Jeans, Genes, and The Independent Domestications Of Cotton

The cotton genus (Gossypium) provides a replicated model for studying the domestication process, as it encompasses the independent domestication of four species, two from the Americas, G. hirsutum and G. barbadense, and two from Africa-Asia, G. arboreum and G. herbaceum. In each case, aboriginal domesticators and subsequent generations transformed photoperiodic wild perennials with seeds bearing tightly adherent, short epidermal trichomes into modern day-neutral annuals with long, strong, white “fiber”, thereby providing the world’s most important textile plant. Old World cultigens are diploid, whereas those from the New World are allopolyploids arising from a biological reunion, 1-2 MYA, of divergent diploids from different hemispheres. We are studying the transcriptional, genomic and proteomic changes accompanying this remarkable parallel domestication process, using a combination of genomic technologies, QTL analysis, and synthesis of isogenic lines that collectively tile the donor genome of wild plants in the recipient genomes of cultigens. The fiber transcriptome is both extraordinarily complex, with at least 15,000 genes expressed in this single celled structure, and dynamic, with thousands of genes coordinately regulated during primary and secondary wall synthesis. Transcriptomic and proteomic analysis demonstrate massive alteration by domestication, involving mutations that propagate through developmental networks significantly altering the expression of thousands of genes. Ongoing experiments are designed to dissect that architecture of this network, discover the genes targeted during each domestication, the biological processes affected by the mutations selected by domesticators and during crop improvement, and their phenotypic effects. This work provides insights into the genetic architecture underlying the parallel evolution of the apparently similar morphological transformation of single-celled structures, and the enabling role of allopolyploidy in providing a vastly increased combinatorial complexity as a substrate for selection.