8. Alleles in three rice panicle genes, Dn1, Ur1 and Cl, and the effects of genetic backgrounds

F. TAGUCHI-SHIOBARA¹ and H. KATO²

1) National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan

2) National Institute of Crop Science, Kannondai 2-1-18, Tsukuba, Ibaraki, 305-8518 Japan

Allelism tests were performed among semi-dominant mutants of Dense panicle 1 (Dn1), Undulated rachis 1 (Ur1) or Clustered (Cl) (Table 1) available on Oryzabase (http://www.shigen.nig.ac.jp/rice/oryzabase/top/top.jsp). These mutants were maintained in different laboratories for many years. Several mutants of each gene were regarded as alleles without allelism tests, since they were phenotypically alike and were mapped on the same chromosomal regions using a limited number of morphological markers (Iwata and Omura 1971,  Nagao and Takahashi 1963).

Table 2 summarizes the allelism tests performed in the present study. Two mutations in HO576 and N53 were estimated to be derived from independent loci, because the segregation ratio of F₂ plants of HO576 x N53 fitted to 15 (Dn):1 (normal). Thus, a new gene name should be assigned for the causal gene of the mutation in N53. Two strains, FL197 and A32, were verified to be alleles of Ur1, since all F₂ plants of FL197 x A32 showed the Ur1 phenotype and did not segregate normal plants. Similarly, HO797 and H339 were revealed to be allelic on the CL locus. For one strain showing the Cl phenotype, C5287, the allelism test was unsuccessful, because of the low seed fertility of F₁ plants when C5287 was crossed with japonica varieties/strains.

The expression of a mutant allele frequently depends on its genetic background. Complete penetrance, which means that the mutant allele is expressed equally in any genetic background, is desirable for mapping, but altered expression provides important clues about gene function (Freeling and Fowler 1989). We introduced alleles of Dn, Cl and Ur1 into cvs Nipponbare and Koshihikari and established BC₄F₂ or BC₂F₂ plants (Table 1). The HO576 allele of Dn1 and the HO797 allele of Cl showed severe phenotypes in both Nipponbare and Koshihikari. In contrast, the FL197 allele of Ur1 showed a mild phenotype in the Koshihikari background, whereas a milder phenotype was observed in the Nipponbare background. Accordingly, the penetrance of Ur1 depends on the genetic background.

Acknowledgments

We thank Drs. Atsushi Yoshimura (Kyushu University), Yoshio Sano and Itsuo Takamure (Hokkaido University), and the National Institute of Genetics for providing panicle mutants.

Table 1.  Panicle mutants used in allelism test

Table 2.  Allelism tests among strains of three panicle genes

References

Freeling, M. and J. Fowler, 1989. A nine-step way to characterize a morphological mutant. In: The maize handbook. Springer-Verlag. pp. 209-211.

Iwata, N. and T. Omura, 1971. Linkage analysis by reciprocal translocation method in rice plants (Oryza sativa L.). I. Linkage groups corresponding to the chromosome 1, 2, 3 and 4. Japan. J. Breed. 21: 19-28 (in Japanese with English summary).

Nagao, S. and M. Takahashi, 1963. Trial construction of twelve linkage groups in Japanese rice. (Genetical studies on rice plant, XXVII) Journ. Fac. Agr., Hokkaido Univ. 53: 72-130.