Distinct selection signatures during domestication and improvement in crops: a tale of two genes in mungbean
Domestication and improvement are two crucial processes underlying the evolution of crops. Domestication transformed wild plants into a utilizable form for humans; improvement refined cultivars adapting to distinct environments and local preferences. Using whole-genome re-sequencing of Vigna radiata, we investigated the demographic history and compared the genetic footprints of domestication and improvement. The Asian wild population migrated to Australia at about 50 kya, and domestication happened in Asia about 9 kya selecting for non-shattering pods. The key candidate gene for this trait, VrMYB26a, has lower expression in cultivars, consistent with the reduced polymorphism in the promoter region reflecting hard selective sweep. The determinate stems were later selected as an improvement phenotype and associated with the gene VrDet1. Two ancient haplotypes reducing gene expression exhibit intermediate frequencies in cultivars, consistent with selection favoring independent haplotypes in soft selective sweep. Our results suggest domestication and improvement may leave different genomic signatures of selection, reflecting the fundamental differences in the two processes and highlighting the limitations of genome-scan methods relying on hard selective sweep.