Genetic analysis and QTL mapping of seed coat color in sesame (Sesamum indicum L.).
ABSTRACT: 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: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 trait highly affecting the seed quality and flesh appearance of watermelon (Citrullus lanatus). However, the molecular regulation mechanism of seed coat color in watermelon is still unclear. In the present study, genetic analysis was performed by evaluating F1, F2 and BC1 populations derived from two parental lines (9904 with light yellow seeds and Handel with black seeds), suggesting that a single dominant gene controls the black seed coat. The initial mapping result revealed a region of interest spanning 370 kb on chromosome 3. Genetic mapping with CAPS and SNP markers narrowed down the candidate region to 70.2 kb. Sequence alignment of the three putative genes in the candidate region suggested that there was a single-nucleotide insertion in the coding region of Cla019481 in 9904, resulting in a frameshift mutation and premature stop codon. The results indicated that Cla019481 named ClCS1 was the candidate gene for black seed coat color in watermelon. In addition, gene annotation revealed that Cla019481 encoded a polyphenol oxidase (PPO), which involved in the oxidation step of the melanin biosynthesis. This research finding will facilitate maker-assisted selection in watermelon and provide evidence for the study of black seed coat coloration in plants.
Project description:Seed coat color is an important agronomic trait in <i>Brassica rapa</i>. Yellow seeds are a desirable trait for breeding oilseed <i>Brassica</i> crops. To identify quantitative trait loci (QTLs) that condition seed coat color in <i>B. rapa</i>, we used a population of recombinant inbred lines (RILs) derived from crossing 09A001, a standard rapid-cycling (RcBr) inbred line of <i>B. rapa</i> L. ssp. <i>dichotoma</i> with yellow seeds, with 08A061, an inbred line of heading Chinese cabbage with dark brown seeds. Using two phenotypic scoring methods, we detected a total of nine QTLs distributed on four chromosomes (Chrs.), A03, A06, A08, and A09, that explained 3.17 to 55.73% of the phenotypic variation for seed color. To validate the effects of the identified QTLs in the RIL population, chromosome segment substitution lines (CSSLs) harboring the chromosomal segment carrying the candidate QTL region from 08A061 were selected, and two co-localized major QTLs, <i>qSC9.1</i> and <i>qSCb9.1</i>, and one minor QTL, <i>qSC3.1</i>, were successfully validated. The validated QTL located on Chr. A03 appears to be a new locus underlying seed coat color in <i>B. rapa</i>. These findings provide additional insight that will help explain the complex genetic mechanisms underlying the seed coat color trait in <i>B. rapa</i>.
Project description:Different species of edible seed watermelons (Citrullus spp.) are cultivated in Asia and Africa for their colorful nutritious seeds. Consumer preference varies for watermelon seed coat color. Therefore, it is an important consideration for watermelon breeders. In 1940s, a genetic model of four genes, R, T, W and D, was proposed to elucidate the inheritance of seed coat color in watermelon. In this study, we developed three segregating F2 populations: Sugar Baby (dotted black seed, RRTTWW) × plant introduction (PI) 482379 (green seed, rrTTWW), Charleston Gray (dotted black seed, RRTTWW) × PI 189225 (red seed, rrttWW), and Charleston Gray (dotted black seed, RRTTWWdd) × UGA147 (clump seed, RRTTwwDD) to re-examine the four-gene model and to map the four genes. In the dotted black × green population, the dotted black seed coat color (R_) is dominant to green seed coat color (rr). In the dotted black × red population, the dominant dotted black seed coat color and the recessive red seed coat color segregate for the R and T genes, where the R gene is dominantly epistatic to the T gene. However, the inheritance of the T locus did not fit the four-gene model, thus we named it T1 . In the dotted black × clump population, the clump seed coat color and the dotted black seed coat color segregate for W and D, where D is recessively epistatic to W. The R, T1 , W, and D loci were mapped on chromosomes 3, 5, 6, and 8, respectively, using QTL-seq and genotyping-by-sequencing (GBS). Kompetitive Allele Specific PCR (KASP™) assays and SNP markers linked to the four loci were developed to facilitate maker-assisted selection (MAS) for watermelon seed coat color.
Project description:The study identified 9045 high-quality SNPs employing both genome-wide GBS- and candidate gene-based SNP genotyping assays in 172, including 93 cultivated (desi and kabuli) and 79 wild chickpea accessions. The GWAS in a structured population of 93 sequenced accessions detected 15 major genomic loci exhibiting significant association with seed coat color. Five seed color-associated major genomic loci underlying robust QTLs mapped on a high-density intra-specific genetic linkage map were validated by QTL mapping. The integration of association and QTL mapping with gene haplotype-specific LD mapping and transcript profiling identified novel allelic variants (non-synonymous SNPs) and haplotypes in a MATE secondary transporter gene regulating light/yellow brown and beige seed coat color differentiation in chickpea. The down-regulation and decreased transcript expression of beige seed coat color-associated MATE gene haplotype was correlated with reduced proanthocyanidins accumulation in the mature seed coats of beige than light/yellow brown seed colored desi and kabuli accessions for their coloration/pigmentation. This seed color-regulating MATE gene revealed strong purifying selection pressure primarily in LB/YB seed colored desi and wild Cicer reticulatum accessions compared with the BE seed colored kabuli accessions. The functionally relevant molecular tags identified have potential to decipher the complex transcriptional regulatory gene function of seed coat coloration and for understanding the selective sweep-based seed color trait evolutionary pattern in cultivated and wild accessions during chickpea domestication. The genome-wide integrated approach employed will expedite marker-assisted genetic enhancement for developing cultivars with desirable seed coat color types in chickpea.
Project description:KEY MESSAGE:Two major QTLs associated with low seed coat deficiency of soybean seeds were identified in two biparental populations, and three SNP markers were validated to assist low-SCD natto soybean breeding selection. Soybean seed coat deficiency (SCD), known as seed coat cracking during soaking in the natto production process, is problematic because split or broken beans clog production lines and increases production costs. Development of natto soybean cultivars with low SCD is crucial to support the growth of the natto industry. Unfortunately, information on the genetic control of SCD in soybean, which is desperately needed to facilitate breeding selection, remains sparse. In this study, two F2 populations derived from V11-0883?×?V12-1626 (Pop 1) and V11-0883?×?V12-1885 (Pop 2) were developed and genotyped with BARCSoySNP6K Beadchips and F2-derived lines were evaluated for SCD in three consecutive years (2016-2018) in order to identify quantitative trait loci (QTLs) associated with low SCD in soybean. A total of 17 QTLs underlying SCD were identified in two populations. Among these, two major and stable QTLs, qSCD15 on chromosome 15 and qSCD20 on chromosome 20, were detected across multiple years. These QTLs explained up to 30.3% of the phenotypic variation for SCD in Pop 1 and 6.1% in Pop 2 across years. Three SNP markers associated with the qSCD20 were validated in additional four biparental populations. The average selection efficiency of low-SCD soybean was 77% based on two tightly linked markers, Gm20_34626867 and Gm20_34942502, and 64% based on the marker Gm20_35625615. The novel and stable QTLs identified in this study will facilitate elucidation of the genetic mechanism controlling SCD in soybean, and the markers will significantly accelerate breeding for low-SCD soybean through marker-assisted selection.
Project description:The adzuki bean (<i>Vigna angularis</i>) is an important grain legume. Fine mapping of quantitative trait loci (QTL) and qualitative trait genes plays an important role in gene cloning, molecular-marker-assisted selection (MAS), and trait improvement. However, the genetic control of agronomic traits in the adzuki bean remains poorly understood. Single-nucleotide polymorphisms (SNPs) are invaluable in the construction of high-density genetic maps. We mapped 26 agronomic QTLs and five qualitative trait genes related to pigmentation using 1,571 polymorphic SNP markers from the adzuki bean genome via restriction-site-associated DNA sequencing of 150 members of an F<sub>2</sub> population derived from a cross between cultivated and wild adzuki beans. We mapped 11 QTLs for flowering time and pod maturity on chromosomes 4, 7, and 10. Six 100-seed weight (SD100WT) QTLs were detected. Two major flowering time QTLs were located on chromosome 4, firstly <i>VaFld4.1</i> (PEVs 71.3%), co-segregating with SNP marker s690-144110, and <i>VaFld4.2</i> (PEVs 67.6%) at a 0.974 cM genetic distance from the SNP marker s165-116310. Three QTLs for seed number per pod (<i>Snp3.1, Snp3.2</i>, and <i>Snp4.1</i>) were mapped on chromosomes 3 and 4. One QTL <i>VaSdt4.1</i> of seed thickness (SDT) and three QTLs for branch number on the main stem were detected on chromosome 4. QTLs for maximum leaf width (LFMW) and stem internode length were mapped to chromosomes 2 and 9, respectively. Trait genes controlling the color of the seed coat, pod, stem and flower were mapped to chromosomes 3 and 1. Three candidate genes, <i>VaAGL, VaPhyE</i>, and <i>VaAP2</i>, were identified for flowering time and pod maturity. <i>VaAGL</i> encodes an agamous-like MADS-box protein of 379 amino acids. <i>VaPhyE</i> encodes a phytochrome E protein of 1,121 amino acids. Four phytochrome genes (<i>VaPhyA1, VaPhyA2, VaPhyB</i>, and <i>VaPhyE</i>) were identified in the adzuki bean genome. We found candidate genes <i>VaAP2/ERF.81</i> and <i>VaAP2/ERF.82</i> of SD100WT, <i>VaAP2-s4</i> of SDT, and <i>VaAP2/ERF.86</i> of LFMW. A candidate gene <i>VaUGT</i> related to black seed coat color was identified. These mapped QTL and qualitative trait genes provide information helpful for future adzuki bean candidate gene cloning and MAS breeding to improve cultivars with desirable growth periods, yields, and seed coat color types.
Project description:Soybean seed coat exists in a range of colors from yellow, green, brown, black, to bicolor. Classical genetic analysis suggested that soybean seed color was a moderately complex trait controlled by multi-loci. However, only a couple of loci could be detected using a single biparental segregating population. In this study, a combination of association mapping and bulk segregation analysis was employed to identify genes/loci governing this trait in soybean. A total of 14 loci, including nine novel and five previously reported ones, were identified using 176,065 coding SNPs selected from entire SNP dataset among 56 soybean accessions. Four of these loci were confirmed and further mapped using a biparental population developed from the cross between ZP95-5383 (yellow seed color) and NY279 (brown seed color), in which different seed coat colors were further dissected into simple trait pairs (green/yellow, green/black, green/brown, yellow/black, yellow/brown, and black/brown) by continuously developing residual heterozygous lines. By genotyping entire F2 population using flanking markers located in fine-mapping regions, the genetic basis of seed coat color was fully dissected and these four loci could explain all variations of seed colors in this population. These findings will be useful for map-based cloning of genes as well as marker-assisted breeding in soybean. This work also provides an alternative strategy for systematically isolating genes controlling relative complex trait by association analysis followed by biparental mapping.
Project description:Sesame (Sesamum indicum L.) is one of the main oilseed crops, providing vegetable oil and protein to human. Landrace is the gene source of variety, carrying many desire alleles for genetic improvement. Despite the importance of sesame landrace, genome of sesame landrace remains unexplored and genomic variations between landrace and variety still is not clear. To identify the genomic variations between sesame landrace and variety, two representative sesame landrace accessions, "Baizhima" and "Mishuozhima," were selected and re-sequenced. The genome sequencing and de novo assembling of the two sesame landraces resulted in draft genomes of 267 Mb and 254 Mb, respectively, with the contig N50 more than 47 kb. Totally, 1,332,025 SNPs and 506,245 InDels were identified from the genome of "Baizhima" and "Mishuozhima" by comparison of the genome of a variety "Zhongzhi13." Among the genomic variations, 70,018 SNPs and 8311 InDels were located in the coding regions of genes. Genomic variations may contribute to variation of sesame agronomic traits such as flowering time, plant height, and oil content. The identified genomic variations were successfully used in the QTL mapping and the black pigment synthesis gene, PPO, was found to be the candidate gene of sesame seed coat color. The comprehensively compared genomes of sesame landrace and modern variety produced massive useful genomic information, constituting a powerful tool to support genetic research, and molecular breeding of sesame.