Cotton fibers are composed of almost pure cellulose. The first CesA genes encoding catalytic subunits of plant cellulose synthase were identified from cotton fibers a decade ago. The enzyme complex is localized in the plasma membrane and is organized into 36-subunit rosette structures composed of three related CesA proteins. More than 10 CesA isoforms have been isolated from other plant species, but very limited numbers of fully sequenced cotton CesA genes are available in public databases. Due to the possible formation of intergenic chimeras from homeologous genes of polyploid plants, PCR-based techniques are limited in their usefulness to obtain genomic sequences from allotetraploid cotton.

To compare the sequences of CesA genes and their promoters from Gossypium hirsutum, we screened a cotton BIBAC library using overgoes and probes carefully designed to select specific CesAs that had not previously been sequenced. Eighteen GhCesA candidates were isolated from the libraries. Fingerprinting and in silico analyses showed that there were six different CesAs for genes expressed during cell elongation (primary cell wall), four new CesAs for genes expressed during secondary wall cellulose synthesis, and two putative cellulose synthase-like genes.

The large-insert clones containing the CesA genes involved in secondary wall cellulose biosynthesis are being sequenced. Comparison of the gene sequence will permit us to understand how CesA genes have evolved between A and D subgenomes and will offer insight into how the regulation of this enzyme helps establish key fiber quality traits.