2010 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.
For Objective 1, the tests from 2009 were successful so the experiment was repeated in 2010 in the field and the greenhouse with several modifications. The modifications included: 1)removing smooth leaf lines from the study that were incorrectly reported to be hairy leaf; 2)adding a T2 locus line and its near isogenic counterpart. With this modification, the three loci known to be involved in determining hairy/smooth leaf (T1, T2, and T3) will be included; 3)adding lines of unknown genotype that were reported to be completely smooth without any hairs. Five synthetic genes were constructed with maximized codon usage for expression in Pichia pastoris. The synthetic genes are being tested for expression in Pichia pastoris. For Objective 2, DNA marker (SSRs) screening is continuing with new markers and genotypes being identified. Gossypol 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 will be evaluated to determine the inheritance of the two forms. Evaluation of the toxic compounds present in the seed, vegetative and reproductive cotton tissues revealed that there are differences in type and amount of compounds present in the various tissues.
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 evidence that cotton leaf trichome initiation mechanisms may be similar to those involved in the initiation of cotton seed fibers. Using cotton lines with varying leaf trichome densities ARS researchers in Stoneville, MS, found: 1)at least two trichome initiation mechanisms are functioning in cotton;.
2)in general leaf trichomes increase in number and complexity (branching) from the bottom to the top of the plant with the most complexity occurring on the abaxial side of the leaf; and.
3)leaf trichomes were very woody and are probably used for protection of small leaves. These results indicate that the mechanisms for leaf trichomes and fiber initiation share common components; however, the post initiation development of these two types of trichomes differs due to the evolutionary function of each. While using Arabidopsis as a model will still be useful, the conclusions that can be drawn will be limited and may not apply to cotton fiber.
Romano, G.B., Sacks, E.J., Stetina, S.R., Robinson, A.F., Fang, D.D., Gutierrez, O., Scheffler, J.A. 2009. Identification and Genomic Location of a Reniform Nematode (Rotylenchulus reniformis) Resistance locus (Ren_ari) Introgressed from Gossypium aridum into Upland Cotton (G. hirsutum). Theoretical and Applied Genetics. 120:139-150