The Genome Sequence of Gossypioides kirkii Illustrates a Descending Dysploidy in Plants

One of the extraordinary aspects of plant genome evolution is variation in chromosome number, particularly that among closely related species. This is exemplified by the cotton genus ( ) and its relatives, where most species and genera have a base chromosome number of 13. The two exceptions are sister genera that have n = 12 (the Hawaiian and the East African and Madagascan ). We generated a high-quality genome sequence of (n = 12) using PacBio, Bionano, and Hi-C technologies, and compared this assembly to genome sequences of (n = 12) and diploids (n = 13). Previous analysis demonstrated that the directionality of their reduced chromosome number was through large structural rearrangements. A series of structural rearrangements were identified comparing the genome sequence to genome sequences of including chromosome fusions and inversions. Genome comparison between and suggests that multiple steps are required to generate the extant structural differences.