The Genome Sequences of Cultivated Peanut’s Diploid Ancestors

Cultivated peanut (Arachis hypogaea) is an allotetraploid with closely related subgenomes of total size ~2.7 Gb (2n = 4x = 40; genome type AABB). This makes its genome assembly very challenging. Therefore as first step to understanding the genome of cultivated peanut, its diploid ancestors A. duranensis and A. ipaënsis, which contributed the A- and B-subgenomes respectively, were sequenced. We show that the sum of the diploid genomes is a good proxy for the cultivated peanut genome. However, there are distinct signs that the cultivated peanut genome is evolving by genetic exchange between the subgenomes. Based on remarkably high DNA identity of A. ipaënsis and the B-subgenome of cultivated peanut, and biogeographical evidence, we conclude that A. ipaënsis may be a direct descendant of the same population that contributed the B-subgenome to cultivated peanut.