The chloroplast view of the evolution of polyploid wheat

Abstract

SummaryPolyploid wheats comprise four species: Triticum turgidum (AABB genomes) and T. aestivum (AABBDD) in the Emmer lineage, and T. timopheevii (AAGG) and T. zhukovskyi (AAGGA m A m ) in the Timopheevi lineage. Genetic relationships between chloroplast genomes were studied to trace the evolutionary history of the species. Twenty-five chloroplast genomes were sequenced, and 1127 plant accessions were genotyped, representing 13 Triticum and Aegilops species.The A. speltoides (SS genome) diverged before the divergence of T. urartu (AA), A. tauschii (DD) and the Aegilops species of the Sitopsis section. Aegilops speltoides forms a monophyletic clade with the polyploid Emmer and Timopheevi wheats, which originated within the last 0.7 and 0.4 Myr, respectively. The geographic distribution of chloroplast haplotypes of the wild tetraploid wheats and A. speltoides illustrates the possible geographic origin of the Emmer lineage in the southern Levant and the Timopheevi lineage in northern Iraq.Aegilops speltoides is the closest relative of the diploid donor of the chloroplast (cytoplasm), as well as the B and G genomes to Timopheevi and Emmer lineages. Chloroplast haplotypes were often shared by species or subspecies within major lineages and between the lineages, indicating the contribution of introgression to the evolution and domestication of polyploid wheats.

Genetic and epigenetic modifications to the BBAA component of common wheat during its evolutionary history at the hexaploid level

“…First, allotetraploidization between diploid wheat (T. urartu, genome AA) and a diploid Aegilops species of the Sitopsis section, which is closely related to A. speltoides (genome SS), gave rise to allotetraploid wheat (Triticum turgidum, genome BBAA) about 0.36-0.5 million years ago (MYA) (Dvořák 1976;Huang et al 2002;Dvorak and Akhunov 2005). Notably, however, it was reported recently that A. speltoides does not belong to the Sitopsis section, and the allotetraploidization event(s) likely occurred much earlier, about 0.7 MYA (Gornicki et al 2014). Second, allohexaploidization between a domesticated form of T. turgidum and diploid A. tauschii (genome DD) led to formation of hexaploid common wheat which occurred <10,000 years ago (Feldman 2000;Salamini et al 2002;Matsuoka 2011).…”

Genome-wide characterization of microsatellites in Triticeae species: abundance, distribution and evolution

“…The combination of homoelogous chromosomes from divergent species not only promotes functional divergence of duplicate genes, but also generates heterozygosity and novel interactions leading to genetic and phenotypic variability12. There have been numerous studies devoted to understanding the mechanisms and evolution of polyploidy in T. aestivum 131415, while the roles of microsatellites have not been well understood.…”

Recurrence of Chromosome Rearrangements and Reuse of DNA Breakpoints in the Evolution of the Triticeae Genomes

“…, goatgrass ( Aegilops L.), a model for cytogenetic studies of polyploidy and chromosomal variation. Diploid species of Triticum and Aegilops diverged 1.4 MYA (Gornicki et al 2014) and their genomes remain highly collinear except for a few CRs, such as a translocation between incipient 4L and 5L chromosome arms detected in diploid wheat T. urartu (genome AA) (King et al 1994) and T. monococcum (genome A m A m ) (Devos et al 1995; Dubcovsky et al 1996). Both T. urartu and T. monococcum are involved in the origin of polyploid wheat lineages.…”

“…Both T. urartu and T. monococcum are involved in the origin of polyploid wheat lineages. T. urartu (genome AA) pollinated A. speltoides (genome SS) in two separate hybridization events, giving rise to tetraploid wheat T. turgidum (genomes AABB) ∼0.7 MYA and T. timopheevii (genomes AAGG) ∼0.4 MYA (Gornicki et al 2014). More recently, crosses between T. turgidum and A. tauschii (genome DD) produced common wheat or bread wheat ( T. aestivum ; genomes AABBDD); and hybridization between T. timopheevii and another diploid wheat, einkorn ( T. monococcum subsp.…”

“…The gene orders on 4HL and 5HL are tentative based on the barley draft genome sequences and the gene orders on 5RL and 7RS were deduced based on assumption of wheat-rye collinearity. The divergence time for the major Triticeae lineages was adopted from Huang et al (2002) and Gornicki et al (2014). …”