Genetic engineering to confer useful agronomic and fibre traits will lower the cost and time

required for producing improved cotton varieties and will promote environmentally-friendly

farm practices. 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 promoters within the cotton genome 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, in transient assays, shown to

direct reporter gene expression that was confined to the fibres. The six promoter::GUS

constructs were then used to transforrn whole cotton plants and a large number of transgenic

lines were recovered. These have been tested for presence of the transgene and T2 seed

collected. Future work involves quantitative GUS assays on fibre extracts in order to confirm

the fibre-specificity of each promoter and to determine the temporal expression pattern and

relative strength of each promoter in cotton fibres ofT2 plants.

The second aim of this project wasto identify which of our candidate genes have potential

for alteration of fibre characteristics, by preparing gene constructs designed to change their

expression and testing their effects in whole-plant transformants. The most promising of our

genes encodes an expansin, a protein thought to control plant cell growth by chemical

modification of cell wall components. Expansins could therefore play a critical role in

determination of fibre quality and yield. Four constructs were made, in which the expansin

gene was placed under the control offour different promoters, designed to alter native

expansin expression. These promoters were available from our bank of fibre-specific gene

promoters. The gene constructs were used to transform whole cotton plants and a large

number of transformed lines were recovered. These have been tested for presence of the

transgene and T2 seed collected. T2 plants will be tested for the effects of the transgene on

fibre properties such as length, strength, micronaire, uniformity and maturity.