Tianzhen Zhang
Nanjing Agricultural University, China
Title: Asymmetric sub-genomic evolution and domestication of allotetraploid cotton (Gossypium hirsutum l.)
Biography
Biography: Tianzhen Zhang
Abstract
Cotton is an important textile and oil crop throughout the world. The cotton species include two commercially important cultivated allotetraploid species, G. hirsutum L. and G. barbadense L., which have a genome size of 2.5 Gb and large numbers of repetitive sequences derived from an allopolyploidization event between G. herbaceum L. (A1) and G. raimondii (D5) Ulbrich approximately 1-2 million years ago. Upland cotton (G. hirsutum) is an ideal model for polyploid crop domestication and transgenic improvement. We sequenced the allotetraploid Gossypium hirsutum L. acc. TM-1 and G. barbadense L. cv. Xinhai 21 genomes by integrating whole-genome shotgun reads, bacterial artificial chromosome (BAC)-end sequences and ultra-dense inter-specific genetics genetic map. By comparing the A and D subgenomes, we revealed the asymmetric subgenomic evolution and domestication of allotetraploid cotton. More structural rearrangements were characterized in the A subgenome than in the D subgenome. The A subgenome have evolved faster than the D subgenome and the rich transposable elements make nearly twice the size difference between these two subgenomes. Consistent with asymmetric structural rearrangement and evolved rate, there were significantly more genes lost and disrupted in the A sugenome than in the D subgenome. On the contrary, the centromeric retro-element sequence of tetraploid cotton derived from the D subgenome progenitor have invade the A subgenome centromeres after allotetrapolyploid formation. Although no genome-wide expression dominance was found between the subgenomes, gene expression bias for homoeologous gene pairs is widespread, frequently 20-40% range, depending on the tissue. The asymmetric domestication is associated with positively selected genes for fiber yield and quality in the A subgenome and for stress tolerance in the D subgenome. Our studies provide valuable genomic resource for cotton research and benefit the understanding of the basis of many other allopolyploids in which two or more subgenomes retain sufficient divergence.