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

Abstract

<p>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 (<em>Gossypium</em>) 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 <em>Kokia</em> and the East African and Madagascan <em>Gossypioides</em>). We generated a high-quality genome sequence of <em>Gossypioides kirkii</em> (n = 12) using PacBio, Bionano, and Hi-C technologies, and compared this assembly to genome sequences of <em>Kokia</em> (n = 12) and <em>Gossypium</em> 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 <em>de novo G. kirkii</em> genome sequence to genome sequences of <em>Gossypium,</em> including chromosome fusions and inversions. Genome comparison between <em>G. kirkii</em> and <em>Gossypium</em> suggests that multiple steps are required to generate the extant structural differences.</p>