| Rice (Oryza sativa L.) is the most important staple foods in the world. During the process of dwarf breeding, several kinds of dwarf gene sources have been used. Moreover, genetic analysis had revealed that the dwarf genes of these sources were allelic to sd-1. The frequent use of these single semi-dwarf genes might cause genetic vulnerability to pests and diseases. Therefore, identifying and developing new useful semi-dwarf genes is becoming a crucial subject for practical rice breeding.In this study, we described the identification and characterization of a new rice semi-dwarf gene obtained from Aitaiyin-3, a natural dwarf mutant from rice cultivar Taiyin-1.Genetic analysis showed that its dwarfism was controlled by two recessive semi-dwarf genes, sd1 and a new semi-dwarf gene sdt2.In order to clone sdt2, two F2 populations of A-3//N6 and A-3//zhonghua 11 plus their F3, F4 offsprings were totally established for fine mapping the sdt2 gene .It was found to be roughly located between two SSR markers RM1305 and RM5633 on chromosome 4 with the genetic distances of 3.8 cM and 0.4 cM, respectively. Then we enlarged the populations and according to the known rice genomic sequences, developed new SSR markers. Then using 10 polymorphic markers, the sdt2 was further mapped between two SSR markers Chr4-48 and SSR404, with genetic distances of 0.009 cM and 0.04 cM, respectively. In addition, SSR398, SSR406 and Chr4-60 were found to co-segregate with sdt2 locus. The mapping result showed that sdt2 gene was tightly adjacent to the centromere of chromosome 4. Based on this finding, the high-resolution genetic map of sdt2 gene was integrated with the physical map on chromosome 4. In accordance with the annotation data in the sdt2 gene-encompassing region, a candidate-gene strategy was adopted to surmise 11 genes as the candidate genes of sdt2. Based on earlier research in our laboratory, one glycosyltransferase gene namely GTase1 was identified. DNA sequenceing analysis indicated that this gene had a insertion of 25 bp at the upstream of the start codon ATG with 830 bp length, leading to the gene expression level obviously lower in mutant A-3 than that in N6. Based on the PLACE results, a short sequence insertion was presumed to change the interactions among cis-acting regulatory elements, which effected the expression of this gene.Complementary test was employed to further identify GTase1 as the candidate gene of sdt2. Firstly ,full sequences of glycosyltransferase genes involved GTase1 (geneâ… ) and another one (geneâ…¡) were introduced to the back-cross offerings of A-3/N6 and A-3/Z11. Subsequently, the height of transformed plants of geneâ… significantly increased. According to the analysis above, we could conclude that the GTase1 was the candidate gene of sdt2. As a result of follow up overexpression test, the height of zhonghua11 plants transformed with full cDNA length AK059031 and AK10089 evidently increased, and the roots became thicker comparing to the control. Simultaneously, we also discovered the seeding rate of transgenic plants with AK059031 obviously decreased, but the spikelet numbers of plants transformed AK100189 increased significantly. Furthermore, the phylogenetic tree was constructed of glycosyltransferase family 1 gene members in japonica rice by Clustalx. The results suggested that the genetic relationships among geneâ… ,â…¢andâ…£mentioned in our research were closer, and they were attributed to one sub-family,while the geneâ…¡which was far from the three might belong to another family. |
