Hybridization preceded radiation in diploid wheats.

Area of Science:

• Plant evolutionary biology
• Genomics
• Phylogenetics

Background:

• The evolutionary history of Aegilops-Triticum, the wild relatives of cultivated wheats, is complex due to incomplete lineage sorting and reticulate evolution.
• Previous hypotheses suggested a hybrid origin for the wheat D-genome lineage, but this required further robust phylogenetic evidence.

Purpose of the Study:

• To reconstruct the evolutionary history and phylogenetic relationships of Aegilops-Triticum diploid species.
• To test the hypothesis of a hybrid origin for the D-genome lineage using comprehensive genomic data.

Main Methods:

• High-throughput sequencing of 38 nuclear low-copy loci from multiple accessions of 13 Aegilops-Triticum species.
• Phylogenetic inference using the full-parameterized MCMC_SEQ method.
• Analysis of tree dilation and compression patterns, and ABBA-BABA tests to detect hybridization.

Main Results:

• A monophyletic Aegilops-Triticum lineage was recovered, diversifying approximately 6.6 million years ago into four sublineages: A, B, D, and T.
• Phylogenetic analyses strongly supported a hybrid origin of the D-genome lineage from the A and B lineages around 3.0-4.0 million years ago.
• Conflicting signals from ABBA-BABA tests were attributed to ancestral population structure, not additional hybridization events.

Conclusions:

• The study provides a dated phylogeny clarifying the origin of the wheat D-genome lineage as a hybridization event between A and B genomes.
• The emergence of the D-genome lineage was followed by rapid diversification, leading to most extant diploid and allopolyploid wild wheats.