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Identification, Fine Mapping And Candidate-gene Screening Of A New Semi-dwarf Gene Sdt2 In Rice (Oryza Sativa L.)

Posted on:2006-09-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:X Q ZhaoFull Text:PDF
GTID:1103360152492746Subject:Crop Genetics and Breeding
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Rice (Oryza sativa L.) is one of the most important staple foods and more than half of the world's population depends on it as main source of nutrition. Since the 1960s, the rapid expansion of the world population and dramatic decrease in cultivated land raised concerns about a probable global food crisis. However, the development and widespread adoption of high yielding semi-dwarf varieties of wheat and rice, led to major increases in food production and a large-scale famine was avoided. This great achievement has been well known as the so-called "green revolution" and the exploitation and utilization of semi-dwarf genes was one of the most important factors contributed to the success of the "green revolution". However, there were only several kinds of dwarf sources to have been used in rice breeding, and moreover, genetic analysis revealed the dwarf genes of these sources were mainly limited to sdl and its alleles. It is well known that the narrow background of varivation and frequent use of single gene source might become a potential bottleneck of crop breeding. Therefore, identifying new useful semi-dwarf genes is an important subject for practical rice breeding. On the other hand, rice hasbecome a model plant of monocots. So to isolate and characterize new rice dwarf genes also provide good chances for elucidating regulatory mechanisms for plant growth and development.In this study, we described the identification, characterization, fine mapping and candidate-gene screening of a new rice semi-dwarf gene, which was segregated from Aitaiyin 3, a natural dwarf mutant origined from rice cultivar Taiyin 1. The main results were as follows:1. To clarify the inheritance of dwarfism in Aitaiyin 3, Aitaiyin 3 was crossed with a tall indica rice cultivar Nanjing 6. The F1 progeny was as tall as the taller parent and the segregation of the F2 generation appeared to be 9 tall:6 semi-dwarf: 1 dwarf, which indicated the dwarfism of Aitaiyin 3 was controlled by two recessive semi-dwarf genes without linkage. The allelism test showed that the one semi-dwarf gene of Aitaiyin 3 was an allelic to sdl gene and the other was a new one nonallelic to sdl gene. The semi-dwarf F3 lines with the new semi-dwarf gene were backcrossed with Nanjing 6. A monogenic inheritance 3 tall: 1 semi-dwarf was exhibited in the BC1F2 populations and the semi-dwarfing effect of this new gene was confirmed. This gene was named as sdt2 temporarily. Based on these results, a cross was created between Aitaiyin 3 and Zhonghua 11 and was used to assess the genetic effect of sdt2 gene in japonica genetic background. By analysis of F1, F2, F3 and F4 progenies, an obvious dwarfing effect of sdt2 gene was observed in japonica genetic background.2. To gain an overall understanding of the genetic effects of sdt2 gene, we characterized the sdt2 mutant in details by comparing with the wild-type plant (Nanjing 6) and the sdl mutant (Nanjing 11). The results revealed that sdt2 gene and sdl gene have quite different effects on the elongation pattern of the rice culm architecture. sdt2 gene was more severely inhibited in panicle and the uppermost internode than sdl genedid. Leaf sheaths and leaf blades of sdt2 mutant were also shortened in comparison to sdl mutant. On the contrary, the lower internodes were more weakly defect on elongation in sdt2 mutant than in sdl mutant. Based on the elongation pattern of the internodes, we categorized sdt2 gene into the nl-type of dwarf gene.3. To determine whether the dwarf phenotype in sdt2 mutant was relative to gibberellin (GA) or brassinosteroid (BR), the two major reasons for plant dwarf phenotype, we characterized the seedling growth of sdt2 mutant in response to exogenous gibberellic acid (GA3) and darkness. The results showed that sdt2 mutant was sensitive to GA3 and had a skotomorphogenic phenotype as wild-type plants did. Longitudinal sections of the fifth leaf sheaths revealed that the cell length along the longitudinal axis was reduced in sdt2 mutant and the cell elongation of sdt2 mutant can be partially rescued by...
Keywords/Search Tags:rice (Oryza sativa L.), semi-dwarf gene, genetic effect, SSR markers, fine mapping, candidate gene
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