Rice Genetics Newsletter, Vol. 18

Rgn18

11.

Mapping of the rice MORI1 gene

A.NISHIMURA^1,4, Y. SATO¹, H. KITANO², Y. NAGATO³, M. ASHIKARI¹ , and M. MATSUOKA¹

1)BioScience Center, Nagoya University, Nagoya, 464-8601 Japan
2)Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan
3)Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, 113-8657 Japan
4)Present Address:Honda R&D Co., Ltd. Wako Research Center, Wako, Saitama, 351-0113 Japan

The development of shoot architecture of plants is strictly controlled by genetic programs. In the rice mutant, mori1, the shoot architecture is drastically changed (Asai 2000). The shoot apical meristem (SAM) of mori1 rapidly produces small leaves and short tillers under an appropriate condition in vitro. The mori1 plants show severe dwarfing and plants that are over a year old do not induce the reproductive phase even after sowing more than twelve month under the short-day condition. Leaves at any position of mori1 are very small, and both the size and shape are similar to those of the wild-type 2nd leaf. The node and internode differentiation in culms do not occur, and the culms contain randomly oriented vascular bundles. These results indicate that mori1 stays at the juvenile phase and fails to develop to the adult stage. All these observations suggest that MORI1 involves in the construction of rice shoot architecture. We are interested in the molecular mechanisms of shoot development in rice, so we are attempting to isolate the MORI1 gene. As the first step, we have mapped the MORI1 locus on the rice chromosomes.

For mapping MORI1, we crossed the japonica rice cv. Taichung 65 MORI1 heterozygous plants with an indica rice, cv. Kasalath, homozygous for the wild-type allele (MORI1/MORI1) . The F₁ plants were cultivated and self-pollinated for obtaining F₂ seeds. We isolated genomic DNAs from 109 F₂ seedlings (MORI / MORI, MORI / mori1, and mori1/mori1) for PCR analysis. We investigated the linkage between the MORI1 locus and about sixty PCR-based makers located throughout all the chromosomes. The linkage analyses revealed that the MORI1 locus was linked with some markers located on the middle of long arm of chromosome 3. For further analysis, we have selected three microsatellite markers, RM16, RM55 and RM293 (Temnykh et al., 2000), and one microsatellite marker, OSR 31 (Akagi et al., 1996), located near the MORI1 locus. MORI1 was mapped between RM16 and RM55 and tightly linked with OSR 31 marker (Fig. 1). We are now doing fine mapping with several new markers located near OSR 31.

Reference

Akagi, H., Y. Yokozeki, A. Inagaki and T. Fujimura, 1996. Microsatellite DNA markers for rice chromosomes. Theor Appl Genet 93: 1071-1077.

Asai, K., N. Satoh, H. Sasaki, H. Sato and Y. Nagato, 2000. A heterochronic gene associated with juvenile-adult phase change in rice. RGN 17: 34-37.

Temnykh, S., W.D. Park, N. Ayres, S. Cartinhour, N. Hauck, L. Lipovich, Y.G. Cho, T. Ishii and S. R. Mccouch, 2000. Mapping and genome organization of microsatellite sequences in rice (Oryza sativa L. ). Theor Appl Genet 100: 697-712.