Cellulose is a crystalline B-I, 4 glucan found in all higher plants and comprises over 90% of the dry matter of the mature cotton fibre. Selection for improved cotton fibre properties has not usually targeted cellulose characteristics directly but comparisons of fibres with different properties suggest that varietal differences between fibres often reflect unconscious selection for differences in cellulose properties. For example, changes in the quantities of cellulose produced, in the timing of production and in physical properties such as chain length, all impact on fibre properties. For many years the genes involved in cellulose production in plants remained elusive.However, our work identified the first gene involved in this process. It encoded the catalytic subunit of cellulose synthase, the enzyme that sequentially adds the glucose units onto the growing cellulose chain. This gene is currently protected by patent. The work exploited our collection of cellulose mutants to identify the gene and most importantly to prove its function and its ability to change the physical properties of cellulose. (The cellulose deficiency causes radial swelling of the roots, so the mutants are referred to as rsw mutants. An Arabidopsis gene can be used to identify equivalent genes in cotton by standard methods of molecular biology and then the Arabidopsis mutant can be used to rapidly prove the function of the cotton gene by showing that it restores wild type function to the mutant.

The basis of this project was to identify the genes which were affected in two of the other cellulose deficient mutants of the collection, rsw2 and rsw3. Cellulose production, like most biosyntheses, is almost certain to be controlled by several genes whose products may, for example, activate or inhibit the already identified catalytic subunit in response to environmental or developmental changes or may be required in some other capacity for cellulose to be generated. It is the identification of those additional genes, their functional characterisation and their protection for use in Australian cottonbreeding that was the basis for undertaking this project.