Updated sesame genome assembly and fine mapping of plant height and seed coat color QTLs using a new high-density genetic map.
ABSTRACT: Sesame is an important high-quality oil seed crop. The sesame genome was de novo sequenced and assembled in 2014 (version 1.0); however, the number of anchored pseudomolecules was higher than the chromosome number (2n?=?2x?=?26) due to the lack of a high-density genetic map with 13 linkage groups.We resequenced a permanent population consisting of 430 recombinant inbred lines and constructed a genetic map to improve the sesame genome assembly. We successfully anchored 327 scaffolds onto 13 pseudomolecules. The new genome assembly (version 2.0) included 97.5 % of the scaffolds greater than 150 kb in size present in assembly version 1.0 and increased the total pseudomolecule length from 233.7 to 258.4 Mb with 94.3 % of the genome assembled and 97.2 % of the predicted gene models anchored. Based on the new genome assembly, a bin map including 1,522 bins spanning 1090.99 cM was generated and used to identified 41 quantitative trait loci (QTLs) for sesame plant height and 9 for seed coat color. The plant height-related QTLs explained 3-24 % the phenotypic variation (mean value, 8 %), and 29 of them were detected in at least two field trials. Two major loci (qPH-8.2 and qPH-3.3) that contributed 23 and 18 % of the plant height were located in 350 and 928-kb spaces on Chr8 and Chr3, respectively. qPH-3.3, is predicted to be responsible for the semi-dwarf sesame plant phenotype and contains 102 candidate genes. This is the first report of a sesame semi-dwarf locus and provides an interesting opportunity for a plant architecture study of the sesame. For the sesame seed coat color, the QTLs of the color spaces L*, a*, and b* were detected with contribution rates of 3-46 %. qSCb-4.1 contributed approximately 39 % of the b* value and was located on Chr4 in a 199.9-kb space. A list of 32 candidate genes for the locus, including a predicted black seed coat-related gene, was determined by screening the newly anchored genome.This study offers a high-density genetic map and an improved assembly of the sesame genome. The number of linkage groups and pseudomolecules in this assembly equals the number of sesame chromosomes for the first time. The map and updated genome assembly are expected to serve as a platform for future comparative genomics and genetic studies.
Project description:Seed coat color is an important agronomic trait in sesame, as it is associated with seed biochemical properties, antioxidant content and activity and even disease resistance of sesame. Here, using a high-density linkage map, we analyzed genetic segregation and quantitative trait loci (QTL) for sesame seed coat color in six generations (P1, P2, F1, BC1, BC2 and F2). Results showed that two major genes with additive-dominant-epistatic effects and polygenes with additive-dominant-epistatic effects were responsible for controlling the seed coat color trait. Average heritability of the major genes in the BC1, BC2 and F2 populations was 89.30%, 24.00%, and 91.11% respectively, while the heritability of polygenes was low in the BC1 (5.43%), in BC2 (0.00%) and in F2 (0.89%) populations. A high-density map was constructed using 724 polymorphic markers. 653 SSR, AFLP and RSAMPL loci were anchored in 14 linkage groups (LG) spanning a total of 1,216.00 cM. The average length of each LG was 86.86 cM and the marker density was 1.86 cM per marker interval. Four QTLs for seed coat color, QTL1-1, QTL11-1, QTL11-2 and QTL13-1, whose heritability ranged from 59.33%-69.89%, were detected in F3 populations using CIM and MCIM methods. Alleles at all QTLs from the black-seeded parent tended to increase the seed coat color. Results from QTLs mapping and classical genetic analysis among the P1, P2, F1, BC1, BC2 and F2 populations were comparatively consistent. This first QTL analysis and high-density genetic linkage map for sesame provided a good foundation for further research on sesame genetics and molecular marker-assisted selection (MAS).
Project description:BACKGROUND:Sesame (Sesamum indicum L., 2n?=?2x?=?26) is an important oilseed crop with high oil content but small seed size. To reveal the genetic loci of the quantitative seed-related traits, we constructed a high-density single nucleotide polymorphism (SNP) linkage map of an F2 population by using specific length amplified fragment (SLAF) technique and determined the quantitative trait loci (QTLs) of seed-related traits for sesame based on the phenotypes of F3 progeny. RESULTS:The genetic map comprised 2159 SNP markers distributed on 13 linkage groups (LGs) and was 2128.51?cM in length, with an average distance of 0.99?cM between adjacent markers. QTL mapping revealed 19 major-effect QTLs with the phenotypic effect (R2) more than 10%, i.e., eight QTLs for seed coat color, nine QTLs for seed size, and two QTLs for 1000-seed weight (TSW), using composite interval mapping method. Particularly, LG04 and LG11 contained collocated QTL regions for the seed coat color and seed size traits, respectively, based on their close or identical locations. In total, 155 candidate genes for seed coat color, 22 for seed size traits, and 54 for TSW were screened and analyzed. CONCLUSIONS:This report presents the first QTL mapping of seed-related traits in sesame using an F2 population. The results reveal the location of specific markers associated with seed-related traits in sesame and provide the basis for further seed quality traits research.
Project description:Plant height (PH) is an important agronomic trait that is closely related to soybean yield and quality. However, it is a complex quantitative trait governed by multiple genes and is influenced by environment. Unraveling the genetic mechanism involved in PH, and developing soybean cultivars with desirable PH is an imperative goal for soybean breeding. In this regard, the present study used high-density linkage maps of two related recombinant inbred line (RIL) populations viz., MT and ZM evaluated in three different environments to detect additive and epistatic effect quantitative trait loci (QTLs) as well as their interaction with environments for PH in Chinese summer planting soybean. A total of eight and 12 QTLs were detected by combining the composite interval mapping (CIM) and mixed-model based composite interval mapping (MCIM) methods in MT and ZM populations, respectively. Among these QTLs, nine QTLs viz., QPH-2, qPH-6-2MT, QPH-6, qPH-9-1ZM, qPH-10-1ZM, qPH-13-1ZM, qPH-16-1MT, QPH-17 and QPH-19 were consistently identified in multiple environments or populations, hence were regarded as stable QTLs. Furthermore, Out of these QTLs, three QTLs viz., qPH-4-2ZM, qPH-15-1MT and QPH-17 were novel. In particular, QPH-17 could detect in both populations, which was also considered as a stable and major QTL in Chinese summer planting soybean. Moreover, eleven QTLs revealed significant additive effects in both populations, and out of them only six showed additive by environment interaction effects, and the environment-independent QTLs showed higher additive effects. Finally, six digenic epistatic QTLs pairs were identified and only four additive effect QTLs viz., qPH-6-2MT, qPH-19-1MT/QPH-19, qPH-5-1ZM and qPH-17-1ZM showed epistatic effects. These results indicate that environment and epistatic interaction effects have significant influence in determining genetic basis of PH in soybean. These results would not only increase our understanding of the genetic control of plant height in summer planting soybean but also provide support for implementing marker assisted selection (MAS) in developing cultivars with ideal plant height as well as gene cloning to elucidate the mechanisms of plant height.
Project description:Subterranean clover is an important annual forage legume, whose diploidy and inbreeding nature make it an ideal model for genomic analysis in Trifolium. We reported a draft genome assembly of the subterranean clover TSUd_r1.1. Here we evaluate genome mapping on nanochannel arrays and generation of a transcriptome atlas across tissues to advance the assembly and gene annotation. Using a BioNano-based assembly spanning 512 Mb (93% genome coverage), we validated the draft assembly, anchored unplaced contigs and resolved misassemblies. Multiple contigs (264) from the draft assembly coalesced into 97 super-scaffolds (43% of genome). Sequences longer than >1 Mb increased from 40 to 189 Mb giving 1.4-fold increase in N50 with total genome in pseudomolecules improved from 73 to 80%. The advanced assembly was re-annotated using transcriptome atlas data to contain 31 272 protein-coding genes capturing >96% of the gene content. Functional characterization and GO enrichment confirmed gene expression for response to water deprivation, flavonoid biosynthesis and embryo development ending in seed dormancy, reflecting adaptation to the harsh Mediterranean environment. Comparative analyses across Papilionoideae identified 24 893 Trifolium-specific and 6325 subterranean-clover-specific genes that could be mined further for traits such as geocarpy and grazing tolerance. Eight key traits, including persistence, improved livestock health by isoflavonoid production in addition to important agro-morphological traits, were fine-mapped on the high-density SNP linkage map anchored to the assembly. This new genomic information is crucial to identify loci governing traits allowing marker-assisted breeding, comparative mapping and identification of tissue-specific gene promoters for biotechnological improvement of forage legumes.
Project description:BACKGROUND:Elymus sibiricus is an ecologically and economically important perennial, self-pollinated, and allotetraploid (StStHH) grass, widely used for forage production and animal husbandry in Western and Northern China. However, it has low seed yield mainly caused by seed shattering, which makes seed production difficult for this species. The goals of this study were to construct the high-density genetic linkage map, and to identify QTLs and candidate genes for seed-yield related traits. RESULTS:An F2 mapping population of 200 individuals was developed from a cross between single genotype from "Y1005" and "ZhN06". Specific-locus amplified fragment sequencing (SLAF-seq) was applied to construct the first genetic linkage map. The final genetic map included 1971 markers on the 14 linkage groups (LGs) and was 1866.35?cM in total. The length of each linkage group varied from 87.67?cM (LG7) to 183.45?cM (LG1), with an average distance of 1.66?cM between adjacent markers. The marker sequences of E. sibiricus were compared to two grass genomes and showed 1556 (79%) markers mapped to wheat, 1380 (70%) to barley. Phenotypic data of eight seed-related traits (2016-2018) were used for QTL identification. A total of 29 QTLs were detected for eight seed-related traits on 14 linkage groups, of which 16 QTLs could be consistently detected for two or three years. A total of 6 QTLs were associated with seed shattering. Based on annotation with wheat and barley genome and transcriptome data of abscission zone in E. sibiricus, we identified 30 candidate genes for seed shattering, of which 15, 7, 6 and 2 genes were involved in plant hormone signal transcription, transcription factor, hydrolase activity and lignin biosynthetic pathway, respectively. CONCLUSION:This study constructed the first high-density genetic linkage map and identified QTLs and candidate genes for seed-related traits in E. sibiricus. Results of this study will not only serve as genome-wide resources for gene/QTL fine mapping, but also provide a genetic framework for anchoring sequence scaffolds on chromosomes in future genome sequence assembly of E. sibiricus.
Project description:Sesame is poised to become a major oilseed crop owing to its high oil quality and adaptation to various ecological areas. However, the seed yield of sesame is very low and the underlying genetic basis is still elusive. Here, we performed genome-wide association studies of 39 seed yield-related traits categorized into five major trait groups, in three different environments, using 705 diverse lines. Extensive variation was observed for the traits with capsule size, capsule number and seed size-related traits, found to be highly correlated with seed yield indexes. In total, 646 loci were significantly associated with the 39 traits (p < 10-7) and resolved to 547 quantitative trait loci QTLs. We identified six multi-environment QTLs and 76 pleiotropic QTLs associated with two to five different traits. By analyzing the candidate genes for the assayed traits, we retrieved 48 potential genes containing significant functional loci. Several homologs of these candidate genes in Arabidopsis are described to be involved in seed or biomass formation. However, we also identified novel candidate genes, such as SiLPT3 and SiACS8, which may control capsule length and capsule number traits. Altogether, we provided the highly-anticipated basis for research on genetics and functional genomics towards seed yield improvement in sesame.
Project description:Castor bean (Ricinus communis L., Euphorbiaceae) is a critical biodiesel crop and its seed derivatives have important industrial applications. Due to lack of a high-density genetic map, the breeding and genetic improvement of castor bean has been largely restricted. In this study, based on a recombinant inbred line (RIL) population consisting of 200 individuals, we generated 8,896 high-quality genomic SNP markers and constructed a high-resolution genetic map with 10 linkage groups (LGs), spanning 1,852.33 centiMorgan (cM). Based on the genetic map, 996 scaffolds from the draft reference genome were anchored onto 10 pseudo-chromosomes, covering 84.43% of the castor bean genome. Furthermore, the quality of the pseudo-chromosome scale assembly genome was confirmed via genome collinearity analysis within the castor bean genome as well as between castor bean and cassava. Our results provide new evidence that the phylogenetic position of castor bean is relatively solitary from other taxa in the Euphorbiaceae family. Based on the genetic map, we identified 16 QTLs that control seed size and weight (covering 851 candidate genes). The findings will be helpful for further research into potential new mechanisms controlling seed size and weight in castor bean. The genetic map and improved pseudo-chromosome scale genome provide crucial foundations for marker-assisted selection (MAS) of QTL governing important agronomic traits, as well as the accelerated molecular breeding of castor bean in a cost-effective pattern.
Project description:Sesame (Sesamum indicum L., 2n = 26) is an important oilseed crop with an estimated genome size of 369 Mb. The genetic basis, including the number and locations of quantitative trait loci (QTLs) of sesame grain yield and quality remain poorly understood, due in part to the lack of reliable markers and genetic maps. Here we report on the construction of a hitherto most high-density genetic map of sesame using the restriction-site associated DNA sequencing (RAD-seq) combined with 89 PCR markers, and the identification of grain yield-related QTLs using a recombinant inbred line (RIL) population.In total, 3,769 single-nucleotide polymorphism (SNP) markers were identified from RAD-seq, and 89 polymorphic PCR markers were identified including 44 expressed sequence tag-simple sequence repeats (EST-SSRs), 10 genomic-SSRs and 35 Insertion-Deletion markers (InDels). The final map included 1,230 markers distributed on 14 linkage groups (LGs) and was 844.46 cM in length with an average of 0.69 cM between adjacent markers. Using this map and RIL population, we detected 13 QTLs on 7 LGs and 17 QTLs on 10 LGs for seven grain yield-related traits by the multiple interval mapping (MIM) and the mixed linear composite interval mapping (MCIM), respectively. Three major QTLs had been identified using MIM with R2 > 10.0% or MCIM with ha 2 > 5.0%. Two co-localized QTL groups were identified that partially explained the correlations among five yield-related traits.Three thousand eight hundred and four pairs of new DNA markers including SNPs and InDels were developed by RAD-seq, and a so far most high-density genetic map was constructed based on these markers in combination with SSR markers. Several grain yield-related QTLs had been identified using this population and genetic map. We report here the first QTL mapping of yield-related traits with a high-density genetic map using a RIL population in sesame. Results of this study solidified the basis for studying important agricultural traits and implementing marker-assisted selection (MAS) toward genetic improvement in sesame.
Project description:White lupin (Lupinus albus L.) is a valuable source of seed protein, carbohydrates and oil, but requires genetic improvement to attain its agronomic potential. This study aimed to (i) develop a new high-density consensus linkage map based on new, transcriptome-anchored markers; (ii) map four important agronomic traits, namely, vernalization requirement, seed alkaloid content, and resistance to anthracnose and Phomopsis stem blight; and, (iii) define regions of synteny between the L. albus and narrow-leafed lupin (L. angustifolius L.) genomes. Mapping of white lupin quantitative trait loci (QTLs) revealed polygenic control of vernalization responsiveness and anthracnose resistance, as well as a single locus regulating seed alkaloid content. We found high sequence collinearity between white and narrow-leafed lupin genomes. Interestingly, the white lupin QTLs did not correspond to previously mapped narrow-leafed lupin loci conferring vernalization independence, anthracnose resistance, low alkaloids and Phomopsis stem blight resistance, highlighting different genetic control of these traits. Our suite of allele-sequenced and PCR validated markers tagging these QTLs is immediately applicable for marker-assisted selection in white lupin breeding. The consensus map constitutes a platform for synteny-based gene cloning approaches and can support the forthcoming white lupin genome sequencing efforts.
Project description:Sesame is one of the oldest oilseed crops grown mainly in Africa and Asia. Although genetic and genomic studies on sesame have started late, the past 5 years have witnessed extensive progresses in these areas on this crop. Important genomic sequence resources such as functional markers, genes and QTLs linked to agronomically important traits, have been generated through linkage mapping and association analysis to assist sesame improvement programs. However, most of these data are scattered in different maps making them hard to be exploited efficiently in breeding programs. In this study, we report a comprehensive physical map gathering 151 published genomic sequence resources which highlighted some hotspot functional regions in the sesame genome. Moreover, 83,135 non-redundant SSRs have been supplied along with their physical position and motif composition. This will assist future research in fine mapping or pinpointing more functional genes based on the already published QTLs and functional markers. This physical map represents a good landmark for further non-overlapping genetic and genomic studies working towards sesame improvement.