Pipeline for the Rapid Development of Cytogenetic Markers Using Genomic Data of Related Species

Comparative Characterization of Pseudoroegneria libanotica and Pseudoroegneria tauri Based on Their Repeatome Peculiarities

Pseudoroegneria species play an important role among Triticeae grasses, as they are the putative donors of the St genome in many polyploid species. Satellite repeats are widely used as a reliable tool for tracking evolutionary changes because they are distributed throughout the genomes of plants. The aim of our work is to perform a comparative characterization of the repeatomes of the closely related species Ps. libanotica and Ps. tauri, and Ps. spicata was also included in the analysis. The overall repeatome structures of Ps. libanotica, Ps. tauri, and Ps. spicata were similar, with some individual peculiarities observed in the abundance of the SIRE (Ty1/Copia) retrotransposons, Mutator and Harbinger transposons, and satellites. Nine new satellite repeats that have been identified from the whole-genome sequences of Ps. spicata and Ps. tauri, as well as the CL244 repeat that was previously found in Aegilops crassa, were localized to the chromosomes of Ps. libanotica and Ps. tauri. Four satellite repeats (CL69, CL101, CL119, CL244) demonstrated terminal and/or distal localization, while six repeats (CL82, CL89, CL168, CL185, CL192, CL207) were pericentromeric. Based on the obtained results, it can be assumed that Ps. libanotica and Ps. tauri are closely related species, although they have individual peculiarities in their repeatome structures and patterns of satellite repeat localization on chromosomes. The evolutionary fate of the identified satellite repeats and their related sequences, as well as their distribution on the chromosomes of Triticeae species, are discussed. The newly developed St genome chromosome markers developed in the present research can be useful in population studies of Ps. libanotica and Ps. tauri; auto- and allopolyploids that contain the St genome, such as Thinopyrum, Elymus, Kengyilia, and Roegneria; and wide hybrids between wheat and related wild species.

qPCR as a Selective Tool for Cytogenetics

qPCR is widely used in quantitative studies of plant genomes and transcriptomes. In this article, this method is considered as an auxiliary step in the preparation and selection of markers for FISH analysis. Several cases from the authors' research on populations of the same species were reviewed, and a comparison of the closely related species, as well as the adaptation of the markers, based on satellite tandem repeats (TRs) using quantitative qPCR data was conducted. In the selected cases, TRs with contrast abundance were identified in the cases of the Dasypyrum, Thinopyrum and Aegilops species, and the transfer of TRs between the wheat and related species was demonstrated. TRs with intraspecific copy number variation were revealed in Thinopyrum ponticum and wheat-wheatgrass partial amphidiploids, and the TR showing predominant hybridization to the sea buckthorn Y chromosome was identified. Additionally, problems such as the absence of a reference gene for qPCR, and low-efficiency and self-complementary primers, were illustrated. In the cases considered here, the qPCR results clearly show high correlation with the subsequent results of the FISH analysis, which confirms the value of this method for cytogenetic studies.

Aegilops crassa Boiss. repeatome characterized using low-coverage NGS as a source of new FISH markers: Application in phylogenetic studies of the Triticeae

Aegilops crassa Boiss. is polyploid grass species that grows in the eastern part of the Fertile Crescent, Afghanistan, and Middle Asia. It consists of tetraploid (4x) and hexaploid (6x) cytotypes (2n = 4x = 28, D¹D (Abdolmalaki et al., 2019) X^crX^cr and 2n = 6x = 42, D¹D (Abdolmalaki et al., 2019) X^crX^crD²D (Adams and Wendel, 2005), respectively) that are similar morphologically. Although many Aegilops species were used in wheat breeding, the genetic potential of Ae. crassa has not yet been exploited due to its uncertain origin and significant genome modifications. Tetraploid Ae. crassa is thought to be the oldest polyploid Aegilops species, the subgenomes of which still retain some features of its ancient diploid progenitors. The D¹ and D² subgenomes of Ae. crassa were contributed by Aegilops tauschii (2n = 2x = 14, DD), while the X^cr subgenome donor is still unknown. Owing to its ancient origin, Ae. crassa can serve as model for studying genome evolution. Despite this, Ae. crassa is poorly studied genetically and no genome sequences were available for this species. We performed low-coverage genome sequencing of 4x and 6x cytotypes of Ae. crassa, and four Ae. tauschii accessions belonging to different subspecies; diploid wheatgrass Thinopyrum bessarabicum (J^b genome), which is phylogenetically close to D (sub)genome species, was taken as an outgroup. Subsequent data analysis using the pipeline RepeatExplorer2 allowed us to characterize the repeatomes of these species and identify several satellite sequences. Some of these sequences are novel, while others are found to be homologous to already known satellite sequences of Triticeae species. The copy number of satellite repeats in genomes of different species and their subgenome (D¹ or X^cr) affinity in Ae. crassa were assessed by means of comparative bioinformatic analysis combined with quantitative PCR (qPCR). Fluorescence in situ hybridization (FISH) was performed to map newly identified satellite repeats on chromosomes of common wheat, Triticum aestivum, 4x and 6x Ae. crassa, Ae. tauschii, and Th. bessarabicum. The new FISH markers can be used in phylogenetic analyses of the Triticeae for chromosome identification and the assessment of their subgenome affinities and for evaluation of genome/chromosome constitution of wide hybrids or polyploid species.

Developing Oligo Probes for Chromosomes Identification in Hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L., 2n = 20) is a valuable crop that is successfully used as a food, technical and medicinal crop. It is a dioecious plant with an XX\XY sex determination system. Some chromosomes of C. sativa have almost the same lengths and centromeric indexes. Cytogenetic markers help to distinguish similar plant chromosomes, including sex chromosomes, which is important for the breeding process. Two repeats (CS-1 and CS-237) were used to develop labeled oligo-probes for rapid and low-cost oligo-FISH. These oligos can be recommended for use as cytological markers to distinguish sex chromosomes (X and Y) and somatic chromosome pairs 3, 6, and 8 by rapid oligo-FISH in a short time.

Raise and characterization of a bread wheat hybrid line (Tulaykovskaya 10 × Saratovskaya 29) with chromosome 6Agi2 introgressed from Thinopyrum intermedium

Wheatgrass Thinopyrum intermedium is a source of agronomically valuable traits for common wheat. Partial wheat–wheatgrass amphidiploids and lines with wheatgrass chromosome substitutions are extensively used as intermediates in breeding programs. Line Agis 1 (6Agi2/6D) is present in the cultivar Tulaykovskaya 10 pedigree. Wheatgrass chromosome 6Agi2 carries multiple resistance to fungal diseases in various ecogeographical zones. In this work, we studied the transfer of chromosome 6Agi2 in hybrid populations Saratovskaya 29 × skaya 10 (S29 × T10) and Tulaykovskaya 10 × Saratovskaya 29 (T10 × S29). Chromosome 6Agi2 was identif ied by PCR with chromosome-specif ic primers and by genomic in situ hybridization (GISH). According to molecular data, 6Agi2 was transmitted to nearly half of the plants tested in the F2 and F3 generations. A new breeding line 49-14 (2n = 42) with chromosome pair 6Agi2 was isolated and characterized in T10 × S29 F5 by GISH. According to the results of our f ield experiment in 2020, the line had high productivity traits. The grain weights per plant (10.04 ± 0.93 g) and the number of grains per plant (259.36 ± 22.49) did not differ signif icantly from the parent varieties. The number of grains per spikelet in the main spike was signif icantly higher than in S29 ( p ≤ 0.001) or T10 ( p ≤ 0.05). Plants were characterized by the ability to set 3.77 ± 0.1 grains per spikelet, and this trait varied among individuals from 2.93 to 4.62. The grain protein content was 17.91 %, and the gluten content, 40.55 %. According to the screening for fungal disease resistance carried out in the f ield in 2018 and 2020, chromosome 6Agi2 makes plants retain immunity to the West Siberian population of brown rust and to dominant races of stem rust. It also provides medium resistant and medium susceptible types of response to yellow rust. The possibility of using lines/varieties of bread wheat with wheatgrass chromosomes 6Agi2 in breeding in order to increase protein content in the grain, to confer resistance to leaf diseases on plants and to create multif lowered forms is discussed.

Development of Specific Thinopyrum Cytogenetic Markers for Wheat-Wheatgrass Hybrids Using Sequencing and qPCR Data

The cytogenetic study of wide hybrids of wheat has both practical and fundamental values. Partial wheat-wheatgrass hybrids (WWGHs) are interesting as a breeding bridge to confer valuable genes to wheat genome, as well as a model object that contains related genomes of Triticeae. The development of cytogenetic markers is a process that requires long and laborious fluorescence in situ hybridization (FISH) testing of various probes before a suitable probe is found. In this study, we aimed to find an approach that allows to facilitate this process. Based on the data sequencing of Thinopyrum ponticum, we selected six tandem repeat (TR) clusters using RepeatExplorer2 pipeline and designed primers for each of them. We estimated the found TRs' abundance in the genomes of Triticum aestivum, Thinopyrum ponticum, Thinopyrum intermedium and four different WWGH accessions using real-time qPCR, and localized them on the chromosomes of the studied WWGHs using fluorescence in situ hybridization. As a result, we obtained three tandem repeat cytogenetic markers that specifically labeled wheatgrass chromosomes in the presence of bread wheat chromosomes. Moreover, we designed and tested primers for these repeats, and demonstrated that they can be used as qPCR markers for quick and cheap monitoring of the presence of certain chromosomes of wheatgrass in breeding programs.

Development of new cytogenetic markers for Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang

Thinopyrum ponticum (Podpěra, 1902) Z.-W. Liu & R.-C.Wang, 1993 is an important polyploid wild perennial Triticeae species that is widely used as a source of valuable genes for wheat but its genomic constitution has long been debated. For its chromosome identification, only a limited set of FISH probes has been used. The development of new cytogenetic markers for Th. ponticum chromosomes is of great importance both for cytogenetic characterization of wheat-wheatgrass hybrids and for fundamental comparative studies of phylogenetic relationships between species. Here, we report on the development of five cytogenetic markers for Th. ponticum based on repetitive satellite DNA of which sequences were selected from the whole genome sequence of Aegilops tauschii Cosson, 1849. Using real-time quantitative PCR we estimated the abundance of the found repeats: P720 and P427 had the highest abundance and P132, P332 and P170 had lower quantity in Th. ponticum genome. Using fluorescence in situ hybridization (FISH) we localized five repeats to different regions of the chromosomes of Th. ponticum. Using reprobing multicolor FISH we colocalized the probes between each other. The distribution of these found repeats in the Triticeae genomes and its usability as cytogenetic markers for chromosomes of Th. ponticum are discussed.