Demographic history and distinct selection signatures of two domestication genes in mungbean.

Abstract

Domestication is the long and complex process underlying the evolution of crops, in which artificial directional selection transformed wild progenitors into the desired form, affecting genomic variation and leaving traces of selection at targeted loci. However, whether genes controlling important domestication traits follow the same evolutionary pattern expected under the standard selective sweep model remains unclear. With whole-genome re-sequencing of mungbean (Vigna radiata), we investigated this issue by resolving its global demographic history and targeted dissection of the molecular footprints of genes underlying two key traits representing different stages of domestication. Mungbean originated in Asia, and the Southeast Asian wild population migrated to Australia about 50 thousand generations ago (kga). Later in Asia, the cultivated form diverged from the wild progenitor. We identified the gene associated with the pod shattering resistance trait, VrMYB26a, with lower expression across cultivars and reduced polymorphism in the promoter region, reflecting a hard selective sweep. On the other hand, the stem determinacy trait was associated with VrDet1. We found two ancient haplotypes of this gene have lower gene expression and exhibited intermediate frequencies in cultivars, consistent with selection favoring independent haplotypes in a soft selective sweep. In mungbean, contrasting signatures of selection were identified from the detailed dissection of two important domestication traits. The results suggest complex genetic architecture underlying the seemingly simple process of directional artificial selection and highlight the limitations of genome-scan methods relying on hard selective sweeps.