Genetic variability of spelt factor gene in Triticum and Aegilops species.

BACKGROUND: Threshability, rachis fragility and spike shape are critical traits for the domestication and evolution of wheat, determining the crop yield and efficiency of the harvest. Spelt factor gene Q controls a wide range of domestication-related traits in polyploid wheats, including those mentioned above. The main goal of the present study was to characterise the Q gene for uninvestigated accessions of wheats, including four endemics, and Aegilops accessions, and to analyze the species evolution based on differences in Q gene sequences. RESULTS: We have studied the spike morphology for 15 accessions of wheat species, including four endemics, namely Triticum macha, T. tibetanum, T. aestivum ssp. petropavlovskyi and T. spelta ssp. yunnanense, and 24 Aegilops accessions, which are donors of B and D genomes for polyploid wheat. The Q-5A, q-5D and q-5S genes were investigated, and a novel allele of the Q-5A gene was found in accessions of T. tibetanum (KU510 and KU515). This allele was similar to the Q allele of T. aestivum cv. Chinese Spring but had an insertion 161 bp in length within exon 5. This insertion led to a frameshift and premature stop codon formation. Thus, the T. tibetanum have spelt spikes, which is probably determined by the gene Tg, rather than Q. We determined the variability within the q-5D genes among hexaploid wheat and their D genome donor Aegilops tauschii. Moreover, we studied the accessions C21-5129, KU-2074, and K-1100 of Ae. tauschii ssp. strangulata, which could be involved in the origin of hexaploid wheats. CONCLUSIONS: The variability and phylogenetic relationships of the Q gene sequences studied allowed us to clarify the relationships between species of the genus Triticum and to predict the donor of the D genome among the Ae. tauschii accessions. Ae. tauschii ssp. strangulata accessions C21-5129, KU-2074 and K-1100 are the most interesting among the analysed accessions, since their partial sequence of q-5D is identical to the q-5D of T. aestivum cv. Chinese Spring. This result indicates that the donor is Ae. tauschii ssp. strangulata but not Ae. tauschii ssp. tauschii. Our analysis allowed us to clarify the phylogenetic relationships in the genus Triticum.

Molecular Cytogenetic Identification of Wheat-Aegilops Biuncialis 5Mb Disomic Addition Line with Tenacious and Black Glumes.

Production of wheat-alien disomic addition lines is of great value to the exploitation and utilization of elite genes originated from related species to wheat. In this study, a novel wheat-Aegilops biuncialis 5Mb disomic addition line WA317 was characterized by in situ hybridization (ISH) and specific-locus amplified fragment sequencing (SLAF-seq) markers. Compared to its parent Chinese Spring (CS), the glumes of WA317 had black color and were difficult to remove after harvesting, suggesting chromosome 5Mb carried gene(s) related to glume development and Triticeae domestication process. A total of 242 Ae. biuncialis SLAF-based markers (298 amplified patterns) were developed and further divided into four categories by Ae. biuncialis Y17, Ae. umbellulata Y139 and Ae. comosa Y258, including 172 markers amplifying the same bands of U and M genome, six and 102 markers amplifying U-specific and M-specific bands, respectively and eighteen markers amplifying specific bands in Y17. Among them, 45 markers had the specific amplifications in WA317 and were 5Mb specific markers. Taken together, line WA317 with tenacious and black glumes should serve as the foundation for understanding of the Triticeae domestication process and further exploitation of primitive alleles for wheat improvement. Ae. biuncialis SLAF-based markers can be used for studying syntenic relationships between U and M genomes as well as rapid tracking of U and M chromosomal segments in wheat background.

Diploid genome differentiation conferred by RNA sequencing-based survey of genome-wide polymorphisms throughout homoeologous loci in Triticum and Aegilops.

BACKGROUND: Triticum and Aegilops diploid species have morphological and genetic diversity and are crucial genetic resources for wheat breeding. According to the chromosomal pairing-affinity of these species, their genome nomenclatures have been defined. However, evaluations of genome differentiation based on genome-wide nucleotide variations are still limited, especially in the three genomes of the genus Aegilops: Ae. caudata L. (CC genome), Ae. comosa Sibth. et Sm. (MM genome), and Ae. uniaristata Vis. (NN genome). To reveal the genome differentiation of these diploid species, we first performed RNA-seq-based polymorphic analyses for C, M, and N genomes, and then expanded the analysis to include the 12 diploid species of Triticum and Aegilops. RESULTS: Genetic divergence of the exon regions throughout the entire chromosomes in the M and N genomes was larger than that between A- and Am-genomes. Ae. caudata had the second highest genetic diversity following Ae. speltoides, the putative B genome donor of common wheat. In the phylogenetic trees derived from the nuclear and chloroplast genome-wide polymorphism data, the C, D, M, N, U, and S genome species were connected with short internal branches, suggesting that these diploid species emerged during a relatively short period in the evolutionary process. The highly consistent nuclear and chloroplast phylogenetic topologies indicated that nuclear and chloroplast genomes of the diploid Triticum and Aegilops species coevolved after their diversification into each genome, accounting for most of the genome differentiation among the diploid species. CONCLUSIONS: RNA-sequencing-based analyses successfully evaluated genome differentiation among the diploid Triticum and Aegilops species and supported the chromosome-pairing-based genome nomenclature system, except for the position of Ae. speltoides. Phylogenomic and epigenetic analyses of intergenic and centromeric regions could be essential for clarifying the mechanisms behind this inconsistency.

Origin of wheat B-genome chromosomes inferred from RNA sequencing analysis of leaf transcripts from section Sitopsis species of Aegilops.

Dramatic changes occasionally occur in intergenic regions leading to genomic alterations during speciation and will consequently obscure the ancestral species that have contributed to the formation of allopolyploid organisms. The S genome of five species of section Sitopsis of genus Aegilops is considered to be an origin of B-genome in cultivated tetraploid and hexaploid wheat species, although its actual donor is still unclear. Here, we attempted to elucidate phylogenetic relationship among Sitopsis species by performing RNA sequencing of the coding regions of each chromosome. Thus, genome-wide polymorphisms were extensively analyzed in 19 accessions of the Sitopsis species in reference to the tetraploid and hexaploid wheat B genome sequences and consequently were efficiently anchored to the B-genome chromosomes. The results of our genome-wide exon sequencing and resultant phylogenetic analysis indicate that Ae. speltoides is likely to be the direct donor of all chromosomes of the wheat B genome. Our results also indicate that the genome differentiation during wheat allopolyploidization from S to B proceeds at different speeds over the chromosomes rather than at constant rate and recombination could be a factor determining the speed. This observation is potentially generalized to genome differentiation during plant allopolyploid evolution.

Sr33 & Sr35 gene homolog indentification in genomes of cereals related with Aegilops tauschii & Triticum monococcum.

Using bioinformatics analysis, the homologues of the genes Sr33 and Sr35 were identifed in the genomes of Triticum aestivum, Hordeum vulgare and Triticum urartu. It is known that these genes provide resistance to hightly virulent wheat stem rust races (Ug99). To identify important for resistance amino acid sites, the comparison of the founded homologues with the Sr33 and Sr35 protein sequences was performed. It was found that the sequences S5DMA6 and E9P785 are the closest homologues of RGA1e protein ­ a product of the Sr33 gene, and the sequences M7YFA9 (CNL-C) and F2E9R2 are the homologues of CNL9 ­ a product of the gene Sr35. It is assumed that the homologues of the genes Sr33 and Sr35, which derived from the wild relatives of wheat and barley, can provide resistance to various forms of a stem rust and can be used in the future breeding programs for wheat improvement.