Genomic Targeting and Mapping of the Major Leaf Shape Gene (L) in Upland Cotton (Gossypium hirsutum L.).

Leaf shape in cotton is an important trait that influences yield, flowering rates, disease resistance, lint trash, and the efficacy of foliar chemical application. The leaves of okra leaf cotton display a significantly enhanced lobing pattern, as well as ectopic outgrowths along the lobe margins when compared to normal leaf cotton.  These phenotypes are the hallmark characteristics of mutations in various known modifiers of leaf shape that culminate in the mis/over-expression of Class I KNOX genes. To better understand the molecular and genetic processes underlying leaf shape in cotton, a normal leaf landrace accession was crossed to an okra leaf germplasm line. An F₂ mapping population of 236 individuals was used to confirm the partially dominant single gene nature of the leaf shape gene (L^o) controlling okra leaf shape in cotton and its location on chromosome 15. Molecular mapping with simple sequence repeat (SSR) markers localized the leaf shape gene L to a 5.4 cM interval in the distal region of the short arm of chromosome 15. Orthologous mapping of the closely linked markers with the sequenced diploid D-genome (Gossypium raimondii) more finely resolved the leaf shape locus to a 337 kb region. RT-PCR based expression analysis and candidate gene mapping indicated that the okra leaf shape gene (L^o) in cotton may be an upstream regulator of Class I KNOX genes. The linked molecular markers and delineated genomic region in the sequenced diploid D-genome will assist in the future high-resolution mapping and map-based cloning of the leaf shape gene in cotton.