The Genomic Signatures of Highland Adaptation in Maize

Maize (Zea mays ssp. mays) was domesticated in southwest Mexico ~9000 BP from the lowland teosinte, Zea mays ssp. parviglumis.  Subsequent to domestication maize spread across the Americas, with pre-Columbian cultivation stretching from New England to the Andes of South America.  In multiple instances maize was brought into highland regions, presumably adapting to cooler temperatures and higher ultraviolet radiation.  We have utilized genome-wide single nucleotide polymorphism data to assess evidence for maize adaptation to highland conditions in parallel in independent geographic regions and through introgression from highland-adapted wild relatives.  We find that initial post-domestication spread of maize into the highlands of the Central Plateau in Mexico was likely facilitated by introgression from the highland teosinte, Zea mays ssp. mexicana.  This introgression was found in genomic regions previously shown to underlie phenotypic traits associated with highland adaptation (e.g., pigment extent and leaf sheath macrohairs).  In the Andes, where maize wild relatives have historically not been found, highland adaptation appears to have occurred from standing variation at a largely independent set of loci.  We are currently working toward characterization of the genetic architecture of highland adaptation traits in Mexico and South America using mapping populations followed by functional characterization of genes in candidate regions.