13. Characterization and mapping of tillering dwarf rice 2, tdr2

Y. HASEGAWA¹, E. YAMAMOTO², M. ASHIKARI¹, T. SAZUKA¹, A. MIYAO³, H. HIROCHIKA³, H. KITANO¹ and M. MATSUOKA¹

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

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

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

Variation in branching pattern is one of the typical morphologies distinguishable between monocotyledonous and dicotyledonous plants, and also its regulation is an important agricultural target for crop breeding. Cloning of genes regulating the shoot branching is essential for understanding the mechanism of branching pattern. Mutants defected in shoot branching genes show low or high tillering phenotype. Based on such unique phenotypes, we have screened mutants as a first step to isolate and characterize genes related to the branching mechanism. We succeeded to isolate some mutants showing abnormal branching and focused on a mutant called tillering dwarf rice 2 (tdr2). tdr2 was isolated from the Tos17 mutants pools (Hirochika 2001), and showed about 5 times higher tiller number than the wild-type plant (Fig. 1). So far, a few genes, such as D3, MOC1, OsTB1 and HTD1, which are associated with branching mechanism, has been isolated (Ishikawa et al. 2005, Li et al. 2003, Takeda et al. 2003, Zou et al. 2005). However, tdr2 was located at a different position of the rice genome and therefore it should encode a novel factor involved in the branching mechanism. As an initial step of positional cloning of tdr2, we constructed the linkage map of tdr2.

An F2 population, which was produced crossing between recessive homozygote tdr2 (joponica cultivar) and Kasalath (indica cultivar), was used for linkage analysis. Twenty-four recessive homozygote tdr2 plants were selected from the F2 population and 65 molecular markers covering the whole rice genome were applied for mapping tdr2. As the result of linkage analysis of tdr2 and 65 molecular markers, tdr2 is located between molecular markers RM237 and R30008 within 29.5cM on the long arm of chromosome 1 (Fig. 2). This information is useful to start cloning the tdr2 and now we are conducting the high resolution mapping tdr2.

References

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Ishikawa, S., M. Maekawa, T. Arite, K. Onishi, I. Takemura and J. Kyozuka, 2005. Supression of tiller bud activity in tillering dwarf mutants of rice. Plant Cell Physiol. 46: 79-86.

Li, X., Q. Qian, Z. Fu, Y. Wang, G. Xiong, D. Zeng, X. Wang, X. Liu, S. Teng, H. Fujimoto, M. Yuan, D. Luo, B. Han and J. Li, 2003. Control of tillering in rice. Nature 422: 618-621.

Takeda, T., Y. Suwa, M. Suzuki, H. Kitano, M. Ueguchi-Tanaka, M. Ashikari, M. Matsuoka and C. Ueguchi, 2003. The OsTB1 gene negatively regulates lateral branching in rice. Plant J. 33: 513-520.

Zou J., Z. Chen, S. Zheng, W. Zhang, G. Jiang, X. Zhao, W. Zhai, X. Pan and L. Zhu, 2005. Chracterizations and fine mapping of a mutant gene for high tillering and dwarf in rice (Oryza sativa L.). Planta 222: 604-612.