11. Characterization and mapping of tillering dwarf rice 1, tdr1

E. YAMAMOTO¹, M. ASHIKARI², T. SAZUKA², A. MIYAO³, H. HIROCHIKA³, H. KITANO² and M. MATSUOKA²

1) Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan

2) Bioscience and Biotechnology Center, Nagoya University, Nagoya, Aichi, 464-8601 Japan

3) Molecular Genetics Department, National Institute of Agrobiological Sciences, Tukuba Ibaraki, 305-8602 Japan

Molecular cloning and functional analysis of genes associate with tillering will help us understanding for rice branching mechanism. So far, a few genes, D3, MOC1, OsTB1 and HTD1 associated with tillering has been isolated (Ishiwata et al. 2005, Li et al. 2003, Takeda et al. 2003, Zou et al. 2005). However, cloning of these genes is not enough to illustrate the model of branching mechanism. To further study on the tillering mechanism in rice, we have screened some rice tillering mutants. A tillering dwarf rice 1 (tdr1) mutant, which was isolated from the Tos17 mutants pools (Hirochika 2001), shows high tillering phenotype (Fig. 1). In this study, as an initial step of positional cloning and functional analysis of tdr1, we characterized and mapped tdr1.

tdr1 shoots were shorter than wild type Nipponbare, by reduction of the culm length (Table 1). The tiller number of tdr1 is about three times larger than that in Nipponbare (Table 1).  Panicle length and number of primary panicle branches of tdr1 are about half of those in Nipponbare (Table 1). These phenotypes indicate that the mutation of Tdr1 increases the growth of vegetative axillary bud, and consequently, it is a useful candidate for analysis of branching mechanism.

For mapping, F2 population from the crosses between recessive homozygote tdr1 (joponica cultivar) and Kasalath (indica cultivar), were produced. Ninety-four recessive homozygote tdr1 plants were selected from F2 population and used for mapping. As the result of linkage analysis of 65 molecular markers covering the whole rice genome, tdr1 is located between a CAPS marker C1232 and the end of short arm of chromosome 9 (Fig. 2). According to the linkage map of RGP (Rice Genome Project) map (Harushima et al. 1998), the genetic distance from a CAPS marker C1232 to the end of short arm of chromosome 9 is 0.8 cM.  Fine mapping of tdr1 by using more genetic markers and more recombinants in this region are under progression. The positional cloning of tdr1 and learning the function of TDR1 in tillering is our next objective.

Fig. 1.  Phenotype of the tdr1 mutant. Wild type (cv. Nipponbare; left) and tdr1 mutant (right).

Fig. 2. The linkage map of tdr1 with molecular markers on chromosome 9. The recessive mutant gene, tdr1, is located between marker C1232 and end of short arm of chromosome 9.

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