The GhTT2_A07 Gene Is Linked to the Brown Color and Natural Flame Retardancy Phenotypes of Lc1 Cotton (Gossypium hirsutum L.) Fibers

Some naturally colored brown cotton fibers from accessions of Gossypium hirsutum L. can be used to make textiles with enhanced flame retardancy (FR). Here we show that both the brown color and enhanced FR of the Lc1 lint color locus are linked to a 1.4Mb inversion on chromosome A07 that is immediately upstream of a gene with similarity to Arabidopsis TRANSPARENT TESTA 2 (TT2). As a result of the alternative upstream sequence, the transcription factor GhTT2_A07 is highly up-regulated in developing fibers. In turn, genes in the phenylpropanoid metabolic pathway are activated, leading to biosynthesis of proanthocyanidins and accumulation of inorganic elements. We show that enhanced FR and anthocyanin precursors appear in developing brown fibers well before the brown color is detectible, demonstrating for the first time that the polymerized proanthocyanidins that constitute the brown color are not themselves the source of enhanced FR. Identifying the particular colorless metabolite that provides Lc1 cotton with enhanced FR could help minimize the use of synthetic chemical flame retardant additives in textiles.