Translocation Lines Research Articles

Long‐range assembly of sequences helps to unravel the genome structure and small variation of the wheat–Haynaldia villosa translocated chromosome 6VS.6AL

SummaryGenomics studies in wild species of wheat have been limited due to the lack of references; however, new technologies and bioinformatics tools have much potential to promote genomic research. The wheat–Haynaldia villosa translocation line T6VS·6AL has been widely used as a backbone parent of wheat breeding in China. Therefore, revealing the genome structure of translocation chromosome 6VS·6AL will clarify how this chromosome formed and will help to determine how it affects agronomic traits. In this study, chromosome flow sorting, NGS sequencing and Chicago long‐range linkage assembly were innovatively used to produce the assembled sequences of 6VS·6AL, and gene prediction and genome structure characterization at the molecular level were effectively performed. The analysis discovered that the short arm of 6VS·6AL was actually composed of a large distal segment of 6VS, a small proximal segment of 6AS and the centromere of 6A, while the collinear region in 6VS corresponding to 230–260 Mb of 6AS‐Ta was deleted when the recombination between 6VS and 6AS occurred. In addition to the molecular mechanism of the increased grain weight and enhanced spike length produced by the translocation chromosome, it may be correlated with missing GW2‐V and an evolved NRT‐V cluster. Moreover, a fine physical bin map of 6VS was constructed by the high‐throughput developed 6VS‐specific InDel markers and a series of newly identified small fragment translocation lines involving 6VS. This study will provide essential information for mining of new alien genes carried by the 6VS·6AL translocation chromosome.

Genotypic and Phenotypic Characterization of Two Triticum aestivum L.—Dasypyrum villosum Translocations Lines in the Same Wheat Genetic Background

A wheat 660K chip was used to genotype two wheat-Dasypyrum villosum 6V#4S.6DL and 6V#2S.6AL translocation lines (A303 and B303) and their common wheat recurrent parent Wan7107. The results showed that these three lines have similar characteristics of base composition except for the translocation chromosomes. The alien translocation chromosomes have fewer homozygous and more heterozygous genotypes with more invalid probes. Distributions of SNPs between the translocation lines and Wan7107 were mainly dense on the regions of 6AS or 6DS as expected, but unexpectedly also on near the telomere of 2BS, and some regions of other wheat chromosomes. Meanwhile, the translocation lines A303 and B303 have 99.44% and 98.81% identical genotypes to Wan7107, respectively. Under the same genetic background, A303 and B303 showed different reactions to Blumeria graminis f. sp. tritici (Bgt) strains of powdery mildew. Both translocation lines have higher grain weight and plant height, and B303 has fewer spikelets compared to Wan7107. These results provide us a new insight into the genomic variation between the backcross generation plant and the recurrent parent, which is valuable information for understanding the relationship between wheat and the 6VS chromosome of D. villosum as well as the application potential of the alien chromosome arms.

Development and Characterization of Wheat-Agropyron cristatum Introgression Lines Induced by Gametocidal Genes and Wheat ph1b Mutant

The P genome of Agropyron cristatum Gaertn. contains many desirable genes that can be utilized as genetic resources to improve wheat. In this research, we used both the gametocidal chromosome 2Cc and the pairing homologous gene (Ph1b) mutant to induce structural aberrations and translocations between wheat and the 4P, 5P, and 6P genome chromosomes. By using the two approaches, a total of 19 wheat-A. cristatum translocations have been identified, in which 13 were induced by the Triticum aestivum cv. Chinese Spring (CS) ph1b mutant (CS ph1b) and six were induced by gametocidal chromosome 2Cc from Aegilops cylindrica Host. The wheat-4P, -5P and -6P A. cristatum translocations were characterized by in situ hybridization and by a set of conserved orthologous set (COS) molecular markers. The aberrations included centromeric translocations, terminal translocations, dicentric translocations, and deletions. The average induction frequency of chromosome structural aberrations was 10.9% using gametocidal 2Cc chromosome and 8.8% using ph1b mutant. The highest frequency obtained was for chromosome 4P using both approaches. All the wheat-A. cristatum translocation lines obtained were valuable for identifying A. cristatum chromosome 4P, 5P, and 6P related genes. In addition, these lines provided genetic resources and new germplasm accessions for the genetic improvement of wheat.

Production and characterization of a disomic 1M/1D Triticum aestivum-Aegilops comosa substitution line.

The online version contains supplementary material available at 10.1007/s11032-021-01207-2.

Karyotyping Dasypyrum breviaristatum chromosomes with multiple oligonucleotide probes reveals the genomic divergence in Dasypyrum.

The perennial species Dasypyrum breviaristatum (genome Vb) contains many potentially valuable genes for the improvement of common wheat. Construction of a detailed karyotype of D. breviaristatum chromosomes will be useful for the detection of Dasypyrum chromatin in wheat background. We established the standard karyotype of 1Vb-7Vb chromosomes through nondenaturing fluorescence in situ hybridization (ND-FISH) technique using 28 oligonucleotide probes from the wheat - D. breviaristatum partial amphiploid TDH-2 (AABBVbVb) and newly identified wheat - D. breviaristatum disomic translocation and addition lines D2138 (6VbS.2VbL), D2547 (4Vb), and D2532 (3VbS.6VbL) by comparative molecular marker analysis. The ND-FISH with multiple oligo probes was conducted on the durum wheat - D. villosum amphiploid TDV-1 and large karyotype differences between D. breviaristatum and D. villosum was revealed. These ND-FISH probes will be valuable for screening the wheat - Dasypyrum derivative lines for chromosome identification, and the newly developed wheat - D. breviaristatum addition lines may broaden the gene pool of wheat breeding. The differences between D. villosum and D. breviaristatum chromosomes revealed by ND-FISH will help us understand evolutionary divergence of repetitive sequences within the genus Dasypyrum.

Physical mapping of chromosome 7J and a purple coleoptile gene from Thinopyrum intermedium in the common wheat background.

A physical map of Thinopyrum intermedium chromosome 7J was constructed using translocation mapping, and a new seedling purple coleoptile gene was mapped to the bin of FL 0.35-0.63 of 7JS. Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt), a wild relative of common wheat, harbors numerous beneficial genes for wheat improvement. Previous studies showed that wheat-Th. intermedium partial amphiploid TAF46 and its derived addition line L1 had a purple coleoptile, which was derived from Th. intermedium chromosome 7J. To identify and physically map the purple coleoptile gene, 12 wheat-Th. intermedium 7J translocation lines were analyzed by sequential multicolor fluorescence in situ hybridization (mc-FISH), PCR-based landmark unique gene (PLUG) and intron targeting (IT) markers. A physical map of the 7J chromosome was constructed, consisting of eight chromosomal bins with 89 markers. Seedling evaluation of the coleoptile colors of all tested materials indicated that the purple coleoptile gene was located to the bin with a fraction length (FL) of 0.35-0.63 on chromosome 7JS. Furthermore, based on the syntenic relationships between Th. intermedium and wheat chromosomes, we developed a new chromosome 7J-specific EST-PCR marker from the chromosomal region corresponding to the purple coleoptile gene through the Triticeae multi-omics database. The approach of designing chromosome-specific markers has facilitated fine mapping of the Thinopyrum-specific purple coleoptile gene, and these translocation lines will be valuable for studying the function of the purple coleoptile gene in anthocyanin biosynthesis.

Development and characterization of new allohexaploid resistant to web blotch in peanut

Peanut diseases seriously threaten peanut production, creating disease-resistant materials via interspecific hybridization is an effective way to deal with this problem. In this study, the embryo of an interspecific F1 hybrid was obtained by crossing the Silihong (Slh) cultivar with Arachis duranensis (ZW55), a diploid wild species. Seedlings were generated by embryo rescue and tissue culture. A true interspecific hybrid was then confirmed by cytological methods and molecular markers. After treating seedlings with colchicine during in vitro multiplication, the established interspecific F1 hybrid produced seeds which were named as Am1210. With oligonucleotide fluorescence in situ hybridization (Oligo FISH), molecular marker evaluations, morphological and web blotch resistance characterization, we found that: 1) Am1210 was an allohexaploid between Slh and ZW55; 2) the traits of spreading lateral branches, single-seeded or double-seeded pods and red seed coats were observed to be dominant compared to the erect type, multiple-seeded pods and brown seed coats; 3) the web blotch resistance of Am1210 was significantly improved than that of Slh, indicating the contribution of the web blotch resistance from the wild parent A. duranensis. In addition, 69 dominant and co-dominant molecular markers were developed which could be both used to verify the hybrid in this study and to identify translocation or introgression lines with A. duranensis chromosome fragments in future studies as well.

Pm67, a new powdery mildew resistance gene transferred from Dasypyrum villosum chromosome 1V to common wheat (Triticum aestivum L.)

Powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a global disease that poses a serious threat to wheat production. To explore additional resistance gene, a wheat-Dasypyrum villosum 1V#5 (1D) disomic substitution line NAU1813 (2n = 42) with high level of seedling resistance to powdery mildew was used to generate the recombination between chromosomes 1V#5 and 1D. Four introgression lines, including t1VS#5 ditelosomic addition line NAU1815, t1VL#5 ditelosomic addition line NAU1816, homozygous T1DL·1VS#5 translocation line NAU1817, and homozygous T1DS·1VL#5 translocation line NAU1818 were developed from the selfing progenies of 1V#5 and 1D double monosomic line that derived from F1 hybrids of NAU1813/NAU0686. All of them were characterized by fluorescence in situ hybridization, genomic in situ hybridization, 1V-specific markers analysis, and powdery mildew tests at different developmental stages. A new powdery mildew resistance gene named Pm67 was physically located in the terminal bin (FL 0.70–1.00) of 1VS#5. Lines with Pm67 exhibited seedling stage immunity and tissue-differentiated reactions at adult plant stage. The sheaths, stems, and spikes of the Pm67 line were still immune, but the leaves showed a low degree of susceptibility. Microscopic observation showed that most penetration attempts were stopped in association with papillae on the sheath, and colonies cannot form conidia on the susceptible leaf of Pm67 line at adult plant stage, suggesting that the defence layers of the Pm67 line is tissue-differentiated. Thus, the T1DL·1VS#5 translocation line NAU1817 provides a new germplasm in wheat breeding for improvement of powdery mildew resistance.

Grain proteomic analysis reveals central stress responsive proteins caused by wheat-Haynaldia villosa 6VS/6AL translocation

Haynaldia villosa (2n=14, VV), a wild grass of the subtribe Triticeae, serves as potential gene resources for wheat genetic improvement. In this study, the proteome characterization during grain development of Yangmai 5 and Yangmai 5-H. villosa 6VS/6AL translocation line was investigated by a comparative proteomic approach. Two-dimensional electrophoresis identified 81 differentially accumulated proteins (DAPs) during five grain developmental stages in wheat-H. villosa translocation line. These proteins were mainly involved in stress defense, storage protein, energy metabolism, protein metabolism and folding, carbon metabolism, nitrogen metabolism, and starch metabolism. In particular, 6VS/6AL translocation led to significant upregulation of 36 DAPs and specific expression of 11 DAPs such as chitinase, thaumatin-like proteins, glutathione transferase, α-amylase inhibitor, heat shock proteins, and betaine aldehyde dehydrogenase. These proteins mainly involved in biotic and abiotic stress responses. Further analysis found that the upstream 1 500 promoter regions of these stress-responsive DAP genes contained multiple high-frequency cis-acting elements related to stress defense such as abscisic acid response element ABRE, methyl jasmonate (MeJA)-response element TGACG-motif and CGTCA-motif involved in oxidative stress and antioxidant response element (ARE). RNA-seq and RT-qPCR analyses revealed the high expression of these stress-defensive DAP genes in the developing grains, particularly at the early-middle grain filling stages. Our results demonstrated that 6VS chromosome of H. villosa contains abundant stress-defensive proteins that have potential values for wheat genetic improvement.

RNA interference targeting ω-secalin genes differentially affects the processing quality in a wheat T1BL·1RS translocation line

Wheat-rye T1BL·1RS translocation lines are widely used, especially in China, but their processing quality is generally poor. An interfering expression vector targeting the ω-secalin genes was constructed with the 1Bx7 seed-specific promoter. Biolistic-mediated genetic transformation of the wheat cultivar KN199 carrying the T1BL·1RS translocation generated 10 transgenic lines. Two representative transgenic lines, 8-2 and 13-7, were selected for analysis. Compared with the control, the two transformants showed an up to 4.5-fold decrease in total ω-secalins and various levels of decrease in ω-gliadins, γ-gliadins, and low-molecular-weight glutenins. A decrease in high molecular weight (HMW) glutenin 1Bx7 was detected only in 8-2, owing possibly to promoter methylation. Increased levels of α-gliadins were observed in both transformants, but increased levels of HMW glutenins were observed only in 13-7. Line 13-7 showed increases in gluten index, Zeleny sedimentation value, stabilization time, and maximum resistance. Its bread volume was 849.6 mL, an 11.9% increase over that of the control. Line 8-2 showed decreases in these parameters, but its total cake-making quality score was 88, an 17.3% increase over that of the control. The study demonstrates that the same RNAi construct may produce different effects on wheat processing quality and highlights the influence of the vector promoter in RNA interference.

Identification of an Elite Wheat-Rye T1RS·1BL Translocation Line Conferring High Resistance to Powdery Mildew and Stripe Rust.

Wheat-rye T1RS·1BL translocations have been widely used worldwide in wheat production for multiple disease resistance and superior yield traits. However, many T1RS·1BL translocations have successively lost their resistance to pathogens due to the coevolution of pathogen virulence with host resistance. Because of the extensive variation in rye (Secale cereale L.) as a naturally cross-pollinating relative of wheat, it still has promise to widen the variation of 1RS and to fully realize its application value in wheat improvement. In the present study, the wheat-rye breeding line R2207 was characterized by comprehensive analyses using genomic in situ hybridization (GISH), multicolor fluorescence in situ hybridization with multiple probes, multicolor GISH, and molecular marker analysis, and then was proven to be a cytogenetically stable wheat-rye T1RS·1BL translocation line. Based on the disease responses to different isolates of powdery mildew and genetic analysis, R2207 appears to possess a novel variation for resistance, which was confirmed to be located on the rye chromosome arm 1RS. Line R2207 also exhibited high levels of resistance to stripe rust at both seedling and adult stages, as well as enhanced agronomic performance, so it has been transferred into a large number of commercial cultivars using an efficient 1RS-specific kompetitive allele specific PCR marker for marker-assisted selection.

Molecular and Cytogenetic Characterization of a Wheat-Rye 7BS.7RL Translocation Line with Resistance to Stripe Rust, Powdery Mildew, and Fusarium Head Blight.

Secale cereale is used as a source of genes for disease resistance in wheat cultivation. In this study, a homozygous translocation line (RT14-245) that originated from a cross between a commercial wheat cultivar (Mianyang 11) and a local Chinese variety of rye (Baili) was developed. Multicolor fluorescence in situ hybridization and PCR analysis demonstrated that the translocation chromosome was 7BS.7RL. Resistance analysis showed that RT14-245 was resistant to prevalent pathotypes of stripe rust and powdery mildew. RT14-245 also exhibited high resistance to Fusarium head blight, which was similar to the resistance exhibited by the wheat cultivar Sumai 3. The results indicated that RT14-245 simultaneously exhibited high levels of resistance against stripe rust, powdery mildew, and Fusarium head blight. These results indicate that chromosome arm 7RL in the translocation line RT14-245 is an excellent new resource for wheat breeding programs.

The consensus rye microsatellite map with EST-SSRs transferred from wheat.

Microsatellite (SSR) markers with known precise intrachromosomal locations are widely used for mapping genes in rye and for the investigation of wheat-rye translocation lines and triticale highly demanded for mapping economically important genes and QTL-analysis. One of the sources of novel SSR markers in rye are microsatellites transferable from the wheat genome. Broadening the list of available SSRs in rye mapped to chromosomes is still needed, since some rye chromosome maps still have just a few microsatellite loci mapped. The goal of the current study was to integrate wheat EST-SSRs into the existing rye genetic maps and to construct a consensus rye microsatellite map. Four rye mapping populations (P87/P105, N6/N2, N7/N2 and N7/N6) were tested with CFE (EST-SSRs) primers. A total of 23 Xcfe loci were mapped on rye chromosomes: Xcfe023, -136 and -266 on chromosome 1R, Xcfe006, -067, -175 and -187 on 2R, Xcfe029 and -282 on 3R, Xcfe004, -100, -152, -224 and -260 on 4R, Xcfe037, -208 and -270 on 5R, Xcfe124, -159 and -277 on 6R, Xcfe010, -143 and -228 on 7R. With the exception of Xcfe159 and Xcfe224, all the Xcfe loci mapped were found in orthologous positions considering multiple evolutionary translocations in the rye genome relative to those of common wheat. The consensus map was constructed using mapping data from the four bi-parental populations. It contains a total of 123 microsatellites, 12 SNPs, 118 RFLPs and 2 isozyme loci.

Integrated single-molecule long-read sequencing and Illumina sequencing reveal the resistance mechanism of Psathyrostachys huashanica in response to barley yellow dwarf virus-GAV

Although Psathyrostachys huashanica has excellent potential for resistance gene mining and molecular genetic breeding, no reference genome is available. To date, most studies of P. huashanica have been focused on the creation of translocation lines and additional lines, as well as the development of molecular markers. Therefore, research at the transcriptional level is lacking. In this study, the full-length transcriptome of P. huashanica was sequenced using PacBio isoform sequencing (Iso-Seq) of a pooled RNA sample to explore the potential full-length transcript isoforms. We obtained 112,596 unique transcript isoforms with a total length of 114,957,868 base pairs (bp). Subsequently, Illumina sequencing reads were used to correct and trim the PacBio isoforms. We annotated 103,875 unigenes in at least one functional database, and identified a plethora of differentially-expressed genes (DEGs) that are involved in the defense responses of P. huashanica against barley yellow dwarf virus-GAV (BYDV-GAV). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these DEGs were mostly involved in plant-pathogen interaction, plant hormone signal transduction, and the mitogen-activated protein kinase (MAPK) signaling pathway. Additionally, we selected twenty of the RNA-seq identified resistance-related up-regulated genes, including MAPKs, cysteine-rich receptor-like protein kinases (CRPKs), calcium-dependent protein kinases (CDPKs), pathogenesis-related protein (PR) proteins, WRKYs, and disease resistance proteins, and validated their up-regulation in response to BYDV-GAV by quantitative real-time PCR. Our results indicate that a series of defense-related genes were induced in P. huashanica during BYDV-GAV infection. The full-length transcriptome dataset will contribute to improved use of stress-resistance genes of P. huashanica, and serves as a reference database for the analysis of transcript expression in P. huashanica.

Screening and functional characterization of candidate resistance genes to powdery mildew from Dasypyrum villosum#4 in a wheat line Pm97033.

Three genes designated DvLox, Pm21#4, and Pm21#4-H identified in a wheat-Dasypyrum villosum#4 T6V#4S·6DL translocation line Pm97033 conferred wheat for powdery mildew resistance. Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most devastating diseases in wheat. To date, only a few genes conferring resistance to wheat PM are cloned. Dasypyrum villosum is a wild relative of wheat, which provides Pm21 conferring wheat immunity to PM. In this study, we obtained many differentially expressed genes (DEGs) from a wheat-D. villosum#4 T6V#4S·6DL translocation line Pm97033 using RNA-sequencing. Among them, 7 DEGs associated with pathogen resistance were up-regulated in front of Bgt infection. Virus-induced gene silencing and transformation assays demonstrated that two of them, DvLox and Pm21#4 encoding a lipoxygenase and a encoding coiled-coil/nucleotide-binding site/leucine-rich repeat resistance protein, conferred wheat PM resistance. The transgenic wheat plants expressing DvLox enhanced PM resistance, and the transgenic wheat plants expressing Pm21#4 showed PM immunity. The Pm21#4-silenced Pm97033 plants by the cluster regularly interspaced short palindromic repeats-associated endonuclease (CRISPR/Cas9) system were susceptible to PM. Thus, Pm21#4 is a key gene contributing PM immune resistance in Pm97033. Constitutively expression of Pm21#4-H, which is silenced in Pm97033 and D. villosum#4, endowed a PM-susceptible wheat variety Fielder with PM immune resistance.

Molecular cytogenetic characterization of a novel wheat\u2013Psathyrostachys huashanica Keng T3DS-5NsL\u20225NsS and T5DL-3DS\u20223DL dual translocation line with powdery mildew resistance

BackgroundPsathyrostachys huashanica Keng (2n = 2x = 14, NsNs) carries many outstanding agronomic traits, therefore is a valuable resource for wheat genetic improvement. Wheat–P. huashanica translocation lines are important intermediate materials for wheat breeding and studying the functions of alien chromosomes. However, powdery mildew resistance in these translocation lines has not been reported previously.ResultsThis study developed a novel wheat–P. huashanica translocation line TR77 by selecting a F7 progeny from the cross between heptaploid hybrid H8911 (2n = 7x = 49, AABBDDNs) and durum wheat line Trs-372. Chromosome karyotype of 2n = 42 = 21II was observed in both mitotic and meiotic stages of TR77. Genomic in situ hybridization analysis identified two translocated chromosomes that paired normally at meiosis stage in TR77. Molecular marker analysis showed that part of chromosome 5D was replaced by part of alien chromosome fragment 5Ns. It meant replacement made part 5DL and part 5NsL·5NsS existed in wheat background, and then translocation happened between these chromosomes and wheat 3D chromosome. Fluorescence in situ hybridization demonstrated that TR77 carries dual translocations: T3DS-5NsL·5NsS and T5DL-3DS·3DL. Analysis using a 15 K-wheat-SNP chip confirmed that SNP genotypes on the 5D chromosome of TR77 matched well with these of P. huashanica, but poorly with common wheat line 7182. The translocation was physically located between 202.3 and 213.1 Mb in 5D. TR77 showed longer spikes, more kernels per spike, and much better powdery mildew resistance than its wheat parents: common wheat line 7182 and durum wheat line Trs-372.ConclusionsTR77 is a novel stable wheat–P. huashanica T3DS-5NsL·5NsS and T5DL-3DS·3DL dual translocation line and showed significant improved spike traits and resistance to powdery mildew compared to its parents, thus, it can be an useful germplasm for breeding disease resistance and studying the genetic mechanism of dual translocations.

Molecular dissection of Secale africanum chromosome 6Rafr in wheat enabled localization of genes for resistance to powdery mildew and stripe rust

BackgroundIntrogression of chromatin from Secale species into common wheat has for decades been a successful strategy for controlling the wheat diseases. The wild Secale species, Secale africanum Stapf., is a valuable source for resistance to foliar disease of wheat. A wheat-S. africanum chromosome 6Rafr substitution line displayed resistance to both powdery mildew and stripe rust at the adult-plant stage.ResultsWheat-S. africanum chromosome 6Rafr deletion and translocation lines were produced and identified by sequential non-denaturing fluorescence in situ hybridization (ND-FISH) using multiple Oligo-based probes. Different ND-FISH patterns were observed between S. cereale 6R and S. africanum 6Rafr. With reference to the physical map of the draft genome sequence of rye inbred line Lo7, a comprehensive PCR marker analysis indicated that insertions and deletions had occurred by random exchange between chromosomes 6R and 6Rafr. A survey of the wheat- S. africanum 6Rafr lines for disease resistance indicated that a powdery mildew resistance gene(s) was present on the long arm of 6Rafr at FL0.85–1.00, and that a stripe rust resistance gene(s) was located in the terminal region of 6RafrS at FL0.95–1.00. The wheat-S. africanum 6Rafr introgression lines also displayed superior agronomic traits, indicating that the chromosome 6Rafr may have little linkage drag in the wheat background.ConclusionsThe combination of molecular and cytogenetic methods allowed to precisely identify the chromosome rearrangements in wheat- S. africanum 6Rafr substitution, deletion and translocation lines, and compare the structural difference between chromosomes 6R and 6Rafr. The wheat- S. africanum 6Rafr lines containing gene(s) for powdery mildew and stripe rust resistance could be used as novel germplasm for wheat breeding by chromosome engineering.

A 1BL/1RS translocation contributing to kernel length increase in three wheat recombinant inbred line populations

The 1BL/1RS wheat-rye translocation has been widely utilized in wheat genetic improvement and breeding programs. Our understanding on the effects of the 1BL/1RS translocation on wheat kernel size (e.g. length and width) is limited despite of numerous studies reporting about the effects on kernel weight. Here, we identified a wheat 1BL/1RS translocation line 88-1643 with higher kernel length (KL) using fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH) and molecular markers. To detect the possible role of the 1BL/1RS translocation in KL, kernel width (KW), and thousand-kernel weight (TKW), three recombinant inbred line (RIL) populations were constructed by crossing 88-1643 and three other wheat lines. As expected, the results showed that the values of KL in lines carrying 1RS were significantly higher than those carrying 1BS in three RIL populations at multiple environments, indicating that a major and stably expressed allele or gene responsible for increasing KL is most likely located on 1RS from 88-1643. Additionally, in one RIL population, the increased KL contributed significantly to the increase in TKW. Collectively, the 1BL/1RS translocation reported here is of interest to reveal molecular mechanism of the gene controlling KL and will be useful for improving wheat yield.

The LATERAL ROOT DENSITY gene regulates root growth during water stress in wheat.

SummaryDrought stress is the major limiting factor in agriculture. Wheat, which is the most widely grown crop in the world, is predominantly cultivated in drought‐prone rainfed environments. Since roots play a critical role in water uptake, root response to water limitations is an important component for enhancing wheat adaptation. In an effort to discover novel genetic sources for improving wheat adaptation, we characterized a wheat translocation line with a chromosomal segment from Agropyron elongatum, a wild relative of wheat, which unlike common wheat maintains root growth under limited‐water conditions. By exploring the root transcriptome data, we found that reduced transcript level of LATERAL ROOT DENSITY (LRD) gene under limited water in the Agropyron translocation line confers it the ability to maintain root growth. The Agropyron allele of LRD is down‐regulated in response to water limitation in contrast with the wheat LRD allele, which is up‐regulated by water deficit stress. Suppression of LRD expression in wheat RNAi plants confers the ability to maintain root growth under water limitation. We show that exogenous gibberellic acid (GA) promotes lateral root growth and present evidence for the role of GA in mediating the differential regulation of LRD between the common wheat and the Agropyron alleles under water stress. Suppression of LRD also had a positive pleiotropic effect on grain size and number under optimal growth conditions. Collectively, our findings suggest that LRD can be potentially useful for improving wheat response to water stress and altering yield components.

Development, identification, and characterization of blue-grained wheat-Triticum boeoticum substitution lines.

Diploid wild einkorn wheat, Triticum boeoticum Boiss (AbAb, 2n = 2x = 14), is a wheat-related species with a blue aleurone layer. In this study, six blue-grained wheat lines were developed from F8 progeny of crosses between common wheat and T. boeoticum. The chromosome constitutions of these lines were characterized by fluorescence in situ hybridization (FISH) using the oligonucleotide probes Oligo-pTa535-1, Oligo-pSc119.2-1, Oligo-pTa71-2, and (AAC)7. Multicolor FISH using Oligo-pTa535-1, Oligo-pSc119.2-1, and Oligo-pTa71-2 identified all 42 common wheat chromosomes, while Oligo-pTa535-1 and (AAC)7 discriminated the 14 chromosomes of T. boeoticum. FISH revealed that all six blue-grained lines were wheat-T. boeoticum 4Ab (4B) disomic substitution lines. The substitution lines were validated by genotyping using the wheat 55K single nucleotide polymorphism (SNP) array containing 53,063 markers. These 4Ab (4B) substitution lines represent novel germplasm for blue-grained wheat breeding. The FISH probes and SNP markers used here can be applied in the development of blue-grained wheat-Triticum boeoticum translocation lines.