Quantitative Trait Loci For Length Research Articles

Genome-wide QTL mapping for agronomic traits in the winter wheat cultivar Pindong 34 based on 90K SNP array.

Agronomic traits are key components of wheat yield. Exploitation of the major underlying quantitative trait loci (QTLs) can improve the yield potential in wheat breeding. In this study, we constructed a recombinant inbred line (RIL) population from Mingxian 169 (MX169) and Pindong 34 (PD34) to determine the QTLs for grain length (GL), grain width (GW), grain length-to-width ratio (LWR), plant height (PH), spike length (SL), grain number per spike (GNS), and the thousand grain weight (TGW) across four environments using wheat 90K SNP array. A QTL associated with TGW, i.e., QTGWpd.swust-6BS, was identified on chromosome 6B, which explained approximately 14.1%-16.2% of the phenotypic variation. In addition, eight QTLs associated with GL were detected across six chromosomes in four different test environments. These were QGLpd.swust-1BL, QGLpd.swust-2BL, QGLpd.swust-3BL.1, QGLpd.swust-3BL.2, QGLpd.swust-5DL, QGLpd.swust-6AL, QGLpd.swust-6DL.1, and QGLpd.swust-6DL.2. They accounted for 9.0%-21.3% of the phenotypic variation. Two QTLs, namely, QGWpd.swust-3BS and QGWpd.swust-6DL, were detected for GW on chromosomes 3B and 6D, respectively. These QTLs explained 12.8%-14.6% and 10.8%-15.2% of the phenotypic variation, respectively. In addition, two QTLs, i.e., QLWRpd.swust-7AS.1 and QLWRpd.swust-7AS.2, were detected on chromosome 7A for the grain LWR, which explained 10.9%-11.6% and 11.6%-11.2% of the phenotypic variation, respectively. Another QTL, named QGNSpd-swust-6DS, was discovered on chromosome 6D, which determines the GNS and which accounted for 11.4%-13.8% of the phenotypic variation. Furthermore, five QTLs associated with PH were mapped on chromosomes 2D, 3A, 5A, 6B, and 7B. These QTLs were QPHpd.swust-2DL, QPHpd.swust-3AL, QPHpd.swust-5AL, QPHpd.swust-6BL, and QPHpd.swust-7BS, which accounted for 11.3%-19.3% of the phenotypic variation. Lastly, a QTL named QSLpd.swust-3AL, conferring SL, was detected on chromosome 3A and explained 16.1%-17.6% of the phenotypic variation. All of these QTLs were defined within the physical interval of the Chinese spring reference genome. The findings of this study have significant implications for the development of fine genetic maps, for genomic breeding, and for marker-assisted selection to enhance wheat grain yield.

Fine mapping of a major QTL, qKl-1BL controlling kernel length in common wheat.

A major stable QTL, qKl-1BL, for kernel length of wheat was narrowed down to a 2.04-Mb interval on chromosome 1BL; the candidate genes were predicated and the genetic effects on yield-related traits were characterized. As a key factor influencing kernel weight, wheat kernel shape is closely related to yield formation, and in turn affects both wheat processing quality and market value. Fine mapping of the major quantitative trait loci (QTL) for kernel shape could provide genetic resources and a theoretical basis for the genetic improvement of wheat yield-related traits. In this study, a major QTL for kernel length (KL) on 1BL, named qKl-1BL, was identified from the recombinant inbred lines (RIL) in multiple environments based on the genetic map and physical map, with 4.76-21.15% of the phenotypic variation explained. To fine map qKl-1BL, the map-based cloning strategy was used. By using developed InDel markers, the near-isogenic line (NIL) pairs and eight key recombinants were identified from a segregating population containing 3621 individualsderived from residual heterozygous lines (RHLs)self-crossing. In combination with phenotype identification, qKl-1BL was finely positioned into a 2.04-Mb interval, KN1B:698.15-700.19Mb, with eight differentially expressed genes enriched at the key period of kernel elongation. Based on transcriptome analysis and functional annotation information, two candidate genes for qKl-1BL controlling kernel elongation were identified. Additionally, genetic effect analysis showed that the superior allele of qKl-1BL from Jing411 could increase KL, thousand kernel weight (TKW), and yield per plant (YPP) significantly, as well as kernel bulk density and stability time. Taken together, this study identified a QTL interval for controlling kernel length with two possible candidate genes, whichprovides an important basis for qKl-1BL cloning, functional analysis, and application in molecular breeding programs.

Fine mapping of the panicle length QTL qPL5 in rice

Panicle length is a crucial trait tightly associated with spikelets per panicle and grain yield in rice. To dissect the genetic basis of panicle length, a population of 161 recombinant inbred lines (RILs) was developed from the cross between an aus variety Chuan 7 (C7) and a tropical Geng variety Haoboka (HBK). C7 has a panicle length of 30 cm, 7 cm longer than that of HBK, and the panicle length was normally distributed in the RIL population. A total of six quantitative trait loci (QTLs) for panicle length were identified, and single QTLs explained the phenotypic variance from 4.9 to 18.1%. Among them, three QTLs were mapped to the regions harbored sd1, DLT, and Ehd1, respectively. To validate the genetic effect of a minor QTL qPL5, a near-isogenic F2 (NIF2) population segregated at qPL5 was developed. Interestingly, panicle length displayed bimodal distribution, and heading date also exhibited significant variation in the NIF2 population. qPL5 accounted for 66.5% of the panicle length variance. The C7 allele at qPL5 increased panicle length by 2.4 cm and promoted heading date by 5 days. Finally, qPL5 was narrowed down to an 80-kb region flanked by markers M2197 and M2205 using a large NIF2 population of 7600 plants. LOC_Os05g37540, encoding a phytochrome signal protein whose homolog in Arabidopsis enlarges panicle length, is regarded as the candidate gene because a single-nucleotide mutation (C1099T) caused a premature stop codon in HBK. The characterization of qPL5 with enlarging panicle length but promoting heading date makes its great value in breeding early mature varieties without yield penalty in rice.

Mapping and Candidate Gene Prediction of qPL7-25: A Panicle Length QTL in Dongxiang Wild Rice

Panicle length (PL) is an important trait closely related to rice yield. More than 200 quantitative trait loci (QTL) for PL have been identified, but only a few can be used for breeding. Dongxiang wild rice contains many excellent genes, and mining favorable PL-related QTL from DXWR is helpful for rice variety improvement. Here, we report a QTL analysis for PL using a recombinant inbred line population consisting of 143 individuals derived from a cross between Dongxiang wild rice and indica cultivar Guangluai 4. A total of four QTL (qPL1-37, qPL4-26, qPL7-25, and qPL8-4) for PL were identified and located on chromosomes 1, 4, 7, and 8. Among them, qPL7-25 showed the largest F-value of 32.32 and 16.80, and the QTL explained 18.66% and 13.06% of the phenotypic variation of Dongxiang wild rice in Hangzhou and Hainan, respectively. QTL mapping was performed using a population of 1800 individuals derived from the crossing of NIL-qPL7-25 and GLA4. qPL7-25 was located between two InDel markers, InDel-24591 and InDel-24710, in a 119 kb region containing 14 predicted genes. Using Sanger sequencing and qRT-PCR analysis, we propose that LOC_Os07g41200 is probably a new allele of the well-known GL7 gene, which affects grain length and appearance quality in rice. These results provide new insights into the use of molecular marker-assisted selection for breeding high-yielding and high-quality rice varieties.

Genetic Effects Analysis of QTLs for Rice Grain Size Based on CSSL-Z403 and Its Dissected Single and Dual-Segment Substitution Lines.

Rice chromosomal segment substitution lines (CSSLs) are ideal materials for studying quantitative traits such as grain size. Here, a rice large-grain CSSL-Z403 was identified among progeny of the recipient Xihui18 and the donor Jinhui35 based on molecular marker-assisted selection. Z403 carried 10 substitution segments with average length of 3.01 Mb. Then, a secondary F2 population derived from a cross between Xihui18 and Z403 was used to map quantitative trait loci (QTL) for grain size. Six QTLs distributed on chromosomes 5, 6, 7, 9 and 12 were detected. Finally four single-segment substitution lines (SSSLs) and two dual-segment substitution lines (DSSLs) carrying these target QTLs were constructed, and 10 novel QTLs were identified by four SSSLs. The large grain of Z403 was controlled at least by qGWT5, qGWT7, qGWT9 and qGWT12, and its grain weight was influenced through grain length QTL such as qGL5, qGL6, qGL9 and qGL12, as well as grain width QTL such as qGW5, qGW7, qGW9 and qGW12. Among 16 QTLs, four QTLs including qGL6, etc., might be novel compared with the reported documents. Again, positive or less negative epistatic effects between two non-allelic QTLs (additive effect > 0) may assist screening the genotype with larger grain size in further selection.

Genetics of evolved load resistance in the skeletons of unusually large mice from Gough Island.

A primary function of the skeleton is to resist the loads imparted by body weight. Genetic analyses have identified genomic regions that contribute to differences in skeletal load resistance between laboratory strains of mice, but these studies are usually restricted to 1 or 2 bones and leave open the question of how load resistance evolves in natural populations. To address these challenges, we examined the genetics of bone structure using the largest wild house mice on record, which live on Gough Island (GI). We measured structural traits connected to load resistance in the femur, tibia, scapula, humerus, radius, ulna, and mandible of GI mice, a smaller-bodied reference strain from the mainland, and 760 of their F2s. GI mice have bone geometries indicative of greater load resistance abilities but show no increase in bone mineral density compared to the mainland strain. Across traits and bones, we identified a total of 153 quantitative trait loci (QTL) that span all but one of the autosomes. The breadth of QTL detection ranges from a single bone to all 7 bones. Additive effects of QTL are modest. QTL for bone structure show limited overlap with QTL for bone length and width and QTL for body weight mapped in the same cross, suggesting a distinct genetic architecture for load resistance. Our findings provide a rare genetic portrait of the evolution of load resistance in a natural population with extreme body size.

Introgression of QTL from Aegilops tauschii enhances yield-related traits in common wheat

To break the narrow diversity bottleneck of the wheat D genome, a set of Aegilops tauschii-wheat introgression (A-WI) lines was developed by crossing Ae. tauschii accession T015 with common wheat elite cultivar Zhoumai 18 (Zhou18). A high-density genetic map was constructed based on Single Nucleotide Polymorphism (SNP) markers and 15 yield-related traits were evaluated in 11 environments for detecting quantitative trait loci (QTL). A total of 27 environmentally stable QTL were identified in at least five environments, 20 of which were derived from Ae. tauschii T015, explaining up to 24.27% of the phenotypic variations. The major QTL for kernel length (KL), QKl-2D.5, was delimited to a physical interval of approximately 2.6 Mb harboring 52 candidate genes. Three Kompetitive Allele Specific PCR (KASP) markers were successfully developed based on nonsynonymous nucleotide mutations of candidate gene AetT093_2Dv1G100900.1 and showed that A-WI lines with the T015 haplotype had significantly longer KL than the Zhou18 haplotype across all 11 environments. Four primary valuable A-WIs with good trait performance and carrying yield-related QTL were selected for breeding improvement. The results will facilitate the efficient transfer of beneficial genes from Ae. tauschii into wheat cultivars to improve wheat yield and other traits.

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.

Identification and validation of stable quantitative trait loci for yield component traits in wheat

Grain weight and grain number are important yield component traits in wheat and identification of underlying genetic loci is helpful for improving yield. Here, we identified eight stable quantitative trait loci (QTL) for yield component traits, including five loci for thousand grain weight (TGW) and three for grain number per spike (GNS) in a recombinant inbred line population derived from cross Yangxiaomai/Zhongyou 9507 across four environments. Since grain size is a major determinant of grain weight, we also mapped QTL for grain length (GL) and grain width (GW). QTGW.caas-2D, QTGW.caas-3B, QTGW.caas-5A and QTGW.caas-7A.2 for TGW co-located with those for grain size. QTGW.caas-2D also had a consistent genetic position with QGNS.caas-2D, suggesting that the pleiotropic locus is a modulator of trade-off effect between TGW and GNS. Sequencing and linkage mapping showed that TaGL3-5A and WAPO-A1 were candidate genes of QTGW.caas-5A and QTGW.caas-7A.2, respectively. We developed Kompetitive allele specific PCR (KASP) markers linked with the stable QTL for yield component traits and validated their genetic effects in a diverse panel of wheat cultivars from the Huang-Huai River Valley region. KASP-based genotyping analysis further revealed that the superior alleles of all stable QTL for TGW but not GNS were subject to positive selection, indicating that yield improvement in the region largely depends on increased TGW. Comparative analyses with previous studies showed that most of the QTL could be detected in different genetic backgrounds, and QTGW.caas-7A.1 is likely a new QTL. These findings provide not only valuable genetic information for yield improvement but also useful tools for marker-assisted selection.

Discovery and Validation of Grain Shape Loci in U.S. Rice Germplasm Through Haplotype Characterization.

Rice grain shape is a major determinant of rice market value and the end-use. We mapped quantitative trait loci (QTL) for grain shape traits in a bi-parental recombinant inbred line population (Trenasse/Jupiter) and discovered two major grain length QTLs—qGL3.1 and qGL7.1. Previously, a major grain shape gene GS3 was reported in the qGL3.1 region and grain length gene GL7 was reported to be encompassing qGL7.1 locus. The re-sequencing SNP data on the International Rice Research Institute (IRRI) 3K Rice Genome Project (RGP) panel were obtained from the IRRI SNP-Seek database for both genes and haplotype diversity was characterized for each gene in this diverse panel. United States rice germplasm was not well represented in the IRRI 3K RGP database. Therefore, a minimum SNP set was identified for each gene that could differentiate all the characterized haplotypes. These haplotypes in the 3K RGP panel were screened across 323 elite U.S. genotypes using the minimum SNP set. The screening of haplotypes and phenotype association confirmed the role of GS3 under qGL3.1. However, screening of the GL7 haplotypes in the U.S. germplasm panel showed that GL7 did not play a role in qGL7.1, and in addition, GL7.1 did not segregate in the Trenasse/Jupiter RIL population. This concluded that qGL7.1 is a novel QTL discovered on chr7 for grain shape in the Trenasse/Jupiter RIL population. A high-throughput KASP-based SNP marker for each locus (GS3 and qGL7.1) was identified and validated in elite U.S. rice germplasm to be used in an applied rice breeding program.

Analyses and identifications of quantitative trait loci and candidate genes controlling mesocotyl elongation in rice

Rice direct seeding has the significant potential to save labor and water, conserve environmental resources, and reduce greenhouse gas emissions tremendously. Therefore, rice direct seeding is becoming the major cultivation technology applied to rice production in many countries. Identifying and utilizing genes controlling mesocotyl elongation is an effective approach to accelerate breeding procedures and meet the requirements for direct-seeded rice (DSR) production. This study used a permanent mapping population with 144 recombinant inbred lines (RILs) and 2 828 bin-markers to detect quantitative trait loci (QTLs) associated with mesocotyl length in 2019 and 2020. The mesocotyl lengths of the rice RILs and their parents, Lijiangxintuanheigu (LTH) and Shennong 265 (SN265), were measured in a growth chamber at 30°C in a dark environment. A total of 16 QTLs for mesocotyl length were identified on chromosomes 1(2), 2(4), 3(2), 4, 5, 6, 7, 9, 11(2), and 12. Seven of these QTLs, including qML1a, qML1b, qML2d, qML3a, qML3b, qML5, and qML11b, were reproducibly detected in both years via the interval mapping method. The major QTL, qML3a, was reidentified in two years via the composite interval mapping method. A total of 10 to 413 annotated genes for each QTL were identified in their smallest genetic intervals of 37.69 kb to 2.78 Mb, respectively. Thirteen predicted genes within a relatively small genetic interval (88.18 kb) of the major mesocotyl elongation QTL, qML3a, were more thoroughly analyzed. Finally, the coding DNA sequence variations among SN265, LTH, and Nipponbare indicated that the LOC_Os03g50550 gene was the strongest candidate gene for the qML3a QTL controlling the mesocotyl elongation. This LOC_Os03g50550 gene encodes a mitogen-activated protein kinase. Relative gene expression analysis using qRT-RCR further revealed that the expression levels of the LOC_Os03g50550 gene in the mesocotyl of LTH were significantly lower than in the mesocotyl of SN265. In conclusion, these results further strengthen our knowledge about rice's genetic mechanisms of mesocotyl elongation. This investigation's discoveries will help to accelerate breeding programs for new DSR variety development.

QTL Mapping of Mesocotyl Elongation and Confirmation of a QTL in Dongxiang Common Wild Rice in China

Direct-seeded rice (DSR) cultivation is an effective and important way to resolve agricultural labor scarcity, water scarcity and high production cost issues. Mesocotyl elongation (ME) is the main driver of the rapid emergence of rice seedlings from the soil and is an important indicator of the suitability of rice varieties for direct seeding. Hence, discovering ME-related genes is particularly important for breeding rice varieties suitable for direct seeding. In this study, a chromosome segment substitution line (CSSL) population generated from a cross between Dongxiang common wild rice and Nipponbare (Nip) was used to map quantitative trait loci (QTLs) for ME. Two QTLs for mesocotyl length were identified on chromosomes 3 and 6 with logarithm of odds (LOD) scores ranging from 5.47 to 6.04 and explaining 15.95–16.79% of the phenotypic variance. Among these QTLs, qML6 accounted for the highest phenotypic variance (16.79%). Then, to confirm the strongest QTL, we generated an F2 segregating population via the CSL127 line harboring the qML6 locus and the recurrent parent Nip. The QTL qML6-1 associated with ME was mapped to a location between markers DX-C6-2 and DX-C6-4, which is consistent with the location of the previously mapped QTL qML6. qML6-1 had an LOD score of 8.45 and explained 30.56% of the phenotypic variance. The QTLs detected in this study provide promising targets for further genetic characterization and for use in marker-assisted selection to develop varieties with improved ME for the cultivation of DSR.

Identification and validation of major QTL for grain size and weight in bread wheat (Triticum aestivum L.)

Grain size and weight are key components of wheat yield. Exploitation of major underlying quantitative trait loci (QTL) can improve yield potential in wheat breeding. A recombinant inbred line (RIL) population was constructed to detect QTL for thousand-grain weight (TGW), grain length (GL) and grain width (GW) across eight environments. Genomic regions associated with grain size and grain weight were identified on chromosomes 4A and 6A using bulked segregant exome sequencing (BSE-Seq) analysis. After constructing genetic maps, six major QTL detected in at least four individual environments and in best linear unbiased estimator (BLUE) datasets, explained 7.50%–23.45% of the phenotypic variation. Except for QGl.cib-4A, the other five QTL were co-located in two regions, namely QTgw/Gw.cib-4A and QTgw/Gw/Gl.cib-6A. Interactions of these QTL were analyzed. Unlike QTgw/Gw/Gl.cib-6A, QTgw/Gw.cib-4A and QGl.cib-4A had no effect on grain number per spike (GNS). The QTL were validated in a second cross using Kompetitive Allele Specific PCR (KASP) markers. Since QTgw/Gw.cib-4A was probably a novel locus, it and the KASP markers reported here can be used in wheat breeding. TraesCS4A03G0191200 was predicted to be potential candidate gene for QTgw/Gw.cib-4A based on the sequence differences, spatiotemporal expression patterns, gene annotation and haplotype analysis. Our findings will be useful for fine mapping and for marker-assisted selection in wheat grain yield improvement.

Mapping of quantitative trait loci for root elongation in rice (Oryza sativa L.) treated with various nitrogen sources and concentrations

ABSTRACT Roots are important plant organs that absorb water and nutrients. Root length responses are influenced by the plants’ sources of nitrogen (N), such as ammonium (NH4 +) and nitrate (NO3 −) ions and their concentrations. Here, to determine the genetic resources with the potential to improve the root system of rice (Oryza sativa L.), the root development traits of a core set of 334 introgression lines (ILs) were assessed in plants grown in hydroponic culture medium containing low (5 μM) or high (500 μM) concentrations of N in the form of NH4 + or NO3 −. ILs were classified into three clusters. The mean value of maximum root length (MRL) in cluster I was significantly higher than that in the other two clusters under all conditions. Root number (RN) differed significantly between clusters IIa and IIb, with the mean RN being higher in cluster IIa. In addition, the order of the mean total root length of the clusters was cluster I > IIa > IIb. Therefore, ILs in cluster I are considered genetic resources for improving root development traits under all tested N conditions. Among the ILs, YTH187 – which is derived from YP5 as a donor – had a longer MRL under all conditions. Quantitative trait loci (QTL) analyses, performed using recombinant inbred lines derived from a cross between IR 64 and YTH187, revealed that qRL5.3-YP5 and qRL6.5-YP5 were detected under all N conditions. In contrast, qRL4.1-YP5 was detected only under low KNO3 concentrations, whereas qRL8.1-YP5 was detected under high concentrations of NH4Cl and KNO3. YP5 alleles at these QTLs increased MRL. QTLs for root length in rice grown in hydroponic culture have not previously been detected in the vicinity of qRL8.1-YP5; thus, this may be a novel QTL that controls root length in rice. Moreover, qRL8.1-YP5 and qRL4.1-YP5 could be useful QTLs to determine the mechanism of root elongation under KNO3 conditions because such QTLs have not yet been detected under these conditions in rice. In future studies, further fine-mapping and characterization of qRL8.1-YP5 could reveal the mechanism of root elongation under high KNO3 concentration conditions.

Molecular mapping and validation of quantitative trait loci for spike-related traits and plant height in wheat

<p id="C3">Spike-related traits and plant height are important target traits in wheat breeding. In the present study, a population of 198 recombinant inbred lines (RILs) derived from the cross between a CIMMYT wheat line C615 and Yangmai 13 (YM13) was constructed, followed by genotyping with Wheat 90K SNP array and phenotyping of spike-related traits and plant height in three environments to excavate QTLs (quantitative trait loci) for these traits. Using composite interval mapping method, we identified one QTL for total spikelet number per spike (TSS), two QTLs for spike length (SL), two QTLs for spikelet compactness (SC), and three QTLs for plant height (PH). <italic>QSN.yaas-3B</italic> and <italic>QPH.yaas-3B</italic> overlapped on the chromosome 3B. <italic>QSL.yaas-5A</italic>, <italic>QSC.yaas-5A</italic> and <italic>QPH.yaas-5A</italic> overlapped on the chromosome 5A. <italic>QSL.yaas-6A</italic> and <italic>QSC.yaas-6A</italic> overlapped on the chromosome 6A. <italic>QSN.yaas-3B</italic>/<italic>QPH.yaas-3B</italic> and <italic>QSL.yaas-6A</italic>/<italic>QSC.yaas-6A</italic> had not been reported yet, and were likely to be novel loci. The SNP marker closely linked to <italic>QSL.yaas-5A</italic>/<italic>QSC.yaas-5A</italic>/<italic>QPH.yaas-5A</italic> was then converted into one Kompetitive Allele Specific PCR (KASP) marker (QC615-5A-KASP), and validated in a panel of 105 wheat lines. The results would be useful for improvement of yield related traits in wheat breeding.

Identifying QTLs for Grain Size in a Colossal Grain Rice (Oryza sativa L.) Line, and Analysis of Additive Effects of QTLs.

Grain size is an important component of quality and harvest traits in the field of rice breeding. Although numerous quantitative trait loci (QTLs) of grain size in rice have been reported, the molecular mechanisms of these QTLs remain poorly understood, and further research on QTL observation and candidate gene identification is warranted. In our research, we developed a suite of F2 intercross populations from a cross of 9311 and CG. These primary populations were used to map QTLs conferring grain size, evaluated across three environments, and then subjected to bulked-segregant analysis-seq (BSA-seq). In total, 4, 11, 12 and 14 QTLs for grain length (GL), grain width (GW), 1000-grain weight (TGW), and length/width ratio (LWR), respectively, were detected on the basis of a single-environment analysis. In particular, over 200 splicing-related sites were identified by whole-genome sequencing, including one splicing-site mutation with G>A at the beginning of intron 4 on Os03g0841800 (qGL3.3), producing a smaller open reading frame, without the third and fourth exons. A previous study revealed that the loss-of-function allele caused by this splicing site can negatively regulate rice grain length. Furthermore, qTGW2.1 and qGW2.3 were new QTLs for grain width. We used the near-isogenic lines (NILs) of these GW QTLs to study their genetic effects on individuals and pyramiding, and found that they have additive effects on GW. In summary, these discoveries provide a valuable genetic resource, which will facilitate further study of the genetic polymorphism of new rice varieties in rice breeding.

A complex genetic architecture underlies mandibular evolution in big mice from Gough Island.

Some of the most compelling examples of morphological evolution come from island populations. Alterations in the size and shape of the mandible have been repeatedly observed in murid rodents following island colonization. Despite this pattern and the significance of the mandible for dietary adaptation, the genetic basis of island-mainland divergence in mandibular form remains uninvestigated. To fill this gap, we examined mandibular morphology in 609 F2s from a cross between Gough Island mice, the largest wild house mice on record, and mice from a mainland reference strain (WSB). Univariate genetic mapping identifies 3 quantitative trait loci (QTL) for relative length of the temporalis lever arm and 2 distinct QTL for relative condyle length, 2 traits expected to affect mandibular function that differ between Gough Island mice and WSB mice. Multivariate genetic mapping of coordinates from geometric morphometric analyses identifies 27 QTL contributing to overall mandibular shape. Quantitative trait loci show a complex mixture of modest, additive effects dispersed throughout the mandible, with landmarks including the coronoid process and the base of the ascending ramus frequently modulated by QTL. Additive effects of most shape quantitative trait loci do not align with island-mainland divergence, suggesting that directional selection played a limited role in the evolution of mandibular shape. In contrast, Gough Island mouse alleles at QTL for centroid size and QTL for jaw length increase these measures, suggesting selection led to larger mandibles, perhaps as a correlated response to the evolution of larger bodies.

Registration of seven recombinant inbred lines of upland cotton with improved fiber length or strength

AbstractThe genetic base for upland cotton (Gossypium hirsutum L.) is narrow for the economically important fiber traits of strength and length. We developed random mated population RMUP‐C5 from 11 parental lines and released seed in 2008. We have now developed 550 recombinant inbred lines (RILs) from this population and evaluated them for fiber properties in eight environments. We report the development and release of seven RILs with improved fiber strength and/or upper half mean length: MS‐RIL‐009 (Reg. no. GP‐1100, PI 698460), MS‐RIL‐037 (Reg. no. GP‐1101, PI 698461), MS‐RIL‐204 (Reg. no. GP‐1102, PI 698462), MS‐RIL‐219 (Reg no. GP‐1103, PI 698463), MS‐RIL‐282 (Reg. no. GP‐1104, PI 698464), MS‐RIL‐303 (Reg. no. GP‐1105, PI 698465), and MS‐RIL‐490 (Reg. no. GP‐1106, PI 698466). Fiber strength and length for the seven lines are as follows: MS‐RIL 009 (384, 30.0), MS‐RIL 037 (369, 31.3), MS‐RIL‐204 (333, 32.5), MS‐RIL‐219 (345, 31.8), MS‐RIL‐282 (295, 31.4), MS‐RIL‐303 (379, 31.4) and MS‐RIL‐490 (318, 33.0), kN m kg–1 and mm, respectively. Fibers of MS‐RILS 037, 219, and 303 are significantly stronger and longer, fibers of 009 are significantly stronger, and fibers of 204, 282, and 490 are significantly longer than fibers of ‘Acala Ultima’ or ‘Fibermax 966’, the parental lines with the strongest (326–334 kN m kg–1) and longest (29.3–30.0 mm) fibers. MS‐RIL‐009, MS‐RIL‐037, MS‐RIL‐219, and MS‐RIL‐303 are homozygous for favorable alleles at the A07 strength quantitative trait locus (QTL). All lines except MS‐RIL‐009 are homozygous for favorable alleles at the D11 length QTL.

Identification and validation of two major QTLs for spike compactness and length in bread wheat (Triticum aestivum L.) showing pleiotropic effects on yield-related traits.

Two major and stable QTLs for spike compactness and length were detected and validated in multiple genetic backgrounds and environments, and their pleiotropic effects on yield-related traits were analyzed. Spike compactness (SC) and length (SL) are greatly associated with wheat (Triticum aestivum L.) grain yield. To detect quantitative trait loci (QTL) associated with SC and SL, two biparental populations derived from crosses of Chuanmai42/Kechengmai1 and Chuanmai42/Chuannong16 were employed to perform QTL mapping in five environments. A total of 34 QTLs were identified, in which six major QTLs were repeatedly detected in more than four environments and the best linear unbiased prediction datasets, explaining 7.13-33.6% of phenotypic variation. These major QTLs were co-located in two genomic regions on chromosome 5A and 6A, namely QSc/Sl.cib-5A and QSc/Sl.cib-6A, respectively. By developing kompetitive allele-specific PCR (KASP) markers that linked to them, the two loci were validated in different genetic backgrounds, and their interactions were also analyzed. Comparison analysis showed that QSc/Sl.cib-5A was not Vrn-A1 and Q, and QSc/Sl.cib-6A was likely a new locus for SC and SL. Both QSc/Sl.cib-5A and QSc/Sl.cib-6A had pleiotropic effects on other yield-related traits including plant height, thousand grain weight and grain length. Therefore, the two loci combined with the developed KASP markers might be potentially applicable in wheat breeding. Furthermore, based on the spatiotemporal expression patterns, gene annotation, orthologous search and sequence differences, TraesCS5A01G301400 and TraesCS6A01G090300 were considered as potential candidates for QSc/Sl.cib-5A and QSc/Sl.cib-6A, respectively. These results provided valuable information for fine mapping and cloning of the two loci in the future.

Ultra-High-Density QTL Marker Mapping for Seedling Photomorphogenesis Mediating Arabidopsis Establishment in Southern Patagonia.

Arabidopsis thaliana shows a wide range of genetic and trait variation among wild accessions. Because of its unparalleled biological and genomic resources, Arabidopsis has a high potential for the identification of genes underlying ecologically important complex traits, thus providing new insights on genome evolution. Previous research suggested that distinct light responses were crucial for Arabidopsis establishment in a peculiar ecological niche of southern Patagonia. The aim of this study was to explore the genetic basis of contrasting light-associated physiological traits that may have mediated the rapid adaptation to this new environment. From a biparental cross between the photomorphogenic contrasting accessions Patagonia (Pat) and Columbia (Col-0), we generated a novel recombinant inbred line (RIL) population, which was entirely next-generation sequenced to achieve ultra-high-density saturating molecular markers resulting in supreme mapping sensitivity. We validated the quality of the RIL population by quantitative trait loci (QTL) mapping for seedling de-etiolation, finding seven QTLs for hypocotyl length in the dark and continuous blue light (Bc), continuous red light (Rc), and continuous far-red light (FRc). The most relevant QTLs, Rc1 and Bc1, were mapped close together to chromosome V; the former for Rc and Rc/dark, and the latter for Bc, FRc, and dark treatments. The additive effects of both QTLs were confirmed by independent heterogeneous inbred families (HIFs), and we explored TZP and ABA1 as potential candidate genes for Rc1 and Bc1QTLs, respectively. We conclude that the Pat × Col-0 RIL population is a valuable novel genetic resource to explore other adaptive traits in Arabidopsis.