| A spontaneous dwarf mutant used in this study was identified from somaclones of a japonica variety Zhonghua 11 in our laboratory. The mutated phenotype was segregated among the TI generation as a monogenic recessive mutation. The dwarf phenotype was similar with that of dwarf-1 mutant with short and stout stem, dark green , short, thick but broad leaves. We designated the dwarf gene as d62(t). To clone the gene, fine mapping was carried out using TC1F2 populations derived from a cross between the heterozygous TI plants (D/d) and an indica variety Kasalath. Preliminary mapping of d62(t) showed that it was linked to two SSR markers: RM5302 and RM1 on the short arm of chromosome 1. Through fine mapping using 868 p2 mutant plants, d62(t) was co-segregated with two markers: C62003 and RM6451.Compared with high-density genetic map and genome sequence of the japonica variety Nipponbare (http://rgp.dna.affrc.go.jp/) , we found that the recombination frequency around this region was lower and that an inversion between RM1 and C62003 took place in the region. The dwarf phenotype could not be rescued by GA and BR, indicating that d62(t) might be involved in the signal transduction rather than in the biosynthesis pathway of GA and BR. The fine mapping result suggests that d62(t) be located at different locus with two identified dwarf genes located in this region, d!8 and d2.
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