Genetic diversity of natural orchardgrass (Dactylis glomerata L.) populations in three regions in Europe

Metabolomic approach to investigate Dactylis glomerata L. from the VIR collection

The perennial grass cocksfoot (Dactylis glomerata L.) is a valuable early highly nutritious crop used as green fodder in agricultural production. The species is widespread across the Eurasian continent; it is characterized by plasticity and high ecological and geographical variability. The article considers the metabolic profiles of 15 accessions of the cocksfoot from the collection of the N.I. Vavilov Institute of Plant Genetic Resources (VIR). The material is represented by varieties and wild forms of various origin: the European part of the Russian Federation, Norway and Finland. The study was carried out using gas-liquid chromatography coupled with mass spectrometry. The study and comparison of groups of metabolites of cocksfoot accessions of various ecological and geographical origin was carried out. Statistical processing included the calculation of the main parameters of variability, factor analysis of the correlation system (Q- and R-technique), cluster analysis by Ward's method and discriminant analysis. The variability of the quantitative and qualitative composition of the substances identified was revealed. Based on statistical processing of the results obtained, five groups of cocksfoot accessions were identified, differing in the profile of metabolites. One of the groups with a similar composition of metabolites consisted of accessions from one ecological and geographical region; another, of accessions of different origin. Significant differences were noted in the metabolomic profiles of a late-maturing wild cocksfoot accession from the Republic of Karelia at the booting stage from early- and mid-maturing accessions at the heading stage; it contained the largest number of free amino acids and the smallest number of identified primary and secondary metabolites. Wild-growing accession k-44020 from Norway surpassed other wild-growing accessions in the content of free amino acids, sugars and phosphates at the heading stage. Wild-growing accessions differed from breeding varieties with a high content of proline and threonine, indicators of high resistance to lack of moisture and high air temperature.

A multispecies amplicon sequencing approach for genetic diversity assessments in grassland plant species

Grasslands are widespread and economically relevant ecosystems at the basis of sustainable roughage production. Plant genetic diversity (PGD; i.e., within‐species diversity) is related to many beneficial effects on the ecosystem functioning of grasslands. The monitoring of PGD in temperate grasslands is complicated by the multiplicity of species present and by a shortage of methods for large‐scale assessments. However, the continuous advancement of high‐throughput DNA sequencing approaches has improved the prospects of broad, multispecies PGD monitoring. Among them, amplicon sequencing stands out as a robust and cost‐effective method. Here, we report a set of 12 multispecies primer pairs that can be used for high‐throughput PGD assessments in multiple grassland plant species. The target loci were selected and tested in two phases: a “discovery phase” based on a sequence capture assay (611 nuclear loci assessed in 16 grassland plant species), which resulted in the selection of 11 loci; and a “validation phase”, in which the selected loci were targeted and sequenced using multispecies primers in test populations of Dactylis glomerata L., Lolium perenne L., Festuca pratensis Huds., Trifolium pratense L. and T. repens L. The multispecies amplicons had nucleotide diversities per species from 5.19 × 10⁻³ to 1.29 × 10⁻², which is in the range of flowering‐related genes but slightly lower than pathogen resistance genes. We conclude that the methodology, the DNA sequence resources, and the primer pairs reported in this study provide the basis for large‐scale, multispecies PGD monitoring in grassland plants.

Genotyping by Sequencing and Plastome Analysis Finds High Genetic Variability and Geographical Structure in Dactylis glomerata L. in Northwest Europe Despite Lack of Ploidy Variation

Large collections of the forage and bioenergy grass Dactylis glomerata were made in northwest (NW) Europe along east to west and north to south clines for genetic resource conservation and to inform breeding programmes of genetic diversity, genepools, and ploidy. Leaves were sampled for genetic analysis and seed and rhizome for ex-situ conservation. Genotyping by sequencing (GBS) was used to assay nuclear DNA diversity and plastome single nucleotide polymorphism (SNP) discovery was undertaken using a long-read PCR and MiSeq approach. Nuclear and plastid SNPs were analysed by principal component analysis (PCA) to compare genotypes. Flow cytometry revealed that all samples were tetraploid, but some genome size variation was recorded. GBS detected an average of approximately 10,000 to 15,000 SNPs per country sampled. The highest average number of private SNPs was recorded in Poland (median ca. 2000). Plastid DNA variation was also high (1466 SNPs, 17 SNPs/kbp). GBS data, and to a lesser extent plastome data, also show that genetic variation is structured geographically in NW Europe with loose clustering matching the country of plant origin. The results reveal extensive genetic diversity and genetic structuring in this versatile allogamous species despite lack of ploidy variation and high levels of human mediated geneflow via planting.

Combinations of Small RNA, RNA, and Degradome Sequencing Uncovers the Expression Pattern of microRNA⁻mRNA Pairs Adapting to Drought Stress in Leaf and Root of Dactylis glomerata L

Drought stress is a global problem, and the lack of water is a key factor that leads to agricultural shortages. MicroRNAs play a crucial role in the plant drought stress response; however, the microRNAs and their targets involved in drought response have not been well elucidated. In the present study, we used Illumina platform (https://www.illumina.com/) and combined data from miRNA, RNA, and degradome sequencing to explore the drought- and organ-specific miRNAs in orchardgrass (Dactylis glomerata L.) leaf and root. We aimed to find potential miRNA⁻mRNA regulation patterns responding to drought conditions. In total, 519 (486 conserved and 33 novel) miRNAs were identified, of which, 41 miRNAs had significant differential expression among the comparisons (p < 0.05). We also identified 55,366 unigenes by RNA-Seq, where 12,535 unigenes were differently expressed. Finally, our degradome analysis revealed that 5950 transcripts were targeted by 487 miRNAs. A correlation analysis identified that miRNA ata-miR164c-3p and its target heat shock protein family A (HSP70) member 5 gene comp59407_c0 (BIPE3) may be essential in organ-specific plant drought stress response and/or adaptation in orchardgrass. Additionally, Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analyses found that "antigen processing and presentation" was the most enriched downregulated pathway in adaptation to drought conditions. Taken together, we explored the genes and miRNAs that may be involved in drought adaptation of orchardgrass and identified how they may be regulated. These results serve as a valuable genetic resource for future studies focusing on how plants adapted to drought conditions.

AFLP-based genetic diversity of wild orchardgrass germplasm collections from Central Asia and Western China, and the relation to environmental factors

Dactylis glomerata L. (orchardgrass) is an important perennial forage species in temperate areas of the world. It is usually used for silage, grazing and hay because of its high nutritional value and reproducibility. Central Asia, Xinjiang and Tibetan Plateau in China possess various special micro-environments that harbor many valuable resources, while different degrees of degradation of the grassland ecosystem occurred due to climatic changing and human activities. Investigating the genetic diversity of wild D. glomerat could provide basis for collection, protection, and utilization of some excellent germplasm resources. Totally 210 individuals from 14 populations—five from Xinjiang, two from Kangding (Tibetan Plateau), and seven from Central Asia were identified using AFLP technology. The average values of Nei’s genetic diversity (H_j) and Shannon information index (H_o) were 0.383 and 0.394 respectively. UPGMA tree, STRUCTURE analysis and principal coordinate analysis (PCoA) showed populations from same region clustered together. AMOVA revealed 35.10% of the genetic differentiation (F_st) occurred among populations. Gene flow (N_m) was limited among all populations. Genetic diversity of D. glomerata was high but limited under isolation-by-distance pattern, resulting in high genetic differentiation and low gene flow among populations. Adjacent regions also exhibited similar results because of the barriers of high mountains. The environmental factors, such as precipitation, elevation, latitude and longitude also had some impacts on genetic diversity and structure pattern of populations.

Analysis of Genetic Diversity and Structure Pattern of Indigofera Pseudotinctoria in Karst Habitats of the Wushan Mountains Using AFLP Markers

Indigofera pseudotinctoria Mats is an agronomically and economically important perennial legume shrub with a high forage yield, protein content and strong adaptability, which is subject to natural habitat fragmentation and serious human disturbance. Until now, our knowledge of the genetic relationships and intraspecific genetic diversity for its wild collections is still poor, especially at small spatial scales. Here amplified fragment length polymorphism (AFLP) technology was employed for analysis of genetic diversity, differentiation, and structure of 364 genotypes of I. pseudotinctoria from 15 natural locations in Wushan Montain, a highly structured mountain with typical karst landforms in Southwest China. We also tested whether eco-climate factors has affected genetic structure by correlating genetic diversity with habitat features. A total of 515 distinctly scoreable bands were generated, and 324 of them were polymorphic. The polymorphic information content (PIC) ranged from 0.694 to 0.890 with an average of 0.789 per primer pair. On species level, Nei’s gene diversity (H_j), the Bayesian genetic diversity index (H_B) and the Shannon information index (I) were 0.2465, 0.2363 and 0.3772, respectively. The high differentiation among all sampling sites was detected (F_ST = 0.2217, G_ST = 0.1746, G’_ST = 0.2060, θ^B = 0.1844), and instead, gene flow among accessions (N_m = 1.1819) was restricted. The population genetic structure resolved by the UPGMA tree, principal coordinate analysis, and Bayesian-based cluster analyses irrefutably grouped all accessions into two distinct clusters, i.e., lowland and highland groups. The population genetic structure resolved by the UPGMA tree, principal coordinate analysis, and Bayesian-based cluster analyses irrefutably grouped all accessions into two distinct clusters, i.e., lowland and highland groups. This structure pattern may indicate joint effects by the neutral evolution and natural selection. Restricted N_m was observed across all accessions, and genetic barriers were detected between adjacent accessions due to specifically geographical landform.

Genetic Structure and Eco-Geographical Differentiation of Wild Sheep Fescue (Festuca ovina L.) in Xinjiang, Northwest China

Glaciation and mountain orogeny have generated new ecologic opportunities for plants, favoring an increase in the speciation rate. Moreover, they also act as corridors or barriers for plant lineages and populations. High genetic diversity ensures that species are able to survive and adapt. Gene flow is one of the most important determinants of the genetic diversity and structure of out-crossed species, and it is easily affected by biotic and abiotic factors. The aim of this study was to characterize the genetic diversity and structure of an alpine species, Festuca ovina L., in Xinjiang, China. A total of 100 individuals from 10 populations were analyzed using six amplified fragment length polymorphism (AFLP) primer pairs. A total of 583 clear bands were generated, of which 392 were polymorphic; thus, the percentage of polymorphic bands (PPB) was 67.24%. The total and average genetic diversities were 0.2722 and 0.2006 (0.1686-0.2225), respectively. The unweighted group method with arithmetic mean (UPGMA) tree, principal coordinates analysis (PCoA) and Structure analyses revealed that these populations or individuals could be clustered into two groups. The analysis of molecular variance analysis (AMOVA) suggested that most of the genetic variance existed within a population, and the genetic differentiation (Fst) among populations was 20.71%. The Shannon differentiation coefficient (G'st) among populations was 0.2350. Limited gene flow (Nm = 0.9571) was detected across all sampling sites. The Fst and Nm presented at different levels under the genetic barriers due to fragmentation. The population genetic diversity was significant relative to environmental factors such as temperature, altitude and precipitation.

AFLP assessment of genetic variability and relationships in an Asian wild germplasm collection of Dactylis glomerata L

Orchardgrass (Dactylis glomerata L.), an excellent perennial and cool season forage species distributed in most temperate regions, has been cultivated widely in Western China. Amplified fragment length polymorphism markers were employed to determine the genetic variability and population structure among 41 indigenous orchardgrass accessions from Central Asia and Western China. On the basis of 531 polymorphic fragments resulted from eight primer combinations, polymorphic information content (PIC), marker index (MI) and resolving power (RP) averaged 0.252, 16.34 and 25.27 per primer combination, respectively, demonstrating the high efficiency and reliability of the markers used. We found relatively low differentiation (Fst=0.135) for three geographical groups, where Central Asia (CA) and Southwest China (SWC) group exhibited higher intra-population diversity (He=0.20 and 0.21) than that of the Xinjiang (XJ) group (He=0.14). We also did not detect a clear pattern of isolation by distance with a low value of r=0.301 in the Mantel test. STRUCTURE, FLOCK, UPGMA clustering and PCoA analyses showed that CA group is more related to the SWC Group rather than to the XJ Group. In addition, this study strongly suggests that geographical and ecological environmental factors together could better explain the genetic differentiation between different geographical regions than geographic isolation alone, especially for Xinjiang accessions. The present study also could support that Southwest China might be the internal diversity center of D. glomerata in China. The knowledge about the genetic variability of the Asian accessions examined contributes to rapid characterization, defining gene pools of wild accessions, and selecting appropriate germplasms for plant improvement.

Comparison of RAPD, ISSR, and AFLP Molecular Markers to Reveal and Classify Orchardgrass (Dactylis glomerata L.) Germplasm Variations

Three different DNA-based techniques, Random Amplified Polymorphic DNA (RAPD), Inter Simple Sequence Repeat (ISSR) and Amplified Fragment Length Polymorphism (AFLP) markers, were used for fingerprinting Dactylis glomerata genotypes and for detecting genetic variation between the three different subspecies. In this study, RAPD assays produced 97 bands, of which 40 were polymorphic (41.2%). The ISSR primers amplified 91 bands, and 54 showed polymorphism (59.3%). Finally, the AFLP showed 100 bands, of which 92 were polymorphic (92%). The fragments were scored as present (1) or absent (0), and those readings were entered in a computer file as a binary matrix (one for each marker). Three cluster analyses were performed to express–in the form of dendrograms–the relationships among the genotypes and the genetic variability detected. All DNA-based techniques used were able to amplify all of the genotypes. There were highly significant correlation coefficients between cophenetic matrices based on the genetic distance for the RAPD, ISSR, AFLP, and combined RAPD-ISSR-AFLP data (0.68, 0.78, 0.70, and 0.70, respectively). Two hypotheses were formulated to explain these results; both of them are in agreement with the results obtained using these three types of molecular markers. We conclude that when we study genotypes close related, the analysis of variability could require more than one DNA-based technique; in fact, the genetic variation present in different sources could interfere or combine with the more or less polymorphic ability, as our results showed for RAPD, ISSR and AFLP markers. Our results indicate that AFLP seemed to be the best-suited molecular assay for fingerprinting and assessing genetic relationship among genotypes of Dactylis glomerata.