Evolution of the alcohol dehydrogenase gene family in diploid and tetraploid Gossypium L

Abstract

Most plant nuclear-encoded genes exist in gene families of various sizes. We present a characterization of the structure and evolution of the alcohol dehydrogenase {Adh) gene family in diploid and tetraploid members of the cotton genus {Gossypium). A PCR-based approach was employed to isolate and sequence multiple Adh gene family members. We used Southern hybridization analyses to docimient variation in gene copy number in three diploids which represent the primary centers of Gossypium diversity (Australia — G. robinsonii, Africa — G. herbaceum. New World — G. raimondii), as well as one of the five allotetraploid species (G. hirsutum). The diploid species of Gossypium contain at least seven Adh loci in two primary gene lineages. One of these lineages contains two loci that are the result of a local duplication; the other lineage contains at least five loci. Sequence analysis reveals extensive variation in intron lengths between loci, and one locus has lost two introns usually found in other plant Adh genes. Evolutionary rate estimates differ between loci and in some cases between organismal lineages at the same locus. Finally, the Adh gene family appears relatively active in that multiple examples of apparent gene duplication events were found and at least one case of pseudogenization and one case of gene elimination were also found. Key Words; Adh, cotton, genetic mapping, molecular evolution, gene family, polj^loidy