Phenotype Analysis And Gene Mapping Of Sdt4, A Semi-Dwarfness Mutant In Rice (Oryza Sativa L.)

Plant height is one of the crucial factors for rice yield. Too high plant would easily result in plant lodging and yield decreasing. Appropriate dwarfism can avoid lodging and gain high yield. Dwarf mutants are ideal materials for studying of the mechanism of dwarfism in rice. Up to date, many dwarf mutants have been reported in rice. However, only a few have been used in rice breeding. Therefore, screening and identification of new semi-dwarf genes useful in rice breeding practice is very important. In addition, as a model plant of monocot, the discovery and cloning of new rice semi-dwarf genes in rice have the vital significance to clarify the mechanism underlying plant growth and development.The sdt4 was isolated from the radiation induced mutant library of Guichao2, an indica cultivar in Guangdong province of China. The heredity of sdt4 was analyzed. Through a systematic analysis of physiological and biochemical characteristics, combined with cytological observation and hormone sensitivity analysis, the reasons for semi-dwarfism were discussed. Finally, the target gene was mapped. The main results are as follows:(1) Plant height of the mature sdt4 mutant was 63.53cm or so, about 56% of wild type (113.17 cm). The tiller number of the sdt4 mutant is 17 or so, about twice that of wide type (8 or so). The sdt4 showed semi-dwarfism with shortened panicle and all internodes, increased tillering angle, shortened leaves, delayed heading date and decreased spikelet fertility.(2) Cytological observation of the internode cell of wild type and the sdt4 mutant. The longitudinal section revealed that the cells of the sdt4 was similar with wild type; Transverse section revealed that the number of the sclerenchyma cells decreased and the parenchyma cells become smaller which may be the reason why the sdt4 internode is slender than wide type.(3) Exogenous hormone treatment experiment showed that the sdt4 mutant was sensitive to GA and BR, indicating that these two hormones signaling pathway of sdt4 were intact. In the darkness,the sdt4 mutant showed a typical’de-etiolated phenotype’ of BR mutants, indicating that it might also be a BR mutant.(4) Genetic analysis revealed that the sdt4 mutant phenotype was controlled by a single recessive gene. A F2 mapping population was constructed by crossing sdt4 with a japonica variety, Dianjingyou. The sdt4 locus was finally mapped to a 5283-kb interval around the centromere on the chromosome 4.