Genome of Linum usitatissimum convar. crepitans expands the view on the section Linum

Sequencing whole plant genomes provides a solid foundation for applied and basic studies. Genome sequences of agricultural plants attract special attention, as they reveal information on the regulation of beneficial plant traits. Flax is a valuable crop cultivated for oil and fiber. Genome sequences of its representatives are rich sources of genetic information for the improvement of cultivated forms of the plant. In our work, we sequenced the first genome of flax with the dehiscence of capsules—Linum usitatissimum convar. сrepitans (Boenn.) Dumort—on the Oxford Nanopore Technologies (ONT) and Illumina platforms. We obtained 23 Gb of raw ONT data and 89 M of 150 + 150 paired-end Illumina reads and tested different tools for genome assembly and polishing. The genome assembly produced according to the Canu—Racon ×2—medaka—POLCA scheme had optimal contiguity and completeness: assembly length—412.6 Mb, N50—5.2 Mb, L50—28, and complete BUSCO—94.6% (64.0% duplicated, eudicots_odb10). The obtained high-quality genome assembly of L. usitatissimum convar. crepitans provides opportunities for further studies of evolution, domestication, and genome regulation in the section Linum

Repeatome Analyses and Satellite DNA Chromosome Patterns in Deschampsia sukatschewii, D. cespitosa, and D. antarctica (Poaceae)

Subpolar and polar ecotypes of Deschampsia sukatschewii (Popl.) Roshev, D. cespitosa (L.) P. Beauv, and D. antarctica E. Desv. are well adapted to stressful environmental conditions, which make them useful model plants for genetic research and breeding. For the first time, the comparative repeatome analyses of subpolar and polar D. sukatschewii, D. cespitosa, and D. antarctica was performed using RepeatExplorer/TAREAN pipelines and FISH-based chromosomal mapping of the identified satellite DNA families (satDNAs). In the studied species, mobile genetic elements of class 1 made up the majority of their repetitive DNA; interspecific variations in the total amount of Ty3/Gypsy and Ty1/Copia retroelements, DNA transposons, ribosomal, and satellite DNA were revealed; 12–18 high confident and 7–9 low confident putative satDNAs were identified. According to BLAST, most D. sukatschewii satDNAs demonstrated sequence similarity with satDNAs of D. antarctica and D. cespitosa indicating their common origin. Chromosomal mapping of 45S rDNA, 5S rDNA, and satDNAs of D. sukatschewii allowed us to construct the species karyograms and detect new molecular chromosome markers important for Deschampsia species. Our findings confirmed that genomes of D. sukatschewii and D. cespitosa were more closely related compared to D. antarctica according to repeatome composition and patterns of satDNA chromosomal distribution

Clarification of the Position of Linum stelleroides Planch. within the Phylogeny of the Genus Linum L.

The phylogeny of members of the family Linaceae DC. ex Perleb has not been adequately studied. In particular, data on the phylogenetic relationship between Linum stelleroides Planch. and other representatives of the blue-flowered flax are very controversial. In the present work, to clarify this issue, we obtained DNA sequences of three nuclear loci (IGS and ITS1 + 5.8S rDNA + ITS2 of the 35S rRNA gene and the 5S rRNA gene) and eight chloroplast loci (rbcL, the trnL–trnF intergenic spacer, matK, the 3′ trnK intron, ndhF, trnG, the psbA–trnH intergenic spacer, and rpl16) of 10 Linum L. species (L. stelleroides, L. hirsutum, L. perenne, L. leonii, L. lewisii, L. narbonense, L. decumbens, L. grandiflorum, L. bienne (syn. L. angustifolium), and L. usitatissimum) using high-throughput sequencing data. The phylogenetic analysis showed that L. stelleroides forms a basal branch in the blue-flowered flax clade. Previously found inconsistencies in the position of L. stelleroides and some other species in the Linaceae phylogenetic tree resulted from the erroneous species identification of some of the studied plant samples

Comparative molecular cytogenetic characterization of seven Deschampsia (Poaceae) species.

The genus Deschampsia P. Beauv (Poaceae) involves a group of widespread polymorphic species. Some of them are highly tolerant to stressful and variable environmental conditions, and D. antarctica is one of the only two vascular plants growing in Antarctic. This species is a source of useful for selection traits and a valuable model for studying an environmental stress tolerance in plants. Genome diversity and comparative chromosomal phylogeny within the genus have not been studied yet as karyotypes of most Deschampsia species are poorly investigated. We firstly conducted a comparative molecular cytogenetic analysis of D. antarctica (Antarctic Peninsula) and related species from various localities (D. cespitosa, D. danthonioides, D. elongata, D. flexuosa (= Avenella flexuosa), D. parvula and D. sukatschewii by fluorescence in situ hybridization with 45S and 5S rDNA, DAPI-banding and sequential rapid in situ hybridization with genomic DNA of D. antarctica, D. cespitosa, and D. flexuosa. Based on patterns of distribution of the examined markers, chromosomes of the studied species were identified. Within these species, common features as well as species peculiarities in their karyotypic structure and chromosomal distribution of molecular cytogenetic markers were characterized. Different chromosomal rearrangements were detected in D. antarctica, D. flexuosa, D. elongata and D. sukatschewii. In karyotypes of D. antarctica, D. cespitosa, D. elongata and D. sukatschewii, 0-3 B chromosomes possessed distinct DAPI-bands were observed. Our findings suggest that the genome evolution of the genus Deschampsia involved polyploidy and also different chromosomal rearrangements. The obtained results will help clarify the relationships within the genus Deschampsia, and can be a basis for the further genetic and biotechnological studies as well as for selection of plants tolerant to extreme habitats

Gene expression profiling of flax (Linum usitatissimum L.) under edaphic stress

Abstract Background Cultivated flax (Linum usitatissimum L.) is widely used for production of textile, food, chemical and pharmaceutical products. However, various stresses decrease flax production. Search for genes, which are involved in stress response, is necessary for breeding of adaptive cultivars. Imbalanced concentration of nutrient elements in soil decrease flax yields and also results in heritable changes in some flax lines. The appearance of Linum Insertion Sequence 1 (LIS-1) is the most studied modification. However, LIS-1 function is still unclear. Results High-throughput sequencing of transcriptome of flax plants grown under normal (N), phosphate deficient (P), and nutrient excess (NPK) conditions was carried out using Illumina platform. The assembly of transcriptome was performed, and a total of 34924, 33797, and 33698 unique transcripts for N, P, and NPK sequencing libraries were identified, respectively. We have not revealed any LIS-1 derived mRNA in our sequencing data. The analysis of high-throughput sequencing data allowed us to identify genes with potentially differential expression under imbalanced nutrition. For further investigation with qPCR, 15 genes were chosen and their expression levels were evaluated in the extended sampling of 31 flax plants. Significant expression alterations were revealed for genes encoding WRKY and JAZ protein families under P and NPK conditions. Moreover, the alterations of WRKY family genes differed depending on LIS-1 presence in flax plant genome. Besides, we revealed slight and LIS-1 independent mRNA level changes of KRP2 and ING1 genes, which are adjacent to LIS-1, under nutrition stress. Conclusions Differentially expressed genes were identified in flax plants, which were grown under phosphate deficiency and excess nutrition, on the basis of high-throughput sequencing and qPCR data. We showed that WRKY and JAS gene families participate in flax response to imbalanced nutrient content in soil. Besides, we have not identified any mRNA, which could be derived from LIS-1, in our transcriptome sequencing data. Expression of LIS-1 flanking genes, ING1 and KRP2, was suggested not to be nutrient stress-induced. Obtained results provide new insights into edaphic stress response in flax and the role of LIS-1 in these process

Integration of Physical, Genetic, and Cytogenetic Mapping Data for Cellulose Synthase (CesA) Genes in Flax (Linum usitatissimum L.)

Flax, Linum usitatissimum L., is a valuable multi-purpose plant, and currently, its genome is being extensively investigated. Nevertheless, mapping of genes in flax genome is still remaining a challenging task. The cellulose synthase (CesA) multigene family involving in the process of cellulose synthesis is especially important for metabolism of this fiber crop. For the first time, fluorescent in situ hybridization (FISH)-based chromosomal localization of the CesA conserved fragment (KF011584.1), 5S, and 26S rRNA genes was performed in landrace, oilseed, and fiber varieties of L. usitatissimum. Intraspecific polymorphism in chromosomal distribution of KF011584.1 and 5S DNA loci was revealed, and the generalized chromosome ideogram was constructed. Using BLAST analysis, available data on physical/genetic mapping and also whole-genome sequencing of flax, localization of KF011584.1, 45S, and 5S rRNA sequences on genomic scaffolds, and their anchoring to the genetic map were conducted. The alignment of the results of FISH and BLAST analyses indicated that KF011584.1 fragment revealed on chromosome 3 could be anchored to linkage group (LG) 11. The common LG for 45S and 5S rDNA was not found probably due to the polymorphic localization of 5S rDNA on chromosome 1. Our findings indicate the complexity of integration of physical, genetic, and cytogenetic mapping data for multicopy gene families in plants. Nevertheless, the obtained results can be useful for future progress in constructing of integrated physical/genetic/cytological maps in L. usitatissimum which are essential for flax breeding

Characterization of repeated DNA sequences in genomes of blue-flowered flax

Abstract Background Members of different sections of the genus Linum are characterized by wide variability in size, morphology and number of chromosomes in karyotypes. Since such variability is determined mainly by the amount and composition of repeated sequences, we conducted a comparative study of the repeatomes of species from four sections forming a clade of blue-flowered flax. Based on the results of high-throughput genome sequencing performed in this study as well as available WGS data, bioinformatic analyses of repeated sequences from 12 flax samples were carried out using a graph-based clustering method. Results It was found that the genomes of closely related species, which have a similar karyotype structure, are also similar in the repeatome composition. In contrast, the repeatomes of karyologically distinct species differed significantly, and no similar tandem-organized repeats have been identified in their genomes. At the same time, many common mobile element families have been identified in genomes of all species, among them, Athila Ty3/gypsy LTR retrotransposon was the most abundant. The 30-chromosome members of the sect. Linum (including the cultivated species L. usitatissimum) differed significantly from other studied species by a great number of satellite DNA families as well as their relative content in genomes. Conclusions The evolution of studied flax species was accompanied by waves of amplification of satellite DNAs and LTR retrotransposons. The observed inverse correlation between the total contents of dispersed repeats and satellite DNAs allowed to suggest a relationship between both classes of repeating sequences. Significant interspecific differences in satellite DNA sets indicated a high rate of evolution of this genomic fraction. The phylogenetic relationships between the investigated flax species, obtained by comparison of the repeatomes, agreed with the results of previous molecular phylogenetic studies

Chromosome spread of <i>D</i>. <i>antarctica</i> specimen from Darboux Island.

<p>Chromosome localization of 45S (green) and 5S (red) rDNA sites and inverted image of DAPI/C-banded B-chromosomes (bottom right). Arrows point to the B-chromosomes. Scale bar—5 μm.</p

Chromosome spreads of <i>D</i>. <i>antarctica</i>.

<p>(A) Giemsa C-banded chromosomes of the specimen from Galindez Island. (B) Inverted image of the DAPI/C-banded karyotype and (C) localization of 45S (green) and 5S (red) rDNA sites on chromosomes of the specimen from Galindez Island. (D) Ag-NOR staining patterns (dark segments) of chromosomes of the specimen from Skua Island. (E) Localization of telomeric repeats (green), 45S (green) and 5S (red) rDNA loci and in the karyotype of the specimen from Skua Island. Arrows point to the intercalary loci of telomere repeats detected on the largest chromosome pair. (F) Distribution of 5S rDNA sites (red) and GAA microsatellite sequence (green) on chromosomes of the specimen from Skua Island. Scale bar—5 μm.</p