|Kim, Hee Jin|
|Cehn, Z. Jeffrey|
Submitted to: Proceedings of Int'l Association of Plant Tissue Culture and Biotechnology
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2006
Publication Date: 8/13/2006
Citation: Triplett, B.A., Kim, H., Hinchliffe, D.J., Sze, S., Thaxton, P., Stelly, D., Cehn, Z. 2007. Phytohormone regulation of cotton fiber development in vitro.. Proceedings of Int'l Association of Plant Tissue Culture and Biotechnology. 153-156. Interpretive Summary: Immature cotton seeds (ovules) can be dissected from cotton flowers and cultured on a defined liquid medium. When the medium contains the correct nutrients and plant hormones, cotton fibers will develop on the seed surface. Our team uses this culture system to investigate how cotton fibers begin their growth. Genes that are active are copied into a messenger ribonucleic acid (mRNA) or transcript. Using a sensitive method to monitor the transcripts of thousands of genes, we are comparing cultures containing two plant hormones with cultures that are missing these two growth regulators. This approach will identify specific genes that are critical for initiating fiber development. The preliminary experiments reported at this conference are encouraging that this experimental plan is revealing the most important genes in the process of fiber initiation. A second line of investigation using cotton ovule cultures is focused on determining the signals responsible for switching the fiber away from a growth pattern that causes the fiber to elongate and toward a pathway that stimulates the fiber wall to become thicker. Transcript abundance of the genes causing the increase in cell wall thickness was measured in cultures established under different plant hormone compositions. Two hormones stimulated the expression of the specific genes under investigation and a third hormone counter-acted this effect. Analysis of cotton ovule cultures using contemporary techniques in plant molecular biology offers the potential for uncovering fundamental aspects of plant growth and development that will also be useful for designing applied approaches for cotton improvement.
Technical Abstract: Our team is interested in the regulation of two time points in cotton fiber development: initiation of fiber growth from ovule epidermal cells and the transition from fiber elongation to secondary wall biogenesis. These two developmental phases determine key properties of fiber quality and yield. Cotton ovules, excised from ovaries prior to fertilization, will continue development in vitro under defined conditions when auxin and gibberellic acid are present. By transcript profiling with oligo-microarrays we have begun to identify genes that are differentially regulated in cultures established with auxin and gibberellin compared to cultures where the phytohormones are absent. This approach will identify essential targets for increasing fiber number per seed, an important component of yield. After initiating growth, seed trichomes (fibers) elongate for about 13 days in culture and then begin producing thick, cellulosic secondary cell walls. A distinct set of cellulose synthase or '-glucan synthase (CesA) genes are up-regulated during secondary wall biogenesis. We have investigated culture conditions for prematurely inducing CesA expression in vitro. Abscisic acid in combination with auxin is very effective in increasing transcript abundance of CesA genes as measured by quantitative, reverse transcription PCR. Gibberellic acid acts as an antagonist to abscisic acid activity in this assay. In silico analysis of cotton CesA promoters shows an abundance of phytohormone-responsive cis-acting elements. Analysis of cotton ovule cultures using contemporary techniques in plant molecular biology offers the potential for uncovering fundamental aspects of plant growth and development that will also be useful for designing applied approaches for cotton improvement.