Molecular and Cytogenetic Characterization of New Wheat-Dasypyrum breviaristatum Derivatives with Post-Harvest Re-Growth Habit

Cytological and molecular characterization of wheat lines carrying leaf rust and stem rust resistance genes Lr24 and Sr24

Previous studies showed that Australian wheat cultivars Janz and Sunco carry leaf rust and stem rust resistance genes Lr24 and Sr24 derived from Thinopyrum ponticum chromosome arm 3AgL. However, the size of the alien segments carrying Lr24 and Sr24 in the lines were not determined. In this study, we used non-denaturing fluorescence in situ hybridization (ND-FISH), genomic in situ hybridization (GISH), and PCR-based landmark unique gene (PLUG) markers to visualize the alien segments in Janz and Sunco, and further compared them with the segments in US cultivars Agent and Amigo. The fraction length (FL) of the alien translocation in Agent was 0.70-1.00, whereas those in Janz, Sunco, and Amigo were smaller, at FL 0.85-1.00. It was deduced that the alien gene RAg encoding for red grain color and rust resistance genes Lr24 and Sr24 on chromosome arm 3AgL were in bins of FL 0.70-0.85 and 0.85-1.00, respectively. We retrieved and extracted nucleotide-binding site-leucine-rich repeat (NBS-LRR) receptor genes corresponding to the region of Lr24 and Sr24 on chromosomes 3E, and 3J, 3Js and 3St from the reference genome sequences of Th. elongatum and Th. intermedium, respectively. A set of molecular markers developed for Lr24 and Sr24 from those extracted NBS-LRR genes will provide valuable information for fine mapping and cloning of these genes.

The launch of satellite: DNA repeats as a cytogenetic tool in discovering the chromosomal universe of wild Triticeae

Fluorescence in situ hybridization is a powerful tool that enables plant researchers to perform systematic, evolutionary, and population studies of wheat wild relatives as well as to characterize alien introgression into the wheat genome. This retrospective review reflects on progress made in the development of methods for creating new chromosomal markers since the launch of this cytogenetic satellite instrument to the present day. DNA probes based on satellite repeats have been widely used for chromosome analysis, especially for "classical" wheat probes (pSc119.2 and Afa family) and "universal" repeats (45S rDNA, 5S rDNA, and microsatellites). The rapid development of new-generation sequencing and bioinformatical tools, and the application of oligo- and multioligonucleotides has resulted in an explosion in the discovery of new genome- and chromosome-specific chromosome markers. Owing to modern technologies, new chromosomal markers are appearing at an unprecedented velocity. The present review describes the specifics of localization when employing commonly used vs. newly developed probes for chromosomes in J, E, V, St, Y, and P genomes and their diploid and polyploid carriers Agropyron, Dasypyrum, Thinopyrum, Pseudoroegneria, Elymus, Roegneria, and Kengyilia. Particular attention is paid to the specificity of probes, which determines their applicability for the detection of alien introgression to enhance the genetic diversity of wheat through wide hybridization. The information from the reviewed articles is summarized into the TRepeT database, which may be useful for studying the cytogenetics of Triticeae. The review describes the trends in the development of technology used in establishing chromosomal markers that can be used for prediction and foresight in the field of molecular biology and in methods of cytogenetic analysis.

Identification and Evaluation of Wheat-Aegilops bicornis Lines with Resistance to Powdery Mildew and Stripe Rust

Wheat pathogens, especially those causing powdery mildew and stripe rust, seriously threaten yield worldwide. Utilizing newly identified disease resistance genes from wheat relatives is an effective strategy to minimize disease damage. In this study, chromosome-specific molecular markers for the 3S^b and 7S^b chromosomes of Aegilops bicornis were developed using PCR-based landmark unique gene primers for screening wheat-A. bicornis progenies. Fluorescence in situ hybridization (FISH) was performed to further identify wheat-A. bicornis progenies using oligonucleotides probes Oligo-pSc119.2-1, Oligo-pTa535-1, and Oligo-(GAA)₈. After establishing A. bicornis 3S^b and 7S^b chromosome-specific FISH markers, Holdfast (common wheat)-A. bicornis 3S^b addition, 7S^b addition, 3S^b(3A) substitution, 3S^b(3B) substitution, 3S^b(3D) substitution, 7S^b(7A) substitution, and 7S^b(7B) substitution lines were identified by the molecular and cytological markers. Stripe rust and powdery mildew resistance, along with agronomic traits, were investigated to evaluate the breeding potential of these lines. Holdfast and Holdfast-A. bicornis progenies were all highly resistant to stripe rust, indicating that the stripe rust resistance might derive from Holdfast. However, Holdfast-A. bicornis 3S^b addition, 3S^b(3A) substitution, 3S^b(3B) substitution, and 3S^b(3D) substitution lines showed high resistance to powdery mildew while Holdfast was highly susceptible, indicating that chromosome 3S^b of A. bicornis carries previously unknown powdery mildew resistance gene(s). Additionally, the transfer of the 3S^b chromosome from A. bicornis to wheat significantly increased tiller number, but chromosome 7S^b has a negative effect on agronomic traits. Therefore, wheat germplasm containing A. bicornis chromosome 3S^b has potential to contribute to improving powdery mildew resistance and tiller number during wheat breeding.

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

The perennial species Dasypyrum breviaristatum (genome V^b) 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 1V^b-7V^b chromosomes through nondenaturing fluorescence in situ hybridization (ND-FISH) technique using 28 oligonucleotide probes from the wheat - D. breviaristatum partial amphiploid TDH-2 (AABBV^bV^b) and newly identified wheat - D. breviaristatum disomic translocation and addition lines D2138 (6V^bS.2V^bL), D2547 (4V^b), and D2532 (3V^bS.6V^bL) 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.

Molecular Cytogenetic Characterization of New Wheat-Dasypyrum breviaristatum Introgression Lines for Improving Grain Quality of Wheat

As an important relative of wheat (Triticum aestivum L), Dasypyrum breviaristatum contains novel high molecular weight glutenin subunits (HMW-GSs) encoded by Glu-1Vb genes. We identified new wheat-D. breviaristatum chromosome introgression lines including chromosomes 1V^b and 1V^bL.5V^bL by fluorescence in situ hybridization (FISH) combined with molecular markers. We found that chromosome changes occurred in the wheat-D. breviaristatum introgression lines and particularly induced the deletion of 5BS terminal repeats and formation of a new type of 5B-7B reciprocal translocation. The results imply that the D. breviaristatum chromosome 1V^b may contain genes which induce chromosomal recombination in wheat background. Ten putative high molecular weight glutenin subunit (HMW-GS) genes from D. breviaristatum and wheat-D. breviaristatum introgression lines were isolated. The lengths of the HMW-GS genes in Dasypyrum were significantly shorter than typical HMW-GS of common wheat. A new y-type HMW-GS gene, named Glu-Vb1y, was characterized in wheat-D. breviaristatum 1V^b introgression lines. The new wheat-D. breviaristatum germplasm displayed reduced plant height, increased tillers and superior grain protein and gluten contents, improved gluten performance index. The results showed considerable potential for utilization of D. breviaristatum chromosome 1V^b segments in future wheat improvement.