Tailoring new cotton genes for industry
Thursday, 13 July 2000
It was once the proud boast that Australia rode on the sheep's back. We were known worldwide for the quality of our wool, and export income showed it. Synthetic fibres changed that picture. Modern fabrics are often blends of natural and man-made fibres, and Australian wool exports have suffered accordingly.
The other major natural fibre is cotton. Traditionally grown offshore, it has recently been introduced as an Australian crop. Like wool, it is often blended with synthetic fibres, but Adelaide University scientists are working to improve the quality of natural cotton fibres themselves.
Cotton fibres are unique. Each is a single cell up to 2.5 cm long. Thousands of them together form a white, fluffy cotton boll that is harvested when mature, and all the fibres from a single boll are developmentally identical. Identifying and modifying the genes that control the development of these fibres promises many potential benefits in changing their properties and, therefore, the properties of threads and fabrics produced from them.
In Australia, Upland cotton is mainly grown in Northern New South Wales and Southern Queensland. In the 1998-1999 season, 553,000 hectares were planted to cotton, with 15% of the crop being genetically modified (transgenic).
Ingard, Australia's transgenic cotton, has a natural resistance to a major pest, the cotton bollworm. Growth of Ingard cotton has resulted in a drop of 40-50% in overall pesticide use as measured over three seasons from 96-99.
90% of Australian cotton is exported to buyers in Indonesia, Korea and Japan and its value is more than $1 billion per year, recently overtaking export earnings from wool for the first time. Lake Tandou near Broken Hill grows Pima cotton; lower-yielding than Upland cotton but finer, and exported mainly to Italy and Switzerland.
Dr Sharon Orford and her colleagues in Adelaide University's Genetics Department are interested in the regulatory aspects of fibre development. They have already characterised several genes that are expressed only in fibre cells. "We are trying to elucidate the answers to questions such as why only one in four epidermal cells elongates," said Dr Orford.
The project, which began in 1992, is funded by the Cotton Research and Development Corporation (CRDC), and aims to improve cotton fibre quality by genetic engineering. It is a challenge which means not only identifying but modifying genes that find their expression in fibre cells.
"We have isolated the controlling regions, or promoters, of these genes and they are being tested in transgenic plants," said Dr Orford. "If they are fibre-specific, they can be used to drive the expression of other genes, such as pigment genes," she said. "Manipulation of genes such as these could improve the fibre characteristics or increase the number of fibres, and therefore the yield, of each boll."
The most promising fibre-specific gene for such manipulation encodes a protein called "Expansin", pivotal in the control of plant cell growth. Expansin in cotton is encoded by a complex gene family. PhD student, Sarah Harmer, is being funded by an ARC-SPIRT grant to characterise the members of the family. The industrial partner in the research is Cotton Seed Distributors (CSD).
While the end result will be to improve cotton, the researchers use results from other plant systems which offer possible short-cuts to successful manipulation of cotton fibres. One such plant is Arabidopsis thaliana. Cotton has 52 chromosomes, an enormous genome, takes three months to flower and is difficult to transform. By contrast, Arabidopsis has a small, simple genome and a short generation time It is readily grown in the lab and easily transformed.
Arabidopsis has been used as an experimental system for many studies on plant development and cell-cell interactions, and a large number of mutants have been characterised at the molecular level. The genome of the species, being sequenced by an international consortium, is 90% complete and will be finished by the end of the year.
"Arabidopsis does not grow long fibres, but it does grow trichomes, " said Dr Jeremy Timmis, who works with Dr Orford on the project. " These are leaf hairs that, in their early stages, closely resemble the early development of cotton fibres. By isolating and characterising cotton genes that correspond to the Arabidopsis genes, we hope we can find out how cotton fibres are initiated," he said.
The common practice of blending natural and synthetic fibres suggests that transgenic cotton could usefully be modified to provide fibres with different characteristics. In America, an experimental form of transgenic cotton has a gene for a polyester compound, and produces fibres with superior insulating qualities. More conventional parameters for measuring cotton fibres involve their length, strength and fineness; qualities that are primary targets in the Adelaide University research.
The CRDC- and CSD-funded research is complemented by results from an Honours student, Katherine Malone, who is investigating how particular genes form proteins that control aspects of fruit, ovule and seed development in plants. A chance discovery showed that at least one of these genes affects the growing cotton fibres, and Ms Malone's project involves finding out more about them.
Knowledge of the genes which are expressed in cotton fibres will contribute to our understanding of how these unique cells develop, and may ultimately provide a basis for genetic engineering of fibre properties in Australian cotton varieties.
Photos available from: /pr/media/photos/2000/
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