A mutable slender glume mutant (mutant line IM294) was induced by gamma-ray irradiation of japonica variety Gimbozu seeds. This mutant slender glume character is controlled by a recessive mutant gene slg (slender glume), but has never been fixed in spite of repeated selfpropagation. Successive generations showed not only wild-type glume plants (revertants) but also chimeric plants which appear in low frequency. The mutability of slg resulted from a precise excision of an active MITE (miniature inverted-repeat transposable element) 'mPing' inserted in exon 4 of the Rurm1^m gene (locus: Rice ubiquitin-related modifier-1), the same gene as slg (Teraishi et al. 1999, Nakazaki et al. 2002). The revertants (wild-type glume plants: slg⁺slg) are useful materials for functional genomics in rice because they have a mPing insertional mutation at a new site in the genome. However, IM294 exhibits very low seed fertility due to mPing-insertion at Rurm1 locus, which brings about frequent outcrosses with other variety/lines. Therefore, recessive marker genes tightly linked to slg and quite visible in the field are required for efficient screening of true revertants. The objectives of the present study are to develop a new line carrying slg and a recessive marker gene, and to develop isogenic lines for these two loci.

Based on Teraishi et al. (1999), we targeted the rolled fine stripe leaf gene rfs as a recessive marker of slg. A KL1005 line carrying rfs was crossed with IM294 (Fig. 1). In the F₂ population, no recombinants appeared. In the F₃ population, however, we obtained three plants with the genotype slgslg rfsrfs. One plant was crossed with T65 A-Pn line. This is an isogenic line of japonica Taichung 65 carrying a dominant anthocyanin pigmentation gene A and a dominant purple node gene Pn. In the F₄ population, we found a fixed line for node coloration and

morphological traits other than glume shape and leaf surface pattern. To develop isogenic lines for slg and rfs loci, we repeated self-propagation until F₉. Consequently, almost all loci except for slg and rfs were regarded as fixed. A progeny line of F₉ plants with genotype slgslg rfsrfs could be used for screening true revertants from slender glume to its wild type. This line carries A and Pn. Three other genotypic lines for slg and rfs loci, isogenic to slgslg rfsrfs line, will be developed in the near future.

Acknowledgements

We would like to thank Dr. Nobuo Iwata and Dr. Shigetoshi Sato for providing KL1005 and T65 A-Pn, respectively.

References

Nakazaki, T., Y. Okumoto, A. Horibata, S. Yamahira, H. Nishida, H. Inoue and T. Tanisaka, 2002. Mobilization of a transposon in the rice genome. Nature (in press).

Teraishi, M., Y. Okumoto, H. Hirochika, A. Horibata, H. Yamagata and T. Tanisaka, 1999. Identification of a mutable slender glume gene in rice (Oryza sativa L.). Mol. Gen. Genet. 261: 487-494.