Tissue-specific and developmental regulation of cotton gene FbL2A. Demonstration of promoter activity in transgenic plants.

A gene (FbL2A) that is preferentially expressed in cotton (Gossypium barbadense L. cv Sea Island) fiber was isolated and characterized. Genomic and cDNA analyses suggest multiple FbL2A genes in cotton. The gene is developmentally regulated and is activated during late primary and early secondary wall synthesis stages. FbL2A encodes a polypeptide of 43.4 kD and a predicted isoelectric point of 5.97. The nucleotide-derived protein is highly hydrophilic except for a hydrophobic N terminus and has a compositional bias for glutamic acid (26.3 mol%) and lysine (18.9 mol%). Sixty-two percent of the putative protein is composed of repeat motifs. A 55-amino-acid peptide region is repeated four times in a concatenate fashion within the protein. The function of the protein in the fiber cells is not known. A 2.3-kb DNA fragment 5' from the FbL2A gene is shown to direct expression of heterologous proteins in transgenic cotton in a fiber-specific and developmentally regulated fashion. The FbL2A promoter was used to express in transgenic cotton genes encoding acetoacetyl-coenzyme A reductase and polyhydroxyalkanoic acid synthase, which are involved in the synthesis of the thermoplastic polymer polyhydroxybutyric acid. Transgenic plants containing both enzymes produced polyhydroxybutyric acid in fiber. Thus, the FbL2A promoter is useful in genetic engineering schemes to modify cotton fiber.