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Background Cannabis, an important industrial crop, has a high sensitivity to photoperiods. The flowering time of cannabis is one of its important agronomic traits, and has a significant effect on its yield and quality. The CONSTANS-like (COL) gene plays a key role in the regulation of flowering in this plant. However, the specific roles of the COL gene family in cannabis are still unknown. Results In this study, 13 CsCOL genes were identified in the cannabis genome. Phylogenetic analysis implied that the CsCOL proteins were divided into three subgroups, and each subgroup included conserved intron/exon structures and motifs. Chromosome distribution analysis showed that 13 CsCOL genes were unevenly distributed on 7 chromosomes, with chromosome 10 having the most CsCOL members. Collinearity analysis showed that two syntenic gene pairs of CsCOL4 and CsCOL11 were found in both rice and Gossypium raimondii. Of the 13 CsCOL genes, CsCOL6 and CsCOL12 were a pair of tandem duplicated genes, whereas CsCOL8 and CsCOL11 may have resulted from segmental duplication. Furthermore, tissue-specific expression showed that 10 CsCOL genes were preferentially expressed in the leaves, 1 CsCOL in the stem, and 2 CsCOL in the female flower. Most CsCOL exhibited a diurnal oscillation pattern under different light treatment. Additionally, sequence analysis showed that CsCOL3 and CsCOL7 exhibited amino acid differences among the early-flowering and late flowering cultivars. Conclusion This study provided insight into the potential functions of CsCOL genes, and highlighted their roles in the regulation of flowering time in cannabis. Our results laid a foundation for the further elucidation of the functions of COL genes in cannabis.

Flax (Linum usitatissimum L.) is an important industrial crop and is widely cultivated in North America, Europe, and China for its fiber and oil. Identifying flax molecular markers is a vital step towards improving flax yield and quality via marker-assisted breeding. Simple sequence repeat (SSR) markers have proven to be the most valuable type of genetic marker for molecular breeding and genetic diversity studies. However, the development of genome-wide SSRs in flax has not yet been reported, which limits their use in molecular breeding. In this study, we screened 25,871 SSR motifs from L. usitatissimum, mainly consisting of trinucleotide (52.8%) and dinucleotide (36.1%) repeats. Based on the 24,375 SSR motifs, 71,184 primers pairs of SSR markers were designed for the flax genome, covering the whole genome at a density of 225.3/Mb. Furthermore, 96 pairs of SSR markers from different chromosomes were used to assess a panel of 26 flax accessions obtained from different parts of the world. The 21 SSR markers exhibited polymorphisms across the 26 flax accessions, and the flax varieties were accurately clustered into two groups and two subgroups corresponding to their type (wild species or cultivar) and use (fiber or oilseed). This study demonstrates the potential value in analyzing genetic diversity in flax, and the large-scale development of SSR markers developed in this study will facilitate future molecular analyses in flax.

Backgroud: Heavy metal pollutant, Cadmium (Cd), is an inorganic pollutant in China. Hemp (Cannabis sativa L.) is an important fiber crop to remediate heavy metal-contaminated soils. The MYB family is one of the largest and most important gene families that influences plant growth and produce secondary metabolites. Results: 115 CsMYB genes were identified in the hemp genome. The 1R-MYB subfamily had 17 genes, the 2R-MYB subfamily 88 genes, and the 3R-MYB subfamily 8 genes. The synteny analysis of the CsMYB genes indicated that there were 3 pairs of tandem repeats, 21 pairs of segmental duplication, 6 CsMYB genes present before species differentiation, and 60 genes belonging to the hemp-specific CsMYB genes. 7 CsMYB genes were identified to influence the response to Cd stress by combining the transcriptome data of two hemp species under Cd stress. Based on the changes in the Cannabinoid content of hemp under Cd stress, the expression of different CsMYB genes in hemp with high and low cannabidiol (CBD) contents, and tissue-specific expression, it was inferred that CsMYB024 may be affected by Cd stress and mediate the CBD synthesis pathway.Conclusions: This study provides a comprehensive analysis of the hemp MYB family. These results should be helpful in understanding of their potential functions in Cd-Stress Response and the Regulation of Cannabinoid Biosynthesis in Hemp. In addition, lays the foundation for the further study of biological functions of CsMYBs in hemp.

It is important to develop DNA markers closely linked to the first flower node for molecular marker-assisted selection in kenaf breeding. Kenaf (Hibiscus cannabinus L.) is an annual, multipurpose industrial crop with a worldwide distribution. The higher the node of the first flower, the greater is the fiber yield. In this study, a population of 130 F2 individuals was constructed through the cross of K215(♀)×K89(♂). Twenty-five individuals with higher first flower node and twenty-five individuals with lower first flower node were chosen and their DNA were pooled to construct two bulked DNA pools according to the phenotype. Specific-locus amplified fragment sequencing (SLAF-seq) combined with bulked segregant analysis (BSA) was used to identify candidate DNA markers closely linked to the first flower node. Sixteen single-nucleotide polymorphism (SNP) loci were obtained from 11 related SLAF markers associated with the first flower node. SNP locus validation was performed using Sanger sequencing method. The SNP locus S961-2 in Sanger sequencing by using the primer M41961 was consistent with the SNP locus in the related SLAF-seq. The accuracy rate of the genotypes consistent with the first flower node was 91.2% (31/34). To our knowledge, S961-2 is the first SNP locus to be identified that is closely linked to the first flower node. This SNP locus may be useful for marker-assisted selection in breeding of high fiber yielding varieties of kenaf.

For the dissection and identification of the molecular response mechanisms to salt stress in cannabis, an experiment was conducted surveying the diversity of physiological characteristics. RNA-seq profiling was carried out to identify differential expression genes and pathway which respond to salt stress in different cannabis materials. The result of physiological diversity analyses showed that it is more sensitive to proline contents in K94 than in W20, 6 h was needed to reach the maximum in K94, compared to 12 h in W20. For profiling 0–72 h after treatment, a total of 10,149 differentially expressed genes were identified, and 249 genes exhibited significantly diverse expression levels in K94, which were clustered in plant hormone signal transduction and the MAPK signaling pathway. A total of 371 genes showed significant diversity expression variations in W20, which were clustered in the phenylpropanoid biosynthesis and plant hormone signal transduction pathway. The pathway enrichment by genes which were identified in K94 and W20 showed a similar trend to those clustered in plant hormone signal transduction pathways and MAPK signaling. Otherwise, there were 85 genes which identified overlaps between the two materials, indicating that these may be underlying genes related to salt stress in cannabis. The 86.67% agreement of the RNA-seq and qRT-PCR indicated the accuracy and reliability of the RNA-seq technique. Additionally, the result of physiological diversity was consistent with the predicted RNA-seq-based findings. This research may offer new insights into the molecular networks mediating cannabis to respond to salt stress.

Drought is the main environmental factor impairing hemp growth and yield. In order to decipher the molecular responses of hemp to drought stress, transcriptome changes of drought-stressed hemp (DS1 and DS2), compared to well-watered control hemp (CK1 and CK2), were studied with RNA-Seq technology. RNA-Seq generated 9.83, 11.30, 11.66, and 11.31 M clean reads in the CK1, CK2, DS1, and DS2 libraries, respectively. A total of 1292 differentially expressed genes (DEGs), including 409 (31.66%) upregulated and 883 (68.34%) downregulated genes, were identified. The expression patterns of 12 selected genes were validated by qRT-PCR, and the results were accordant with Illumina analysis. Gene Ontology (GO) and KEGG analysis illuminated particular important biological processes and pathways, which enriched many candidate genes such as NAC, B3, peroxidase, expansin, and inositol oxygenase that may play important roles in hemp tolerance to drought. Eleven KEGG pathways were significantly influenced, the most influenced being the plant hormone signal transduction pathway with 15 differentially expressed genes. A similar expression pattern of genes involved in the abscisic acid (ABA) pathway under drought, and ABA induction, suggested that ABA is important in the drought stress response of hemp. These findings provide useful insights into the drought stress regulatory mechanism in hemp.

Boehmeria tricuspis includes sexually reproducing diploid and apomictic triploid individuals. Previously, we established that triploid B. tricuspis reproduces through obligate diplospory. To understand the molecular basis of apomictic development in B. tricuspis, we sequenced and compared transcriptomic profiles of the flowers of sexual and apomictic plants at four key developmental stages. A total of 283,341 unique transcripts were obtained from 1,463 million high-quality paired-end reads. In total, 18,899 unigenes were differentially expressed between the reproductive types at the four stages. By classifying the transcripts into gene ontology categories of differentially expressed genes, we showed that differential plant hormone signal transduction, cell cycle regulation, and transcription factor regulation are possibly involved in apomictic development and/or a polyploidization response in B. tricuspis. Furthermore, we suggest that specific gene families are possibly related to apomixis and might have important effects on diplosporous floral development. These results make a notable contribution to our understanding of the molecular basis of diplosporous development in B. tricuspis.

Cannabis sativa L. is an important economic plant for the production of food, fiber, oils, and intoxicants. However, lack of sufficient simple sequence repeat (SSR) markers has limited the development of cannabis genetic research. Here, large-scale development of expressed sequence tag simple sequence repeat (EST-SSR) markers was performed to obtain more informative genetic markers, and to assess genetic diversity in cannabis (Cannabis sativa L.). Based on the cannabis transcriptome, 4,577 SSRs were identified from 3,624 ESTs. From there, a total of 3,442 complementary primer pairs were designed as SSR markers. Among these markers, trinucleotide repeat motifs (50.99%) were the most abundant, followed by hexanucleotide (25.13%), dinucleotide (16.34%), tetranucloetide (3.8%), and pentanucleotide (3.74%) repeat motifs, respectively. The AAG/CTT trinucleotide repeat (17.96%) was the most abundant motif detected in the SSRs. One hundred and seventeen EST-SSR markers were randomly selected to evaluate primer quality in 24 cannabis varieties. Among these 117 markers, 108 (92.31%) were successfully amplified and 87 (74.36%) were polymorphic. Forty-five polymorphic primer pairs were selected to evaluate genetic diversity and relatedness among the 115 cannabis genotypes. The results showed that 115 varieties could be divided into 4 groups primarily based on geography: Northern China, Europe, Central China, and Southern China. Moreover, the coefficient of similarity when comparing cannabis from Northern China with the European group cannabis was higher than that when comparing with cannabis from the other two groups, owing to a similar climate. This study outlines the first large-scale development of SSR markers for cannabis. These data may serve as a foundation for the development of genetic linkage, quantitative trait loci mapping, and marker-assisted breeding of cannabis.