Cytogenetic identification and molecular mapping for the wheat-Thinopyrum ponticum introgression line with resistance to Fusarium head blight.

KEY MESSAGE: Xinong 511, a new wheat-Thinopyrum ponticum variety with excellent fusarium head blight resistance, the QTLs were mapped to the wheat chromosomes 5B and 7A with named QFhb.nwafu-5B and QFhb.nwafu-7A, respectively. Novel Fusarium head blight (FHB) resistance germplasms and genes are valuable for wheat improvement and breeding efforts. Thinopyrum ponticum, a wild relative of common wheat, is a valuable germplasm of disease resistance for wheat improvement and breeding. Xinong 511 (XN511) is a high-quality wheat variety widely cultivated in the Yellow and Huai Rivers Valley of China with stable FHB-resistance. Through analysis of pedigree materials of the wheat cultivar XN511, we found that the genetic material and FHB resistance from Th. ponticum were transmitted to the introgression line, indicating that the FHB resistance in XN511 likely originates from Th. ponticum. To further explore the genetic basis of FHB resistance in XN511, QTL mapping was conducted using the RILs population of XN511 and the susceptible line Aikang 58 (AK58). Survey with makers closely-linked to Fhb1, Fhb2, Fhb4, Fhb5, and Fhb7, indicated that both XN511 and the susceptible lines do not contain these QTL. Using bulked segregant analysis RNA-seq (BSR-Seq) and newly developed allele-specific PCR (AS-PCR) markers, QTLs in XN511 were successfully located on wheat chromosomes 5B and 7A. These findings are significant for further understanding and utilizing FHB resistance genes in wheat improvement.

Genome-Wide Comparative Analysis of the Cytochrome P450 Monooxygenase Family in 19 Aphid Species and Their Expression Analysis in 4 Cereal Crop Aphids.

Cytochrome P450 monooxygenases (CYP450s) play a variety of physiological roles, including pesticide resistance, plant allelochemical detoxification, and hormone metabolism catalysis. However, limited information is available on the classification and expression profiles of the CYP450 gene family in aphid species. This is the first study to identify the cytochrome P450 gene family in 19 aphid species at the whole genome level. A total of 1100 CYP450 genes were identified in 19 aphid species. Three hundred CYP450 genes belonged to six cereal crop aphid species, which were further classified into four subfamilies according to the phylogenetic relationship. The conserved motifs, exon-intron structures, and genomic organization of the same subfamilies were similar. Predictions of subcellular localization revealed that the endoplasmic reticulum harbored the majority of CYP450 proteins. In Sitobion avenae and Rhopalosiphum maidis, the increase in the CYP450 gene was primarily caused by segmental duplication events. However, only tandem duplication occurred in the CYP450 gene family of Diuraphis noxia, Rhopalosiphum padi, Schizaphis graminum, and Sitobion miscanthi. Synteny analysis found three continuous colinear CYP450 gene pairs among six cereal crop aphid species. Furthermore, we obtained the expression profiles of four cereal crop aphids, including R. padi, D. noxia, S. graminum, and S. avenae. Differential expression analysis provided growth stage specificity genes, tissue specificity genes, organ specificity genes and some detoxification metabolic genes among these four cereal crop aphids. Meanwhile, their expression patterns were showed. The related functions and pathways of CYP450s were revealed by GO and KEGG enrichment analysis. Above all, we picked the differentially expressed CYP450 genes from all of the differentially expressed genes (DEGs). These differentially expressed CYP450 genes provided some new potential candidates for aphid control and management. This work establishes the foundation for further investigations into the regulatory functions of the CYP450 gene family in aphid species and beyond.

Switching action modes of miR408-5p mediates auxin signaling in rice.

MicroRNAs (miRNAs) play fundamental roles in many developmental and physiological processes in eukaryotes. MiRNAs in plants generally regulate their targets via either mRNA cleavage or translation repression; however, which approach plays a major role and whether these two function modes can shift remains elusive. Here, we identify a miRNA, miR408-5p that regulates AUXIN/INDOLE ACETIC ACID 30 (IAA30), a critical repressor in the auxin pathway via switching action modes in rice. We find that miR408-5p usually inhibits IAA30 protein translation, but in a high auxin environment, it promotes the decay of IAA30 mRNA when it is overproduced. We further demonstrate that IDEAL PLANT ARCHITECTURE1 (IPA1), an SPL transcription factor regulated by miR156, mediates leaf inclination through association with miR408-5p precursor promoter. We finally show that the miR156-IPA1-miR408-5p-IAA30 module could be controlled by miR393, which silences auxin receptors. Together, our results define an alternative auxin transduction signaling pathway in rice that involves the switching of function modes by miR408-5p, which contributes to a better understanding of the action machinery as well as the cooperative network of miRNAs in plants.

Combined GWAS and eGWAS reveals the genetic basis underlying drought tolerance in emmer wheat (Triticum turgidum L.).

Drought is one of the major environmental constraints for wheat production world-wide. As the progenitor and genetic reservoir of common wheat, emmer wheat is considered as an invaluable gene pool for breeding drought-tolerant wheat. Combining GWAS and eGWAS analysis of 107 accessions, we identified 86 QTLs, 105 462 eQTLs as well as 68 eQTL hotspots associating with drought tolerance (DT) in emmer wheat. A complex regulatory network composed of 185 upstream regulator and 2432 downstream drought-responsive candidates was developed, of which TtOTS1 was found to play a negative effect in determining DT through affecting root development. This study sheds light on revealing the genetic basis underlying DT, which will provide the indispensable genes and germplasm resources for elite drought tolerance wheat improvement and breeding.

GenoBaits®WheatplusEE: a targeted capture sequencing panel for quick and accurate identification of wheat-Thinopyrum derivatives.

KEY MESSAGE: A total of 90,000 capture probes derived from wheat and Thinopyrum elongatum were integrated into one chip, which served as an economical genotype for explorating Thinopyrumspecies and their derivatives. Thinopyrum species play a crucial role as a source of new genetic variations for enhancing wheat traits, including resistance to both abiotic and biotic factors. Accurate identification of exogenous chromosome(s) or chromosome segments or genes is essential following the introduction of alien genetic material into wheat, but this task remains challenging. This study aimed to develop a high-resolution wheat-Thinopyrum elongatum array, named GenoBaits®WheatplusEE, to trace alien genetic information by genotyping using a target sequencing system. This GenoBaits®WheatplusEE array included 90,000 capture probes derived from two species and integrated into one chip, with 10,000 and 80,000 originating from wheat and Th. elongatum, respectively. The capture probes were strategically positioned in genes and evenly distributed across the genome, facilitating the development of a roadmap for identifying each alien gene. The array was applied to the high-throughput identification of the alien chromosomes or segments in Thinopyrum and distantly related species and their derivatives. Our results demonstrated that the GenoBaits®WheatplusEE array could be used for direct identification of the breakpoint of alien segments, determine copy number of alien chromosomes, and reveal variations in wheat chromosomes by a single round of target sequencing of the sample. Additionally, we could efficiently and cost-effectively genotype, supporting the exploration of subgenome composition, phylogenetic relationships, and polymorphisms in essential genes (e.g., Fhb7 gene) among Thinopyrum species and their derivatives. We hope that GenoBaits®WheatplusEE will become a widely adopted tool for exporting wild germplasm for wheat improvement in the future.

Genome resources for the elite bread wheat cultivar Aikang 58 and mining of elite homeologous haplotypes for accelerating wheat improvement.

Despite recent progress in crop genomics studies, the genomic changes brought about by modern breeding selection are still poorly understood, thus hampering genomics-assisted breeding, especially in polyploid crops with compound genomes such as common wheat (Triticum aestivum). In this work, we constructed genome resources for the modern elite common wheat variety Aikang 58 (AK58). Comparative genomics between AK58 and the landrace cultivar Chinese Spring (CS) shed light on genomic changes that occurred through recent varietal improvement. We also explored subgenome diploidization and divergence in common wheat and developed a homoeologous locus-based genome-wide association study (HGWAS) approach, which was more effective than single homoeolog-based GWAS in unraveling agronomic trait-associated loci. A total of 123 major HGWAS loci were detected using a genetic population derived from AK58 and CS. Elite homoeologous haplotypes (HHs), formed by combinations of subgenomic homoeologs of the associated loci, were found in both parents and progeny, and many could substantially improve wheat yield and related traits. We built a website where users can download genome assembly sequence and annotation data for AK58, perform blast analysis, and run JBrowse. Our work enriches genome resources for wheat, provides new insights into genomic changes during modern wheat improvement, and suggests that efficient mining of elite HHs can make a substantial contribution to genomics-assisted breeding in common wheat and other polyploid crops.

An intron-located single nucleotide variation of TaGS5-3D is related to wheat grain size through accumulating intron retention transcripts.

KEY MESSAGE: Thirty-three stable QTL for 13 yield-related traits across ten environments were identified in the PD34/MY47 RIL population, and a candidate gene TaGS5-3D in Qmt.nwafu.3D was preliminarily identified to affect grain-related traits through accumulation of specific transcripts. Dissecting the genetic basis of yield-related traits is pivotal for improvement of wheat yield potential. In this study, a recombinant inbred line (RIL) population genotyped by SNP markers was used to detect quantitative trait loci (QTL) related to yield-related traits in ten environments. A total of 102 QTL were detected, including 33 environmentally stable QTL and 69 putative QTL. Among them, Qmt.nwafu.3D was identified as a pleiotropic QTL in the physical interval of 149.77-154.11 Mb containing a potential candidate gene TaGS5-3D. An SNP (T > C) was detected in its ninth intron, and TaGS5-3D-C was validated as a superior allele associated with larger grains using a CAPS marker. Interestingly, we found that TaGS5-3D-C was closely related to significantly up-regulated expression of intron-retained transcript (TaGS5-3D-PD34.1), while TaGS5-3D-T was related to dominant expression of normal splicing transcript (TaGS5-3D-MY47.1). Our results indicated that alternative splicing associated with the SNP T/C could be involved in the regulation of grain-related traits, laying a foundation for the functional analysis of TaGS5-3D and its greater potential application in high-yield wheat breeding.

Intra-Varietal Diversity and Its Contribution to Wheat Evolution, Domestication, and Improvement in Wheat.

Crop genetic diversity is essential for adaptation and productivity in agriculture. A previous study revealed that poor allele diversity in wheat commercial cultivars is a major barrier to its further improvement. Homologs within a variety, including paralogs and orthologs in polyploid, account for a large part of the total genes of a species. Homolog diversity, intra-varietal diversity (IVD), and their functions have not been elucidated. Common wheat, an important food crop, is a hexaploid species with three subgenomes. This study analyzed the sequence, expression, and functional diversity of homologous genes in common wheat based on high-quality reference genomes of two representative varieties, a modern commercial variety Aikang 58 (AK58) and a landrace Chinese Spring (CS). A total of 85,908 homologous genes, accounting for 71.9% of all wheat genes, including inparalogs (IPs), outparalogs (OPs), and single-copy orthologs (SORs), were identified, suggesting that homologs are an important part of the wheat genome. The levels of sequence, expression, and functional variation in OPs and SORs were higher than that of IPs, which indicates that polyploids have more homologous diversity than diploids. Expansion genes, a specific type of OPs, made a great contribution to crop evolution and adaptation and endowed crop with special characteristics. Almost all agronomically important genes were from OPs and SORs, demonstrating their essential functions for polyploid evolution, domestication, and improvement. Our results suggest that IVD analysis is a novel approach for evaluating intra-genomic variations, and exploitation of IVD might be a new road for plant breeding, especially for polyploid crops, such as wheat.

Molecular Cytological Analysis and Specific Marker Development in Wheat-Psathyrostachys huashanica Keng 3Ns Additional Line with Elongated Glume.

Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs) is an excellent gene resource for wheat breeding, which is characterized by early maturity, low plant height, and disease resistance. The wheat-P. huashanica derivatives were created by the elite genes of P. huashanica and permeate into common wheat through hybridization. Among them, a long-glume material 20JH1155 was identified, with larger grains and longer spike than its parents. In the present study, the methods of cytological observation, GISH, and sequential FISH analysis showed that 20JH1155 contained 21 pairs of wheat chromosomes and a pair of P. huashanica. There were some differences in 5A and 7B chromosomes between 20JH1155 and parental wheat 7182. Molecular marker, FISH, and sequence cloning indicated 20JH1155 alien chromosomes were 3Ns of P. huashanica. In addition, differentially expressed genes during immature spikelet development of 20JH1155 and 7182 and predicted transcription factors were obtained by transcriptome sequencing. Moreover, a total of 7 makers derived from Ph#3Ns were developed from transcriptome data. Taken together, the wheat-P. huashanica derived line 20JH1155 provides a new horizon on distant hybridization of wheat and accelerates the utilization of genes of P. huashanica.

Complexity and regulation of age-dependent alternative splicing in Brachypodium distachyon.

Alternative splicing (AS) is a gene regulatory mechanism that generates multiple transcripts of the same gene precursor by the spliceosome complex, promoting messenger RNA complexity, and proteome diversity. Although AS is extensively studied in response to environmental stresses, whether it mediates age-dependent development and how it is adjusted by growth transitions are largely unknown. Here, we comprehensively explored the AS landscape at different developmental stages in the grass model plant Brachypodium (Brachypodium distachyon). We identified abundant coding genes and noncoding transcripts subject to dynamic AS regulation during juvenile, adult, and reproductive transitions. Moreover, we revealed that SC35-LIKE SPLICING FACTOR 33 (SCL33), a serine/arginine-rich splicing factor in spliceosomes, plays a redundant and antagonistic role with its putative paralog, SCL33L, in regulating intron assembly across distinct developmental stages. In addition, we determined global AS variations in microRNA156 (miR156)-overproducing plants, in which growth transitions are delayed, and found that SPLs were regulated by miR156 in intron retention alteration in addition to mRNA clearance and translation inhibition manners. Finally, we demonstrated a complex regulatory process of age-dependent AS events in B. distachyon that was coincidently or separately regulated by miR156 and SCL33/SCL33L. These results illustrate a substantial machinery of AS that mediates phase transitions in plants.

Physical mapping of a new powdery mildew resistance locus from Thinopyrum ponticum chromosome 4AgS.

Thinopyrum ponticum (Podp.) Barkworth and D.R. Dewey is a decaploid species that has served as an important genetic resource for improving wheat for the better part of a century. The wheat-Th. ponticum 4Ag (4D) disomic substitution line Blue 58, which was obtained following the distant hybridization between Th. ponticum and common wheat, has been stably resistant to powdery mildew under field conditions for more than 40 years. The transfer of 4Ag into the susceptible wheat cultivar Xiaoyan 81 resulted in powdery mildew resistance, indicating the alien chromosome includes the resistance locus. Irradiated Blue 58 pollen were used for the pollination of the recurrent parent Xiaoyan 81, which led to the development of four stable wheat-Th. ponticum 4Ag translocation lines with diverse alien chromosomal segments. The assessment of powdery mildew resistance showed that translocation line L1 was susceptible, but the other three translocation lines (WTT139, WTT146, and WTT323) were highly resistant. The alignment of 81 specific-locus amplified fragments to the Th. elongatum genome revealed that 4Ag originated from a group 4 chromosome. The corresponding physical positions of every 4Ag-derived fragment were determined according to a cytogenetic analysis, the amplification of specific markers, and a sequence alignment. Considering the results of the evaluation of disease resistance, the Pm locus was mapped to the 3.79-97.12 Mb region of the short arm of chromosome 4Ag. Because of its durability, this newly identified Pm locus from a group 4 chromosome of Th. ponticum may be important for breeding wheat varieties with broad-spectrum disease resistance.

Genome-wide identification and characterization of lipoxygenase genes related to the English grain aphid infestation response in wheat.

MAIN CONCLUSION: 44 wheat LOX genes were identified by silico genome-wide search method. TaLOX5, 7, 10, 24, 29, 33 were specifically expressed post aphid infestation, indicating their participation in wheat-aphid interaction. In plants, LOX genes play important roles in various biological progresses including seed germination, tuber development, plant vegetative growth and most crucially in plant signal transduction, stress response and plant defense against plant diseases and insects. Although LOX genes have been characterized in many species, the importance of the LOX family in wheat has still not been well understood, hampering further improvement of wheat under stress conditions. Here, we identified 44 LOX genes (TaLOXs) in the whole wheat genome and classified into three subfamilies (9-LOXs, Type I 13-LOXs and Type II 13-LOXs) according to phylogenetic relationships. The TaLOXs belonging to the same subgroup shared similar gene structures and motif organizations. Synteny analysis demonstrated that segmental duplication events mainly contributed to the expansion of the LOX gene family in wheat. The results of protein-protein interaction network (PPI) and miRNA-TaLOXs predictions revealed that three TaLOXs (TaLOX20, 22 and 37) interacted mostly with proteins related to methyl jasmonate (MeJA) signaling pathway. The expression patterns of TaLOXs in different tissues (root, stem, leaf, spike and grain) under diverse abiotic stresses (heat, cold, drought, drought and heat combined treatment, and salt) as well as under diverse biotic stresses (powdery mildew pathogen, Fusarium graminearum and stripe rust pathogen) were systematically analyzed using RNA-seq data. We obtained aphid-responsive candidate genes by RNA-seq data of wheat after the English grain aphid infestation. Aphid-responsive candidate genes, including TaLOX5, 7, 10, 24, 29 and 33, were up-regulated in the wheat aphid-resistant genotype (Lunxuan144), while they were little expressed in the susceptible genotype (Jimai22) during late response (48 h and 72 h) to the English grain aphid infestation. Meanwhile, qRT-PCR analysis was used to validate these aphid-responsive candidate genes. The genetic divergence and diversity of all the TaLOXs in bread wheat and its relative species were investigated by available resequencing data. Finally, the 3D structure of the TaLOX proteins was predicted based on the homology modeling method. This study not only systematically investigated the characteristics and evolutionary relationships of TaLOXs, but also provided potential candidate genes in response to the English grain aphid infestation and laid the foundation to further study the regulatory roles in the English grain aphid infestation of LOX family in wheat and beyond.

Cytogenetic identification and molecular marker development of a novel wheat-Leymus mollis 4Ns(4D) alien disomic substitution line with resistance to stripe rust and Fusarium head blight.

Leymus mollis (Trin.) Pilg. (2n = 4x = 28, NsNsXmXm) potentially harbours useful genes that might contribute to the improvement of wheat. We describe M862 as a novel wheat-L. mollis alien disomic substitution line from a cross between wheat cv. 7182 and octoploid Tritileymus M47. Cytological observations indicate that M862 has a chromosome constitution of 2n = 42 = 21II. Two 4D chromosomes of wheat substituted by two L. mollis Ns chromosomes were observed, using the GISH and ND-FISH analyses. Molecular marker, 55K SNP array and wheat-P. huashanica liquid array (GenoBaits®WheatplusPh) analyses further indicate that the alien chromosomes are L. mollis 4Ns. Therefore, it was deduced that M862 was a wheat-L. mollis 4Ns(4D) alien disomic substitution line. There were also changes in chromosomes 1A, 1D, 2B and 5A detected by ND-FISH analysis. Transcriptome sequencing showed that the structural variation of 1D, 1A and 5A may have smaller impact on gene expression than that for 2B. In addition, a total of 16 markers derived from Lm#4Ns were developed from transcriptome sequences, and these proved to be highly effective for tracking the introduced chromosome. M862 showed reduced height, larger grains (weight and width), and was highly resistance to CYR32 and CYR34 stripe rust races at the seedling stage and mixed stripe rust races (CYR32, CYR33 and CYR34) at the adult stage. It was also resistance to Fusarium head blight (FHB). This alien disomic substitution line M862 may be exploited as an important genetic material in the domestication of stipe rust and FHB resistance wheat varieties.

Population-level transcriptomes reveal gene expression and splicing underlying cadmium accumulation in barley.

Genetic variation is an important determinant of gene transcription, which in turn contributes to functional and phenotypic diversity. Identification of the genetic variants controlling gene expression and alternative splicing in crops responding to cadmium (Cd), an important issue for food safety and human health, is of great value to improve our understanding of Cd accumulation-related genes. Here we report an in-depth survey of population-level transcriptome variation of barley (Hordeum vulgare) core accessions under Cd exposure. We reveal marked transcriptomic changes in response to Cd exposure, and these are largely independent of tissues. A genome-wide association study (GWAS) revealed 59 498 expression quantitative trait loci (eQTLs) and 23 854 splicing quantitative trait loci (sQTLs), leading to a complex network that covers 66.6% of the expressed genes, including 68 metal transporter genes. On average, 41.0% of sQTLs overlapped with eQTLs across different tissues, indicating that these two dimensions of transcript variation are largely independent. Moreover, we found that 34.5% of GWAS QTLs that underlie 10 Cd accumulation traits in barley are co-localized with eQTLs and sQTLs, which could imply a mechanistic role of different genetic variants affecting gene expression and alternative splicing in these traits. This study highlights the role of distal and proximal genetic effects on gene expression, splicing, and phenotypic plasticity. We anticipate that our results on the genetic control of expression and splicing underlying Cd accumulation provide a bridge to better understand genetic variation and phenotypic diversity to elucidate the mechanisms underlying Cd accumulation in plants.

Population transcriptomic analysis identifies the comprehensive lncRNAs landscape of spike in wheat (Triticum aestivum L.).

BACKGROUND: Long noncoding RNAs (lncRNAs) are emerging as the important regulators involving in growth and development as well as stress response in plants. However, current lncRNA studies were mainly performed at the individual level and the significance of it is not well understood in wheat. RESULTS: In this study, the lncRNA landscape of wheat spike was characterized through analysing a total of 186 spike RNA-seq datasets from 93 wheat genotypes. A total of 35,913 lncRNAs as well as 1,619 lncRNA-mRNA pairs comprised of 443 lncRNAs and 464 mRNAs were obtained. Compared to coding genes, these lncRNAs displayed rather low conservation among wheat and other gramineous species. Based on re-sequencing data, the genetic variations of these lncRNA were investigated and obvious genetic bottleneck were found on them during wheat domestication process. Furthermore, 122 lncRNAs were found to act as ceRNA to regulate endogenous competition. Finally, association and co-localization analysis of the candidate lncRNA-mRNA pairs identified 170 lncRNAs and 167 target mRNAs significantly associated with spike-related traits, including lncRNA.127690.1/TraesCS2A02G518500.1 (PMEI) and lncRNA.104854.1/TraesCS6A02G050300.1 (ATG5) associated with heading date and spike length, respectively. CONCLUSIONS: This study reported the lncRNA landscape of wheat spike through the population transcriptome analysis, which not only contribute to better understand the wheat evolution from the perspective of lncRNA, but also lay the foundation for revealing roles of lncRNA playing in spike development.

Genetic identification of the pleiotropic gene Tasg-D1/2 affecting wheat grain shape by regulating brassinolide metabolism.

Improving yield potential is a major goal of wheat breeding that depends on identifying key genetic loci. In this study, two residual heterozygous line RHL351- and RHL78-derived populations were employed for genetic linkage map construction and QTL detection. Two genetic populations indicated a robust grain-size QTL between Marker6 and Marker10. It covered a 95.54-99.38 Mb physical interval and was named Qpleio.nwafu.3D, containing the candidate gene Tasg (TraesCS3D02G137200). Intriguingly, RNA-seq analysis and sequencing revealed two different allelic variants in Tasg, named Tasg-D1 (G>A) and Tasg-D2 (C>G), respectively. Although the relationship between Tasg-D1 and grain size had been demonstrated previously, here we provided the first genetic evidence that C/G allelic variation in Tasg-D2 was associated with grain shape and size through a newly developed dCAPS marker. In addition, transcriptome comparison indicated that Tasg-D1/2 might primarily contribute to significant expression differences in brassinolide (BR) metabolism-related genes rather than those related to BR responses in developing grains and spikes. Our study provided new evidence and a breeder-friendly dCAPS marker for improving grain size through the selection of Tasg, as well as a basis to understand Tasg function in the future.

Identification of Differentially Expressed Genes in Resistant Tetraploid Wheat (Triticum turgidum) under Sitobion avenae (F.) Infestation.

The grain aphid Sitobion avenae (Fabricius) is one of the most destructive pests of wheat (Triticum aestivum). Deployment of resistant wheat germplasm appears as an excellent solution for this problem. Elite bread wheat cultivars only have limited resistance to this pest. The present study was carried out to investigate the potential of the tetraploid wheat (Triticum turgidum) variety Lanmai, which showed high resistance to S. avenae at both seedling and adult plant stages, as a source of resistance genes. Based on apterous adult aphids' fecundity tests and choice bioassays, Lanmai has been shown to display antixenosis and antibiosis. Suppression subtractive hybridization (SSH) was employed to identify and isolate the putative candidate defense genes in Lanmai against S. avenae infestation. A total of 134 expressed sequence tags (ESTs) were identified and categorized based on their putative functions. RT-qPCR analysis of 30 selected genes confirmed their differential expression over time between the resistant wheat variety Lanmai and susceptible wheat variety Polan305 during S. avenae infestation. There were 11 genes related to the photosynthesis process, and only 3 genes showed higher expression in Lanmai than in Polan305 after S. avenae infestation. Gene expression analysis also revealed that Lanmai played a critical role in salicylic acid and jasmonic acid pathways after S. avenae infestation. This study provided further insights into the role of defense signaling networks in wheat resistance to S. avenae and indicates that the resistant tetraploid wheat variety Lanmai may provide a valuable resource for aphid tolerance improvement in wheat.

Molecular cytogenetics and development of St-chromosome-specific molecular markers of novel stripe rust resistant wheat-Thinopyrum intermedium and wheat-Thinopyrum ponticum substitution lines.

BACKGROUND: Owing to their excellent resistance to abiotic and biotic stress, Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt) and Th. ponticum (2n = 10x = 70) are both widely utilized in wheat germplasm innovation programs. Disomic substitution lines (DSLs) carrying one pair of alien chromosomes are valuable bridge materials for transmission of novel genes, fluorescence in situ hybridization (FISH) karyotype construction and specific molecular marker development. RESULTS: Six wheat-Thinopyrum DSLs derived from crosses between Abbondanza nullisomic lines (2n = 40) and two octoploid Trititrigia lines (2n = 8x = 56), were characterized by sequential FISH-genome in situ hybridization (GISH), multicolor GISH (mc-GISH), and an analysis of the wheat 15 K SNP array combined with molecular marker selection. ES-9 (DS2St (2A)) and ES-10 (DS3St (3D)) are wheat-Th. ponticum DSLs, while ES-23 (DS2St (2A)), ES-24 (DS3St (3D)), ES-25(DS2St (2B)), and ES-26 (DS2St (2D)) are wheat-Th. intermedium DSLs. ES-9, ES-23, ES-25 and ES-26 conferred high thousand-kernel weight and stripe rust resistance at adult stages, while ES-10 and ES-24 were highly resistant to stripe rust at all stages. Furthermore, cytological analysis showed that the alien chromosomes belonging to the same homoeologous group (2 or 3) derived from different donors carried the same FISH karyotype and could form a bivalent. Based on specific-locus amplified fragment sequencing (SLAF-seq), two 2St-chromosome-specific markers (PTH-005 and PTH-013) and two 3St-chromosome-specific markers (PTH-113 and PTH-135) were developed. CONCLUSIONS: The six wheat-Thinopyrum DSLs conferring stripe rust resistance can be used as bridging parents for transmission of valuable resistance genes. The utility of PTH-113 and PTH-135 in a BC1F2 population showed that the newly developed markers could be useful tools for efficient identification of St chromosomes in a common wheat background.

Identification and DNA Marker Development for a Wheat-Leymus mollis 2Ns (2D) Disomic Chromosome Substitution.

Leymus mollis (2n = 4x = 28, NsNsXmXm), a wild relative of common wheat (Triticum aestivum L.), carries numerous loci which could potentially be used in wheat improvement. In this study, line 17DM48 was isolated from the progeny of a wheat and L. mollis hybrid. This line has 42 chromosomes forming 21 bivalents at meiotic metaphase I. Genomic in situ hybridization (GISH) demonstrated the presence of a pair chromosomes from the Ns genome of L. mollis. This pair substituted for wheat chromosome 2D, as shown by fluorescence in situ hybridization (FISH), DNA marker analysis, and hybridization to wheat 55K SNP array. Therefore, 17DM48 is a wheat-L. mollis 2Ns (2D) disomic substitution line. It shows longer spike and a high level of stripe rust resistance. Using specific-locus amplified fragment sequencing (SLAF-seq), 13 DNA markers were developed to identify and trace chromosome 2Ns of L. mollis in wheat background. This line provides a potential bridge germplasm for genetic improvement of wheat stripe rust resistance.

Characteristics and Expression Analysis of Invertase Gene Family in Common Wheat (Triticum aestivum L.).

Invertase (INV) irreversibly catalyzes the conversion of sucrose into glucose and fructose, playing important role in plant development and stress tolerance. However, the functions of INV genes in wheat have been less studied. In this study, a total of 126 TaINV genes were identified using a genome-wide search method, which could be classified into five classes (TaCWI-α, TaCWI-ß, TaCI-α, TaCI-ß, and TaVI) based on phylogenetic relationship. A total of 101 TaINVs were collinear with their ancestors in the synteny analysis, and we speculated that polyploidy events were the main force in the expansion of the TaINV gene family. Compared with TaCI, TaCWI and TaVI are more similar in gene structure and protein properties. Transcriptome sequencing analysis showed that TaINVs expressed in multiple tissues with different expression levels. Among 19 tissue-specific expressed TaINVs, 12 TaINVs showed grain-specific expression pattern and might play an important role in wheat grain development. In addition, qRT-PCR results further confirmed that TaCWI50 and TaVI27 show different expression in grain weight NILs. Our results demonstrated that the high expression of TaCWI50 and TaVI27 may be associated with a larger TGW phenotype. This work provides the foundations for understanding the grain development mechanism.