The Ligon lintless-2 Short Fiber Mutation Is Located within a Terminal Deletion of Chromosome 18 in Cotton¹

Abstract

Extreme elongation distinguishes about one-fourth of cotton (Gossypium sp.) seed epidermal cells as “lint” fibers, useful for the textile industry, from “fuzz” fibers (,5 mm). Ligon lintless-2 (Li2), a dominant mutation that results in no lint fiber but normal fuzz fiber, offers insight into pathways and mechanisms that differentiate spinnable cotton from its progenitors. A genetic map developed using 1,545 F2 plants showed that marker CISP15 was 0.4 cM from Li2, and “dominant” simple sequence repeat (SSR) markers (i.e. with null alleles in the Li2 genotype) SSR7 and SSR18 showed complete linkage with Li2. Nonrandom distribution of markers with null alleles suggests that the Li2 phenotype results from a 176- to 221-kb deletion of the terminal region of chromosome 18 that may have been masked in prior pooled-sample mapping strategies. The deletion includes 10 genes with putative roles in fiber development. Two Glycosyltransferase Family 1 genes showed striking expression differences during elongation of wild-type versus Li2 fiber, and virus-induced silencing of these genes in the wild type induced Li2-like phenotypes. Further, at least 7 of the 10 putative fiber development genes in the deletion region showed higher expression in the wild type than in Li2 mutants during fiber development stages, suggesting coordinated regulation of processes in cell wall development and cell elongation, consistent with the hypothesis that some fiber-related quantitative trait loci comprise closely spaced groups of functionally diverse but coordinately regulated genes.