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Cotton is one of the most important natural fiber crops in the world, which occupies a pivotal position in China’s national economy. The cotton fibers are used as natural fibers, and they are important raw materials for the textile industry.Flavonoids compose of an important class of plant secondary metabolites, which influnce various life activities of plants. Flavonoids are synthesized from the precursor4-Coumaroyl-CoA by a branch of the phenylpropanoid pathway. The flavonone3-hydroxylase (F3H) and dihydroflavonol reductase (DFR) catalyze the formation of flavanonol and leucoanthocyanin, respectively, are key synthases in flavonoid pathway. In order to clarify the role of flavonoids in cotton growth and development, this thesis detected the effects of suppression of GhF3H and GhDFR on flavonoid synthesis and cotton growth and development, on the basis of sequence and expression analyses.The main results are as follows:1. F3H gene sequence and expression analysisUsing GhF3H gene as the inquiry probe, two F3H genes, named GrF3Hl and GrF3H2, were acquired from the sequenced genome of G. raimondii. GhF3H and GrF3H2shared highly sequence similarity with identity of99%at nucleotide level, indicating they are orthologous genes. Hommology analysis showed that GhF3H, GrF3H1and GrF3H2protein shared high sequence similarity with F3H proteins from various plants, and relatively low similiarity with other2-oxoglutarate-dependent dioxygenases, suggesting that these cotton F3Hs belong to F3H subfamily of2-oxoglutarate-dependent dioxygenases family.Quantitative RT-PCR analysis showed that F3H1and F3H2genes had different expression profiles in the various cotton tissues, but their expression levels in white fiber were significantly lower than in brown fiber, suggesting that F3H1and F3H2gene may both be involved in the synthesis of brown fiber pigment. 2. DFR gene sequence and expression analysisUsing GhDFR gene as the inqury probe, four DFR genes, named GrDFR1, GrDFR2, GrDFR3and GrDFR4, were acquired from the genomic sequence of G. raimondii. GhDFR and GrDFRl shared high sequence similarity with identity of97%at nucleotide level, indicating they are orthologous genes. Hommology analysis showed that GhDFR, GrDFR1, GrDFR2, GrDFR3and GrDFR4protein shared high sequence similarity with DFR protein from various plants, and relatively low similiarity with other short-chain reductase (SDR), suggesting that these cotton DFRs belong to DFR subfamily of short-chain reductase family.Quantitative RT-PCR analysis showed that DFR1, DFR3and DFR4genes had different expression profiles in the various cotton tissues, and the expression levels of DFR1and DFR3gene in white fiber were significantly lower than in brown fiber, but the expression level of DFR4gene was not significantly different in the white and brown fiber, suggesting that DFR1and DFR3gene may be involved in the synthesis of brown fiber pigment.3. Inhibition of GhF3H expression in cottonRNAi transformants (GhF3Hi) with significantly reduced expression of GhF3H were obtained by transferring GhF3H RNAi vector into cotton. DPBA-flavonoid staining showed that down-regulation of GhF3H changed the category and quantity of flavonoids accumulated in cotton ovules. Compared with the wild type, the GhF3Hi transgenic plants exhibited dwarfism, lighter-colored petals, lower anthocyanin content in petals, significantly reduced pollen viability, smaller seed, and shorter fibers. These results showed that inhibition of GhF3H expression, affect flavonoid biosynthesis and cotton growth and development.4. Influence of inhibition of GhDFR gene on cotton growth and developmentRNAi transformants (GhDFRi) with significantly reduced expression of GhDFR were obtained by transferring GhDFR RNAi vector into cotton. DPBA-flavonoid staining showed that down-regulation of GhDFR changed the category and quantity of flavonoids accumulated in cotton ovules. Compared with the wild type, the GhDFRi transgenic plants exhibited lighter-colored petals, lower anthocyanin content in petals, significantly reduced pollen viability, smaller seed, and shorter fibers.These results showed that inhibition of GhDFR expression, affect flavonoid biosynthesis and cotton growth and development.
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