The intriguing domestication processes of crops have remained mostly elusive as living examples of wild and cultivated accessions only capture the present evolutionary state of the crops. In this regard, ancient samples are exceptionally advantageous in assisting our understanding of the domestication process. To better understand maize domestication, Jazmín Ramos-Madrigal, from the University of Copenhagen, and colleagues sequenced the genome of a 5,310-year-old maize cob that was excavated in the Tehuacán Valley of Mexico, a location of ancient maize cultivation.
By comparing this genome against accessions of teosinte, the ancestral plant from which maize is derived, as well as against modern landraces, the researchers found that the ancient sample belongs to the same lineage of maize and represents a basal branch that diverged from teosinte earlier than the modern cultivars. Genomic composition analysis showed that the ancient cob is genetically intermediate between modern landraces and teosinte, but somewhat closer to the landraces.
The ancient genome is a mosaic of wild and cultivated alleles at the domestication-related loci: some domestication genes exist in ancestral states but others display derived alleles, suggesting that although maize domestication occurred very rapidly, it nevertheless took place gradually through multiple steps.