Abstract
Agropyron cristatum (L.) Gaertn. (P genome) is cultivated as pasture fodder and can provide many desirable genes for wheat improvement. With the development of genomics and fluorescence in situ hybridization (FISH) technology, probes for identifying plant chromosomes were also developed. However, there are few reports on A. cristatum chromosomes. Here, FISH with the repeated sequences pAcTRT1 and pAcpCR2 enabled the identification of all diploid A. cristatum chromosomes. An integrated idiogram of A. cristatum chromosomes was constructed based on the FISH patterns of five diploid A. cristatum individuals. Structural polymorphisms of homologous chromosomes were observed not only among different individuals but also within individuals. Moreover, seventeen wheat-A. cristatum introgression lines containing different P genome chromosomes were identified with pAcTRT1 and pAcpCR2 probes. The arrangement of chromosomes in diploid A. cristatum was determined by identifying correspondence between the P chromosomes in these genetically identified introgression lines and diploid A. cristatum chromosomes. The two probes were also effective for discriminating all chromosomes of tetraploid A. cristatum, and the differences between two tetraploid A. cristatum accessions were similar to the polymorphisms among individuals of diploid A. cristatum. Collectively, the results provide an effective means for chromosome identification and phylogenetic studies of P genome chromosomes.
Highlights
Chromosome identification plays an important role in genomic relationships, flow sorting, and polyploidization
Two of the seven chromosome pairs were discriminated when pAcpCR2 was used as a probe: the short arms of one chromosome pair were full of fluorescence signals, whereas the short arms of another pair showed a discontinuous distribution of fluorescence signals (Supplementary Fig. 1d). These findings indicated that these two probes can be used for the identification of A. cristatum chromosomes
With the development of Fluorescence in situ hybridization (FISH) probes, an increasing number of plant chromosomes can be discriminated by FISH, such as those in Arabidopsis, wheat, barley, maize, soybean, and rye[14,40,41,42,43,44]
Summary
Chromosome identification plays an important role in genomic relationships, flow sorting, and polyploidization. FISH with genome-specific dispersed repetitive sequences as probes can identify alien chromosomes in wheat backgrounds and reveal their distributions on chromosomes. Oligonucleotide probes developed based on repetitive sequences have been used to identify chromosomes of wheat and structural chromosomal rearrangements and polymorphisms in widely grown wheat cultivars and their founders[17,18,19,20]. A series of wheat-A. cristatum derivative lines conferring many desirable traits were obtained, including wheat-A. cristatum addition lines, substitution lines, deletion lines, and translocation lines[25,26,27,28,29,30,31,32,33,34,35] These lines have been applied as bridge materials or novel germplasms in wheat improvement. The aim of this study was to identify P genome chromosomes using FISH with pAcTRT1 and pAcpCR2 as probes and to unveil the structural polymorphisms of diploid A. cristatum chromosomes. The results provide insights into the A. cristatum chromosomes involved in alien gene introgression and into the evolution of A. cristatum
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