Durum wheat evolution: a genomic analysis

Durum wheat appears in the archaeological record, very sporadically, ~7000 years before present, but becomes the dominant tetraploid wheat in the Levant and in the Mediterranean basin ~2500 years ago. Here, we discuss the archeological insights on durum wheat evolution and we focus on the analysis of the genomic changes that are correlated with the process of domestication and evolution of modern durum by comparing four genetic groups: wild emmer, domestic emmer, durum landraces and modern durum varieties. Changes in gene expression and copy number variation of genes and transposons were analyzed in the genetic groups. Genes were clustered based on their pattern of change during Durum evolution, e.g. gradual increase, or decrease, or increase at the onset of domestication and plateauing later on. There were not many genes that changed >2 fold in copy number. However, interestingly, the copy number of transposons increased with domestication, possibly relecting the genomic plasticity that was required for adaptation under cultivation. Extensive changes in gene expression were seen in developing grains. For example, there was an enrichment for certain functions: genes involved in vesicle traficking in the endosperm showed a gradual increase in expression during durum evolution and genes related to germination and germination inhibition increased in expression in the embryo, in the more recent stages of durum evolution. The approach described here enables better understanding of the genetic events that shaped modern wheat and identiies genes that can be used for crop improvement.