Improvement in sesame drought tolerance at seedling stage is important for yield stability. Genetic approaches combing with conventional breeding is the most effective way to develop drought-tolerant cultivars. In this study, three traits and their relative values, including seedling weight (SW), shoot length (SL) and root length (RL), were evaluated under control and osmotic conditions in a recombinant inbred line (RIL) population derived from cross of Zhushanbai and Jinhuangma. Significant variation and high broad sense heritability were observed for all traits except SW under stress condition in the population. With this population, a high-density linkage map with 1354 bin markers was constructed through whole genome re-sequencing (WGS) strategy. Quantitative trait loci (QTL) mapping was performed for all the traits. A total of 34 QTLs were detected on 10 chromosomes. Among them, 13 stable QTLs were revealed in two independent experiments, eight of them were associated with traits under water stress condition. One region on chromosome 12 related to RL under osmotic condition and relative RL had the highest LOD value and explained the largest phenotypic variation among all the QTLs detected under water stress condition. These findings will provide new genetic resources for molecular improvement of drought tolerance and candidate gene identification in sesame.

Background: The plant trihelix gene family is among the earliest discovered transcription factor families, and it is vital in modulating light, plant growth, and stress responses. Methods: The identification and characterization of trihelix family members in the sesame genome were analyzed by bioinformatics methods, and the expression patterns of sesame trihelix genes were assessed by quantitative real-time PCR. Results: There were 34 trihelix genes discovered in the genome of sesame, which were irregularly distributed among 10 linkage groups. Also, the genome contained 5 duplicate gene pairs. The 34 trihelix genes were divided into six sub-families through a phylogenetic study. A tissue-specific expression revealed that SiTH genes exhibited spatial expression patterns distinct from other trihelix genes in the same subfamily. The cis-element showed that the SiTHs gene promoter contained various elements associated with responses to hormones and multiple abiotic stresses. Additionally, the expression patterns of 8 SiTH genes in leaves under abiotic stresses demonstrated that all selected genes were significantly upregulated or downregulated at least once in the stress period. Furthermore, the SiTH4 gene was significantly induced in response to drought and salt stress, showing that SiTH genes may be engaged in the stress response mechanisms of sesame. Conclusion: These findings establish a foundation for further investigation of the trihelix gene-mediated response to abiotic stress in sesame.

BackgroundImprovement in sesame (Sesamum indicum L.) drought tolerance at seedling stage is important for yield stability. Genetic approaches combing with conventional breeding is the most effective way to develop drought-tolerant cultivars. So far, only a few studies have been reported to reveal gene/ quantitative trait loci (QTL) controlling drought tolerance in sesame. To identify the genomic regions associated with drought tolerance, we constructed a high-density genetic map using a recombinant inbred line (RIL) population through whole genome re-sequencing (WGRS) technique. QTLs contributing to three seedling traits were identified under both non-stress and water stress conditions.ResultsThree drought tolerance related traits and their relative values (the ratio of value under stress to value under control condition), including seedling weight (SW), shoot length (SL) and root length (RL), were evaluated under control and PEG-induced osmotic conditions at seedling stage in a RIL population derived from cross of Zhushanbai (ZSB) and Jinhuangma (JHM). Significant variation and high broad sense heritability were observed for all traits except SW under stress condition in the population. With this population, a high-density linkage map with 1354 bin markers was constructed through WGRS strategy. Composite interval mapping analysis was performed for all the traits as well as their relative phenotypic data. A total of 34 QTLs were detected for these traits under both conditions and their relative values, and 13 stable QTLs associated with seven traits were revealed in two independent experiments, explaining on average, 4.95-16.26% of phenotypic variation for each QTL. Four of them contributed more than 10% of phenotypic variation. One region on chromosome 12 contained two major QTLs related to RL under osmotic condition and relative RL. Seven candidate genes underlying major QTLs for drought tolerance were identified according to gene descriptions and variations between parents.ConclusionThe current study reports the first QTL mapping of drought tolerance related traits through a RIL population and first QTL detection of root related trait (root length) in sesame. These findings will provide new genetic resources for molecular improvement of drought tolerance and candidate gene identification in sesame.