Entire nucleotide sequences of Gossypium raimondii and G. arboreum mitochondrial genomes revealed A-genome species as cytoplasmic donor of the allotetraploid species

Abstract

Cotton (Gossypium spp.) is commonly grouped into eight diploid genomic groups, designated A-G and K, and an allotetraploid genomic group, AD. Gossypium raimondii (D₅ ) and G. arboreum (A₂ ) are the putative contributors to the progenitor of G. hirsutum (AD₁ ), the economically important fibre-producing cotton species. Mitochondrial DNA from week-old etiolated seedlings was extracted from isolated organelles using discontinuous sucrose density gradient method. Mitochondrial genomes were sequenced, assembled, annotated and analysed in orderly. Gossypium raimondii (D₅ ) and G. arboreum (A₂ ) mitochondrial genomes were provided in this study. The mitochondrial genomes of two diploid species harboured circular genome of 643,914 bp (D₅ ) and 687,482 bp (A₂ ), respectively. They differ in size and number of repeat sequences, both contain illuminating triplicate sequences with 7317 and 10,246 bp, respectively, demonstrating dynamic difference and rearranged genome organisations. Comparing the D₅ and A₂ mitogenomes with mitogenomes of tetraploid Gossypium species (AD₁ , G. hirsutum; AD₂ , G. barbadense), a shared 11 kbp fragment loss was detected in allotetraploid species, three regions shared by G. arboreum (A₂ ), G. hirsutum (AD₁ ) and G. barbadense (AD₂ ), while eight regions were specific to G. raimondii (D₅ ). The presence/absence variations and gene-based phylogeny supported that A-genome is a cytoplasmic donor to the progenitor of allotetraploid species G. hirsutum and G. barbadense. The results present structure variations and phylogeny of Gossypium mitochondrial genome evolution.

Keywords: Comparative genomics; Gossypium mitochondrial genome; phylogenetic analysis; unique regions.