The Australian cotton industry occupies a niche market in optimal fibre quality, but this must be constantly developed in order to “stay ahead”. Biotechnology provides an opportunity to continually improve fibre quality at lower cost and time, and in a more targeted way, than conventional plant breeding. Genetic improvement of cotton fibre morphology requires both useful genes and appropriate expression of the genes in cotton fibres. Previous CRDC-funded research in our laboratory has aimed to address both these requisites, concentrating on genes which are expressed in fibres but not in other cotton tissues.

We have identified six different controlling regions, or promoters, within cotton DNA which directly control the fibre-specificity and timing of expression of genes. Fibre-specific promoters allow the expression of any particular transgene to be targeted to the fibres only, avoiding any detrimental effects of expression on growth and morphology elsewhere within the plant. Each of the six promoters was fused to a reporter gene, GUS, and used to transform whole cotton plants. A large number of transgenic lines were recovered. Quantitative GUS assays were carried out the tissues of one transgenic line, showing that the reporter gene was strongly expressed in fibres only and that expression peaked during the elongation phase of growth.

One gene which is only expressed in cotton fibres encodes an interesting protein called an expansin. Expansins are thought to control plant cell growth by chemically modifying components of the cell wall, chiefly cellulose. As cellulose comprises such a large percentage of the cotton fibre, it could be that expansin proteins play a critical role in determination of fibre quality parameters such as length. Four genetic constructs were made, in which the expansin gene was placed under the control of four different cotton promoters, designed to alter normal expansin expression. The gene constructs were used to transform whole cotton plants and a large number of transformed lines were recovered. Ten lines have been screened for homozygousity and sent to the ACRI where the effects of the transgene on fibre properties such as length, strength and micronaire will be tested.

Results from this research will contribute valuable information on the role of the expansin gene in cotton fibre development, as well as providing novel germplasm for use in cotton breeding programs. In addition, it will provide a valuable bank of molecular tools which would allow expression of any gene in a defined manner in cotton fibre cells. Such tools could be used in other research aimed at producing fibres with improved or innovative properties.