Influence Of Specific Expression Of GhGA20ox1 Gene On Fiber Development Of Cotton (Gossypium Hirsutum L.)

Cotton fiber is an important raw material for textile industry, and cotton has an important strategic status in our national economy. In recent years, textile industry focus their economic considerations on fiber quality, and consistently demand better lint quality. Because of the negative relationship between fiber productivity and quality; cotton breeding nowadays faces a big challenge to simultaneously improve cotton yield and fiber quality. Genetic engineering provided a new strategy and excellent perspectives to cotton breeders. These limitations in traditional breeding can be overcome through genetic engineering, which enables the transfer of genes from any source into cotton and changes the negative associability of yield and quality.Gibberellins are endogenous hormones controlling numerous aspects of plant growth and development such as seeds germination, stem elongation, leaf shape and the development of flower and fruit. Pre- and post-anthesis application of exogenous GA can improve fiber production in upland cotton. A cotton GA 20-oxidase gene (GhGA20ox1) was cloned previously in our lab, and overexpression of this gene promote GA biosynthesis in cotton, and further fiber initiation and elongation at the early stage. On the basis of previous researches, the phenotypic variations in the GhGA20ox1 overexpressing was analyzed in depth, and by cotton transformation, the influence of Fbp7-, E6-, and Sub-driven GhGA20ox1 on fiber development was further studied in the present thesis.The main results are as following:35S:GA20 transgenic cotton plants showed GA-overproduction phenotype. This phenotype includes higher plant, longer internodes and fiber, smaller leaf and seed, later flowering and lower boll setting rate.A total of eighty-three GUS positive primary (T₀) transgenic lines (Fbp7:GA20, Fbp7:AntiGA20, E6:GA20, E6:AntiGA20, Sub:GA20 and Sub:AntiGA20 ) were generated in this study. RT-PCR was employed to assess GhGA20ox1 mRNA levels in these transgenic cottons, and several lines with enhanced or reduced expression of targeted genes were identified and were used to analyze the effects of transgenes on cotton development. Southern blotting analysis indicated that there was single copy of T-DNA present in the investigated cotton lines.There were no significant phenotypic changes in plant growth observed between wild-type and Fbp7-, E6-, and Sub-driven GhGA20ox1 transformed cottons. Scanning electron microscope (SEM) observation indicated that the number of fibers initial decreased in 0-DPA ovules of Fbp7:AntiGA20 transgenic cotton, but fiber initiation showed no obvious changes in Fbp7:GA20 cottons, compared to the control ovules. Furthermore, the 1DPA ovules of 35S:GA20, 35S:GA20RNAi, Fbp7:GA20 and Fbp7:AntiGA20 cottons were observed by optical microscope. Only the fibers initiation in 35S:GA20RNAi ovules were found to be reduced.The number of mature fiber from the 35S:GA20, 35S:GA20RNAi, Fbp7:GA20, Fbp7:AntiGA20, E6:AntiGA20, Sub:GA20 and Sub:AntiGA20 plants was further investigated. It was found that the number of mature fiber per seed in Fbp7:AntiGA20 and 35S:GA20RNAi transgenic plants were significantly decreased compared to the control.Cotton fiber quality test displayed that the fineness and strength of Fbp7: GA20 fiber was slightly improved compared with control fiber, consistent with the improved quality of 35S: GA20 transgenic fiber.Our results demonstrated that the GhGA20ox1 gene play an important role in fiber development and the quality formation in cotton.