Quantitative Trait Loci Mapping Analysis Research Articles

QTL mapping and omics analysis to identify genes controlling kernel dehydration in maize.

This study mapped and screened three candidate genes related to kernel dehydration in maize. The slow development rate of maize kernels during later stages leads to high kernel moisture content at harvest, posing a challenge for mechanized maize harvesting in China. This study utilized a recombinant inbred line population derived from Zheng 58 (slow dehydration) and PH6WC (fast dehydration) as parents. After four years of trait investigation and analysis, 25 quantitative trait loci (QTLs) associated with kernel dehydration rate and moisture content were identified, with six QTLs showing a significant contribution value exceeding 10% in the phenotype. Furthermore, a comparison was made between the QTLs identified in this study and those from previous research on maize kernel moisture content and dehydration rate, followed by screening through the omics analysis of the parental lines. Three candidate genes related to kernel dehydration rate were identified, primarily involving carbohydrate metabolism, energy metabolism processes (Zm00001d014030 and Zm00001d006476), and stimulus resistance (Zm00001d040113). These findings provide valuable insights to assist and guide future breeding efforts for mechanical harvesting of maize.

Identification of candidate genes and genomic prediction of soybean fatty acid components in two soybean populations.

Soybean, a source of plant-derived lipids, contains an array of fatty acids essential for health. A comprehensive understanding of the fatty acid profiles in soybean is crucial for enhancing soybean cultivars and augmenting their qualitative attributes. Here, 180 F10 generation recombinant inbred lines (RILs), derived from the cross-breeding of the cultivated soybean variety 'Jidou 12' and the wild soybean 'Y9,' were used as primary experimental subjects. Using inclusive composite interval mapping (ICIM), this study undertook a quantitative trait locus (QTL) analysis on five distinct fatty acid components in the RIL population from 2019 to 2021. Concurrently, a genome-wide association study (GWAS) was conducted on 290 samples from a genetically diverse natural population to scrutinize the five fatty acid components during the same timeframe, thereby aiming to identify loci closely associated with fatty acid profiles. In addition, haplotype analysis and the Kyoto Encyclopedia of Genes and Genomes pathway analysis were performed to predict candidate genes. The QTL analysis elucidated 23 stable QTLs intricately associated with the five fatty acid components, exhibiting phenotypic contribution rates ranging from 2.78% to 25.37%. In addition, GWAS of the natural population unveiled 102 significant loci associated with these fatty acid components. The haplotype analysis of the colocalized loci revealed that Glyma.06G221400 on chromosome 6 exhibited a significant correlation with stearic acid content, with Hap1 showing a markedly elevated stearic acid level compared with Hap2 and Hap3. Similarly, Glyma.12G075100 on chromosome 12 was significantly associated with the contents of oleic, linoleic, and linolenic acids, suggesting its involvement in fatty acid biosynthesis. In the natural population, candidate genes associated with the contents of palmitic and linolenic acids were predominantly from the fatty acid metabolic pathway, indicating their potential role as pivotal genes in the critical steps of fatty acid metabolism. Furthermore, genomic selection (GS) for fatty acid components was conducted using ridge regression best linear unbiased prediction based on both random single nucleotide polymorphisms (SNPs) and SNPs significantly associated with fatty acid components identified by GWAS. GS accuracy was contingent upon the SNP set used. Notably, GS efficiency was enhanced when using SNPs derived from QTL mapping analysis and GWAS compared with random SNPs, and reached a plateau when the number of SNP markers exceeded 3,000. This study thus indicates that Glyma.06G221400 and Glyma.12G075100 are genes integral to the synthesis and regulatory mechanisms of fatty acids. It provides insights into the complex biosynthesis and regulation of fatty acids, with significant implications for the directed improvement of soybean oil quality and the selection of superior soybean varieties. The SNP markers delineated in this study can be instrumental in establishing an efficacious pipeline for marker-assisted selection and GS aimed at improving soybean fatty acid components.

Mining Candidate Genes for Leaf Angle in Brassica napus L. by Combining QTL Mapping and RNA Sequencing Analysis.

Leaf angle (LA) is an important trait of plant architecture, and individuals with narrow LA can better capture canopy light under high-density planting, which is beneficial for increasing the overall yield per unit area. To study the genetic basis and molecular regulation mechanism of leaf angle in rapeseed, we carried out a series of experiments. Quantitative trait loci (QTL) mapping was performed using the RIL population, and seven QTLs were identified. Transcriptome analysis showed that the cell wall formation/biogenesis processes and biosynthesis/metabolism of cell wall components were the most enrichment classes. Most differentially expressed genes (DEGs) involved in the synthesis of lignin, xylan, and cellulose showed down-regulated expression in narrow leaf material. Microscopic analysis suggested that the cell size affected by the cell wall in the junction area of the stem and petiole was the main factor in leaf petiole angle (LPA) differences. Combining QTL mapping and RNA sequencing, five promising candidate genes BnaA01G0125600ZS, BnaA01G0135700ZS, BnaA01G0154600ZS, BnaA10G0154200ZS, and BnaC03G0294200ZS were identified in rapeseed, and most of them were involved in cell wall biogenesis and the synthesis/metabolism of cell wall components. The results of QTL, transcriptome analysis, and cytological analysis were highly consistent, collectively revealing that genes related to cell wall function played a crucial role in regulating the LA trait in rapeseed. The study provides further insights into LA traits, and the discovery of new QTLs and candidate genes is highly beneficial for genetic improvement.

Quantitative Trait Loci Mapping and Comparative Transcriptome Analysis of Fruit Weight (FW) in Watermelon (Citrullus lanatus L.).

The watermelon (Citrullus lanatus L.) holds substantial economic value as a globally cultivated horticultural crop. However, the genetic architecture of watermelon fruit weight (FW) remains poorly understood. In this study, we used sh14-11 with small fruit and N14 with big fruit to construct 100 recombinant inbred lines (RILs). Based on whole-genome resequencing (WGR), 218,127 single nucleotide polymorphisms (SNPs) were detected to construct a high-quality genetic map. After quantitative trait loci (QTL) mapping, a candidate interval of 31-38 Mb on chromosome 2 was identified for FW. Simultaneously, the bulked segregant analysis (BSA) in the F2 population corroborated the identification of the same interval, encompassing the homologous gene linked to the known FW-related gene fas. Additionally, RNA-seq was carried out across 11 tissues from sh14-11 and N14, revealing expression profiles that identified 1695 new genes and corrected the annotation of 2941 genes. Subsequent differential expression analysis unveiled 8969 differentially expressed genes (DEGs), with 354 of these genes exhibiting significant differences across four key developmental stages. The integration of QTL mapping and differential expression analysis facilitated the identification of 14 FW-related genes, including annotated TGA and NAC transcription factors implicated in fruit development. This combined approach offers valuable insights into the genetic basis of FW, providing crucial resources for enhancing watermelon cultivation.

Genetic insights into hypoxia tolerance in silver sillago (Sillago sihama) through QTL mapping and SNP association analysis

Oxygen is vital for the survival, growth, development, and reproduction of organisms. This study investigates the genetic basis of hypoxia tolerance in the silver sillago (Sillago sihama), a species highly valued in aquaculture despite its traditional susceptibility to low oxygen environments. By employing quantitative trait locus (QTL) mapping and single nucleotide polymorphism (SNP) association studies, the study enhances our comprehension of the genetic factors involved in hypoxia tolerance. Six QTLs associated with hypoxia tolerance have been identified, spanning five distinct linkage groups. Enrichment analyses highlighted important biological processes and pathways, particularly those related to potassium ion transport and cytochrome P450-mediated drug metabolism, which play a critical role in responding to hypoxia stress. Seven candidate genes have been identified as relevant to hypoxia tolerance: cyp20a1, mgst3b, kcnh2, cluh, adk, xdh, and slc19a2. Notably, the SNP association analysis has identified 13 SNPs within the mgst3b gene, with five SNPs (g.583 T > C, g.611 A > G, g.629 T > A, g.633 T > A, g.937 A > G) showing a significant association with hypoxia tolerance. This study sheds light on the molecular mechanisms underlying hypoxia tolerance and suggests potential genetic markers that could be used to enhance S. sihama's ability to withstand hypoxic conditions through selective breeding, providing valuable insights for the improvement of sustainable aquaculture practices.

QTL mapping and candidate gene analysis reveal two major loci regulating green leaf color in non-heading Chinese cabbage.

Two major-effect QTL GlcA07.1 and GlcA09.1 for green leaf color were fine mapped into 170.25kb and 191.41kb intervals on chromosomes A07 and A09, respectively, and were validated by transcriptome analysis. Non-heading Chinese cabbage (NHCC) is a leafy vegetable with a wide range of green colors. Understanding the genetic mechanism behind broad spectrum of green may facilitate the breeding of high-quality NHCC. Here, we used F2 and F7:8 recombination inbred line (RIL) population from a cross between Wutacai (dark-green) and Erqing (lime-green) to undertake the genetic analysis and quantitative trait locus (QTL) mapping in NHCC. The genetic investigation of the F2 population revealed that the variation of green leaf color was controlled by two recessive genes. Six pigments associated with green leaf color, including total chlorophyll, chlorophyll a, chlorophyll b, total carotenoids, lutein, and carotene were quantified and applied for QTL mapping in the RIL population. A total of 7 QTL were detected across the whole genome. Among them, two major-effect QTL were mapped on chromosomes A07 (GlcA07.1) and A09 (GlcA09.1) corresponding to two QTL identified in the F2 population. The QTL GlcA07.1 and GlcA09.1 were further fine mapped into 170.25kb and 191.41kb genomic regions, respectively. By comparing gene expression level and gene annotation, BraC07g023810 and BraC07g023970 were proposed as the best candidates for GlcA07.1, while BraC09g052220 and BraC09g052270 were suggested for GlcA09.1. Two InDel molecular markers (GlcA07.1-BcGUN4 and GlcA09.1-BcSG1) associated with BraC07gA023810 and BraC09g052220 were developed and could effectively identify leaf color in natural NHCC accessions, suggesting their potential for marker-assisted leaf color selection in NHCC breeding.

Fhb9, a major QTL for Fusarium head blight resistance improvement in wheat

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is one of the most devastating diseases of wheat worldwide. Identification and validation of major quantitative trait loci (QTLs) for FHB resistance without negative effects on agronomic traits is critical to success in breeding FHB-resistant cultivars. In this study, a stable major QTL on chromosome arm 2DL was identified by evaluating a recombinant inbred line (RIL) population derived from Shi4185×Shijiazhuang 8 in both field and greenhouse experiments. QTL mapping and pedigree analyses indicated that the 2DL QTL is the same QTL as QFhb-2DL previously identified in Ji5265, therefore, designated Fhb9. Four kompetitive amplicon sequence polymorphism (KASP) markers were developed based on exome capture sequencing data to enhance marker density in the Fhb9 region, and it was delimited to an interval between single nucleotide polymorphism (SNP) markers KASP-12056 (533.8) and KASP-525 (525.9 Mb) explained 26.0-30.1% of the phenotypic variation. Analysis of the geographic distribution of the Fhb9 resistance allele suggested that it originated from Huang-Huai winter wheat region in China, and very low frequency of Fhb9 in modern Chinese cultivars reveals that it has not been widely deployed in breeding programs. Field and greenhouse evaluation of yield-related traits of near-isogenic lines (NILs) contrasting in Fhb9 alleles indicated that Fhb9 resistance allele did not show any adverse effects on those traits. Fhb9 showed an additive effect on enhancing FHB resistance with Fhb1. Therefore, Fhb9 is a valuable major QTL for improving FHB resistance in wheat and the near-diagnostic markers developed in this study will facilitate its deployment in wheat breeding programs.

The QTL and Candidate Genes Regulating the Early Tillering Vigor Traits of Late-Season Rice in Double-Cropping Systems.

Rice effective panicle is a major trait for grain yield and is affected by both the genetic tiller numbers and the early tillering vigor (ETV) traits to survive environmental adversities. The mechanism behind tiller bud formation has been well described, while the genes and the molecular mechanism underlying rice-regulating ETV traits are unclear. In this study, the candidate genes in regulating ETV traits have been sought by quantitative trait locus (QTL) mapping and bulk-segregation analysis by resequencing method (BSA-seq) conjoint analysis using rice backcross inbred line (BIL) populations, which were cultivated as late-season rice of double-cropping rice systems. By QTL mapping, seven QTLs were detected on chromosomes 1, 3, 4, and 9, with the logarithm of the odds (LOD) values ranging from 3.52 to 7.57 and explained 3.23% to 12.98% of the observed phenotypic variance. By BSA-seq analysis, seven QTLs on chromosomes 1, 2, 4, 5, 7, and 9 were identified using single-nucleotide polymorphism (SNP) and insertions/deletions (InDel) index algorithm and Euclidean distance (ED) algorithm. The overlapping QTL resulting from QTL mapping and BSA-seq analysis was shown in a 1.39 Mb interval on chromosome 4. In the overlap interval, six genes, including the functional unknown genes Os04g0455650, Os04g0470901, Os04g0500600, and ethylene-insensitive 3 (Os04g0456900), sialyltransferase family domain containing protein (Os04g0506800), and ATOZI1 (Os04g0497300), showed the differential expression between ETV rice lines and late tillering vigor (LTV) rice lines and have a missense base mutation in the genomic DNA sequences of the parents. We speculate that the six genes are the candidate genes regulating the ETV trait in rice, which provides a research basis for revealing the molecular mechanism behind the ETV traits in rice.

QTL mapping and candidate gene analysis of low‐temperature tolerance at the germination stage of soybean

AbstractWhen soybean seeds encounter low temperature during germination, the vigour and germination of soybean seeds are affected, which leads to a lack of seedlings and weak seedlings, resulting in yield reduction. In‐depth analysis of the genetic mechanism of soybean seed germination tolerance to low‐temperature stress and the cultivation of soybean‐tolerant varieties is the key to resisting low‐temperature stress at the germination stage. In the present study, a chromosome segment substitution line (CSSL) population constructed by wild soybean ZYD00006 and cultivated soybean SN14 was used to map three quantitative trait loci (QTLs). Five candidate genes were obtained by gene annotation, GO enrichment analysis and protein function prediction. The candidate genes were subjected to bioinformatics analysis, qRT‐PCR analysis, trypsin activity analysis and soluble protein content analysis. The results showed that the secondary and tertiary structures of the Glyma.09G162700 proteins were mutated. Within 0–72 h, the expression of Glyma.09G162700 in the two materials with different tolerances was consistent, and the change in trypsin activity was consistent with the change in protein expression. Through haplotype analysis, Glyma.09G162700 produced two haplotypes at −2420 bp. The germination rate (GR) and relative germination rate (RGR) of the two haplotypes were significantly different, indicating that the two haplotypes have wide applicability in soybean resources. In summary, Glyma.09G162700 may be a candidate gene for low‐temperature tolerance at the germination stage of soybean. These results provide an important theoretical basis and marker information for analysing the mechanism of low‐temperature tolerance in soybean germination stage and cultivating low‐temperature‐tolerant varieties.

QTL mapping and transcriptomic analysis of fruit length in cucumber.

A total of 151 recombinant inbred lines (RILs) were derived from the cross between 'Cucumis sativus L. hardwickii' (HW) and a cultivated Northern Chinese inbred line 'XinTaiMiCi' (XTMC). We used resequencing to construct the genetic map and analyze the genetic background of RIL population, and combined with the phenotypes of RIL population and the analysis of RNA-seq data, we located the major loci controlling the fruit length of cucumber and related analysis. A genetic map containing 600 bin markers was constructed via re-sequencing. Based on the phenotype data collected in two different seasons (spring 2021 and autumn 2022), the major quantitative trait loci (QTLs) controlling cucumber fruit length were located and their transcriptomic analysis carried out. The results revealed three QTLs (Fl2.1, Fl4.1, and Fl6.1) detected repeatedly in the two seasons, of which Fl4.1 was the dominant QTL. From the functional annotation of corresponding genes there, we discovered the gene Csa4G337340 encoding an auxin efflux carrier family protein. The expression of that gene was significantly lower in XTMC and the long-fruit RIL lines than in HW and the short-fruit RIL lines; hence, we speculated the gene could be negatively correlated with the fruit length of cucumber. Transcriptomic analysis showed that 259 differentially expressed genes (DEGs) were enriched in the plant hormone signal transduction pathway. In addition, among those DEGs, 509 transcription factors were detected, these distributed in several transcription factor gene families, such as bHLH, AP2/ErF -ERF, C2H2, and NAC. Therefore, we concluded that the major gene controlling the fruit length of cucumber is located in the interval of Fl4.1, whose gene Csa4G337340 may be involved in the negative regulation of fruit length. Further, genes related to plant hormone signal transduction and several transcription factors were also found involved in the regulation of cucumber fruit length. Our results provide a reference for the fine mapping of major genes and analyzing the mechanism of cucumber fruit length.

Identification of QTLs and their candidate genes for the number of maize tassel branches in F2 from two higher generation sister lines using QTL mapping and RNA-seq analysis.

Tassel branch number is an important agronomic trait that is closely associated with maize kernels and yield. The regulation of genes associated with tassel branch development can provide a theoretical basis for analyzing tassel branch growth and improving maize yield. In this study. we used two high-generation sister maize lines, PCU (unbranched) and PCM (multiple-branched), to construct an F2 population comprising 190 individuals, which were genotyped and mapped using the Maize6H-60K single-nucleotide polymorphism array. Candidate genes associated with tassel development were subsequently identified by analyzing samples collected at three stages of tassel growth via RNA-seq. A total of 13 quantitative trait loci (QTLs) and 22 quantitative trait nucleotides (QTNs) associated with tassel branch number (TBN) were identified, among which, two major QTLs, qTBN6.06-1 and qTBN6.06-2, on chromosome 6 were identified in two progeny populations, accounting for 15.07% to 37.64% of the phenotypic variation. Moreover, we identified 613 genes that were differentially expressed between PCU and PCM, which, according to Kyoto Encyclopedia of Genes and Genomes enrichment analysis, were enriched in amino acid metabolism and plant signal transduction pathways. Additionally, we established that the phytohormone content of Stage I tassels and the levels of indole-3-acetic acid (IAA) and IAA-glucose were higher in PCU than in PCM plants, whereas contrastingly, the levels of 5-deoxymonopolyl alcohol in PCM were higher than those in PCU. On the basis of these findings, we speculate that differences in TBN may be related to hormone content. Collectively, by combining QTL mapping and RNA-seq analysis, we identified five candidate genes associated with TBN. This study provides theoretical insights into the mechanism of tassel branch development in maize.

Quantitative trait loci for sex ratio in monoecious bitter gourd (Momordica charantia)

Sex ratio (male or female flower frequency per plant) is an important trait of monoecious bitter gourds because it directly influences fruit yield. Quantitative trait loci (QTL) for the sex ratio were explored in F2 populations derived from the gynoecious OHB61-5 and monoecious OHB95-1A using both QTL mapping and QTL-seq methods. Female flower frequency data was used as the phenotype data, along with 1,036 bin-marker genotypes, and linkage maps from previous studies to detect sex ratio QTL. For QTL-seq, after the strong effect of the gynoecious locus was masked by marker-assisted selection of its heterozygotes, F2 plants showing higher- or lower-female flower frequency were selected and employed for making bulked samples. Three QTL were found on chromosomes 2 and 5 by QTL-seq, and only the qFR5-2 on chromosome 5 was identified by both QTL mapping and QTL-seq analyses. Focusing on the expressed genes with non-synonymous variations between parental lines in qFR5-2, 16 genes were nominated as candidate causal genes. Four of these encoded L-type lectin receptor kinase (LecRK), and amino acid substitutions in the conserved lectin or kinase domain were observed in three LecRKs between parental lines. Markers or genes for these sex ratio QTL will contribute to the development of bitter gourd inbred lines useful for stable production of fruits.

Identification of candidate genes for soybean seed coat-related traits using QTL mapping and GWAS.

Seed coat color is a typical morphological trait that can be used to reveal the evolution of soybean. The study of seed coat color-related traits in soybeans is of great significance for both evolutionary theory and breeding practices. In this study, 180 F10 recombinant inbred lines (RILs) derived from the cross between the yellow-seed coat cultivar Jidou12 (ZDD23040, JD12) and the wild black-seed coat accession Y9 (ZYD02739) were used as materials. Three methods, single-marker analysis (SMA), interval mapping (IM), and inclusive composite interval mapping (ICIM), were used to identify quantitative trait loci (QTLs) controlling seed coat color and seed hilum color. Simultaneously, two genome-wide association study (GWAS) models, the generalized linear model (GLM) and mixed linear model (MLM), were used to jointly identify seed coat color and seed hilum color QTLs in 250 natural populations. By integrating the results from QTL mapping and GWAS analysis, we identified two stable QTLs (qSCC02 and qSCC08) associated with seed coat color and one stable QTL (qSHC08) related to seed hilum color. By combining the results of linkage analysis and association analysis, two stable QTLs (qSCC02, qSCC08) for seed coat color and one stable QTL (qSHC08) for seed hilum color were identified. Upon further investigation using Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, we validated the previous findings that two candidate genes (CHS3C and CHS4A) reside within the qSCC08 region and identified a new QTL, qSCC02. There were a total of 28 candidate genes in the interval, among which Glyma.02G024600, Glyma.02G024700, and Glyma.02G024800 were mapped to the glutathione metabolic pathway, which is related to the transport or accumulation of anthocyanin. We considered the three genes as potential candidate genes for soybean seed coat-related traits. The QTLs and candidate genes detected in this study provide a foundation for further understanding the genetic mechanisms underlying soybean seed coat color and seed hilum color and are of significant value in marker-assisted breeding.

Fine mapping of a QTL and identification of candidate genes associated with cold tolerance during germination in peanut (Arachis hypogaea L.) on chromosome B09 using whole genome re-sequencing.

Low temperatures significantly affect the growth and yield of peanuts. Temperatures lower than 12 °C are generally detrimental for the germination of peanuts. To date, there has been no report on precise information on the quantitative trait loci (QTL) for cold tolerance during the germination in peanuts. In this study, we developed a recombinant inbred line (RIL) population comprising 807 RILs by tolerant and sensitive parents. Phenotypic frequencies of germination rate low-temperature conditions among RIL population showed normally distributed in five environments. Then, we constructed a high density SNP-based genetic linkage map through whole genome re-sequencing (WGRS) technique and identified a major quantitative trait locus (QTL), qRGRB09, on chromosome B09. The cold tolerance-related QTLs were repeatedly detected in all five environments, and the genetic distance was 6.01 cM (46.74 cM - 61.75 cM) after taking a union set. To further confirm that qRGRB09 was located on chromosome B09, we developed Kompetitive Allele Specific PCR (KASP) markers for the corresponding QTL regions. A regional QTL mapping analysis, which was conducted after taking the intersection of QTL intervals of all environments into account, confirmed that qRGRB09 was between the KASP markers, G22096 and G220967 (chrB09:155637831-155854093), and this region was 216.26 kb in size, wherein a total of 15 annotated genes were detected. This study illustrates the relevance of WGRS-based genetic maps for QTL mapping and KASP genotyping that facilitated QTL fine mapping of peanuts. The results of our study also provided useful information on the genetic architecture underlying cold tolerance during germination in peanuts, which in turn may be useful for those engaged in molecular studies as well as crop improvement in the cold-stressed environment.

A Combination of QTL Mapping and GradedPool-Seq to Dissect Genetic Complexity for Gibberella Ear Rot Resistance in Maize Using an IBM Syn10 DH Population.

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae) is one of the most devastating maize diseases that reduces grain yield and quality worldwide. Utilization of host genetic resistance has become one of the most suitable strategies to control GER. In this study, a set of 246 diverse inbred lines derived from the intermated B 73 × Mo 17 doubled haploid population (IBM Syn10 DH) were used to detect quantitative trait loci (QTL) associated with resistance to GER. Meanwhile, a GradedPool-Seq (GPS) approach was performed to identify genomic variations involved in GER resistance. Using artificial inoculation across multiple environments, GER severity of the population was observed with wide phenotypic variation. Based on the linkage mapping, a total of 14 resistant QTLs were detected, accounting for 5.11 to 14.87% of the phenotypic variation, respectively. In GPS analysis, five significant single nucleotide polymorphisms (SNPs) associated with GER resistance were identified. Combining QTL mapping and GPS analysis, a peak-value SNP on chromosome 4 from GPS was overlapped with the QTL qGER4.2, suggesting that the colocalized region could be the most possible target location conferring resistance to GER. Subsequently, seven candidate genes were identified within the peak SNP, linking them to GER resistance. These findings are useful for exploring the complicated genetic variations in maize GER resistance. The genomic regions and genes identified herein provide a list of candidate targets for further investigation, in addition to the combined strategy that can be used for quantitative traits in plant species.

Genome-Wide Association Study Reveals CLEC7A and PROM1 as Potential Regulators of Paracoccidioides brasiliensis-Induction of Cytokine Production in Peripheral Blood Mononuclear Cells.

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by fungi of the genus Paracoccidioides and the different clinical forms of the disease are associated with the host immune responses. Quantitative trait loci mapping analysis was performed to assess genetic variants associated with mononuclear-cells-derived cytokines induced by P. brasiliensis on 158 individuals. We identified the rs11053595 SNP, which is present in the CLEC7A gene (encodes the Dectin-1 receptor) and the rs62290169 SNP located in the PROM1 gene (encodes CD133) associated with the production of IL-1β and IL-22, respectively. Functionally, the blockade of the dectin-1 receptor abolished the IL-1β production in P. brasiliensis-stimulated PBMCs. Moreover, the rs62290169-GG genotype was associated with higher frequency of CD38+ Th1 cells in PBMCs cultured with P. brasiliensis yeasts. Therefore, our research indicates that the CLEC7A and PROM1 genes are important for the cytokine response induced by P. brasiliensis and may influence the Paracoccidioidomycosis disease outcome.

QTL mapping and transcriptome analysis of sugar content during fruit ripening of Pyrus pyrifolia.

Sugar content is an important trait of fruits. The genetic background of fruits can affect their sugar content in different cultivars. The quantitative trait loci and genes related to sugar content during fruit ripening remain unclear. In this study, we performed quantitative trait locus (QTL) mapping of sugar content. Two QTLs (qSugar-LG6-Chr7 and qSugar-LG12-Chr3) were identified based on their total sugar contents. A total of 577 and 519 genes were annotated around these two QTL loci. The contents of fructose, sorbitol, glucose, and sucrose were measured at six time points in four cultivars before fruit maturation, including two sweet cultivars ("Zaoshengxinshui" and "ZQ65") and two general cultivars ("Qiushui" and "ZQ82"). In sweet cultivars, sucrose and fructose accumulate substantially, and sorbitol content decreases significantly during fruit ripening. A transcriptome analysis identified 125 upregulated and 222 downregulated differentially expressed genes (DEGs) in sweet cultivars. Two sucrose transport genes (PpSUT, LOC103964096, and LOC103940043) were negatively correlated with sugar content. A weighted gene co-expression network analysis showed that two genes, sorbitol dehydrogenase (PpSDH, LOC103960512 and LOC103960513), around the locus of qSugar-LG6-Chr7 were negatively co-expressed with the total sugar content, which was downregulated in the sweet cultivars. PpSDH and PpSUT may play important roles in regulating sugar content during pear ripening. Transcriptome analysis also revealed that some DEGs were related to sugars (PpS6PDH and ATP-PpPFK), hormones (PpARG7), and transcription factors (PpEMB1444, PpCYP734A1, and PpWRKY50). In conclusion, this study provides new insights into the molecular mechanisms associated with sugar content in the fruit ripening of Pyrus pyrifolia.

QTL mapping and candidate gene analysis for yield and grain weight/size in Tartary buckwheat

BackgroundGrain weight/size influences not only grain yield (GY) but also nutritional and appearance quality and consumer preference in Tartary buckwheat. The identification of quantitative trait loci (QTLs)/genes for grain weight/size is an important objective of Tartary buckwheat genetic research and breeding programs.ResultsHerein, we mapped the QTLs for GY, 1000-grain weight (TGW), grain length (GL), grain width (GW) and grain length–width ratio (L/W) in four environments using 221 recombinant inbred lines (XJ-RILs) derived from a cross of 'Xiaomiqiao × Jinqiaomai 2'. In total, 32 QTLs, including 7 for GY, 5 for TGW, 6 for GL, 11 for GW and 3 for L/W, were detected and distributed in 24 genomic regions. Two QTL clusters, qClu-1-3 and qClu-1-5, located on chromosome Ft1, were revealed to harbour 7 stable major QTLs for GY (qGY1.2), TGW (qTGW1.2), GL (qGL1.1 and qGL1.4), GW (qGW1.7 and qGW1.10) and L/W (qL/W1.2) repeatedly detected in three and above environments. A total of 59 homologues of 27 known plant grain weight/size genes were found within the physical intervals of qClu-1-3 and qClu-1-5. Six homologues, FtBRI1, FtAGB1, FtTGW6, FtMADS1, FtMKK4 and FtANT, were identified with both non-synonymous SNP/InDel variations and significantly differential expression levels between the two parents, which may play important roles in Tatary buckwheat grain weight/size control and were chosen as core candidate genes for further investigation.ConclusionsTwo stable major QTL clusters related to grain weight/size and six potential key candidate genes were identified by homology comparison, SNP/InDel variations and qRT‒qPCR analysis between the two parents. Our research provides valuable information for improving grain weight/size and yield in Tartary buckwheat breeding.

High-density genetic linkage mapping reveals low stability of QTLs across environments for economic traits in Eucalyptus.

Eucalyptus urophylla, E. tereticornis and their hybrids are the most important commercial forest tree species in South China where they are grown for pulpwood and solid wood production. Construction of a fine-scale genetic linkage map and detecting quantitative trait loci (QTL) for economically important traits linked to these end-uses will facilitate identification of the main candidate genes and elucidate the regulatory mechanisms. A high-density consensus map (a total of 2754 SNPs with 1359.18 cM) was constructed using genotyping by sequencing (GBS) on clonal progenies of E. urophylla × tereticornis hybrids. QTL mapping of growth and wood property traits were conducted in three common garden experiments, resulting in a total of 108 QTLs. A total of 1052 candidate genes were screened by the efficient combination of QTL mapping and transcriptome analysis. Only ten QTLs were found to be stable across two environments, and only one (qSG10Stable mapped on chromosome 10, and associated with lignin syringyl-to-guaiacyl ratio) was stable across all three environments. Compared to other QTLs, qSG10Stable explained a very high level of phenotypic variation (18.4-23.6%), perhaps suggesting that QTLs with strong effects may be more stably inherited across multiple environments. Screened candidate genes were associated with some transcription factor families, such as TALE, which play an important role in the secondary growth of plant cell walls and the regulation of wood formation. While QTLs such as qSG10Stable, found to be stable across three sites, appear to be comparatively uncommon, their identification is likely to be a key to practical QTL-based breeding. Further research involving clonally-replicated populations, deployed across multiple target planting sites, will be required to further elucidate QTL-by-environment interactions.

QTL Analysis of Morpho-Agronomic Traits in Garden Asparagus (Asparagus officinalis L.)

In order to understand the genetic control of quantitative agronomic traits in garden asparagus, we performed a quantitative trait loci (QTL) analysis. A population (n = 167) derived from a cross between a female and male plants was evaluated for morpho-agronomic traits over three years. Interval mapping (IM) and restricted multiple QTL mapping (rMQM) analysis was applied, and 18 QTLs were detected. QTLs were located in two linkage groups (LG): 5 in LG5 and 13 in LG6. The physical position of markers of both groups was mapped onto the reference genome through BLAST analysis. LG5 and LG6 match with chromosome 1 (sex-determining chromosome) and chromosome 5, respectively. Haplotypes of both chromosomes of the heterozygous parent and their progeny were obtained, and a bin map was developed. Bins were used to map the QTLs on the reference genome and to perform the association analysis with the morpho-agronomic traits. Two major and stable QTLs over the years (R2 > 10%) for number of stalk and earliness were mapped in the end of chromosome 1 into a bin that spans 3.25 Mb and includes the sex-determination locus. In chromosome 5, some QTLs were located in the center of chromosome for the year 2016. Branching is tightly regulated by both internal factors (such as plant hormones) and external factors (such as light conditions). QTLs for branching height and earliness were detected in a bin that spans 4.96 Mb. Functional annotation of genes within the two bins revealed candidate genes with potential roles in SA and light signaling and photomorphogenesis pathways that may be involved in branching and/or tillering. This is the first study providing the identification of genomic regions associated with yield-related morpho-agronomic traits in asparagus.