B. 0. Ahn1, K. Miyoshi1, J.-I. Itoh2, Y. NAGAT02 and N. KURATA’

      1) National Institute of Genetics, Mishima, 411-8540 Japan

      2) Graduate School of Agricultural and Life Sciences, University of Tokyo, 
          Tokyo, 113-8657 Japan

     Heterochromc mutations affecting the timing of developmental events may be of major significance in onotogeny and evolution (Gould 1982). If a single mutation modifies the expression of a gene that controls temporal pattern of organ development, a conspicuous change of body plan would be brought about. In plants, several heterochronic mutations that affect step wise development of vegetative tissue and therefore alter shoot architecture have been identified (Poethig 1988; Itoh et al. 1998). However, molecular mechanisms for the temporal regulation of developmental program are largely unknown.

     The recessive mutations at the rice Plastochron 1 (Plal) locus cause the short plastochron and ectopic expression of vegetative programs in the reproductive phase (Itoh et al. 1998). To understand the molecular aspects of Pial during plant development, we have started to isolate the Plal gene by map-based cloning. Here, we report the chromosomal location of Plal gene mapped by RFLP analysis.

     To generate mapping population, the indica variety Kasalath was crossed by the japonica variety Fukei 71 canyingplal-l mutation. Since the plal-l homozygous plants are sterile, the heterozygous plants were used in this crossing. Among F2 segregants, pla1-1 homozygous plants, which have narrower leaves and a shorter plastochron than wild type siblings, were selected. Preliminary studies for rough mapping using thirty pla1-1 homozygotes and 24 RFLP markers located on all 24 chromosome arms (Harushima et al. 1998) indicated that the marker R2174 on the short arm of chromosome 10 was relatively close to Plal locus. To confirm whether Pial gene locate on chromosome 10, the linkage between Plal locus and several RFLP markers adjacent to the marker R2174 were tested. One recombinant between Plal and the marker R1629 and three recombinants between P/al and the marker R2447 were detected. These results indicate that P/al is located between the marker R2174 and R2447 on the short arm of chromosome 10 (Fig.l). The genetic distances between the P/al locus and the markers R2174, R1629 and R2447 were 13cM, 1.6cM and 6cM, respectively. The construction of high-resolution map of Plal locus is now underway.

 
References

Gould, S. J., 1982. Change in developmental timing as a mechanism of macroevolution. In Evolution and development, J. T. Bonner (ed), Springer Verlag, New York, p. 333-346.