Genetic Analysis And Fine Mapping Of Rice Dwarf Gene Ds(t)

The dwarf mutant was obtained from tissue culture of Kitaake a janpanica variety of rice. Plant height of the dwarf mutant is 40.2 cm on average. The plant height of this mutant was 37% of that of wildtype. Its leaves were dark green, erect and curled up along leaf brim. The analysis of chlorophyll contents showed that dwarf mutant had higher chlorophyll contents than those of wildtype except no difference in Chl a/b ratio. The leaf of mutant showed the same values in the actual PSII efficiency (ΦPSII), photochemical quenching (qP), and the maximal efficiency of PSII photochemistry (Fv/Fm) were similar to those of wild-type. However, the non-photochemical quenching (NPQ) was lower than wildtype significantly, which suggests that this mutant had higher photosynthetic efficiency. Furthermore, ultrastructure of this mutant showed characterizes of senescence. It is highly possible that the comparatively higher level of proline, SOD and MDA contents of mutant is responsible for the inhibition of reproduction pathway of mutant.The dwarf phenotype could not be rescued by GA and BR, indicating that Ds(t) might be involved in the signal transduction rather than in the biosynthesis pathway of GA and BR.Genetic analysis showed the dwarf is controlled by a monogenic recessive gene. We named the dwarf gene Ds(t)(Dwarf strong tentative). To clone the gene, fine mapping was carried out using F2 populations derived from a cross between the heterozygous plants(D/d) and an indica variety 93-11. Preliminary mapping of Ds(t) indicated that it was linked to two SSR markers: RM283 and RM5496 on the short arm of chromosome l. Through fine mapping using 1162 F2 mutant plants, the Ds(t) was finally mapped between SSR marker sc35 and sc50 and the distance of the two makers is 62kb.Searched in genome sequence of the japonica variety Nipponbare (http://rgp.dna.affrc.go.jp/),we found that there is a BR-relative gene D2 in the region. We sequenced the D2 gene in the mutant and wild type, the result showed there are the same sequence in the mutant, wildtype and Nipponbare. The results of phenotype hormone treatment and gene sequencing suggest that Ds(t) located at a different locus with d2, which has been previously identified as a dwarf gene located in this region. Ds(t) may be a new gene related to BR signal transduction pathway and further research of Ds(t) might has very important implications for revealing the mechanism of rice dwarf.