Advances in our knowledge of the genes expressed in cotton fibres make biotechnology a viable means to improve fibre characteristics. Most genetic modification uses ubiquitously expressing promoters that often result in yield penalty. We have developed a strategy which uses fibre-specific promoters to manipulate and confine gene expression to fibre cells.

We used several fibre-specific gene promoters to drive expression of an expansin gene that is native to cotton and fibre-specific as well. Expansin is a protein known to be involved in cell elongation and growth, and therefore could impact on fibre traits such as length. Normally, the fibre-specific expansin gene expresses predominantly in the first 18 days of fibre development. By assembly of the expansin gene with a promoter (FS18) that usually drives expression of a lipid transfer-like protein that is active late in fibre development, we have been able to extend expansin expression for a further 4-10 days in transgenic plants. The chimeric gene increased the total amount of expansin in fibre cells and altered the morphology of the fibre in ways that are potentially advantageous to the industry. Linked experiments in which this promoter was used to drive a GUS reporter gene in a separate set of transgenic plants showed that the FS18 promoter can drive a high level of transcription specifically in fibre cells to a much later stage of fibre development. The FS18 promoter could be used to express any gene of interest in an effective and predictable manner in cotton fibre cells, and could be an important tool in fibre biotechnology.

Transgenic plants containing the FS18-expansin construct have modified fibre characteristics that could be incorporated into existing breeding programs. In this way new fibre variants could be generated, contributing to germplasm stocks and helping to maintain the reputation of the Australian cotton industry as a producer of premium quality cotton. Our strategy of manipulating gene expression in a tissue-specific manner by utilising native cotton genes is feasible and potentially beneficial to the cotton industry.