Discovery and identification of a novel Ligon lintless-like mutant (Lix) similar to the Ligon lintless (Li₁) in allotetraploid cotton

Mutants are a powerful resource for studying gene structure, function, and evolution. In this present study, a novel Ligon lintless-like mutant (Lix), that has short fibers and deformed leaves and stems, was isolated from the progeny of transgenic cottons. The Lix mutant is similar in morphology to the Ligon lintless (Li₁) mutant. Genetic analysis and molecular mapping were performed for the Lix and Li₁ mutants. These two mutants are monogenic dominant mutants with distorted growth of vegetative and reproductive structures. Seedlings of the dominant homozygote Li ₁ Li ₁ genotype are lethal, while LixLix plants are viable but show no reproductive growth. Molecular tagging showed that the Lix gene is located on Chr. 04 in a 30.9-cM region spanned by NAU8376 and NAU3469. In a previous study, the Li ₁ gene was mapped to Chr. 22, and Chr. 04 and Chr. 22 are homoelogous chromosomes in tetraploid cotton. So, we propose that Lix and Li₁ mutants have similar mutated morphology, and Lix is mapped to a homoelogous chromosome carrying Li ₁ . The identification and genetic mapping of Lix/Li ₁ genes using mutants provides a foundation for isolating these genes. In turn, this will permit studies to elucidate the functional and evolutionary roles for these genes in cotton growth and development.