Location: Crop Genetics Research2009 Annual Report
1a. Objectives (from AD-416)
Improve the value of cotton fiber for the grower by identifying key temporal and spatial cellular events which affect the development of ovule epidermal cells into fiber initials, and add value to seed cotton by modifying the amount and distribution of gossypol in the seed and vegetative plant parts.
1b. Approach (from AD-416)
Identify pleiotropic effects associated with a reduction in the number of fibers initiated on the ovule and the number and morphology of leaf trichomes or root hairs in pilose x fuzzless or pilose x fiberless seed crosses; identify key genetic components (transcription factors/enzymes) and cellular events occurring during the development of an ovule epidermal cell into an elongating fiber; determine the genetic control of gossypol content and the proportion of plus/minus forms via transmission genetics and mapping with molecular markers; evaluate if selection in early generations, using a half seed method to test gossypol content, is as effective for identifying the desired genotypes as testing progeny in later generations.
3. Progress Report
The project began in April of 2008 and is on schedule with the first milestones all substantially met. For Objective 1, tests to estimate hair (trichome) density on pilose (hairy leaf) and normal leaf lines were performed in the greenhouse and replicated in the field. Evaluation of the progeny from a cross between pilose and fiberless seed lines is progressing with the first population, pilose X SL1-7-1, grown in the field this summer. The others are on schedule to be evaluated in 2010. The GL3 gene is thought to be involved in cotton fiber initiation. We have fully sequenced GL3 and determined the number of introns for fiberless, pilose and normal lines. No sequence differences occurred in the gene for any of the lines evaluated, indicating a gene controlling GL3 may be the cause of the differences and not GL3 directly. Objective 2A originally proposed screening for DNA markers associated with “total gossypol content” by evaluating eight lines with 104 markers distributed across 13 chromosomes previously targeted as sites for genes influencing gossypol content. An additional 20 lines have been obtained and added to the original group of lines to be evaluated, and 45 more markers have been identified that can be used for the project. We have also expanded our group of lines to evaluate the inheritance of the +/- racemic forms of gossypol. Using a half seed method to select for +/- gossypol in F2 plants has proven successful. Additional populations were created and are currently being analyzed and selections made.
1. Using Leaf Hairs as a Model for Cotton Fiber Development. Cotton is closely related to the model plant Arabidopsis and there is some evidence that they use the same leaf hair (trichome) initiation mechanism, which has been extensively studied in Arabidopsis. There is also some speculation that cotton leaf trichome initiation mechanisms may be similar to those involved in the initiation of cotton seed fibers. In evaluation of 14 cotton lines with varying leaf trichome densities, results showed that: 1) at least two trichome initiation mechanisms are functioning in cotton leaf trichome development; 2) in general leaf trichomes increase in number and complexity (branching) as you progress up the plant, while cotton fibers are unbranched; 3) due to the variation in branching, visual rankings of trichome number with the naked eye are not accurate compared to microscopic assessments; 4) characterization of leaf trichomes and cotton fibers using immuno-localization techniques to identify the carbohydrate composition of their cell walls showed that leaf trichomes were very different from cotton fibers. These results indicate that the mechanisms for leaf trichome and fiber initiation may still share common components (proteins), however, the development of these two types of trichomes may differ due to the evolutionary function of each. While using Arabidopsis as a model will still be useful, the level of similarity needs to be re-assessed.
Turley, R.B., Taliercio, E.W. 2008. Cotton Benzoquinon Reductase: Up-Regulation During Early Fiber Development and Heterologous Expresson and Characterization in Pichia Pastoris. Plant Physiology and Biochemistry. 46:780-785