Lineage-specific positive selection on stress-response genes in wild wheat relatives

Investigating how wild wheat relatives adapt to diverse environments is crucial for evolutionary biology and the development of climate-resilient agriculture. To study this, researchers analyzed whole-transcriptome data from four diploid wild wheat relatives with different mating systems: Aegilops speltoides and Aegilops mutica, which are outcrossing species, and Aegilops tauschii and Triticum urartu, which are selfing species.

By combining the imputed McDonald--Kreitman test (MKT) with lineage-specific estimates of divergence from branch-specific models of molecular evolution, they were able to lessen biases caused by slightly deleterious mutations and pinpoint adaptive substitutions to specific lineages. The study found significant differences in the prevalence of positive selection among the species, with the outcrossing species showing more evidence of adaptive evolution compared to the selfing species.

Furthermore, the researchers discovered that some signals initially thought to be shared among species were later assigned to individual lineages when divergence was estimated on a branch-specific basis, highlighting the importance of accurately localizing adaptive substitutions. Functional annotation of the genes indicated several candidate genes with domains related to stress response, both abiotic and biotic.

This research offers a framework for detecting positive selection in wild wheat relatives and identifies potential candidate genes that could contribute to adaptation, making them valuable targets for future functional analyses and wheat improvement programs.