The role of reproductive isolation in allopolyploid speciation patterns: empirical insights from the progenitors of common wheat

Abstract

The ability to cause reproductive isolation often varies among individuals within a plant species. We addressed whether such polymorphism influenced speciation of the allopolyploid common wheat (Triticum aestivum L., AABBDD genome) by evaluating the expression of pre-pollination (outcrossing potential) and post-pollination (crossability) barriers in Aegilops tauschii Coss. (the D genome progenitor). In total, 201 Ae. tauschii accessions representing the entire natural habitat range of the species were used for anther length measurement and artificial crosses with a Triticum turgidum L. (the AB genome progenitor) tester. Intraspecific comparisons showed that both barriers were more strongly expressed in the TauL1 lineage than in the TauL2 lineage. The ability of Ae. tauschii to cause reproductive isolation in the hybridisation with T. turgidum might have markedly influenced common wheat’s speciation by inducing lineage-associated patterns of gene flow. The TauL2 accessions with high potential for natural hybridisation with T. turgidum clustered in the southern coastal Caspian region. This provided phenotypic support for the derivation of the D genome of common wheat from southern Caspian populations. The present study underscored the importance of approaches that incorporate the genealogical and geographic structure of the parental species’ reproductive isolation in understanding the mechanism of plant allopolyploid speciation.

An Update of Recent Use of Aegilops Species in Wheat Breeding

“…Aegilops tauschii is the easiest species in this genus to utilize in wheat breeding, because there is little to no inhibition to meiotic chromosome pairing with the D genome chromosomes of bread wheat. According to several sources, bread wheat originated about 10,000 years ago (Wang et al, 2013; Matsuoka and Takumi, 2017), which is relatively recent and not long enough for genomic differentiation. Furthermore, Ae.…”

“…It is important to note that the seed setting rates in F 1 plants also depend on Ae. tauschii accessions (Matsuoka and Takumi, 2017).…”

Reproductive and genetic roles of the maternal progenitor in the origin of common wheat (Triticum aestivum L.)

“…Lines of genetic and archeological evidence suggest that the female progenitor of common wheat likely was a free‐threshing cultivar (Matsuoka, 2011). The location in which the original hybridization took place is unknown; however, the southern coastal region of the Caspian Sea is a good candidate based on genetic evidence (Matsuoka & Takumi, 2017; Tsunewaki, 1966; Wang et al., 2013).…”

“…tauschii may have had more opportunities to be involved in the origin of common wheat than others because they frequently hybridized with T. turgidum and because the F 1 hybrids were likely to produce unreduced gametes. In fact, artificial cross-studies have shown that southern Caspian accessions of the TauL2 lineage have a high potential for natural hybridization with T. turgidum (Matsuoka & Takumi, 2017). Thus, the genealogically and geographically structured polymorphism in the crossability with T. turgidum may have had a profound impact on the spatial patterns of common wheat speciation.…”

RNA Sequencing-Based Bulked Segregant Analysis Facilitates Efficient D-genome Marker Development for a Specific Chromosomal Region of Synthetic Hexaploid Wheat

“…The Ae. tauschii strains associated with the origin of common wheat are assumed to be the TauL2 lineage [2,17], and only limited reproductive barriers are thought to exist between tetraploid wheat and many of the TauL2 accessions [19]. TauL1 accessions frequently carry a hybrid incompatibility gene, designated Net2 , that triggers low-temperature-induced necrotic cell death upon interspecific hybridization with tetraploid wheat, impeding the generation of synthetic hexaploid wheat [20,21].…”