Soil salinity constrains agricultural development in arid regions. Flax is an economically important crop in many countries, and screening or breeding salinity-resistant flax cultivars is necessary. Based on the previous screening of flaxseed cultivars C71 (salt-sensitive) and C116 (salt-tolerant) as test materials, flax seedlings stressed with different concentrations of NaCl (0, 100, 150, 200, and 250 mmol/L) for 21 days were used to investigate the effects of salt stress on the growth characteristics, osmotic regulators, and antioxidant capacity of these flax seedlings and to reveal the adaptive responses of flax seedlings to salt stress. The results showed that plant height and root length of flax were inhibited, with C116 showing lower growth than C71. The concentrations of osmotic adjustment substances such as soluble sugars, soluble proteins, and proline were higher in the resistant material, C116, than in the sensitive material, C71, under different concentrations of salt stress. Consistently, C116 showed a better rapid scavenging ability for reactive oxygen species (ROS) and maintained higher activities of antioxidant enzymes to balance salt injury stress by inhibiting growth under salt stress. A transcriptome analysis of flax revealed that genes related to defense and senescence were significantly upregulated, and genes related to the growth and development processes were significantly downregulated under salt stress. Our results indicated that one of the important adaptations to tolerance to high salt stress is complex physiological remediation by rapidly promoting transcriptional regulation in flax.

Functional U6 promoters are widely utilized in CRISPR gene editing systems for crops. The identification of endogenous U6 promoter activity and the establishment of CRISPR/Cas9 gene editing systems in various crops can enhance the efficiency and accuracy of gene editing in molecular breeding. In this study, four U6 snRNAs were identified in the genome of the oil flax (Linum usitatissimum L.) cultivar Longya 10, which exhibit high homology with the promoter regions of Arabidopsis thaliana U6 snRNA. We cloned and constructed fusion expression vectors with U6 promoter-driven dual-luciferase reporter genes. Transient transformation of flax and Nicotiana benthamiana was performed to measure the relative activity of dual luciferase. The U6-4 on chromosome 14 showed the highest transcriptional activity. Truncations of varying lengths from the 5′ end of this promoter were tested, revealing that a 342 bp U6 promoter fragment possesses high transcriptional activity and an optimal length. Subsequently, we constructed a CRISPR/Cas9 gene editing vector with LuU6-5P/AtU6-P driving LusPDS sgRNA. Agrobacterium-mediated infection of flax hypocotyls yielded transgenic albino flax shoots. DNA from these shoots was used as a template to amplify LusPDS fragments, which were then sequenced. Sequencing analysis revealed that CRISPR/Cas9 vectors using Lu14U6-4-5P achieved higher editing frequencies at LusPDS compared to AtU6-P-driven systems.

Endophytic bacteria play a crucial role in the life cycle of Spermatophyta, and exploring the beneficial interactions between seeds and endophytic bacteria is an effective strategy for sustainable agricultural development and improved crop productivity. In this study, we employed Illumina Hiseq high-throughput sequencing technology to analyze the amplified fragments of microbial 16S rRNA sequences from melon seeds of MR-1, HH and their F₁ generation, which displayed varying levels of resistance to bacterial fruit blotch disease. Initially, we extracted endophytes from eight melon samples and performed sequencing, obtaining an average of 84,758 effective tags per sample. At the 97% similarity level, the number of operational taxonomic units (OTUs) derived from melon seed endophytes ranged from 447 to 492. After filtering out low-level OTUs, we obtained an average of 65,866 valid tags from the eight samples, representing approximately 160 genera and 167 species across eight phyla. It was found that the composition of the endophyte communities in the eight samples was basically similar, and their abundance showed some variability. Furthermore, we utilized the KO and COG databases to functionally predict the genes of endophytes in melon seeds. The analysis revealed a significant enrichment of genes associated with pathways related to protein synthesis, carbohydrate metabolism, substance transport, and metabolite synthesis. These findings greatly contribute to our understanding of endophytic bacteria in melon seeds and serve as a vital reference for the selection and breeding of high-quality melon seeds, as well as the prevention of seed diseases.