Genome-wide sequence information reveals recurrent hybridization among diploid wheat wild relatives

Area of Science:

• * Plant evolutionary biology
• * Genomics
• * Phylogenetics

Background:

• * Conflicting hypotheses exist regarding the evolutionary relationships among wheat (Triticum) and its wild relatives (Aegilops, Amblyopyrum).
• * The role of hybridization in the evolution of these taxa is a significant point of debate.
• * Understanding these relationships is crucial for crop improvement and understanding plant evolution.

Purpose of the Study:

• * To resolve phylogenetic relationships among diploid species of wheat wild relatives.
• * To investigate the contribution of hybridization versus incomplete lineage sorting to their evolutionary history.
• * To provide a genome-wide sequence-based phylogeny for the Triticeae wheat group.

Main Methods:

• * Genotyping-by-sequencing (GBS) and a target-enrichment experiment yielding 244 low-copy nuclear loci.
• * Phylogenetic analyses using Bayesian, likelihood, and coalescent-based methods.
• * D statistics employed to differentiate between incomplete lineage sorting and hybridization as drivers of gene tree incongruence.

Main Results:

• * A phylogeny of all diploid species within the wheat wild relatives group was established.
• * Evidence suggests a primordial homoploid hybrid speciation event involving ancestral Triticum and Aegilops muticum lineages.
• * This event, followed by multiple introgressions (excluding Triticum), is hypothesized to have shaped most species, with limited recent gene flow.

Conclusions:

• * The study proposes a novel hypothesis for the evolutionary history of wheat wild relatives, emphasizing a major hybridization event.
• * The composite nature of genomes in wheat-group taxa results from these ancient hybridization and introgression processes.
• * This provides a framework for understanding genome composition in basic evolutionary units and their role in polyploid wheat formation.