Molecular Mapping Of A Strong-tillering Gene,stl,in Japonica Rice(Oryza Sativa L.)

Tillering in rice is one of the most important agronomical traits that determine grain yield. Meanwhile, tillering in rice is also of developmental importance because tiller is a special type of branches, which is quite different from that of dicotplants. Therefore,it is significant in theory and valuable in production to investigate the mechanism of tillering. Identification and isolation of new tillering genes will help to investigate plant molecular biology mechanism of branching , and also to establish a foundation for crop improvement through genetic engineering.A rice mutant, Duonie,characteristic of strong-tillering,was found in the progeny of Zhonghua 11 that was treated with 0.1 EMS.The mutant has several major features: fast tillering, profuse tillers,dwarfing,and narrow leaves. As a female parent, Duonie was hybridized with Dular, a parent with wide compatibility and normal tillering ability, to develop F1 and F1 population. The tiller number of the F1 plants was similar to that of Dular,but the tillering trait in F2 population (738plants) was segregated with a double-peak distribution, and the score of the two peaks was similar to the tiller numbers of Duonie and Dular ,respectively. The normal tillering group (1~39 tillers)and the strong tillering group (39~72 tillers) were classified according to the minimum score between the two peaks in the distribution profile. It was noted that all strong-tiller plants (170 plants) in F2 were dwarfish while the normal tillering plants (568) were all normal in the height of plant.The proportion of the normal and mutant plant fitted to thesegregation ratio of 3:1 ( Xc2 =1.4164 0.05,12=3.84) , indicating that the mutatedtillering trait was controlled by a recessive gene.Firstly,the recessive gene was roughly mapped on chromosome 1 of rice between two microsatellite markers RM297 and SSR149,with genetic distances of 3.10cM and 0.80cM, respectively. Compared with the known linkage map of rice,it can be inferred that the mutated tillering gene is situated on the long arm of chromosome 1 in rice. So far,there is no similar gene site reported on this region.It indicates that this is first report of the kind of gene here.Therefore,the gene is designated as stI (strong tillering 1).Then four new polymorphic microsatellite markers, SSR-st3, SSR-st4, SSR-1-24 and SSR-1-27,were added into this region. The stl was further mapped between two microsatellite markers SSR-1-27 and SSR261, with the genetic distances of 0.30cM and 0.05cM, respectively, while cosegregated with SSR-l-24,SSR-st3 and SSR-st4. A BAC contig was found to span stl locus, the region was delimited to 91kb. The result reported here will be useful for cloning of the stl gene. In the end , several questions about branching and tillering, the process of stl mapping, and the value of stl in production were also discussed.