15. Integration of isozyme genes on chromosome 12 into a linkage map

Ryuji ISHIKAWA

Faculty of Agriculture, Hirosaki University, Hirosaki, 036 Japan

Linkage relations were investigated with regard to three isozyme loci and three morphological markers on chromosome 12. As the rl-1 (rolled leaf) locus with a map position of 28 showed linkage with Acp-1 (acid phosphatase) and Sdh-1 (shikimate dehydrogenase) in the F2 from a cross between KL403 with rl-1 and Acc419 with Acp-11 and Sdh-11, the order of these three genes was determined to be Acp-1-rl-1-Sdh-1 (Fig. 1A). The rl-1 gene is identical with rl-3 (Iwata and Omura 1975; Kinoshita 1987). The spl-1 (spotted leaf) locus showed linkage with Acp-1 and Pox-2 (peroxidase) in the F2 between FL58 (spl- 1) and Acc435 (Acp-11 and Pox-21), their order was determined as shown in Fig. 1B. In addition, the linkage relations among Acp-1, Pox-2 and d-33 (bonsaito dwarf) have been known to be in this order (Ishikawa et al. 1991). With these three linkage maps, however, the gene order of Sdh-1, rl-1 and d-33 was still ambiguous, and further investigations were carried out.

The recombination value between Pox-2 and spl-1 and that between Pox-2 and Sdh-1 were obtained from the above F2 population and from another F2 be- tween IR36 and Kagoshima-zairai. The recombination value between the former two loci was 21.8±4.8 and between the latter two was 16.6±3.8. Therefore, it was suggested that the location of spl-1 was more distant from Pox-2 than that of Sdh-1, although the standard error for the former recombination value was higher than the difference between the two recombination values. The linkage relation between d-33 and rl-1 was analyzed by using the cross between FL27 (d-33) and KL403 (rl-1). The F1 plants showed the same morphology as that of KL403 and the F2 segregated into two types of plants like KL403 and FL27 in a ratio of 164:54. This ratio agreed with the expected 3:1 (X2=0.07). No normal plant appeared showing that the two genes are allelic, rl-1 being dominant over d-33.

Based on these findings, the order of three isozyme genes and three morpholo- gical markers was suggested to be spl-1-Sdh-1-rl-1 (d-33)-Pox-2-Acp-1.


Fig. 1. Linkage relations among Acp-1, r1-3 and Sdh-1 (A), and among Acp-1, Pox-2 and spl-1 (B).

References

Ishikawa, R., H. Morishima, T. Kinoshita, T. Harada, M. Niizeki and K. Saito, 1991. Linkage analysis of nine isozyme genes on the conventional linkage map in rice. Jpn. J. Breed. 41: 265-272.

Iwata, N. and T. Omura, 1975. Studies on the trisomics in rice plants (Oryza sativa L.), III. Relation between trisomics and genetic linkage groups. Jpn. J. Breed. 25: 363-368.

Kinoshita, T., 1987. Report of the committee on gene symbolization, nomenclature and linkage groups. RGN 4: 3-37.