Molecular Mapping of Laciniate Leaf Shape Gene (LL-A2) in Diploid Cotton (G. arboreum)

Gossypium arboreum, which produces spinnable cotton fibers, is an A genome diploid progenitor species of tetraploid cotton. With its diploid genome, publicly available genome sequence, and adapted growth, developmental and agronomic attributes, G. arboreum could make an ideal cotton species to study the genetic basis of biological traits that are controlled by orthologous loci in diploid and polyploid species. Leaf shape is an important agronomic trait in cotton that affects the plant and canopy architecture, yield, stress tolerance, and other production attributes. Normal, sub-okra, okra and laciniate  are predominant leaf shapes in cotton cultivars. Laciniate in diploids is phenotypically similar to okra leaf shape in tetraploid. In the present study, a segregating population of 135 F2 plants derived from accessions NC 501 and NC 505 was used for genetic and molecular mapping of laciniate leaf shape in diploid cotton (G. arboreum). An inheritance study showed that laciniate leaf shape was controlled by a single incompletely dominant gene (L-A2L). Molecular genetic mapping using SSR markers placed the L-A2 locus on chromosome 2. Targeted mapping using the putative genes from the delineated region established that laciniate leaf shape in G. arboreum and okra leaf shape in Upland cotton were controlled by genes at orthologous loci. Collinearity was well conserved between the diploid A (G. arboreum) and D (G. raimondii) genomes in the targeted genomic region narrowing the candidate region for the leaf shape locus (L-A2) to ten putative genes. Establishing the orthologous genomic region for the L loci could help utilize the diploid cotton resources towards the map-based cloning of leaf shape genes in tetraploid Gossypium.