis. This genome assembly is approximately 620 Mb in size with a contig N50 of 11 Mb, with 99.9% of the total assembled sequences anchored to 40 pseudochromosomes. We predicted 60,862 protein-coding genes of which 99.5% were annotated from databases. We further identified 939 tRNAs, 7,297 rRNAs, and 982 ncRNAs. The chromosome-scale genome of C. nepalensis is expected to be a significant resource for understanding the genetic basis of root nodulation with Frankia, toxicity, and tannin biosynthesis.

Ecological niche partitioning is crucial in reducing interspecific competition, fostering species coexistence, and preserving biodiversity. Our research, conducted in a hybrid mixed oak forest in Yushan, Jiangsu, China, focuses on Quercus acutissima, Q. variabilis, Q. fabri, and Q. serrata var. brevipetiolata. Using Point Pattern Analysis, we investigated the spatial relationships and ecological trait autocorrelation, including total carbon (TC), nitrogen (TN), phosphorus (TP), potassium (TK), and breast height diameter (DBH). Our findings show aggregated distribution patterns within the oak populations. The Inhomogeneous Poisson Point model highlights the impact of environmental heterogeneity on Q. variabilis, leading to distinct distribution patterns, while other species showed wider dispersion. This study reveals aggregated interspecific interactions, with a notable dispersal pattern between Q. acutissima and Q. variabilis. We observed significant variability in nutrient elements, indicating distinct nutrient dynamics and uptake processes. The variations in total carbon (TC), nitrogen (TN), phosphorus (TP), and potassium (TK) suggest distinct nutrient dynamics, with TK showing the highest variability. Despite variations in TC, TK, and TP, the species did not form distinct classes, suggesting overlapping nutritional strategies and environmental adaptations. Furthermore, spatial autocorrelation analysis indicates strong positive correlations for DBH, TC, and TP, whereas TK and TN correlations are non-significant. The results suggest habitat filtering as a key driver in intraspecific relationships, with a finer spatial scale of ecological niche division through TC and TP, which is crucial for maintaining coexistence among these oak species.

Abstract Tree architectural attributes demonstrate a significant association with fruit yield. Yellowhorn is the future bioenergy tree in China; however, the species suffers from high reproductive energy and exceedingly low reproductive output. To optimize yellowhorn management and pinpoint priority trees featuring optimal architecture, we employed machine learning modeling to develop high fruit yielding predictive models using five yield indicators (dependent variables: FrW, SeW, ShW, FrW, and SeN) and five tree characteristics (independent variables: CA, TH, DGL, HLC, and MBN) of yellowhorn. Results showed that trees characterized by a substantial canopy area (>1.70 m2) and a large diameter at ground level (>3.71 cm) have been found to yield a higher fruit production. However, increased tree height does not invariably correlate with an elevated yield. Effective selection of high‐yielding individuals can be accomplished by restricting tree height within the range of 192–232.4 cm. This approach emphasizes the importance of integrating considerations of tree architecture into forestry management practices. Such integration can bolster productivity, thereby contributing to both the sustainability and economic viability of yellowhorn forests.

Abstract Perennial shrub willow are increasingly being promoted in short-rotation coppice systems as biomass feedstocks, for phytoremediation applications, and for the diverse ecosystem services that can accrue. This renewed interest has led to widespread willow cultivation, particularly of non-native varieties. However, Canadian willow species have not been widely adopted and their inherent diversity has not yet been thoroughly investigated. In this study, 324 genotypes of Salix famelica and Salix eriocephala collected from 33 sites of origin were analyzed using 26,016 single nucleotide polymorphisms to reveal patterns of population structure and genetic diversity. Analyses by Bayesian methods and principal component analysis detected five main clusters that appeared to be largely shaped by geoclimatic variables including mean annual precipitation and the number of frost-free days. The overall observed (H O ) and expected (H E ) heterozygosity were 0.126 and 0.179, respectively. An analysis of molecular variance revealed that the highest genetic variation occurred within genotypes (69%), while 8% of the variation existed among clusters and 23% between genotypes within clusters. These findings provide new insights into the extent of genetic variation that exists within native shrub willow species which could be leveraged in pan-Canadian willow breeding programs.

Coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is one of the most commercially important softwood species in North America. In British Columbia, Canada, breeding has increased volume gains between 20 and 30%, while 97% of seedlings come from improved seed sources. Branching traits in particular, have a strong influence on strength and stiffness of Douglas-fir wood; however, they are rarely measured. Remotely Piloted Aerial Systems and Airborne Laser Scanning Systems (RPAS-LS) produce high-density three-dimensional point clouds that can be used for the creation of internal geometric features describing individual tree branching structures. We analyzed a Coastal Douglas-fir progeny test trial located in British Columbia, Canada, and developed a new method to estimate branch attributes from RPAS-LS data for inclusion as selection criteria in tree improvement programs. Branch length, angle, width, and volume were estimated for each tree. Narrow-sense heritability (the proportion of variation due to genetics) and genetic correlations were also estimated. The method extracted branch length with a correlation (r) of 0.93 compared to manual measurements. Using these branch attributes, results then show that branch angle had the highest heritability (0.277), while tree height and branch length had the highest genetic correlation (0.668). These findings are encouraging for forest managers as they indicate that branch level metrics should be considered when selecting trees in breeding programs.

Salt stress is a universal abiotic stress that severely affects plant growth and development. Understanding the mechanisms of Maclura tricuspidate’s adaptation to salt stress is crucial for developing salt-tolerant plant varieties. This article discusses the integration of physiology, transcriptome, and metabolome to investigate the mechanism of salt adaptation in M. tricuspidata under salt stress conditions. Overall, the antioxidant enzyme system (SOD and POD) of M. tricuspidata exhibited higher activities compared with the control, while the content of soluble sugar and concentrations of chlorophyll a and b were maintained during salt stress. KEGG analysis revealed that deferentially expressed genes were primarily involved in plant hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, alkaloids, and MAPK signaling pathways. Differential metabolites were enriched in amino acid metabolism, the biosynthesis of plant hormones, butanoate, and 2-oxocarboxylic acid metabolism. Interestingly, glycine, serine, and threonine metabolism were found to be important both in the metabolome and transcriptome–metabolome correlation analyses, suggesting their essential role in enhancing the salt tolerance of M. tricuspidata. Collectively, our study not only revealed the molecular mechanism of salt tolerance in M. tricuspidata, but also provided a new perspective for future salt-tolerant breeding and improvement in salt land for this species.

Polyploid breeding techniques aid in the cultivation of new forestry cultivars, thus expanding the suite of strategies for the improvement of arboreal traits and innovation within the field of forestry. Compared to diploid Robinia pseudoacacia L. (black locust) ‘D26-5①’ (2×), its dwarfed homologous tetraploid ‘D26-5②’ (4×) variety has better application prospects in garden vegetation guardrails and urban landscape. However, the molecular mechanism of the generation and growth of this dwarf variety is still unclear. Here, plant growth and development as well as histological differences between the diploid and its autotetraploid were investigated. Levels of endogenous hormones at three different developmental stages (20, 40, and 70 days) of 2× and homologous 4× tissue culture plantlets were assessed, and it was found that the brassinosteroid (BR) contents of the former were significantly higher than the latter. Transcriptome sequencing data analysis of 2× and homologous 4× showed that differentially expressed genes (DEGs) were significantly enriched in plant hormone synthesis and signal transduction, sugar and starch metabolism, and the plant circadian rhythm pathway, which are closely related to plant growth and development. Therefore, these biological pathways may be important regulatory pathways leading to dwarfism and slow growth in tetraploids. Additionally, utilizing weighted gene coexpression network analysis (WGCNA), we identified three crucial differentially expressed genes (DEGs)—PRR5, CYP450, and SPA1—that potentially underlie the observed ploidy variation. This study provides a new reference for the molecular mechanism of dwarfism in dwarfed autotetraploid black locusts. Collectively, our results of metabolite analysis and comparative transcriptomics confirm that plant hormone signaling and the circadian rhythm pathway result in dwarfism in black locusts.

Abstract Melia azedarach L. is an important economic tree widely distributed in tropical and subtropical regions of China and some other countries. However, it is unclear how the species’ suitable habitat will respond to future climate changes. We aimed to select the most accurate one among seven data mining models to predict the current and future suitable habitats for M. azedarach in China. These models include: maximum entropy (MaxEnt), support vector machine (SVM), generalized linear model (GLM), random forest (RF), naive bayesian model (NBM), extreme gradient boosting (XGBoost), and gradient boosting machine (GBM). A total of 906 M . azedarach locations were identified, and sixteen climate predictors were used for model building. The models’ validity was assessed using three measures (Area Under the Curves (AUC), kappa, and overall accuracy (OA)). We found that the RF provided the most outstanding performance in prediction power and generalization capacity. The top climate factors affecting the species’ suitable habitats were mean coldest month temperature (MCMT), followed by the number of frost-free days (NFFD), degree-days above 18 °C (DD > 18), temperature difference between MWMT and MCMT, or continentality (TD), mean annual precipitation (MAP), and degree-days below 18 °C (DD

Abstract Background Genomic prediction (GP) and genome-wide association (GWA) analyses are currently being employed to accelerate breeding cycles and to identify alleles or genomic regions of complex traits in forest trees species. Here, 1490 interior lodgepole pine (Pinus contorta Dougl. ex. Loud. var. latifolia Engelm) trees from four open-pollinated progeny trials were genotyped with 25,099 SNPs, and phenotyped for 15 growth, wood quality, pest resistance, drought tolerance, and defense chemical (monoterpenes) traits. The main objectives of this study were to: (1) identify genetic markers associated with these traits and determine their genetic architecture, and to compare the marker detected by single- (ST) and multiple-trait (MT) GWA models; (2) evaluate and compare the accuracy and control of bias of the genomic predictions for these traits underlying different ST and MT parametric and non-parametric GP methods. GWA, ST and MT analyses were compared using a linear transformation of genomic breeding values from the respective genomic best linear unbiased prediction (GBLUP) model. GP, ST and MT parametric and non-parametric (Reproducing Kernel Hilbert Spaces, RKHS) models were compared in terms of prediction accuracy (PA) and control of bias. Results MT-GWA analyses identified more significant associations than ST. Some SNPs showed potential pleiotropic effects. Averaging across traits, PA from the studied ST-GP models did not differ significantly from each other, with generally a slight superiority of the RKHS method. MT-GP models showed significantly higher PA (and lower bias) than the ST models, being generally the PA (bias) of the RKHS approach significantly higher (lower) than the GBLUP. Conclusions The power of GWA and the accuracy of GP were improved when MT models were used in this lodgepole pine population. Given the number of GP and GWA models fitted and the traits assessed across four progeny trials, this work has produced the most comprehensive empirical genomic study across any lodgepole pine population to date.

A high-quality genome assembly for the lilac (Syringa oblata) provides insight into the evolution of this shrub and potential mechanisms underlying petal color change.

As a medicinal tree species, ginkgo (Ginkgo biloba L.) and terpene trilactones (TTLs) extracted from its leaves are the main pharmacologic activity constituents and important economic indicators of its value. The accumulation of TTLs is known to be affected by environmental stress, while the regulatory mechanism of environmental response mediated by microRNAs (miRNAs) at the post-transcriptional levels remains unclear. Here, we focused on grafted ginkgo grown in northwestern, southwestern, and eastern-central China and integrally analyzed RNA-seq and small RNA-seq high-throughput sequencing data as well as metabolomics data from leaf samples of ginkgo clones grown in natural environments. The content of bilobalide was highest among detected TTLs, and there was more than a twofold variation in the accumulation of bilobalide between growth conditions. Meanwhile, transcriptome analysis found significant differences in the expression of 19 TTL-related genes among ginkgo leaves from different environments. Small RNA sequencing and analysis showed that 62 of the 521 miRNAs identified were differentially expressed among different samples, especially the expression of miRN50, miR169h/i, and miR169e was susceptible to environmental changes. Further, we found that transcription factors (ERF, MYB, C3H, HD-ZIP, HSF, and NAC) and miRNAs (miR319e/f, miRN2, miRN54, miR157, miR185, and miRN188) could activate or inhibit the expression of TTL-related genes to participate in the regulation of terpene trilactones biosynthesis in ginkgo leaves by weighted gene co-regulatory network analysis. Our findings provide new insights into the understanding of the regulatory mechanism of TTL biosynthesis but also lay the foundation for ginkgo leaves’ medicinal value improvement under global change.

Agroforestry is important for forest management and rehabilitation in the southeast Asia-Pacific Region (APR), where economic issues, intensive land use, deforestation, and forest degradation are common. Species selection is a key process in establishing agroforestry systems. In this study, we reviewed the agroforestry literature across eight economies within the southeast APR, documented the species used, and compared the existing systems to better understand the challenges and opportunities for the region’s agroforestry expansion. We conducted rule and Maptree analyses using 108 species, belonging to 95 genera and 49 families of plants, to unravel the various agroforestry practices in this region. We identified the most common plant families used in agroforestry combinations within each economy. We then divided the economies into three groups based on the most commonly used genera: (1) Thailand, Vietnam, Papua New Guinea and Fiji (Hevea, Oryza, Eucalyptus, Acacia, and Zea); (2) Nepal and Yunnan China (Zea, Leucaena, Morus, and Hevea); and (3) Indonesia and the Philippines (Oryza, Hevea, Zea, and Brassica). Although this study focused on high-level taxonomic classification (family and genus), we believe that this work will fill the current knowledge gaps, offering guidance to economies in the southeast APR regarding species selection and the adoption of sustainable agroforestry practices.

Hypocotyl elongation is an important process in plant growth and development, and is under hormonal regulatory signaling pathways. In our study, exogenous 6-BA significantly inhibited Picea crassifolia hypocotyl elongation more than ethylene in the dark, indicating the existence of different regulatory strategies in conifers, therefore, the P. crassifolia transcriptome was studied to explore the responsive genes and their regulatory pathways for exogenous N6-benzyladenine (6-BA) inhibition of hypocotyl elongation using RNA-Sequencing approach. We present the first transcriptome assembly of P. crassifolia obtained from 24.38 Gb clean data. With lowly-expressed and short contigs excluded, the assembly contains roughly 130,612 unigenes with an N50 length of 1,278 bp. Differential expression analysis found 3,629 differentially expressed genes (DEGs) and found that the differential expression fold of genes was mainly concentrated between 2 and 8 (1 ≤ log2FoldChange ≤ 3). Functional annotation showed that the GO term with the highest number of enriched genes (83 unigenes) was the shoot system development (GO: 0048367) and the KEGG category, plant hormone signal transduction (ko04075), was enriched 30 unigenes. Further analysis revealed that several cytokinin dehydrogenase genes (PcCTD1, PcCTD3 and PcCTD6) catabolized cytokinins, while xyloglucan endotransglucosylase hydrolase gene (PcXTH31), WALLS ARE THIN 1-like gene (PcWAT1-1) and Small auxin-induced gene (PcSAUR15) were strongly repressed thus synergistically completing the inhibition of hypocotyl elongation in P. crassifolia. Besides, PcbHLH149, PcMYB44 and PcERF14 were predicted to be potential core TFs that may form a multi-layered regulatory network with the above proteins for the regulation of hypocotyl growth.

Studying population genetic structure and diversity is crucial for the marker-assisted selection and breeding of coniferous tree species. In this study, using RAD-seq technology, we developed 343,644 high-quality single nucleotide polymorphism (SNP) markers to resolve the genetic diversity and population genetic structure of 233 Chinese fir selected individuals from the 4th cycle breeding program, representing different breeding generations and provenances. The genetic diversity of the 4th cycle breeding population was high with nucleotide diversity (Pi) of 0.003, and Ho and He of 0.215 and 0.233, respectively, indicating that the breeding population has a broad genetic base. The genetic differentiation level between the different breeding generations and different provenances was low (Fst < 0.05), with population structure analysis results dividing the 233 individuals into four subgroups. Each subgroup has a mixed branch with interpenetration and weak population structure, which might be related to breeding rather than provenance, with aggregation from the same source only being in the local branches. Our results provide a reference for further research on the marker-assisted selective breeding of Chinese fir and other coniferous trees.

Clematis is one of the large worldwide genera of the Ranunculaceae Juss. Family, with high ornamental and medicinal value. China is the modern distribution centre of Clematis with abundant natural populations. Due to the complexity and high morphological diversity of Clematis, the genus is difficult to classify systematically, and in particular, the phylogenetic position of the endangered Clematis acerifolia is highly controversial. The use of the mitochondrial complete genome is a powerful molecular method that is frequently used for inferring plants phylogenies. However, studies on Clematis mitogenome are rare, thus limiting our full understanding of its phylogeny and genome evolution. Here, we sequenced and annotated the C. acerifolia mt genome using Illumina short- and Nanopore long-reads, characterized the species first complete mitogenome, and performed a comparative phylogenetic analysis with its close relatives. The total length of the C. acerifolia mitogenome is 698,247 bp and the main structure is multi-branched (linear molecule 1 and circular molecule 2). We annotated 55 genes, including 35 protein-coding, 17 tRNA, and 3 rRNA genes. The C. acerifolia mitogenome has extremely unconserved structurally, with extensive sequence transfer between the chloroplast and mitochondrial organelles, sequence repeats, and RNA editing. The phylogenetic position of C. acerifolia was determined by constructing the species mitogenome with 24 angiosperms. Further, our C. acerifolia mitogenome characteristics investigation included GC contents, codon usage, repeats and synteny analysis. Overall, our results are expected to provide fundamental information for C. acerifolia mitogenome evolution and confirm the validity of mitochondrial analysis in determining the phylogenetic positioning of Clematis plants.

Abstract We investigated the genetic structure of three phenotypically distinct ecotypic groups of Norway spruce (Picea abies) belonging to three elevational classes; namely, low- (acuminata), medium- (europaea), and high-elevation (obovata) form, each represented by 150 trees. After rigorous filtering, we used 1916 Genotyping-by-Sequencing generated SNPs for analysis. Outputs from three multivariate analysis methods (Bayesian clustering algorithm implemented in STRUCTURE, Principal Component Analysis, and the Discriminant Analysis of Principal Components) indicated the presence of a distinct genetic cluster representing the high-elevation ecotypic group. Our findings bring a vital message to forestry practice affirming that artificial transfer of forest reproductive material, especially for stands under harsh climate conditions, should be considered with caution.

Abstract Molecular evolution, including nucleotide substitutions, plays an important role in understanding the dynamics and mechanisms of species evolution. Here, we sequenced whole plastid genomes (plastomes) of Quercus fabri, Quercus semecarpifolia, Quercus engleriana, and Quercus phellos and compared them with 14 other Quercus plastomes to explore their evolutionary relationships using 67 shared protein‐coding sequences. While many previously identified evolutionary relationships were found, our findings do not support previous research which retrieve Quercus subg. Cerris sect. Ilex as a monophyletic group, with sect. Ilex found to be polyphyletic and composed of three strongly supported lineages inserted between sections Cerris and Cyclobalanposis. Compared with gymnosperms, Quercus plastomes showed higher evolutionary rates (Dn/Ds = 0.3793). Most protein‐coding genes experienced relaxed purifying selection, and the high Dn value (0.1927) indicated that gene functions adjusted to environmental changes effectively. Our findings suggest that gene interval regions play an important role in Quercus evolution. We detected greater variation in the intergenic regions (trnH‐psbA, trnK_UUU‐rps16, trnfM_CAU‐rps14, trnS_GCU‐trnG_GCC, and atpF‐atpH), intron losses (petB and petD), and pseudogene loss and degradation (ycf15). Additionally, the loss of some genes suggested the existence of gene exchanges between plastid and nuclear genomes, which affects the evolutionary rate of the former. However, the connective mechanism between these two genomes is still unclear.

Abstract Background In angiosperms, phenotypic variation of floral organs is often considered as the traditional basis for the evolutionary relationship of different taxonomic groups above the species level. However, little is known about that at or below the species level. Here, we experimentally tested the phenotypic variation of Malus floral organs using combined methods of intraspecific uniformity test, interspecific distinctness analysis, principal component analysis, Pearson correlation analysis, and Q-type cluster analysis. The ancestor-inclined distribution characteristic analysis of Malus species and cultivars floral attributes was also carried out, so as to explore its taxonomic significance. Results 15/44 phenotypic traits (e.g., flower shape, flower type, flower diameter, ...) were highly consistent, distinguishable, and independent and could be used as the basis for Malus germplasm taxonomy. The studied 142 taxa were divided into two groups (A, B) and five sub-groups (A1, A2, B1, B2, B3), with significantly variable floral phenotypic attributes between groups and within sub-groups. Malus natural species were relatively clustered in the same section (series) while homologous cultivars showed evidence of ancestor-inclined distribution characteristics. However, no significant correlation between the evolutionary order of sections (Sect. Docyniopsis → Sect. Chloromeles → Sect. Sorbomalus → Sect. Eumalus) and group/sub-groups (B3 → B2 → B1 → A). Conclusions Phenotypic variation of floral organs could better explore the genetic relationship between Malus taxa. The findings improved our cognition of floral phenotypic variation taxonomic significance under the species level.

IntroductionQuercus acutissima is an economic and ecological tree species often used for afforestation of arid and semi-arid lands and is considered as an excellent tree for soil and water conservation.MethodsHere, we combined PacBio long reads, Hi-C, and Illumina short reads to assemble Q. acutissima genome.ResultsWe generated a 957.1 Mb genome with a contig N50 of 1.2 Mb and scaffold N50 of 77.0 Mb. The repetitive sequences constituted 55.63% of the genome, among which long terminal repeats were the majority and accounted for 23.07% of the genome. Ab initio, homology-based and RNA sequence-based gene prediction identified 29,889 protein-coding genes, of which 82.6% could be functionally annotated. Phylogenetic analysis showed that Q. acutissima and Q. variabilis were differentiated around 3.6 million years ago, and showed no evidence of species-specific whole genome duplication.ConclusionThe assembled and annotated high-quality Q. acutissima genome not only promises to accelerate the species molecular biology studies and breeding, but also promotes genome level evolutionary studies.

Few incidents of ancient allopolyploidization (polyploidization by hybridization or merging diverged genomes) were previously revealed, although there is significant evidence for the accumulation of whole genome duplications (WGD) in plants. Here, we focused on Ericales, one of the largest and most diverse angiosperm orders with significant ornamental and economic value. Through integrating 24 high-quality whole genome data selected from ~ 200 Superasterids genomes/species and an algorithm of topology-based gene-tree reconciliation, we explored the evolutionary history of in Ericales with ancient complex. We unraveled the allopolyploid origin of Ericales and detected extensive lineage-specific gene loss following the polyploidization. Our study provided a new hypothesis regarding the origin of Ericales and revealed an instructive perspective of gene loss as a pervasive source of genetic variation and adaptive phenotypic diversity in Ericales.

The significance of stumps and other coarse woody debris in maintaining biodiversity has been widely recognized in temperate rainforests, however, there is a paucity of research on the role of stumps in tree regeneration. We studied vascular plant diversity, island species area-relationship, and tree regeneration on stumps in temperate rainforests across three sites in British Columbia, Canada (Malcom Knapp Research Forest, MKRF; Pacific Spirit Regional Park, PSRP; and Stanley Park, SP). Our results were: 1) identification of 19 vascular plant species on stumps, including eight tree species, 2) the number of plants established on stumps observed convex up shape in MKRF and sigmoid shape for PSRP and SP, 3) the overall species established on stumps were positively associated in MKRF (Variance ratio = 2.74) and SP (Variance ratio = 1.37), but negatively associated in PSRP (Variance ratio = 0.57), and 4) tree species appeared to compete with each other on stumps and likely to co-occur with understorey species. Our results highlight species relationships and stumps diameter are major factors affecting tree regeneration on stumps in these second-growth temperate rainforests. We synthesized our results in a schematic of tree regeneration processes on stumps, which could be used to stimulate ideas for new hypothesis generation and for studies relevant to conservation and management.

Abstract Background Hybridization and introgression are vital sources of novel genetic variation driving diversification during reticulated evolution. Quercus is an important model clade, having extraordinary diverse and abundant members in the Northern hemisphere, that are used to studying the introgression of species boundaries and adaptive processes. China is the second-largest distribution center of Quercus, but there are limited studies on introgressive hybridization. Results Here, we screened 17 co-dominant nuclear microsatellite markers to investigate the hybridization and introgression of four oaks (Quercus acutissima, Quercus variabilis, Quercus fabri, and Quercus serrata) in 10 populations. We identified 361 alleles in the four-oak species across 17 loci, and all loci were characterized by high genetic variability (H E = 0.844–0.944) and moderate differentiation (F ST = 0.037–0.156) levels. A population differentiation analysis revealed the following: allopatric homologous (F ST = 0.064)

Drought frequency and severity are exacerbated by global climate change, which could compromise forest ecosystems. However, there have been minimal efforts to systematically investigate the genetic basis of the response to drought stress in perennial trees. Here, we implemented a systems genetics approach that combines co-expression analysis, association genetics, and expression quantitative trait nucleotide (eQTN) mapping to construct an allelic genetic regulatory network comprising four key regulators (PtoeIF-2B, PtoABF3, PtoPSB33, and PtoLHCA4) under drought stress conditions. Furthermore, Hap_01PtoeIF-2B, a superior haplotype associated with the net photosynthesis, was revealed through allelic frequency and haplotype analysis. In total, 75 candidate genes related to drought stress were identified through transcriptome analyses of five Populus cultivars (P. tremula × P. alba, P. nigra, P. simonii, P. trichocarpa, and P. tomentosa). Through association mapping, we detected 92 unique SNPs from 38 genes and 104 epistatic gene pairs that were associated with six drought-related traits by association mapping. eQTN mapping unravels drought stress-related gene loci that were significantly associated with the expression levels of candidate genes for drought stress. In summary, we have developed an integrated strategy for dissecting a complex genetic network, which facilitates an integrated population genomics approach that can assess the effects of environmental threats.

Progeny test trials in British Columbia are essential in assessing the genetic performance via the prediction of breeding values (BVs) for target phenotypes of parent trees and their offspring. Accurate and timely collection of phenotypic data is critical for estimating BVs with confidence. Airborne Laser Scanning (ALS) data have been used to measure tree height and structure across a wide range of species, ages and environments globally. Here, we analyzed a Coastal Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.)] progeny test trial located in British Columbia, Canada, using individual tree high-density Airborne Laser Scanning (ALS) metrics and traditional ground-based phenotypic observations. Narrow-sense heritability, genetic correlations, and BVs were estimated using pedigree-based single and multi-trait linear models for 43 traits. Comparisons of genetic parameter estimates between ALS metrics and traditional ground-based measures and single- and multi-trait models were conducted based on the accuracy and precision of the estimates. BVs were estimated for two ALS models (ALSCAN and ALSACC) representing two model-building approaches and compared to a baseline model using field-measured traits. The ALSCAN model used metrics reflecting aspects of vertical distribution of biomass within trees, while ALSACC represented the most statistically accurate model. We report that the accuracy of both the ALSCAN (0.8239) and ALSACC (0.8254) model-derived BVs for mature tree height is a suitable proxy for ground-based mature tree height BVs (0.8316). Given the cost efficiency of ALS, forest geneticists should explore this technology as a viable tool to increase breeding programs’ overall efficiency and cost savings.

While the progress made in vitro culture of Chinese fir has produced satisfactory results, further improvements are warranted. To understand the mechanism of somatic embryogenesis (SE) in Chinese fir, we conducted phenotypic observations, physiological and biochemical measurements, and transcriptome analysis of embryonic (EC) and non-embryogenic callus (NEC) to provide a scientific basis for SE in this species. We found that EC and NEC showed significant morphological and physiological-biochemical indicators differences. Compared with NEC, EC had higher levels of soluble protein and proline and lower levels of malondialdehyde (MDA), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Callus transcriptome sequencing assembled 152,229 unigenes, and 438 differentially expressed genes (DEGs) were screened, including transcription factor-related (TFs), DNA methylation-related, cell wall component protein, signal transduction-related, and stress response-related. GO and KEGG enrichment analyses of DEGs identified starch and sucrose, glutathione, and cysteine and methionine metabolism as the most representative pathways significantly enriched in EC and NEC genes and were associated with cell proliferation and embryogenesis. For the first time, the specific patterns of gene expression in Chinese fir callus were found through transcriptome comparison between callus, 16-year-old Chinese fir cambium, and drought-stressed tissue culture seedlings. In Chinese fir callus, 75.1% of genes were co-expressed in 16-year-old Chinese fir cambium and drought-stressed tissue culture seedlings, and 24.9% were only specifically expressed in callus. DEGs from EC and NEC indicated that 68.2 and 31.8% were co-expressed and specifically expressed, respectively. These results provided a basis for Chinese fir rapid propagation, which is expected to have theoretical and practical significance.

MIKCC-type MADS-box genes are involved in floral organ identity determination but remain less studied in the Malus lineage. Based on the conserved domains of this gene family, we identified 341 genes among 13 species. Classification results showed that the MIKCC-type were generated later than the M-type, after the formation of Chlamydomonas reinhardtii. By phylogenetic analysis, three different groups were divided among 12 plant species, and one group was an ancestral MIKCC-type MADS-box homologous gene cluster from lower moss to higher flowering plants. Comparative analysis of these genes in A. thaliana and Malus lineages revealed a similar pattern evolutionary relationship with the phylogenetic analysis. Three classes of genes of the ABC model in A. thaliana had orthologous genes in the Malus species, but they experienced different evolutionary events. Only a whole-genome duplication (WGD) event was considered to act on the expansion of ABC-model-related genes in the Malus lineage. Additionally, the expression pattern of genes showed to be involved in flowering development stages and anther development processes among different M. domestica cultivars. This study systematically traced the evolutionary history and expansion mechanism of the MIKCC-type MADS-box gene family in plants. The results also provided novel insights for ABC model research of flower development in the Malus lineage.

Expansins are pH-dependent enzymatic proteins that irreversibly and continuously facilitate cell-wall loosening and extension. The identification and comprehensive analysis of Ginkgo biloba expansins (GbEXPs) are still lacking. Here, we identified and investigated 46 GbEXPs in Ginkgo biloba. All GbEXPs were grouped into four subgroups based on phylogeny. GbEXPA31 was cloned and subjected to a subcellular localization assay to verify our identification. The conserved motifs, gene organization, cis-elements, and Gene Ontology (GO) annotation were predicted to better understand the functional characteristics of GbEXPs. The collinearity test indicated segmental duplication dominated the expansion of the GbEXPA subgroup, and seven paralogous pairs underwent strong positive selection during expansion. A majority of GbEXPAs were mainly expressed in developing Ginkgo kernels or fruits in transcriptome and real-time quantitative PCR (qRT-PCR). Furthermore, GbEXLA4, GbEXLA5, GbEXPA5, GbEXPA6, GbEXPA8, and GbEXPA24 were inhibited under the exposure of abiotic stresses (UV-B and drought) and plant hormones (ABA, SA, and BR). In general, this study expanded our understanding for expansins in Ginkgo tissues’ growth and development and provided a new basis for studying GbEXPs in response to exogenous phytohormones.

We conducted an integrative system biology of metabolome and transcriptome profile analyses during pomegranate (Punica granatum L.) seed germination and utilized a weighted gene co-expression network analysis (WGCNA) to describe the functionality and complexity of the physiological and morphogenetic processes as well as gene expression and metabolic differences during seed germination stages. In total, 489 metabolites were detected, including 40 differentially accumulated metabolites. The transcriptomic analysis showed the expression of 6 984 genes changed significantly throughout the whole germination process. Using WGCNA, we identified modules related to the various seed germination stages and hub genes. In the initial imbibition stage (stage 1), the pivotal genes involved in RNA transduction and the glycolytic pathway were most active, while in the sprouting stage (stage 4), the pivotal genes were involved in multiple metabolic pathways. In terms of secondary metabolic pathways, we found flavonoid 4-reductase genes of anthocyanin biosynthesis pathway are most significantly affected during pomegranate seed germination, while the flavonol synthase gene was mainly involved in the regulation of isoflavonoid biosynthesis.

Abstract Slope aspect plays a critical role in influencing vegetation pattern in semiarid area. The dry valleys of the Hengduan Mountains Region, southwestern China, are striking geographical landscape, suffering from severe ecological degradation. Here, we comprehensively investigated how slope aspect affects vegetation attributes in one of these valleys- the dry valley in the upper reaches of Min River. Three sites were selected along the valley and we quantitively examined the vegetation difference between slope aspects at the whole valley scale and each site level. We found significant vegetation differences between slope aspects in species composition, vegetative structure, and biodiversity pattern, which were in accordance with the observed significant difference in soil nutrient. Generally, north-facing slopes are associated with higher biomass, coverage and height, and species diversity than south-facing slopes. We also found between-aspect differences varied among the study sites, resulting in increased biomass, height, and β diversity differences, decreased density and coverage differences, and opposite trend observed in α diversity at relatively wet site. In conclusion, slope aspect had significant effect on vegetation attributes, which was significantly influenced by local climate (aridity) in terms of both strength and direction depending on the specific attributes investigated.

Abstract Background Gender and fertility variation have an impact on mating dynamics in a population because they affect the gene exchange among parental members and the genetic composition of the resultant seed crops. Fertility is the proportional gametic contribution of parents to their progeny. An effective number of parents, derivative of effective population size, is the probability that two alleles randomly chosen from the gamete gene pool originated from the same parent. The effective number of parents is directly related to the fertility variation among parents, which should be monitored for manipulating gene diversity of seed crops. We formulated a fundamental equation of estimating the effective number of parents and applied it to a seed production population. Results Effective number of parents (N p ) was derived from fertility variation (Ψ) considering covariance (correlation coefficient, r) between maternal and paternal fertility. The Ψ was calculated from the coefficient of variation in reproductive outputs and divided into female (ψ f ) and male (ψ m ) fertility variation in the population under study. The N p was estimated from the parental Ψ estimated by the fertility variation of maternal (ψ f ) and paternal (ψ m ) parents. The gene diversity of seed crops was monitored by Ψ and N p . in a 1.5 generation Pinus koraiensis seed orchard as a case of monoecious species. A large variation of female and male strobili production was observed among the studied 52 parents over four consecutive years, showing statistically significant differences across all studied years. Parental balance curve showed greater distortion in paternal than maternal parents. The Ψ ranged from 1.879 to 4.035 with greater ψ m than ψ f , and the N p varied from 14.8 to 36.8. When pooled, the relative effective number of parents was improved as 80.0% of the census number. Conclusions We recommend the use of fertility variation (i.e., CV, Ψ), Person’s product-moment correlation (r), and effective number of parents (N p ) as tools for gauging gene diversity of seed crops in production populations. For increasing N p and gene diversity, additional management options such as mixing seed-lots, equal cone harvest and application of supplemental-mass-pollination are recommended.

Abstract Background Inbreeding in seed orchards is expected to increase with the advancement of breeding cycles, which results in the delivery of crops with suboptimal genetic gain, reduced genetic diversity, and lower seed set. Here, a genetic distance-dependent method for clonal spatial deployment in seed orchards was developed and demonstrated, which reduced the inbreeding levels. The method’s main evaluation parameter of inbreeding is the genetic distance among individuals and the deployment method used an improved adaptive parallel genetic algorithm (IAPGA) based on Python language. Using inbreeding-prone Chinese Mongolian pine breeding population material originating from a single natural population, the proposed method was compared to a traditional orchard design and a distance-based design; namely, complete randomized block (RCB) and optimum neighborhood (ONA) designs, respectively. Results With the advancement of selective breeding cycles, group separation among orchard related individuals is expected to increase. Based on the genetic distance among individuals, the IAPGA design was superior in significantly reducing the inbreeding level as compared to the two existing designs, confirming its suitability to advanced-generation orchards where relatedness among parents is common. In the 1st, 2nd, and mixed generations clonal deployment schemes, the IAPGA design produced lower inbreeding with 87.22%, 81.49%, and 87.23% of RCB, and 92.78%, 91.30%, and 91.67% of ONA designs, respectively. Conclusions The IAPGA clonal deployment proposed in this study has the obvious advantage of controlling inbreeding, and it is expected to be used in clonal deployment in seed orchards on a large-scale. Further studies are needed to focus on the actual states of pollen dispersal and mating in seed orchards, and more assumptions should be taken into account for the optimized deployment method.

Transposable elements (TEs) are a class of mobile genetic elements that make effects on shaping rapid phenotypic traits of adaptive significance. TE insertions are usually related to transcription changes of nearby genes, and thus may be subjected to purifying selection. Based on the available genome resources of Populus, we found that the composition of Helitron DNA family were highly variable and could directly influence the transcription of nearby gene expression, which are involving in stress-responsive, programmed cell death, and apoptosis pathway. Next, we indicated TEs are highly enriched in Populus trichocarpa compared with three other congeneric poplar species, especially located at untranslated regions (3′UTRs and 5′UTRs) and Helitron transposons, particularly 24-nt siRNA-targeted, are significantly associated with reduced gene expression. Additionally, we scanned a representative resequenced Populus tomentosa population, and identified 9,680 polymorphic TEs loci. More importantly, we identified a Helitron transposon located at the 3′UTR, which could reduce WRKY18 expression level. Our results highlight the importance of TE insertion events, which could regulate gene expression and drive adaptive phenotypic variation in Populus.

Tree improvement programs often focus on improving productivity-related traits; however, under present climate change scenarios, climate change-related (adaptive) traits should also be incorporated into such programs. Therefore, quantifying the genetic variation and correlations among productivity and adaptability traits, and the importance of genotype by environment interactions, including defense compounds involved in biotic and abiotic resistance, is essential for selecting parents for the production of resilient and sustainable forests. Here, we estimated quantitative genetic parameters for 15 growth, wood quality, drought resilience, and monoterpene traits for Picea glauca (Moench) Voss (white spruce). We sampled 1,540 trees from three open-pollinated progeny trials, genotyped with 467,224 SNP markers using genotyping-by-sequencing (GBS). We used the pedigree and SNP information to calculate, respectively, the average numerator and genomic relationship matrices, and univariate and multivariate individual-tree models to obtain estimates of (co)variance components. With few site-specific exceptions, all traits examined were under genetic control. Overall, higher heritability estimates were derived from the genomic- than their counterpart pedigree-based relationship matrix. Selection for height, generally, improved diameter and water use efficiency, but decreased wood density, microfibril angle, and drought resistance. Genome-based correlations between traits reaffirmed the pedigree-based correlations for most trait pairs. High and positive genetic correlations between sites were observed (average 0.68), except for those pairs involving the highest elevation, warmer, and moister site, specifically for growth and microfibril angle. These results illustrate the advantage of using genomic information jointly with productivity and adaptability traits, and defense compounds to enhance tree breeding selection for changing climate.

Hovenia acerba is a precious medicinal and edible tree. We assessed the genetic variation of H. acerba quality traits and conducted a comprehensive germplasm resource evaluation to provide a theoretical basis for breeding edible, medicinal, and edible/medicine combination varieties. We evaluated 31 H. acerba germplasm resources, including 12 infructescence and 8 fruit quality traits using correlation, principal component, and cluster analyses. The results showed that there were significant differences in all quality traits, with an average coefficient of variation greater than 0.20, an average genetic diversity greater than 1.80, and an average repeatability greater than 0.90. The average genetic variation and repeatability of quality traits in infructescence were higher than fruit. Infructescence K, Ca, Mn, Mg, and reducing sugar contents are important indicators in evaluating infructescence and fruit quality traits, and infructescence K, Mg, and reducing sugar contents are also quality innovation indices of H. acerba germplasms. Tannin, protein, and soluble sugar were the most suitable quality components for screening, followed by reducing sugar, starch, fat, total saponins, and total flavones. According to principal component factor scores and cluster analysis results, specific genotypes were selected as breeding materials for infructescence protein, tannin, flavone, reductive sugar, fruit tannin, fat, flavonoid, saponin, protein, and starch. The correlation analysis with environmental factors showed that the total amount of applied water could influence H. acerba infructescence and fruit quality. In conclusion, the variability of H. acerba germplasm resources was rich, and selection potential is large, which is beneficial to germplasm quality innovation and breeding.

Abstract Background Natural selection on fitness-related traits can be temporally heterogeneous among populations. As climate changes, understanding population-level responses is of scientific and practical importance. We examined 18 phenotypic traits associated with phenology, biomass, and ecophysiology in 403 individuals of natural Populus trichocarpa populations, growing in a common garden. Results Compared with tree origin settings, propagules likely underwent drought exposures in the common garden due to significantly low rainfall during the years of measurement. All study traits showed population differentiation reflecting adaptive responses due to local genetic adaptation. Phenology and biomass traits were strongly under selection and showed plastic responses between years, co-varying with latitude. While phenological events (e.g., bud set and growth period) and biomass were under positive directional selection, post-bud set period, particularly from final bud set to the onset of leaf drop, was selected against. With one exception to water-use efficiency, ecophysiology traits were under negative directional selection. Moreover, extended phenological events jointly evolved with source niches under increased temperature and decreased rainfall exposures. High biomass coevolved with climatic niches of high temperature; low rainfall promoted high photosynthetic rates evolution. Conclusions This work underpins that P. trichocarpa is likely to experience increased fitness (height gain) by evolving toward extended bud set and growth period, abbreviated post-bud set period, and increased drought resistance, potentially constituting a powerful mechanism for long-lived tree species in surviving unpredictably environmental extremes (e.g., drought).

In-depth genome characterization is still lacking for most of biofuel crops, especially for centromeres, which play a fundamental role during nuclear division and in the maintenance of genome stability. This study applied long-read sequencing technologies to assemble a highly contiguous genome for yellowhorn (Xanthoceras sorbifolium), an oil-producing tree, and conducted extensive comparative analyses to understand centromere structure and evolution, and fatty acid biosynthesis. We produced a reference-level genome of yellowhorn, ∼470 Mb in length with ∼95% of contigs anchored onto 15 chromosomes. Genome annotation identified 22,049 protein-coding genes and 65.7% of the genome sequence as repetitive elements. Long terminal repeat retrotransposons (LTR-RTs) account for ∼30% of the yellowhorn genome, which is maintained by a moderate birth rate and a low removal rate. We identified the centromeric regions on each chromosome and found enrichment of centromere-specific retrotransposons of LINE1 and Gypsy in these regions, which have evolved recently (∼0.7 MYA). We compared the genomes of three cultivars and found frequent inversions. We analyzed the transcriptomes from different tissues and identified the candidate genes involved in very-long-chain fatty acid biosynthesis and their expression profiles. Collinear block analysis showed that yellowhorn shared the gamma (γ) hexaploidy event with Vitis vinifera but did not undergo any further whole-genome duplication. This study provides excellent genomic resources for understanding centromere structure and evolution and for functional studies in this important oil-producing plant.

Euonymus alatus, Celastraceae, is a deciduous tree species valued for its ornamental and medicinal properties. Here, the species’ whole chloroplast genome sequence was generated by assembling the Illumina paired-end sequencing reads. The circular genome was 157,611 bp in length, exhibiting a typical quadripartite structure with a large single-copy (LSC: 85,892 bp), a small single-copy (SSC: 18,419 bp), and a pair of inverted repeat regions (IRA and IRB: each of 26,650 bp). The chloroplast genome encoded 131 genes, including 87 protein-coding (78 protein-coding gene species), 36 transfer RNA (29 tRNA species), and 8 ribosomal RNA genes (4 rRNA species). The overall GC content was 37.3%, while the corresponding values of the LSC, SSC and IR regions were 35.1, 31.7 and 42.7%, respectively. Phylogenetic analysis of 12 species complete chloroplast genomes suggested that E. alatus was relatively close to E. japonicus. This complete chloroplast genome is expected to provide valuable insight into further phylogenetic reconstruction of the Celastraceae species.

Platycladus orientalis is an ecologically important native conifer in Northern China and exotic species in many parts of the world; however, knowledge about the species’ genetics and genome are very limited. The availability of well-developed battery of genetic markers, with large genome coverage, is a prerequisite for the species genetic dissection of adaptive attributes and efficient selective breeding. Here, we present a genome-wide genotyping method with double-digestion restriction site associated DNA sequencing (ddRAD-seq) that is effective in generating large number of Mendelian markers for genome mapping and other genetic applications. Using 139 megagametophytes collected from a single mother tree, we assembled 397,226 loci, of which 108,683 (27.4%) were polymorphic. After stringent filtering for 1:1 segregation ratio and missing rate of

Abstract Genetic structure and major climate factors may contribute to the distribution of genetic diversity of a highly valued oil tree species Xanthoceras sorbifolium (yellowhorn). Long‐term over utilization along with climate change is affecting the viability of yellowhorn wild populations. To preserve the species known and unknown valuable gene pools, the identification of genetic diversity “hotspots” is a prerequisite for their consideration as in situ conservation high priority. Chloroplast DNA (cpDNA) diversity was high among 38 natural populations (Hd = 0.717, K = 4.616, Tajmas’ D = −0.22) and characterized by high genetic divergence (FST = 0.765) and relatively low gene flow (Nm = 0.03), indicating populations isolation reflecting the species’ habitat fragmentation and inbreeding depression. Six out of the studied 38 populations are defined as genetic diversity “hotspots.” The number and geographic direction of cpDNA mutation steps supported the species southwest to northeast migration history. Climatic factors such as extreme minimum temperature over 30 years indicated that the identified genetic “hotspots” are expected to experience 5°C temperature increase in next following 50 years. The results identified vulnerable genetic diversity “hotspots” and provided fundamental information for the species’ future conservation and breeding activities under the anticipated climate change. More specifically, the role of breeding as a component of a gene resource management strategy aimed at fulfilling both utilization and conservation goals.

Abstract Background Cupressus gigantea, a rare and endangered tree species with remarkable medicinal value, is endemic to the Tibetan Plateau. Yet, little is known about the underlying genetics of the unique ecological adaptability of this extremely long-lived conifer with a large genome size. Here, we present its first de novo and multi-tissue transcriptome in-depth characterization. Results We performed Illumina paired-end sequencing and RNA libraries assembly derived from terminal buds, male and female strobili, biennial leaves, and cambium tissues taken from adult C. gigantea. In total, large-scale high-quality reads were assembled into 101,092 unigenes, with an average sequence length of 1029 bp, and 6848 unigenes (6.77%) were mapped against the KEGG databases to identify 292 pathways. A core set of 41,373 genes belonging to 2412 orthologous gene families shared between C. gigantea and nine other plants was revealed. In addition, we identified 2515 small to larger-size gene families containing in total 9223 genes specific to C. gigantea, and enriched for gene ontologies relating to biotic interactions. We identified an important terpene synthases gene family expansion with its 121 putative members. Conclusions This study presents the first comprehensive transcriptome characterization of C. gigantea. Our results will facilitate functional genomic studies to support genetic improvement and conservation programs for this endangered conifer.

Quercus acrodonta Seemen is an East Asian evergreen oak tree species belonging to the Quercus section Ilex. Here, we assembled and annotated the complete chloroplast (cp) genome of the species. The circular genome is 161,105 bp in size, presenting a typical quadripartite structure including two copies of inverted repeat (IR) regions (25,864 bp), one large single-copy (LSC) region (90,357 bp), and one small single-copy (SSC) region (19,020 bp). A total of 131 genes are encoded, including 85 protein-coding genes (PCGs), 38 tRNAs, and eight rRNAs. Phylogenetic analysis based on cp genome sequences of 18 Quercus species indicated that Q. acrodonta was more closely related to Q. phillyraeoides.

Pinus densiflora var. zhangwuensis S.J.Zhang, C.X.Li & X.Y.Yuan, a tree species with promising afforestation potential in northern China. Here, we assembled and annotated the complete chloroplast (cp) genome of P. densiflora var. zhangwuensis using the Oxford Nanopore sequencing technology. The cp genome was 119,725 bp in length, exhibiting a typical quadripartite structure with a large single-copy (LSC: 65,552 bp) and a small single-copy (SSC: 53,183 bp) separated by a pair of inverted repeats regions (IRA and IRB: each of 495 bp) region. The overall GC content is 37.3%. The genome was predicted to encode 112 distinct genes, including 72 protein-coding, 36 tRNA, and four rRNA genes. Maximum-likelihood (ML) phylogenetic for cp genome sequences of 18 Pinaceae species revealed that P. densiflora var. zhangwuensis was closely related to Pinus sylvestris.

Poplar is not only an important woody plant, but also a model species for molecular plant studies. We identified PagGRF11 (pAxG07Gg0005700), a homolog of the Arabidopsis AtGRF1 (AT4G37740) and AtGRF2 (AT2G22840) gene. We transformed the poplar clone “84K” with PagGRF11, and the transgenic overexpressed plants (PagGRF11-OE) showed plant height reduction (dwarfing), stem diameter increase, internode shortening, and larger leaf area. The Arabidopsis overexpression line grf-oe (Overexpression of PagGRF11 in Arabidopsis), mutant line atgrf (a loss-of-function mutant of the AtGRF1 gene of Arabidopsis thaliana), and mutant trans-complementary line atgrf+oe (overexpression of PagGRF11 in mutant plants (atgrf)) also showed different leaf size phenotypes. Further, tissue sections revealed that increased xylem production was the main cause of stem thickening. Transcriptome differential expression analysis of PagGRF11 overexpressed and control plants showed that PagGRF11 promoted CCCH39(C3H39) expression. The expression profile of CCCH39 in different tissues showed that it was highly expressed in xylem. Yeast single hybrid and instantaneous double luciferase assay results showed that PagGRF11 directly transcribed and activated CCCH39 expression through interaction with cis-acting element GARE (TCTGTTG), thus promoting xylem development. This is the first finding that GRF positively regulates xylem development through CCCH39 expression activation and further suggests that PagGRF11 is a potential target for increasing wood yield.