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The wheat wild relative Aegilops tauschii was previously used to transfer the Lr42 leaf rust resistance gene into bread wheat. Lr42 confers resistance at both seedling and adult stages, and it is broadly effective against all leaf rust races tested to date. Lr42 has been used extensively in the CIMMYT international wheat breeding program with resulting cultivars deployed in several countries. Here, using a bulked segregant RNA-Seq (BSR-Seq) mapping strategy, we identify three candidate genes for Lr42. Overexpression of a nucleotide-binding site leucine-rich repeat (NLR) gene AET1Gv20040300 induces strong resistance to leaf rust in wheat and a mutation of the gene disrupted the resistance. The Lr42 resistance allele is rare in Ae. tauschii and likely arose from ectopic recombination. Cloning of Lr42 provides diagnostic markers and over 1000 CIMMYT wheat lines carrying Lr42 have been developed documenting its widespread use and impact in crop improvement., (© 2022. The Author(s).)

Aegilops tauschii, the diploid wild progenitor of the D subgenome of bread wheat, is a reservoir of genetic diversity for improving bread wheat performance and environmental resilience. Here we sequenced 242 Ae. tauschii accessions and compared them to the wheat D subgenome to characterize genomic diversity. We found that a rare lineage of Ae. tauschii geographically restricted to present-day Georgia contributed to the wheat D subgenome in the independent hybridizations that gave rise to modern bread wheat. Through k-mer-based association mapping, we identified discrete genomic regions with candidate genes for disease and pest resistance and demonstrated their functional transfer into wheat by transgenesis and wide crossing, including the generation of a library of hexaploids incorporating diverse Ae. tauschii genomes. Exploiting the genomic diversity of the Ae. tauschii ancestral diploid genome permits rapid trait discovery and functional genetic validation in a hexaploid background amenable to breeding., (© 2021. The Author(s).)

Wheat is one of the most important cereal crops for the global food security. Due to its narrow genetic base, modern bread wheat cultivars face challenges from increasing abiotic and biotic stresses. Since genetic improvement is the most sustainable approach, finding novel genes and alleles is critical for enhancing the genetic diversity of wheat. The tertiary gene pool of wheat is considered a gold mine for genetic diversity as novel genes and alleles can be identified and transferred to wheat cultivars. Aegilops geniculata and Ae. umbellulata are the key members of the tertiary gene pool of wheat and harbor important genes against abiotic and biotic stresses. Homoeologous-group five chromosomes (5Uu and 5Mg) have been extensively studied from Ae. geniculata and Ae. umbellulata as they harbor several important genes including Lr57, Lr76, Yr40, Yr70, Sr53 and chromosomal pairing loci. In the present study, using chromosome DNA sequencing and RNAseq datasets, we performed comparative analysis to study homoeologous gene evolution in 5Mg, 5Uu, and group 5 wheat chromosomes. Our findings highlight the diversity of transcription factors and resistance genes, resulting from the differential expansion of the gene families. Both the chromosomes were found to be enriched with the "response to stimulus" category of genes providing resistance against biotic and abiotic stress. Phylogenetic study positioned the M genome closer to the D genome, with higher proximity to the A genome than the B genome. Over 4000 genes were impacted by SNPs on 5D, with 4-5% of those genes displaying nondisruptive variations that affect gene function. [ABSTRACT FROM AUTHOR]

Editorial: Aegilops: Promising Genesources to Improve Agronomical and Quality Traits of Wheat Keywords: Aegilops sp.; stress tolerance; quality traits; genome analysis; alien introgression EN Aegilops sp. stress tolerance quality traits genome analysis alien introgression 1 4 4 07/20/20 20200714 NES 200714 Introduction of Aegilops I Aegilops i species have contributed significantly to wheat improvement despite the challenges in exploiting wild species, such as crossability and incompatibility ([2]; [7]). The 5S rDNA locus of chromosome 1S was probably lost in ancient I A. speltoides i prior to formation of cultivated I Triticum timopheevi i (AAGG genomes), but after the emergence of ancient emmer (AABB genomes). I A. tauschii i (2n = 2x = 14, genome DD), also known as Tausch's goatgrass, is the D genome donor of hexaploid bread wheat ( I T. aestivum i , 2n = 2x = 42, AABBDD genome). [Extracted from the article]

Aegilops tauschii (2n = 2x = 14, genome DD), also known as Tausch's goatgrass, is the D genome donor of bread or hexaploid wheat Triticum aestivum (2n = 2x = 42, AABBDD genome). It is a rich reservoir of useful genes for biotic and abiotic stress tolerance for wheat improvement. We developed a TILLING (Targeting Induced Local Lesions In Genomes) resource for Ae. tauschii for discovery and validation of useful genes in the D genome of wheat. The population, referred to as TILL-D, was developed with ethyl methanesulfonate (EMS) mutagen. The survival rate in M1 generation was 73%, out of which 22% plants were sterile. In the M2 generation 25% of the planted seeds showed phenotypic mutations such as albinos, chlorinas, no germination, variegated, sterile and partially fertile events, and 2,656 produced fertile M2 plants. The waxy gene was used to calculate the mutation frequency (1/70 kb) of the developed population, which was found to be higher than known mutation frequencies for diploid plants (1/89–1/1000 kb), but lower than that for a polyploid species (1/24–1/51 kb). The TILL-D resource, together with the newly published Ae. tauschii reference genome sequence, will facilitate gene discoveries and validations of agronomically important traits and their eventual fine transfer in bread wheat. [ABSTRACT FROM AUTHOR]

Background: The large and complex genome of bread wheat (Triticum aestivum L., ~17 Gb) requires high resolution genome maps with saturated marker scaffolds to anchor and orient BAC contigs/ sequence scaffolds for whole genome assembly. Radiation hybrid (RH) mapping has proven to be an excellent tool for the development of such maps for it offers much higher and more uniform marker resolution across the length of the chromosome compared to genetic mapping and does not require marker polymorphism per se, as it is based on presence (retention) vs. absence (deletion) marker assay. Methods: In this study, a 178 line RH panel was genotyped with SSRs and DArT markers to develop the first high resolution RH maps of the entire D-genome of Ae. tauschii accession AL8/78. To confirm map order accuracy, the AL8/78-RH maps were compared with:1) a DArT consensus genetic map constructed using more than 100 biparental populations, 2) a RH map of the D-genome of reference hexaploid wheat 'Chinese Spring', and 3) two SNP-based genetic maps, one with anchored D-genome BAC contigs and another with anchored D-genome sequence scaffolds. Using marker sequences, the RH maps were also anchored with a BAC contig based physical map and draft sequence of the D-genome of Ae. tauschii. Results: A total of 609 markers were mapped to 503 unique positions on the seven D-genome chromosomes, with a total map length of 14,706.7 cR. The average distance between any two marker loci was 29.2 cR which corresponds to 2.1 cM or 9.8 Mb. The average mapping resolution across the D-genome was estimated to be 0.34 Mb (Mb/cR) or 0.07 cM (cM/cR). The RH maps showed almost perfect agreement with several published maps with regard to chromosome assignments of markers. The mean rank correlations between the position of markers on AL8/78 maps and the four published maps, ranged from 0.75 to 0.92, suggesting a good agreement in marker order. With 609 mapped markers, a total of 2481 deletions for the whole D-genome were detected with an average deletion size of 42.0 Mb. A total of 520 markers were anchored to 216 Ae. tauschii sequence scaffolds, 116 of which were not anchored earlier to the D-genome. Conclusion: This study reports the development of first high resolution RH maps for the D-genome of Ae. tauschii accession AL8/78, which were then used for the anchoring of unassigned sequence scaffolds. This study demonstrates how RH mapping, which offered high and uniform resolution across the length of the chromosome, can facilitate the complete sequence assembly of the large and complex plant genomes. [ABSTRACT FROM AUTHOR]

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Synthetic amphiploids are the immortal sources for studies on crop evolution, genome dissection, and introgression of useful variability from related species. Cytological analysis of synthetic decaploid wheat (Triticum aestivum L.) - Aegilops kotschyi Boiss. amphiploids (AABBDDUkUkSkSk) showed some univalents from the C1 generation onward followed by chromosome elimination. Most of the univalents came to metaphase I plate after the reductional division of paired chromosomes and underwent equational division leading to their elimination through laggards and micronuclei. Substantial variation in the chromosome number of pollen mother cells from different tillers, spikelets, and anthers of some plants also indicated somatic chromosome elimination. Genomic in situ hybridization, fluorescence in situ hybridization, and simple sequence repeat markers analysis of two amphiploids with reduced chromosomes indicated random chromosome elimination of various genomes with higher sensitivity of D followed by the Sk and Uk genomes to elimination, whereas 1D chromosome was preferentially eliminated in both the amphiploids investigated. One of the partial amphiploids, C4T. aestivum 'Chinese Spring' - Ae. kotschyi 396 (2n = 58), with 34 T. aestivum, 14 Uk, and 10 Sk had stable meiosis and high fertility. The partial amphiploids with white glumes, bold seeds, and tough rachis with high grain macro- and micronutrients and resistance to powdery mildew could be used for T. aestivum biofortification and transfer of powdery mildew resistance. Les amphiploïdes synthétiques constituent des ressources immortelles pour des études portant sur l'évolution des cultures, la dissection des génomes et l'introgression de variabilité utile provenant d'espèces apparentées. Une analyse cytogénétique d'amphiploïdes décaploïdes (Triticum aestivum L.) - Aegilops kotschyi Boiss. (AABBDDUkUkSkSk) a permis d'observer des univalents à compter de la génération C1 suivie d'élimination chromosomique. La plupart des univalents ont atteint la plaque de la métaphase I après la division réductionnelle des chromosomes appariés et ont subi la division équationnelle qui a mené à leur élimination sous forme de chromosomes retardataires ou de micronoyaux. Une variation substantielle du nombre de chromosomes observés chez les microsporocytes provenant de différents épis, épillets et anthères chez certaines plantes suggère qu'il se produirait également de l'élimination chromosomique au niveau somatique. Des analyses GISH, FISH et de marqueurs SSR sur deux amphiploïdes avec un nombre réduit de chromosomes a indiqué que l'élimination chromosomique était aléatoire au sein des différents génomes. Globalement, le génome D, suivi des génomes Sk et Uk, était le plus souvent sujet à élimination et le chromosome 1D avait été préférentiellement perdu chez les deux amphiploïdes examinés. Un des amphiploïdes partiels de génération C4, 'Chinese Spring' - Ae. kotschyi 396 (2n = 58), comptait 34 chromosomes du T. aestivum, 14 du génome Uk et 10 du génome Sk et il présentait une méiose stable ainsi qu'une fécondité élevée. Les amphiploïdes partiels à glumes blanches, gros grains, rachis résistant, forte teneur en micro- et macronutriments ainsi que résistants à l'oïdium pourraient s'avérer utiles pour l'amélioration de la valeur nutritive du T. aestivum et le transfert de résistance à l'oïdium. [ABSTRACT FROM AUTHOR]

Graminaceous plants including staple cereals secrete certain phytosiderophores (PS) in calcareous soils with lower iron and zinc availability to enhance their uptake and translocation to the leaves and grains. A few Triticum aestivum cultivars and accessions of six Aegilops species were investigated for release of PS in vitro under iron- and zinc-sufficient and -deficient conditions, and for root and shoot iron and zinc concentrations. All the Aegilops species had three to four times higher release of PS than the wheat cultivars under both nutrient-sufficient and -deficient conditions. The maximum rate of increase of PS was observed on days 11 and 14 under iron- and zinc-deficient conditions, respectively, which levelled off rapidly among the wheat cultivars and continued to be high among Aegilops species till the end of the experiment. The absolute amount of iron and zinc expressed on dry weight basis after 18 d under iron- and zinc-deficient conditions showed nearly three times higher concentration in both roots and shoots of Aegilops species than that of the wheat cultivars. A significantly high correlation between concentrations of iron (r = 0.94) and zinc (r = 0.91) in roots and the PS released was found. The higher grain iron and zinc contents in the Aegilops species reported earlier may be attributed to their diverse and efficient mechanism(s) for PS-mediated micro-nutrient uptake and translocation system, which could be exploited for biofortification of wheat. [ABSTRACT FROM AUTHOR]

Biofortification through genetic manipulation is the best approach for improving micronutrient content of the staple food crops to alleviate hidden hunger, namely, the deficiency of Fe and Zn affecting more than two billion people worldwide. An interspecific hybridization was made between T. aestivum line Chinese Spring (CS) and Aegilops kotschyi accession 3790 selected for high grain iron and zinc concentration. The CS × Ae. kotschyi F1 hybrid with low chromosome pairing was highly male and female sterile. This was backcrossed with wheat cultivars to get seed set. The selfed BC1F1 and BC2F1 plants with high grain iron and zinc concentration were selected in subsequent generations. The selected derivatives showed 60–136% enhanced grain iron and zinc concentration and 50–120% increased iron and zinc content per seed as compared to the recipient wheat cultivars. Thirteen cytologically stable, fertile and agronomically superior plants with high grain iron and zinc concentrations were selected for molecular characterization. The application of anchored wheat SSR markers, transferable to Ae. kotschyi, to the high grain iron and zinc containing derivatives indicated introgression of group 2 and group 7 chromosomes of Ae. kotschyi. GISH and FISH analysis of some derivatives confirmed the substitution of chromosomes 2S and 7U for their homoeologues of the A genome, suggesting that some of the genes controlling high grain micronutrient content in the Ae. kotschyi accession are on these chromosomes. [ABSTRACT FROM AUTHOR]

Four different interspecific hybrids involving three different accessions of Aegilops longissima Schweinf. & Muschl. with high grain iron and zinc content and three Triticum turgidum L. subsp. durum (Desf.) Husn. cultivars with low micronutrient content were made for durum wheat biofortification and investigated for chromosome pairing, fertility, putative amphiploidy, and micronutrient content. The chromosome pairing in the 21-chromosome F1 hybrids (ABSl) consisted of 0-6 rod bivalents and occasionally 1 trivalent. All the F1 hybrids, however, unexpectedly showed partial but variable fertility. The detailed meiotic investigation indicated the simultaneous occurrence of two types of aberrant meiotic divisions, namely first-division restitution and single-division meiosis, leading to regular dyads and unreduced gamete formation and fertility. The F2 seeds, being putative amphiploids (AABBSlSl), had nearly double the chromosome number (40-42) and regular meiosis and fertility. The F1 hybrids were intermediate between the two parents for different morphological traits. The putative amphiploids with bold seed size had higher grain ash content and ash iron and zinc content than durum wheat cultivars, suggesting that Ae. longissima possesses a better genetic system(s) for uptake and seed sequestration of iron and zinc, which could be transferred to elite durum and bread wheat cultivars and exploited. Quatre hybrides interspécifiques différents impliquant trois accessions distinctes de l’Aegilops longissima Schweinf. & Muschl., toutes caractérisées par une forte teneur en fer et en zinc dans les grains, et trois cultivars de blé dur, Triticum turgidum L. subsp. durum (Desf.) Husn., à faible teneur en micronutriments ont été produits pour des fins de biofortification du blé dur. De plus, ces hybrides ont été examinés pour leur appariement chromosomique, leur fécondité, leur amphiploïdie putative ainsi que pour leur teneur en micronutriments. L’appariement chromosomique chez les hybrides F1 à 21 chromosomes (ABS1) produisait entre 0 et 6 bivalents droits et occasionnellement un trivalent. Tous les hybrides F1 affichaient étonnamment une fécondité partielle variable. L’examen attentif de la méiose a révélé l’occurrence simultanée de deux types aberrants de division méiotique, soit une restitution à la première division et une méiose à une seule division produisant des dyades régulières, des gamètes non-réduits et de la fécondité. Les grains F2, vraisemblablement amphiploïdes (AABBS1S1), affichaient un nombre chromosomique près du double (40 à 42), une méiose régulière et la fécondité. Les hybrides F1 étaient intermédiaires entre les deux parents pour les caractères phénotypiques. Les amphiploïdes putatifs portant des grains plus gros affichaient une teneur plus élevée en cendres ainsi que des teneurs plus élevées en zinc et en fer dans les cendres que les cultivars de blé dur. Cela suggère que l’Ae. longissima possède un bagage génétique plus favorable à l’importation et l’accumulation du fer et du zinc et que ce caractère serait transférable à des variétés élites de blé dur et de blé tendre. [ABSTRACT FROM AUTHOR]