Rice Genetics Newsletter, Vol. 18

Rgn18

5.	*High resolution mapping of SHOOT ORGANIZATION 2* gene, SHO2.**
	M. MUKOHHATA¹ M. ASHIKARI¹ H. KITANO² Y. NAGATO³ 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

Mutants for shoot organization (sho) show random phyllotaxy, short plastochron and abnormal leaves with thread-like structure (Fig. 1) (Tamura et al 1992). The mutants also

show the malformed shoot apical meristem (SAM) in the early phase of rice development. So far, three loci of SHO (SHO1~ 3) have been identified (Itoh et al. 2000). A rice KNOTTED1-type homeobox gene, OSH1 which has been thought to be involved in the maintenance of SAM, is specifically expressed in the SAM, while its expression area in sho mutants is severely reduced. The narrowed area of OSH1 expression in sho may be related to the abnormal maintenance of SAM, and therefore SHO genes may function in the SAM maintenance through regulating OSH1 expression. Thus, the isolation and characterization of SHO genes is important for elucidating the molecular mechanism of shoot maintenance via OSH1 function. We have already reported on the high-resolution mapping of SHO1 (Mukohhata et al. 2000). Recently, we have isolated this gene by positional cloning (unpublished results). Subsequently, we are using the same method we used for SHO1 to isolate the second SHO gene, SHO2

As the first step of cloning SHO2, we identified the approximate chromosomal location of SHO2. F₂ progenies derived from the cross between a plant of sho2 heterozygote (SHO2 / sho2) and an Indica rice cv Kasalath were obtained. 188 sho2 homozygous plants selected from 1,225 F₂ progenies were used for linkage analysis with the molecular markers released by RGP (Harushima et al. 1998). The locus of sho2 was located between the RFLP markers on chromosome 3, C80 and C816 (Fig. 2). Out of the 188 selected plants, 3 recombinants between C80 and sho2 were obtained, while 4 recombinants between C816 and sho2 were obtained. Based on these results, the sho2 gene was mapped at a distance of 0.83cM from C80 and 1.1cM from C816. We are constructing a more precise linkage map of sho2 gene between C80 and C816 for its positional cloning.

References

Harushima, Y., 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 high-density rice genetic linkage map with 2275 markers using a single F₂ population. Genetics 148: 479-494

Itoh, J., H. Kitano, M. Matsuoka and Y. Nagato, 2000. SHOOT ORGANIZATION genes regulate the organization of shoot apical meristem and the initiation pattern of leaf primordia in rice. Plant Cell 12: 2161-2174

Mukohhata, M., M. Ashikari, M. Miwa, T. Sasaki, Y. Nagato, H. Kitano and M. Matsuoka, 2000. High resolution mapping of a rice gene affecting shoot organization, SHO1. Rice Genetics Newsletter, 17: 24-26

Tamura, Y., H. Kitano, H. Satoh and Y. Nagato, 1992. A gene profoundly affecting shoot organization in the early phase of rice development. Plant Sci 82: 91-99