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The bHLH transcription factors play pivotal roles in plant growth and development, production of secondary metabolites and responses to various environmental stresses. Although the bHLH genes have been well studied in model plant species, a comprehensive investigation of the bHLH genes is required for tobacco with newly obtained high-quality genome. In the present study, a total of 309 NtbHLH genes were identified and can be divided into 23 subfamilies. The conserved amino acids which are essential for their function were predicted for the NtbHLH proteins. Moreover, the NtbHLH genes were conserved during evolution through analyzing the gene structures and conserved motifs. A total of 265 NtbHLH genes were localized in the 24 tobacco chromosomes while the remained 44 NtbHLH genes were mapped to the scaffolds due to the complexity of tobacco genome. Moreover, transcripts of NtbHLH genes were obviously tissue-specific expressed from the gene-chip data from 23 tobacco tissues, and expressions of 20 random selected NtbHLH genes were further confirmed by quantitative real-time PCR, indicating their potential functions in the plant growth and development. Importantly, overexpressed NtbHLH86 gene confers improve drought tolerance in tobacco indicating that it might be involved in the regulation of drought stress. Therefore, our findings here provide a valuable information on the characterization of NtbHLH genes and further investigation of their functions in tobacco.

Tobacco (Nicotiana tabacum L.) is an economic crop and a model organism for studies of plant biology and genetics. As an allotetraploid plant generated from interspecific hybridization, tobacco has a massive genome (4.5 Gb). Recently, a genetic map with 45,081 single nucleotide polymorphism (SNP) markers was constructed using whole-genome sequencing data for a tobacco population including 274 individuals. This provides a basis for quantitative trait locus (QTL) mapping and genomic selection, which have been widely applied to other crops but have not been feasible in tobacco. Based on this high-density genetic map, we identified QTLs associated with important agronomic traits, chemical compounds in dry leaves, and hazardous substances in processed cigarettes. The LOD values for major QTLs were highest for agronomic traits, followed by chemical compounds and hazardous substances. In addition to the identification of molecular markers, we evaluated genomic selection models and found that BayesB had the highest prediction accuracy for the recombinant inbred line population. Our results offer new insights into the genetic mechanism underlying important traits, such as agronomic traits and quality-related chemical compounds in tobacco, and will be able to support the application of molecular breeding to tobacco.

Backcrossing is a powerful tool for plant breeding. The improved marker-assisted backcrossing intends to transfer targeted genes or quantitative trait loci (QTLs) of interest from a donor parent into a recurrent parent. In this study, a tobacco BC4F3 population was generated using Y3 and K326 as hybrid parents and YF1-1 as F1 parents. High-throughput sequencing data of 381 pedigree populations were used to construct high-density genetic maps containing 24 142 high-quality single nucleotide polymorphism (SNP) markers with an average genetic distance of 0.59 cM. A genome module analysis was then performed for all the offspring. A total of forty-three candidate QTLs for six agronomics traits were identified. This study provides original biomarkers for tobacco breeding and offers clues for prospective backcrossing applications in other plants.

MADS-box genes play a pivotal role in various processes, including floral and seed development, controlling flowering time, regulation of fruits ripening, and respond to abiotic and biotic stressors in planta. Tobacco (Nicotiana tabacum) has been widely used as a model plant for analyzing the gene function, however, there has been less information on the regulation of flowering, and the associated genes. In the present study, a total of 168 NtMADS-box genes were identified from tobacco, and their phylogenetic relationship, chromosome locations, and gene structures were further analyzed. NtMADS-box genes can be clustered into four sub-families of M&alpha, M&gamma, MIKC*, and MIKCC. A total of 111 NtMADS-box genes were distributed on 20 chromosomes, and 57 NtMADS-box genes were located on the unanchored scaffolds due to the complex and incomplete assembly of the tobacco genome. Expression profiles of NtMADS-box genes by microarray from 23 different tissues indicated that members in different NtMADS-box gene subfamilies might play specific roles in the growth and flower development, and the transcript levels of 24 NtMADS-box genes were confirmed by quantitative real-time PCR. Importantly, overexpressed NtSOC1/NtMADS133 could promote early flowering and dwarfism in transgenic tobacco plants. Therefore, our findings provide insights on the characterization of NtMADS-box genes to further study their functions in plant development.

Leaf chemistry traits are some of the key factors influencing tobacco quality, which can be significantly reduced by lower chemical components in cured leaf. To improve tobacco quality through breeding, genetic diversity analysis, population structure analysis, and genome-wide association studies were performed in a panel of 347 tobacco germplasms and the markers associated with five leaf chemistry traits, including total sugar (TS), reducing sugar (RS), total nitrogen (TN), nicotine (NIC), and total potassium (TP) contents were identified. Four groups were classified at a genetic distance of 0.316 by genetic diversity analysis based on coefficient parameter NEI72 using a program NTSYS-pc2.10e, whereas four well-differentiated subpopulations were postulated in the 347 tobacco accessions. A total of 47 target trait-associated SNPs was detected in at least three environments as well as the best linear unbiased predictions (BLUPs) across all environments, among which two, two, four, six, and one highly suggestive associated SNPs were repeatedly detected in all environments and BLUPs for TS, RS, TN, NIC, and TP, respectively. On the basis of the phenotypic effects of the alleles corresponding to suggestive associated SNPs, five tobacco accessions harboring favorable alleles with elite phenotypic performance in leaf chemistry traits were identified. The results could facilitate quality tobacco breeding for higher leaf chemistry trait contents through molecular marker-assisted approaches.

Tobacco (Nicotiana tabacum L.) is an essential commercial crop and an ideal model plant for biological mechanism studies. As an allopolyploid species, tobacco harbors a massive and complex genome, which makes the application of molecular markers complicated and challenging. In our study, we performed whole-genome sequencing of an intraspecific recombinant inbred line (RIL) population, a F1 generation and their parents. With the Nicotiana tabacum (K326 cultivar) genome as reference, a total of 45,081 markers were characterized to construct the genetic map, which spanned a genetic distance of 3486.78 cM. Evaluation of a two-dimensional heat map proved the high quality of the genetic map. We utilized these markers to anchor scaffolds and analyzed the ancestral genome origin of linkage groups (LGs). Furthermore, such a high-density genetic map will be applied for quantitative trait locus (QTL) detection, gene localization, genome-wide association studies (GWAS), and marker-assisted breeding in tobacco.

Tobacco (Nicotiana tabacum L.), particularly flue-cured tobacco, is one of the most economically important nonfood crops and is also an important model system in plant biotechnology. Despite its importance, only limited molecular marker resources are available for genome analysis, genetic mapping, and breeding. Simple sequence repeats (SSR) are one of the most widely-used molecular markers, having significant advantages including that they are generally co-dominant, easy to use, abundant in eukaryotic organisms, and produce highly reproducible results. In this study, based on the genome sequence data of flue-cured tobacco (K326), we developed a total of 13,645 mostly novel SSR markers, which were working in a set of eighteen tobacco varieties of four different types. A mapping population of 213 backcross (BC1) individuals, which were derived from an intra-type cross between two flue-cured tobacco varieties, Y3 and K326, was selected for mapping. Based on the newly developed SSR markers as well as published SSR markers, we constructed a genetic map consisting of 626 SSR loci distributed across 24 linkage groups and covering a total length of 1120.45 cM with an average distance of 1.79 cM between adjacent markers, which is the highest density map of flue-cured tobacco till date.

Background Tobacco (Nicotiana tabacum L.) is an important model system, which has been widely used in plant physiological studies and it is particularly useful as a bioreactor. Despite its importance, only limited molecular marker resources are available for genome analysis, genetic mapping and breeding. Restriction-site associated DNA sequencing (RAD-seq) is a powerful new method for targeted sequencing across the genomes of many individuals. This approach has broad potential for genetic analysis through linkage mapping. Results We constructed a RAD library using genomic DNA from a BC1 backcross population. Sequencing of 196 individuals was performed on an Illumina HiSeq 2500. Two linkage maps were constructed, one with a reference genome and another, termed as de novo identification of single nucleotide polymorphism (SNP) by RAD-seq, without a reference genome. Overall, 4138 and 2162 SNP markers with a total length of 1944.74 and 2000.9 cM were mapped to 24 linkage groups in the genetic maps based on reference genome and without reference, respectively. Conclusions Using two different SNP discovery methods based on next generation RAD sequencing technology, we have respectively mapped 2162 and 4318 SNPs in our backcross population. This study gives an excellent example for high density linkage map construction, irrespective of genome sequence availability, and provides saturated information for downstream genetic investigations such as quantitative trait locus analyses or genomic selection (e.g. bioreactor suitable cultivars). Electronic supplementary material The online version of this article (doi:10.1186/s40709-015-0034-3) contains supplementary material, which is available to authorized users.