A genetic map is an important and valuable tool for quantitative trait locus (QTL) mapping, marker-assisted selection (MAS)-based breeding, and reference-assisted chromosome assembly. In this study, 112 F2 plants from a cross between Linum usitatissimum L. ‘DIANE’ and ‘NY17’ and parent plants were subjected to high-throughput sequencing and specific-locus amplified fragment (SLAF) library construction. After preprocessing, 61.64 Gb of raw data containing 253.71 Mb paired-end reads, each 101 bp in length, were obtained. A total of 192,797 SLAFs were identified, of which 23,115 were polymorphic, with a polymorphism rate of 11.99%. Finally, 2,339 SLAFs were organized into a linkage map consisting of 15 linkage groups (LGs). The total length of the genetic map was 1483.25 centimorgans (cM) and the average distance between adjacent markers was 0.63 cM. Combined with flax chromosome-scale pseudomolecules, 12 QTLs associating with 6 flax fiber-related traits were mapped on the chromosomal scaffolds. This high-density genetic map of flax should serve as a foundation for flax fine QTL mapping, draft genome assembly, and MAS-guided breeding. Ultimately, the genomic regions identified in this research could potentially be valuable for improving flax fiber cultivars, as well as for identification of candidate genes involved in flax fiber formation processes.

Flax (Linum usitatissimum L.) is an important industrial crop that is often cultivated on marginal lands, where salt stress negatively affects yield and quality. High-throughput RNA sequencing (RNA-seq) using the powerful Illumina platform was employed for transcript analysis and gene discovery to reveal flax response mechanisms to salt stress. After cDNA libraries were constructed from flax exposed to water (negative control) or salt (100 mM NaCl) for 12 h, 24 h or 48 h, transcription expression profiles and cDNA sequences representing expressed mRNA were obtained. A total of 431,808,502 clean reads were assembled to form 75,961 unigenes. After ruling out short-length and low-quality sequences, 33,774 differentially expressed unigenes (DEUs) were identified between salt-stressed and unstressed control (C) flax. Of these DEUs, 3669, 8882 and 21,223 unigenes were obtained from flax exposed to salt for 12 h (N1), 24 h (N2) and 48 h (N4), respectively. Gene function classification and pathway assignments of 2842 DEUs were obtained by comparing unigene sequences to information within public data repositories. qRT-PCR of selected DEUs was used to validate flax cDNA libraries generated for various durations of salt exposure. Based on transcriptome sequences, 1777 EST-SSRs were identified of which trinucleotide and dinucleotide repeat microsatellite motifs were most abundant. The flax DEUs and EST-SSRs identified here will serve as a powerful resource to better understand flax response mechanisms to salt exposure for development of more salt-tolerant varieties of flax.

Flax (Linum usitatissimum L.) is a major fiber and oil yielding crop grown in northeastern China. Identification of flax molecular markers is a key step toward improving flax yield and quality via marker-assisted breeding. Simple sequence repeat (SSR) markers, which are based on genomic structural variation, are considered the most valuable type of genetic marker for this purpose. In this study, we screened 1,574 microsatellites from Linum usitatissimum L. obtained using reduced representation genome sequencing (RRGS) to systematically identify SSR markers. The resulting set of microsatellites consisted mainly of trinucleotide (56.10%) and dinucleotide (35.23%) repeats, with each motif consisting of 5 to 8 repeats. We then evaluated marker sensitivity and specificity based on samples of 48 flax isolates obtained from northeastern China. Using the new SSR panel, the results demonstrated that fiber flax and oilseed flax varieties clustered into two well separated groups. The novel SSR markers developed in this study show potential value for selection of varieties for use in flax breeding programs.

Alfalfa species Medicago sativa L. (MS) and Medicago falcata L. (MF), globally prominent perennial leguminous forages, hold substantial economic value. However, our comprehension of the molecular mechanisms governing their resistance to cold stress remains limited. To address this knowledge gap, we scrutinized and compared MS and MF cold-stress responses at the molecular level following 24 h and 120 h low-temperature exposure (4 °C). Our study revealed that MF had superior physiological resilience to cold stress compared with MS, and its morphology was healthier under cold stress, and its malondialdehyde content and superoxide dismutase activity increased, first, and then decreased, while the soluble sugar content continued to accumulate. Transcriptome analysis showed that after 120 h of exposure, there were different gene-expression patterns between MS and MF, including 1274 and 2983 genes that were continuously up-regulated, respectively, and a total of 923 genes were included, including star cold-resistant genes such as ICE1 and SIP1. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed numerous inter-species differences in sustained cold-stress responses. Notably, MS-exclusive genes included a single transcription factor (TF) gene and several genes associated with a single DNA repair-related pathway, whereas MF-exclusive genes comprised nine TF genes and genes associated with 14 pathways. Both species exhibited high-level expression of genes encoding TFs belonging to AP2-EREBP, ARR-B, and bHLH TF families, indicating their potential roles in sustaining cold resistance in alfalfa-related species. These findings provide insights into the molecular mechanisms governing cold-stress responses in MS and MF, which could inform breeding programs aimed at enhancing cold-stress resistance in alfalfa cultivars.

Gummy stem blight (GSB) is a pervasive disease that causes considerable economic losses in cucurbit crops and poses a significant threat to pumpkin production. However, the molecular interaction mechanisms between pumpkin and the pathogen remain largely unexplored. In our previous research, we isolated and identified Stagonosporopsis cucurbitacearum (Sc) as the primary causative agent of pumpkin stem blight in Northeast China. Through whole-genome analysis, we identified several pathogenic genes associated with Sc infection in pumpkins. In this study, we performed a comprehensive comparative transcriptomic and metabolomic analysis of unvaccinated and Sc-inoculated pumpkins. We observed distinct differences in gene expression profiles, with these genes being significantly enriched in pathways related to plant–pathogen interactions, phytohormone signal transduction, and metabolic processes, including phenylpropanoid biosynthesis. Joint analysis revealed that the phenylpropanoid biosynthesis pathway was activated in Sc-infected pumpkins. Notably, two metabolites involved in the phenylpropanoid and flavonoid biosynthesis pathways, p-coumaric acid and quercetin, exhibited significant upregulation, suggesting their potential roles in conferring resistance to GSB. These findings enhance our understanding of the molecular mechanisms underlying the defense response against GSB infection in pumpkins and may provide valuable insights for developing strategies to control GSB disease.