Ancient hybridizations among the ancestral genomes of bread wheat

Abstract

The allohexaploid bread wheat genome consists of three closely related subgenomes (A, B, and D), but a clear understanding of their phylogenetic history has been lacking. We used genome assemblies of bread wheat and five diploid relatives to analyze genome-wide samples of gene trees, as well as to estimate evolutionary relatedness and divergence times. We show that the A and B genomes diverged from a common ancestor ~7 million years ago and that these genomes gave rise to the D genome through homoploid hybrid speciation 1 to 2 million years later. Our findings imply that the present-day bread wheat genome is a product of multiple rounds of hybrid speciation (homoploid and polyploid) and lay the foundation for a new framework for understanding the wheat genome as a multilevel phylogenetic mosaic.

Introgression and repeated co-option facilitated the recurrent emergence of C4photosynthesis among close relatives

“…2014; Marcussen et al. 2014; Li et al. 2016), resulting either in outliers (if few genes are introgressed) or a multimodal distribution of ages (if many genes are introgressed).…”

The Potential of Lr19 and Bdv2 Translocations to Improve Yield and Disease Resistance in the High Rainfall Wheat Zones of Australia

“…Hexaploid wheat (Triticum aestivum L.) has recently been estimated to have formed between 230,000 and 430,000 years ago through rare hybridization events between diploid and tetraploid progenitors [1] with domestication occurring approximately 10,000 years ago. Consequently, modern wheats developed from this original bottleneck [2].…”

“…These chromosomal translocations have been used to enhance resistance to various wheat diseases. However, the incomplete homology, referred to as "homoeology", between the donor and recipient [1] chromosomes, usually prevents recombination. Any deleterious genes that are introgressed along with the useful trait can be difficult to remove.…”

The draft genome of Tibetan hulless barley reveals adaptive patterns to the high stressful Tibetan Plateau

“…The Triticeae species, such as wheat (Triticum aestivum, 2n = 6x = 42) and barley (Hordeum vulgare, 2n = 2x = 14), which account for >30% of cereal production worldwide, are essential food and forage resources (faostat.fao.org). International efforts have been launched to decipher their genomes, and dramatic breakthroughs have been achieved on the reference genome of chromosome 3B (1), whole-genome sequencing (2,3), and in-depth phylogenetic and transcriptome analyses (4,5) of hexaploid wheat, as well as generations of draft genome sequences (6,7) and construction of a physical map of its diploid A-genome (Triticum urartu, 2n = 2x = 14) and D-genome (Aegilops tauschii, 2n = 2x = 14) progenitors (6)(7)(8).…”