4. High resolution map of dwarf mutant gene, dwarf 11 of rice

1) Department of Bioscience, Fukui Prefectural University, Fukui, 910-1195 Japan
2) Bioscience Center, Nagoya University, Nagoya, 464-8601 Japan
3) Rice Genome Research Program, NIAR/STAFF, Tsukuba, 305-8602 Japan
4) Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
5) Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan

More than 60 dwarf mutants of rice are known (Futsuhara and Kikuchi 1993). One of them, Daikoku d1, which displays pleiotropic phenotypes, such as dark-green leaves and small-round grains, in addition to the dwarfism, was recently shown to be lacking in the alpha subunit of a GTP-binding protein (Ashikari et al. 1999, Fujisawa et al. 1999). It was suggested that the d1 is a gibberellin-insensitive mutant, which means that the G

protein may be involved in the gibberellin signaling (Mitsunaga et al. 1994). Therefore, we expect that phenotypes similar to those of d1 would have a defect in the signaling pathway mediated by the G protein. We selected a dwarf mutant conditioned by d11 gene which displays dwarfism, dark-green leaves and small round grains, and we are isolating this gene by map-based cloning, in order to investigate a pathway of the gibberellin signaling.

The d11 locus has been mapped on approximately the long arm of chromosome 4 through linkage mapping (Yoshimura et al. 1997). We crossed this mutant with a substitution line 14, the chromosomes of which are those of Nipponbare (japonica) except for the chromosome 4 substituted by that of Kasalath (indica). Using 104 F2 dwarf plants from this cross, we found that the approximate map position of the d11 gene was about the same as that reported by Yoshimura et al. (1997) (Fig. 1B). We then designed the four kinds of Cleaved Amplified Polymorphic Sequence (CAPS) markers (S10628, R1721, R278 and C377), on the basis of the information of the sequences of Restriction Fragment Length Polymorphism (RFLP) markers on both sides of d11.

In order to decide more precise position of the d11 gene, 15,000 F3 seeds were sown in a nursery. 3,020 dwarf plants (homozygous for d11) were selected at a seedling stage and transplanted into paddy field. We then screened these dwarf plants using the four CAPS markers. 173 dwarf plants, recombinant between R1721 and R278, were obtained. By this way, the d11 gene was mapped at distances of 1.82 cM from R1721 and 1.04 cM from R278 (Fig. 1C). We are constructing more precise linkage map of d11 using RFLP markers located between R1721 and R278.


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