2011 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.
The leaf trichome survey has been completed and a possible genetic linkage identified between the trichomes of cotton leaves (hairs) and ovules (fiber). The next step is to produce near isogenic populations to evaluate this linkage. This linkage is important in that it literally “may be the foot in the door” of understanding the cellular mechanism of cotton ovular trichome (fiber) initiation. The protocol for developing near isogenic lines (NILs) for this population will be to self the heterozygous plants with the phenotype of pilose (extremely hairy) leaves and smooth bolls. The first two rounds of NIL production have established and validated the association of smooth leaf with fiberless cottonseed and pilose leaves with the production of ovular lint. The NIL production should take a total of 3 years followed by one to two years for seed increase of the homozygous lines. These NILs will be a valuable asset for the cotton community and used as tools for mapping and trait evaluation studies. Cotton plants contain a variety of related toxic compounds classed as terpenoid aldehydes (TA) that protect the plant from pests. Cotton seed is a source of high quality protein that could be used for animal feed if the anti-nutritional TA compounds could be reduced. In the seed, the predominant TA compound is gossypol which has two forms (plus and minus) with the minus form being more toxic. Crosses were made between high plus gossypol and high minus gossypol lines and the progeny evaluated to determine the inheritance of total gossypol content and also the plus and minus forms. Evaluation of the TA compounds present in the seed, vegetative and reproductive cotton tissues confirmed that the association between total gossypol content in seed and vegetative tissues is low. Further studies revealed that the association of gossypol and the other major TA compounds is also low, thereby allowing for selection of seeds with low gossypol, but high level of the protective TAs in the other plant parts.
Cotton trichome initiation. Are leaf hairs and ovular fibers produced via the same mechanism? The leaf hair (trichome) initiation mechanism has been studied extensively in the model plant Arabidopsis and there was some evidence that cotton might share the same mechanism. There was also some evidence that the cotton leaf trichome initiation mechanism was similar to that involved in the initiation of cotton seed fibers. ARS researchers in Stoneville, MS, tested these ideas directly on developing cotton and found that the mechanisms for cotton leaf trichome and fiber (seed trichomes) development differ. While the mechanisms for leaf and seed trichome initiation share common components, the post initiation development of these two types of trichomes varies. While using Arabidopsis as a model system may still be useful for some applications, these results show that devising methods to increase the amount of fibers on the seed should be targeted directly to seed trichomes and not other model plants such as Arabidopsis.
Enhanced plant resistance to pests. Cotton seed contains high quality protein that could be used in animal feeding rations and provide an additional income source for the grower. However, the seed is currently under-utilized because it contains a detrimental compound called gossypol. Previous attempts to eliminate gossypol in the seed also eliminated the gossypol and related compounds, called terpenoid aldehydes (TAs), from all parts of the plant leaving the plant vulnerable to insect and disease attack. Studies at ARS Stoneville, MS, evaluating gossypol and related TAs in seeds and vegetative parts of the cotton plant revealed that seed TA levels often do not indicate the level in leaves, roots, bolls and flowers. There is variation not only among germplasm lines, but also among commercial varieties, with some varieties having low seed TAs and high levels in the plant. It should be possible to breed for low seed gossypol lines that can be used as animal feed, while maintaining high TA levels in the plant to protect against pests.
Taliercio, E.W., Scheffler, J.A., and Kwanyuen, P. 2010. Nitrogen Metabolism in Cotton Stems and Roots during Reproductive. Journal of Cotton Science. 14:107–112.
Taliercio, E.W., Scheffler, J.A., Scheffler, B.E. 2010. Characterization of Two Cotton (Gossypium hirsutum) Invertase Genes. (Available online in Molecular Biology Reports).
Bowling, A.J., Vaughn, K.C., Turley, R.B. 2010. Polysaccharide and glycoprotein distribution in the epidermis of cotton ovules during early fiber initiation and growth. Protoplasma. 248:579-590.
Romano, G.B., Taliercio, E.W., Turley, R.B., Scheffler, J.A. 2011. Fiber initiation in eighteen gossypium cultivars and experimental lines. Journal of Cotton Science. 15:61-72.