Wheat, Rye, and Barley Genomes Can Associate during Meiosis in Newly Synthesized Trigeneric Hybrids

Abstract

Polyploidization, or whole genome duplication (WGD), has an important role in evolution and speciation. One of the biggest challenges faced by a new polyploid is meiosis, in particular, discriminating between multiple related chromosomes so that only homologs recombine to ensure regular chromosome segregation and fertility. Here, we report the production of two new hybrids formed by the genomes of species from three different genera: a hybrid between Aegilops tauschii (DD), Hordeum chilense (H^chH^ch), and Secale cereale (RR) with the haploid genomic constitution H^chDR (n = 7× = 21); and a hybrid between Triticum turgidum spp. durum (AABB), H. chilense, and S. cereale with the constitution ABH^chR (n = 7× = 28). We used genomic in situ hybridization and immunolocalization of key meiotic proteins to establish the chromosome composition of the new hybrids and to study their meiotic behavior. Interestingly, there were multiple chromosome associations at metaphase I in both hybrids. A high level of crossover (CO) formation was observed in H^chDR, which shows the possibility of meiotic recombination between the different genomes. We succeeded in the duplication of the ABH^chR genome, and several amphiploids, AABBH^chH^chRR, were obtained and characterized. These results indicate that recombination between the genera of three economically important crops is possible.

Keywords: GISH; Hordeum chilense; Triticeae; WGD (whole genome duplication); hybridization; meiosis; recombination; synapsis; wheat.

Figure 1

Breeding scheme followed to obtain the trigeneric hybrids and corresponding amphiploids used in this work. (a) Production of the hybrid H^chDR between Hordeum chilense (barley), Aegilops tauschii, and Secale cereale (rye). (b) Production of the hybrid ABH^chR between Triticum turgidum (durum wheat), H. chilense, and S. cereale, and the corresponding amphiploid.

Figure 2

Root-tip metaphases of the trigeneric hybrids and amphiploid obtained in this work analyzed by GISH. (a) Hybrid H^chDR (n = 3× = 21) showing seven chromosomes of Hordeum chilense chromosomes (magenta), seven of rye (green), and seven of Aegilops tauschii (grey). (b) Hybrid ABH^chR (n = 4× = 28) using tritordeum HT474, with 14 chromosomes from durum wheat (grey), seven from H. chilense (magenta), and seven from rye (green). (c) Aneuploid amphiploid AABBH^chH^chRR-2-2 with 51 chromosomes. Two centromeric translocation between rye and one of the durum wheat chromosomes are indicated by an arrow. Another centromeric translocation between H. chilense and rye is marked with an asterisk and is enlarged. A reorganized rye chromosome with a NOR (nucleolar organizer region) in the long arm is indicated with two asterisks and is enlarged.

Figure 3

Adult plant and spike from (a) the H^chDR hybrid, (b) the ABH^chR hybrid, (c) the AABBH^chH^chRR-2-1 amphiploid, and (d) the AABBH^chH^chRR-1-1 amphiploid.

Figure 4

GISH of meiotic metaphase I configuration in the trigeneric hybrids H^chDR (a–d), ABH^chR (e–h), and aneuploid amphiploid AABBH^chH^chRR (i–k). Hordeum chilense is shown in magenta and rye in green. In H^chDR, Aegilops tauschii is shown in grey. In ABH^chR and AABBH^chH^chRR, durum wheat is shown in grey. In (a,c) a CO structure between Hordeum and Aegilops is indicated by an asterisk (*) and is enlarged. In (j) a wheat trivalent is indicated by an arrow.

Figure 5

Immunolocalization of meiotic proteins ASY1 (green) and ZYP1 (magenta) in meiocytes from the trigeneric hybrids H^chDR (a) and ABH^chR (b), and the aneuploid amphiploid AABBH^chH^chRR (c). DAPI staining in blue. Scale bar, 10 μm.