Background: Industrial hemp is an important industrial crop and has strong resistance to saline-alkaline stress. However, research on the industrial hemp response to NaHCO₃ stress is limited. Therefore, the response mechanisms of industrial hemp under NaHCO₃ stress were analysed through miRNA–mRNA regulatory networks. Results: Seedlings of two salt–alkali tolerant and sensitive varieties were cultured in a solution containing 100 mM NaHCO₃ and randomly sampled at 0, 6, 12, and 24 h. With prolonged NaHCO₃ stress, the seedlings gradually withered, and the contents of jasmonic acid, lignin, trehalose, soluble protein, peroxidase, and superoxide dismutase in the roots increased significantly. The abscisic acid content decreased and then gradually increased. Overall, 18,215 mRNAs and 74 miRNAs were identified as differentially expressed under NaHCO₃ stress. The network showed that 230 miRNA–mRNA interactions involved 16 miRNAs and 179 mRNAs, including some key hub novel mRNAs of these crucial pathways. Carbon metabolism, starch, sucrose metabolism, plant hormone signal transduction, and the spliceosome (SPL) were crucial pathways in industrial hemp's response to NaHCO₃ stress. Conclusions: It is speculated that industrial hemp can regulate SPL pathway by upregulating miRNAs such as novel_miR_179 and novel_miR_75, thus affecting starch and sucrose metabolism, plant hormone signal transduction and carbon metabolism and improving key physiological indices such as jasmonic acid content, trehalose content, and peroxidase and superoxide dismutase activities under NaHCO₃ stress.

Hemp (Cannabis sativa L.), an ancient crop, is a significant source of high-quality fiber that primarily caters to the textile industry worldwide. Fiber content is a crucial quantitative trait for evaluating fiber yield in hemp. Understanding the genetic mechanisms involved in hemp breeding is essential for improving yield. In this study, we developed 660 F1 plants from a cross between Jindao-15 (high fiber content fiber-use variety) and Fire No.1 (low fiber content fiber-use variety), and thirty plants each with high and low fiber content were selected from 305 monoecious plants of this population according to 5%-10% of population size for quantitative traits. The DNA from these plants was extracted to establish two bulk DNA pools and then subjected to the restriction digestion by the enzymes RsaI and HaeIII to obtain 314–364 bp digestion fragments and subjected to sequencing using specific length amplified fragment sequencing (SLAF-seq). Finally, we successfully developed 368,404 SLAF tags, which led to the detection of 25,133 high-quality SNPs. Combing with the resequencing results of parents, the SNPs of mixed pools were then subjected to the SNP-Index correlation algorithm, which revealed four candidate regions related to fiber content traits on Chromosome 1, with a length of 8.68 Mb and containing 389 annotated genes. The annotation information and the comparison results identified 15 genes that were highly likely to modulate the fiber content of hemp. Further, qPCR validation identified six genes (LOC115705530, LOC115705875, LOC115704794, LOC115705371, LOC115705688 and LOC115707511) that were highly positively correlated with influencing the hemp fiber content. These genes were involved in the transcription regulation, auxin and water transportion, one carbon and sugar metabolism. And non-synnoumous mutation SNPs which may play vital role in influencing the fiber content were detected in LOC115705875, LOC115704794, LOC115705688 and LOC115707511. Thus, our study highlights the importance of the combined use of SLAF-Seq and Bulked Segregant analysis (BSA) to locate genes related to hemp fiber content rapidly. Hence, our study provides novel mechanistic inputs for the fast identification of genes related to important agronomic traits of hemp and other crops catering to the textile industry.

Hemp (Cannabis sativa L.), an ancient crop, is a significant source of high-quality fiber that primarily caters to the textile industry worldwide. Compared to other fiber crops, hemp is an environmentally friendly fiber crop which requires fewer pesticides and purifies the soil during cultivation. Fiber content is a crucial quantitative trait for evaluating fiber yield in hemp. Understanding the genetic mechanisms involved in hemp breeding is essential for improving yield. In this study, to investigate these underlying mechanisms, we developed 660 F1 plants from a cross between Jindao-15(high fiber content fiber-use variety)and Fire No.1༈low fiber content fiber-use variety༉, and thirty plants each with high and low fiber content were selected from 305 monoecious plants of this population according to 5 %-10 % of population size for quantitative traits. The DNA from these plants was extracted to establish two bulk DNA pools. The DNA was then subjected to the restriction digestion by the enzymes RsaI and HaeIII to obtain 314–364 bp digestion fragments and subjected to sequencing using specific length amplified fragment sequencing (SLAF-seq). Then, each fragment was labeled with specific SLAF tags, and single nucleotide polymorphisms (SNPs) were identified to determine the candidate regions related to fiber content through marker association analysis of genotype frequency differences between the mixed pools of DNA. The gene annotation results identified the candidate genes responsible for the fiber content of hemp. In this study, we successfully developed 368,404 SLAF tags, which led to the detection of 389,687 SNPs. These SNPs were then subjected to the SNP-Index correlation algorithm, which revealed four candidate regions related to fiber content traits on Chromosome 1, with a length of 8.68 Mb and containing 389 annotated genes. We found that 199 non-synonymous mutations which change the amino acids sequences existed in the parent population. The annotation information and the comparison results identified 15 genes that were highly likely to modulate the fiber content of hemp. Further, qPCR validation identified six genes (LOC115705530, LOC115705875, LOC115704794, LOC115705371, LOC115705688 and LOC115707511) that were highly positively correlated with influencing the hemp fiber content. These genes were involved in the transcription regulation, auxin and water transportion, one carbon and sugar metabolism. Thus, our study highlights the importance of the combined use of SLAF-Seq and Bulked Segregant analysis (BSA) to locate genes related to hemp fiber content rapidly. Hence, our study provides novel mechanistic inputs for the fast identification of genes related to important agronomic traits of hemp and other crops catering to the textile industry.