Seed shattering is a common trait among wild rice species and related to rice domestication. Eiguchi and Sano (1990) identified Sh3, a gene with the largest effect on seed shattering in Oryza glumaepatula. Sh3 is tightly linked to RFLP marker R1427 on chromosome 4 (Sobrizal et al. 1999). In this study, we performed linkage analyses of Sh3 using introgression lines of two wild rice species, O. meridionalis Ng (W1625) and O. rufipogon Griff. (Acc. IRGC105715).

To perform genetic dissection of the characteristics of A-genome wild rice species, we developed several series of chromosomal segment introgression lines with a Japonica variety Taichung 65 (T65) genetic background. Among them, introgression lines of two wild rice species, O. meridionalis (O. meridionalis introgression lines, merILs) (Kurakazu et al. 2001) and O. rufipogon (O. rufipogon introgression lines, rufILs), were used for the analyses of seed shattering. Shattering plants were observed in BC₄F₁ populations during the process of introgression line development. Two BC₄F₂ populations of merILs and rufILs that were obtained from self-pollinating shattering BC₄F₁ plants were used for mapping.

Field observations showed that BC₄F₂ population of merILs segregated 105 shattering and 28 non-shattering plants. The segregation fitted a 3:1 ratio ( chi² = 1.105, P = 0.29), suggesting that seed shattering was controlled by a single dominant gene. Linkage analysis was subsequently performed using RFLP markers C1016, R1427 and C107 of chromosome 4. The seed shattering gene was tightly linked to R1427 without recombination (Fig 1). Moreover, the analysis of rufILs yielded similar results. The BC₄F₂ population of rufILs segregated 86 shattering and 18 non-shattering plants; the segregation fitted a 3:1 ratio (rufILs; chi² = 3.282, P = 0.07). RFLP analysis revealed that the seed shattering gene of rufILs was also linked to R1427 with no recombinant. Since Sobrizal et al. (1999) located Sh3 from O. glumaepatula (hereafter, the allele is designated as Sh3-glum) in the same map position of chromosome 4, the alleles identified from O. meridionalis and O. rufipogon in this study were designated as Sh3-mer and Sh3-ruf, respectively. This co-linear linkage map suggested that three wild rice species, O. glumaepatula, O. meridionalis and O. rufipogon, have a common shattering gene, Sh3. The loss of function of Sh3 in O. sativa might be a primary cause for rice domestication.

This study was supported by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.

References

Eiguchi, M., and Y. Sano, 1990. A gene complex responsible for seed shattering and panicle spreading found in common wild rices. RGN 7: 105-107.

Sobrizal, K. Ikeda, P. L. Sanchez and A. Yoshimura, 1999. RFLP mapping of a seed shattering gene on chromosome 4 in rice. RGN 16: 74-75.

Kurakazu, T. Sobrizal, K. Ikeda, P. L. Sanchez, K. Doi, E. R. Angeles, G. S. Khush and A. Yoshimura, 2001. Oryza meridionalis chromosomal segment introgression lines in cultivated rice, O. sativa L. RGN 18: 81-82.

Harushima, H., M. Yano, A. Shomura, M. Sato, T. Shimano, Y. Kuboki, T. Yamamoto, S. Y. Lin, B. A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamamoto, Y. Nagamura, N. Kurata, G. S. Khush and T. Sasaki, 1998. A highdensity rice genetic linkage map with 2275 markers using a single F₂ population. Genetics 148: 479-494.