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

Abstract

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.

Genomic and Meiotic Changes Accompanying Polyploidization

“…The presence of the Ph1 locus affects also the dynamics of telomere bouquet formation by delaying it, what suggests that chromosomes might have more time to check potential pairing and consequently, correct homologous chromosome pairing could be facilitated [ 184 ]. Suppression of homoeologous crossovers (COs) instead of preventing chromosome associations between homoeologues has been also assessed to the Ph1 locus [ 185 , 186 , 187 , 188 , 189 ].…”

Telomeres and Subtelomeres Dynamics in the Context of Early Chromosome Interactions During Meiosis and Their Implications in Plant Breeding

“…This again means that there must be a characteristic on the chromosome architecture that might facilitate recognition, pairing, and recombination without DNA damage. For example, in the absence of homologous chromosomes in the wheat background, homoeologs can pair along their full length although crossing over does not occur in the presence of the Ph1 locus but in its absence (Calderón et al, 2018;Calderón and Prieto, 2021).…”

“…Pairing can occur between related chromosomes in lines carrying deletions encompassing the Ph1 locus, but the chromosomes are heavily rearranged, making recombination between the wheat and related chromosomes difficult but possible. However, interspecific recombination between Hordeum species and wheat has been reported at the terminal chromosome regions when the Ph1 locus was not present (Calderón and Prieto, 2021).…”