Tracing the global spread of maize (Zea mays L.) through plastome analysis of landraces.

Maize (Zea mays L.) is the most recently domesticated and dispersed worldwide among major cereals. Chloroplast genomes (plastome), with their highly conserved tetrad structure, hold a significant value in phylogenetic research due to their typical maternal inheritance. In this study, a total of 286 maize plastomes, 262 newly assembled and 24 publicly available, were investigated which included worldwide landraces, nested association mapping founders, and teosinte accessions. The maize plastomes were assembled with the filtered reads of the whole genome sequences from our re-seq data and public database by mapping to the reference plastome of B73. The maize plastomes were put into the phylogenetic analyses, with Z. perennis accession as the outgroup. The maize landraces were divided into four clades, showing a closer relationship with the Z. mays ssp. parviglumis plastome than with mexicana, indicating that parviglumis was the direct donor of the plastome to maize. Landrace diversities in Europe were quite similar to those in China and the Korean Peninsula, suggesting that the dispersal of maize following European contact with America was both rapid and accompanied by the translocation of a broad spectrum of maize germplasm. The introduced landraces have less diversity than the old landraces found in South America. This study provides information for understanding the genetic diversity of maize landraces and the process of maize dispersal in the world for exploiting the maize germplasm in breeding.