Wild and Cultivated Homoeologous Barley Chromosomes Can Associate and Recombine in Wheat in the Absence of the Ph1 Locus

Bread wheat is an allohexaploid that behaves as a diploid during meiosis, the cell division process to produce the gametes occurring in organisms with sexual reproduction. Knowledge of the mechanisms implicated in meiosis can contribute to facilitating the transfer of desirable traits from related species into a crop like wheat in the framework of breeding. It is particularly interesting to shed light on the mechanisms controlling correct pairing between homologous (equivalent) chromosomes and recombination, even more in polyploid species. The Ph1 (Pairing homoeologous 1) locus is implicated in recombination. In this work, we aimed to study whether homoeologous (equivalent chromosomes from different genomes) Hordeum chilense (wild barley) and H. vulgare (cultivated barley) chromosomes can associate and recombine during meiosis in the wheat background in the absence of the Ph1 locus. For this, we have developed H. chilense and H. vulgare double monosomic addition lines for the same and for different homoeology group in wheat in the ph1b mutant background. Using genomic in situ hybridization, we visualized the two (wild and cultivated) barley chromosomes during meiosis and we studied the processes of recognition, association, and recombination between homoeologous chromosomes in the absence of the Ph1 locus. Our results showed that the Ph1 locus does not prevent homoeologous chromosome pairing but it can regulate recombination.

Homoeologous chromosome pairing at metaphase I of meiosis in Hordeum vulgare L. × H. bulbosum L. triploid hybrids (HvHbHb)

Background. One of the ways to use the genetic potential of bulbous barley, which is characterized by a number of valuable traits, is interspecific hybridization. In crosses of H. vulgare (2x) × H. bulbosum (2x) and H. vulgare (4x) × H. bulbosum (4x) with a genome ratio of 1Hv: 1Hb in a hybrid embryo, elimination of bulbous barley chromosomes is observed in many cases, and the intensity of the process and the result of the crossing depend on the genotypes of the parental forms. This limits the possibility of including a significant variety of parental forms in crosses. Сrossing of diploid forms of H. vulgare with tetraploid accessions of H. bulbosum (4x) results in the formation of triploid hybrids (HvHbHb) with stable chromosomal composition in pollen mother cells (PMCs) at metaphase I (MI) of meiosis. These triploid hybrids can serve as a basis for obtaining series of introgressive lines of cultivated barley. One of the tasks of this type of work is to estimate the involvement of various chromosomes and their arms in homoeologous associations. The aim of this work was to study the possibility of homoeologous pairing of chromosomes of parental species at MI of meiosis in triploid hybrids using GISH and FISH with chromosome-specific markers, as well as to register the participation of individual arms of the cultivated barley chromosomes in homoeologous associations with the chromosomes of bulbous barley in triploid hybrids (HvHbHb).Materials and methods. Seven triploid hybrids of H. vulgare × H.bulbosum (HvHbHb) obtained in four combinations of crosses with the participation of three diploid cultivars of cultivated barley and two tetraploid accession of bulbous barley were used in this study. The features of homoeologous pairing of chromosomes at MI were studied using the method of fluorescent in situ hybridization (GISH and FISH) with chromosome-specific markers.Results All the studied hybrid plants are characterized by a stable chromosomal composition in PMCs at the MI stage of meiosis. Meiotic configurations formed by homoeologous chromosomes of the parental species, ranging from 0.87 to 1.40 on average per cell, were identified in all the studied plants. Among them, vbb trivalents prevailed. Analysis of chromosome pairing at MI in triploid hybrids revealed the participation of all chromosome arms of H. vulgare in homoeologous Hv-Hb associations, except for the short arm of chromosome 1H. In all the studied triploid hybrids, there is a tendency for a higher frequency of involvement of the long arms of chromosomes in the formation of homoeologous associations; this feature is most clearly manifested in case of chromosome 5H.Conclusions Intergenomic associations with the participation of all arms of H. vulgare chromosomes, except for the short arm of chromosome 1H, were revealed at MI in H. vulgare × H. bulbosum triploid hybrids (HvHbHb). Chromosome 5H, as well as any other cultivated barley chromosome, is characterized by a higher involvement of its long arm in homoeologous associations Hv-Hb, as compared to the short arm.

Comparison of homoeologous chromosome pairing between hybrids of wheat genotypes Chinese Spring ph1b and Kaixian-luohanmai with rye

The ph-like genes in the Chinese common wheat landrace Kaixian-luohanmai (KL) induce homoeologous pairing in hybrids with alien species. In the present study, meiotic phenotypic differences on homoeologous chromosome pairing at metaphase I between hybrids of wheat genotypes Chinese Spring ph1b (CSph1b) and KL with rye were studied by genomic in situ hybridization (GISH). The frequency of wheat–wheat associations was higher in CSph1b × rye than in KL × rye. However, frequencies of wheat–rye and rye–rye associations were higher in KL × rye than in CSph1b × rye. These differences may be the result of different mechanisms of control between the ph-like gene(s) controlling homoeologous chromosome pairing in KL and CSph1b. Wheat–wheat associations were much more frequent than wheat–rye pairing in both hybriods. This may be caused by lower overall affinity, or homoeology, between wheat and rye chromosomes than between wheat chromosomes.

Development and characterization of Triticum aestivum– Aegilops kotschyi amphiploids with high grain iron and zinc contents

Synthetic amphiploids betweenTriticum aestivum(AABBDD) landrace Chinese Spring (PhI) and cultivar WL711 with different accessions ofAegilops kotschyi(UUSlSl) were developed through colchicine treatment of sterile hybrids. TheF1hybrids and amphiploid plants were intermediate between the parents for plant morphology and spike characteristics. Meiotic metaphase chromosome analysis of theF1hybrids (ABDUSl) showed the expected chromosome number (35) and very little but variable homoeologous chromosome pairing. The amphiploids (AABBDDUUSlSl), however, had variable frequency of univalents at meiotic metaphase-I. The SDS–PAGE of high molecular weight glutenin subunits of amphiploids along with the parents showed the presence and expression of all the parental genomes in the amphiploids. The amphiploids with seeds as large as that of wheat cultivars had higher grain, flag leaf and grain ash iron and zinc concentrations than the wheat parents and comparable with those of theirAe. kotschyiparents suggest thatAe. kotschyipossesses a distinctive genetic system for the micronutrient uptake, translocation and sequestration than the wheat cultivars. This could, however, be demonstrated unequivocally only with comprehensive data on biomass, grain yield and harvest index of theAegilopsdonors and the synthetic amphiploids, which is not feasible due to their shattering and hard threshing. The use of amphiploids for the transfer of high iron and zinc concentrations and development of alien addition and substitution lines in wheat is in progress.

WM5: Isolation and characterisation of a gene expressed during early meiosis and shoot meristem development in wheat

Wheat Meiosis 5 (WM5), isolated from an early meiosis anther cDNA library of wheat by cDNA subtraction encodes a novel glycine–serine–proline–alanine-rich protein. The corresponding homologous genes are located on the short arms of chromosomes 3A, 3B and 3D of allohexaploid wheat (Triticum aestivum L.). The copy on 3DS is located within the region deleted in the wheat mutant ph2a that displays increased homoeologous chromosome pairing in crosses with alien species. While WM5 is expressed primarily in young flower buds during early meiosis it is also expressed in shoot meristems, thus indicating functional roles in both meiosis and meristem development. Overall, the WM5 amino acid sequence shares no significant similarity with other known proteins in the NCBI database. However, the carboxyl-terminal region does have similarity with the Arabidopsis PDF1 (Protodermal Factor 1) protein. Comparing WM5 and PDF1 reveals that the two proteins share 33% identity and have similar hydropathy plots and predicted secondary structures. In situ immuno-staining locates the protein to the nuclei of pollen mother cells undergoing meiosis and the epidermal layer of the shoot and flower meristem, including the cell wall and cuticle. We propose that the WM5 protein has a role in shoot and flower development within this economically important cereal crop.