| The wheat Rht-B1,Rht-D1 and rice semidwarf-1(sd1) genes are well known as the "green revolution genes",and have contributed to the significant increase in wheat and rice production seen in the 1960s and 1970s.So investigation on the sequence structure and molecular evolution in the Rht-D1 locus region is very important to study on wheat Rht-B1 and Rht-D1 genes.On the other hand,we have a little knowledge about the composition and function of homologous sd1 gene in wheat,therefore, Cloning and identifying inheritance mode of this gene is significant to wheat genetic improvement.In this study,we investigated the molecular evolution of wheat Rht-D1 locus region by using sequenced Rht-D1 locus in six wheat genome from diploid,tetraploid and hexaploid species and compared the orthologous regions with Brachypodium and rice.Meanwhile,we obtained full length GA20ox genes from hexaploid wheat(Triticum aestivum) and located GA20ox genes on wheat genomes to give a better understanding of the character and evolutionary relationships of GA20ox genes in wheat.The results obtained are as follows:1.It is the first analyzing sequence structure in the homologus regions of Rht-D1 gene.The results showed gene density is one gene/33-50Kb in this region,which is high to average gene density in the wheat genome(one gene/80-100Kb).Repetitive sequences accounted for about 57-85%of the homologus region sequences.LTR retrotransposons are major types of the repetitive sequences, whereas CACTA and MITE are major of the DNA transposons.Additionally,a new LTR retrotransposons and four MITE sequences were reported in this paper.2.The sequences of a physical contig covering the Rht-D1 locus from the A genome of durum wheat were compared with the orthologous regions from the B and D genome of hexaploid wheat.The results suggested:(1) the colinearity of gene were much better than repetitive or intergenic other sequences.(2) it was found that a WIS element and two three-Kb unknown sequences were retained good colinearity, these sequences maybe unique for wheat genome.(3) most of the repetitive or intergenic other sequences are genome-specific sequence.(4) a gene of B genome specific and two genes of D genome specific were to be found.From this results,it is deduced that collinearity or no collinearity genes, repetitive sequences and intergenic other sequences lead to homeologous between wheat subgenomes. 3.By comparison of homology sequences among different genome,it was found that wheat subgenomes have the different evolution speed.The fact that Carmilla-1 element shared by the A and D genomes,but not by the B genome,indicated that the A and D genomes share a common ancestor that had previously diverged from the B genome ancestor.Several other lines of evidence discovered in this study,including the difference of Rht-B1 sequence between tetraploid and hexaploid more higher than Rht-A1 sequence between tetraploid and hexaploid,and higher sequence homology in the Rht-1 regions between the A and D genomes than the B genome,also support this conclusion.4.A novel gene encoding GA20-oxidase was cloned from hexaploid wheat(Triticum aestivum) using the homologous cloning method.Sequences analysis showed that wheat GA20-oxidase have three sequences:TaGA20ox2-A1,TaGA20ox2-B1 and TaGA20ox2-D1.Sequence alignment proved wheat GA20-oxidase genes have the highest homology with rice GA20-oxidase(80%cDNA sequence identity).A series of 'Chinese Spring' nulli-terasomic stocks were employed to ascertain the chromosomal location of wheat GA20-oxidase gene.The results showed that TaGA20ox2-Al,TaGA20ox2-B1 and TaGA20ox2-D1 were on wheat chromosome 3A,3B and 3D.Using a population of recombinant inbred lines from the cross W7984×Opata85,TaGA20ox2-D1 was mapped on chromosome 3D,and flanked by SSR markers Xfba330 and Xgwm664 at 4.1 and 5.3 cM,respectively.In this region a plant height loci was reported.Based on these results,we think that TaGA20ox2-D1 gene maybe have an impact on wheat height development. |
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