| Rice(Oryza sativa L.)is one of most important food crops in the world, and the floral organ development paly a key role on the yield and quality of the rice. The outmost floral organ is called the hull, including the palea and the lemma. In the early stage, the hull provides photosynthetic products for the inner flower organs. In the later stage, it serves as a protective coating of the seeds to prevent damages from pathogenic bacterias and pests. At the meantime, the shape and size of the hull determine that of the seeds. Therefore, the growth of the rice hull is essential for the yield and quality of the rice.This study investigated a degenerated hull mutant, which derives from the ethyl methyl sulfonate(EMS)-treated mutation restorer rice Jin Hui 10. The lemma and plea of this mutant show narrow and fail to close normally. Therefore it is called degenerated hull 3(dh3). According to the genetic analysis, the trait is controlled by a recessive gene. Through the BSA method, the DH3 gene is located on the chromosome 12. The result of this study provide a theoretical foundation for the cloning and functional analysis of the DH3 gene. The major findings are listed in the following parts: 1. Morphological analysisIt is find that the growth of the hull of dh3 mutants is abnormal, and the growth of the the margin of the lemma primordium is slow, and the growth of palea primordium is relatively slow, and other inner flower organs show no obvious abnormalities.The dh3 flower can be classify into three types: the weak, the heavier, and the severe. In the weak type, the awn of the flower is elongation, and the lemma and palea fail to close. Part of the inner flower organs are exposed. In the heavier type, the head of the lemma becomes a rol-like organ, the lemma and palea also become narrower and the inner flower organs are exposed. In the severe type, the whole lemma is transformed into a rol-like organ, and the inner flower organs are completely exposed. 2. Histological analysisIn the weak type we find that the hooking structure of the lemma are slightly degradated, and it can not hook with the palea. There are little bulliform cells on the internal surface of the palea, the lodicule and the inner floral organs show no abnormalities. In the heavier type, the hooking structure of the lemma are seriously degradated, the number of vascular bundles decreases, there are only a small amount residual bulliform cells on the internal epidermis of the lemma and palea. The lodicules fuse with the palea, other inner flower organs show no obvious abnormalities. In the severe type, the lemma remains only one vascular structure and surrounding silicon cells, there is no bulliform cells on the internal surface of the palea, and the lodicules has completely fuse with the palea. The stamen and the pistil show no abnormalities. 3. Genetic analysisXinong 1A was crossed with the dh3 heterozygote for genetic analysis. In F1 population, all the flower were normally, while the F2 population appear separation between individual. The total number of F2 population were 1168, which 812 were normal and 356 were mutant. The segregation is 3: 1 through the chi-square test(χ2=1.17<χ2 0.05=3.84). The results indicated that a single recessive gene controlled the dh3 mutant. 4. Molecule localizationDH3 gene was preliminary located between SSR primers RM247 and RM7102 on the 12 chromosome by bulked segregation analysis(BSA). There are 7 pairs of primers showing polymorphism between these two markers. Screening of all the 356 mutants with these primers, DH3 gene was finally located between RM27706 and RM27709, the physical distance is 44.72 Kb. 5. Identify of the candidate genesThere are 7 annotated genes in this mapping interval. LOC_Os12g09580, encoded a homologous protein of SUPPRESSOR OF GENE SILENCING 3(SGS3) in Arabidopsis, show a base substitution from cytosine(C) to hymine(T) on that the 847 th of the ORF between the wild type and the dh3 mutant. Then the gene LOC_Os12g09580 was considered as the candidate gene for DH3. |
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