Competition from synthetic fibers and a need to compete in the global marketplace underscore the importance of developing new cotton varieties with enhanced fiber quality. Molecular genetics and biotechnology are expected to play complementary roles to traditional plant breeding for generating high quality cotton varieties in the future. For this objective to be realized, linkages between the physical measures of fiber quality and the regulated expression of cotton fiber genes must be established. Since mature cotton fiber is primarily cellulose deposited in the fiber's secondary cell wall, we are examining how the genes producing this polymer are regulated by combining a culture technique to grow fiber in vitro with quantitative, reverse-transcription PCR (Q-RT-PCR) to measure fiber gene expression. This approach has resulted in identification of specific phytohormone treatments that stimulate expression of the catalytic subunits of cellulose synthase (CesA). Auxin and abscisic acid, individually and in combination, promote expression of cotton fiber secondary wall CesA genes, whereas gibberellin inhibits expression. Expression of genes known to be expressed primarily during fiber elongation is not altered as a result of phytohormone treatment. Expression of &Beta-glucuronidase driven by a cotton CesA promoter in transgenic Arabidopsis is similarly effected by phytohormones. We have also investigated CesA expression in fiber from field-grown plants using Q-RT-PCR. Analysis of gene expression in a near-isogenic high strength cotton line, MD52ne^1,2,revealed that CesA expression occurs earlier and at a higher level than the recurrent parent, MD90ne. The cell walls of MD52ne are slightly thicker and the orientation of cellulose microfibrils relative to the long axis of the fiber is smaller than the recurrent parent. A model linking the physical measurement of fiber strength with cellulose structure, organization, and biosynthesis will be discussed.

¹Meredith, W.R. 2005. Crop Sci. 2005 45: 807-808.

²Meredith, W.R., Jr. 2005. Crop Sci. 45: (in press).