Plant height is an important agronomic trait in rice. So far, many studies have been made on the height of rice plants. This trait has shown genetic models of a major gene and polygenes in different genetic backgrounds of rice. In a major gene model, the dwarfism and semi-dwarfism are generally inherited with a recessive gene, rarely with a dominant gene (Saeda and Kitano, 1992). To date, more than 70 semi-dwarf and dwarf mutants have been reported, but only D53, D-h and Ssi1 are the dominant mutations among them (Iwata et al., 1977 Koh et al., 1993 Wu et al., 1997). Here we report a new semi-dwarf mutant controlled by a dominant gene.
Many mutant genes had been cloned and characterized at molecular and biochemical levels (Ashikari et al., 1999 Sasaki et al., 2002, Hong et al., 2003 Itoh et al., 2004). Exploring novel rice mutant genes can be applied not only in breeding programs but also in scientific research. As a new resource of mutagens, low-energy ion beam irradiation is characterized as less physiological damage, wider mutation spectrum, and higher mutation frequency in comparison with the mutations from other inducing methods (Yu et al., 1991 Wei et al., 1995). By nitrogen ion irradiation, we had screened a semi-dwarf mutant in a japonica rice cultivar Y98148, designated as Y98149(Fig. 1). They had been identified as NILs(near isogenic lines)(Tong et al., 2001 Liu et al., 2004).
To determine the genetic mode of the mutation, the dominant semi-dwarf mutant was crossed to two normal cultivars, Y98148 and Wan3(indica), respectively. Both the F2 populations derived from the two crosses, Mutant/Y98148 and Mutant/Wan3, showed the same segregation ratio of three mutant to one wild-type phenotype (Table 1), which was consistent with the previous result (Tong et al., 2003). It was revealed that the mutation was controlled by a single dominant nuclear gene, henceforth tentatively symbolized as SD-d(t). Then we used 91 ecessive homozygous tall plants from cross of Mutant/Wan3 for mapping of SD-d(t). Among the 506 pairs of SSR (simple sequence repeat) primers throughout all the chromosomes 126 pairs showed polymorphism between the two parents. The linkage between the SD-d(t) locus and SSR markers were investigated by BSA (Bulked Segregation Analysis) method with minor modification. Linkage analysis indicated that the SD-d(t) locus was linked with some SSR markers located on the short arm of chromosome 6 and SD-d(t) gene was successfully mapped between the two SSR markers RM253 and RM7023 with map distances of 7.1 cM and 4.8 cM, respectively (Fig. 2). Fine mapping of SD-d(t) by using more genetic markers and more recombinants in this region are under progression.
This work was supported by the grants of National Natural Science Foundation of China (No.3037863) and Natural Science Foundation of Anhui Province, China (No. 01041103).
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