It has been repeatedly demonstrated that the centromere-specific histone H3 (CENH3), a key component of the centromere, shows considerable variability between species within taxa. We determined the molecular structure and phylogenetic relationships of CENH3 in 11 Secale species and subspecies that possess distinct pollination systems and are adapted to a wide range of abiotic and biotic stresses. The rye (Secale cereale) genome encodes two paralogous CENH3 genes, which differ in intron-exon structure and are transcribed into two main forms of the protein, αCENH3 and βCENH3. These two forms differ in size and amino acid substitutions. In contrast to the reported differences in CENH3 structure between species within other taxa, the main forms of this protein in Secale species and subspecies have a nearly identical structure except some nonsynonymous substitutions. The CENH3 proteins are strictly controlled by genetic factors responsible for purifying selection. A comparison between Hordeum, Secale and Triticum species demonstrates that the structure of CENH3 in the subtribes Hordeinae and Triticinae evolved at different rates. The assumption that reticulate evolution served as a factor stabilizing the structure and evolutionary rate of CENH3 and that this factor was more powerful within Secale and Triticum than in Hordeum, is discussed.

Alloploidization resulting from remote (interspecific or intergeneric) hybridization is one of the main factors in plant evolution, leading to the formation of new species. Triticale (× Triticosecale Wittmack, 1889) is the first artificial species created by crossing wheat (Triticum spp.) and rye (Secale cereale Linnaeus, 1753) and has a great potential as a grain and forage crop. Remote hybridization is a stress factor that causes a rapid reorganization of the parental genomes in hybrid progeny (“genomic shock”) and is accompanied by abnormalities in the chromosome set of hybrids. The formation of the hybrid genome and its subsequent stabilization are directly related to the normalization of meiosis and the correct chromosome segregation. The aim of this work was to cytogenetically characterize triticale (× Triticosecale rimpaui Wittmack, 1899, AABBDDRR) obtained by crossing Triticum aestivum Linnaeus, 1753. Triple Dirk D × Secale cereale L. Korotkostebel’naya 69 in F3–F6 generations of hybrids, and to trace the process of genetic stabilization of hybrid genomes. Also, a comparative analysis of the nucleotide sequences of the centromeric histone CENH3 genes was performed in wheat-rye allopolyploids of various ploidy as well as their parental forms. In the hybrid genomes of octoploid triticale an increased expression of the rye CENH3 variants was detected. The octoploid triticale plants contain complete chromosome sets of the parental subgenomes maintaining the chromosome balance and meiotic stability. For three generations the percentage of aneuploids in the progeny of such plants has been gradually decreasing, and they maintain a complete set of the paternal rye chromosomes. However, the emergence of hexaploid and new aneuploid plants in F5 and F6 generations indicates that stabilization of the hybrid genome is not complete yet. This conclusion was confirmed by the analysis of morphological features in hybrid plants: the progeny of one plant having the whole chromosome sets of parental subgenomes showed significant morphological variations in awn length and spike density. Thus, we expect that the results of our karyotyping of octoploid triticales obtained by crossing hexaploid wheat to diploid rye supplemented by comparative analysis of CENH3 sequences will be applicable to targeted breeding of stable octo- and hexaploid hybrids.

Centromeres are essential for correct chromosome segregation during cell division and are determined by the presence of centromere-specific histone 3 (CENH3). Most of the diploid plant species, in which the structure and copy number of CENH3 genes have been determined, have this gene as a singleton; however, some cereal species in the tribe Triticeae have been found to have CENH3 in two variants. In this work, using the set of the wheat-rye addition lines we wanted to establish the chromosomal assignment of the CENH3 genes in the cultivated rye, Secale cereale (Linnaeus, 1753), in order to expand our knowledge about synteny conservation in the most important cereal species and about their chromosome evolution. To this end, we have also analyzed data in available genome sequencing databases. As a result, the αCENH3 and βCENH3 forms have been assigned to rye chromosomes 1R and 6R: specifically, the commonest variants αCENH3v1 and βCENH3v1 to chromosome 1R, and the rare variants, αCENH3v2 and probably βCENH3v2, to chromosome 6R. No other CENH3 variants have been found by analysis of the rye genome sequencing databases. Our chromosomal assignment of CENH3 in rye has been found to be the same as that in barley, suggesting that both main forms of CENH3 appeared in a Triticeae species before the barley and wheatrye lineages split.

The centromeres perform integral control of the cell division process and proper distribution of chromosomes into daughter cells. The correct course of this process is often disrupted in case of remote hybridization, which is a stress factor. The combination of parental genomes of different species in a hybrid cell leads to a “genomic shock” followed by loss of genes, changes in gene expression, deletions, inversions, and translocations of chromosome regions. The created rye-wheat allopolyploid hybrids, which were collectively called secalotriticum, represent a new interesting model for studying the effect of remote hybridization on the centromere and its components. The main feature of an active centromere is the presence of a specific histone H3 modification in the centromeric nucleosomes, which is referred to as CENH3 in plants. In this paper the results of cytogenetic analysis of the secalotriticum hybrid karyotypes and the comparison of the CENH3 N-terminal domain structure of parent and hybrid forms are presented. It is shown that the karyotypes of the created secalotriticum forms are stable balanced hexaploids not containing minichromosomes with deleted arms, in full or in part. A high level of homology between rye and wheat enables to express both parental forms of CENH3 gene in the hybrid genomes of secalotriticum cultivars. The CENH3 structure in hybrids in each crossing combination has some specific features. The percentage of polymorphisms at several amino acid positions is much higher in one of the secalotriticum hybrids, STr VD, than in parental forms, whereas the other hybrid, STr VM, inherits a high level of amino acid substitutions at the position 25 from the maternal parent.