Sequence Of The Nuclear Ribosomal DNA Of The Silkworm, Bombyx Mori And The Molecular Phylogeny Inferred From RDNA Sequence

We extract the genomic DNA from silkworm, Bombyx mori by the methods of SES,SDS, CTAB, KI, the resultant DNA determined by UV and argrose gel electrophoresisindicates that the DNA can be prepared simply and rapidly by SES method. Then wedesign several pairs of specific primers based on the analysis of the conservative sequencesof rDNA of other orders. We clone and sequence the complete rDNA of thesilkworm ,Bombyx mori and 18S rDNA of Antheraea peryi. The completed sequence of therDNA is comprised of 18S rDNA, ITS1, 5.8S rDNA ITS2 and 28S rDNA and theirmolecular weights are of 1907, 762, 167, 878 and 3981 bp respectively, its full weight is7695 bp. The weight of the 18S rDNA of Antheraea peryi is 1908bp. The multisequencesof 18S rDNA are aligned with those of other 18 kinds of insects retrieved from GenBankby the Clustal 1.83 software, the alignment indicates that 18S rDNA has four highlyconservative regions, Most of variations in homologous sequence in 18S rDNA ofsilkworm are transitions and transversions while there are insertions and deletions invariable regions. The phylogenetic trees are generated by the methods of Parsimony andDistance provided by PHYLIP 3.63 software. The consensus phylogenetic trees suggestthat they are very similar in the topological structure except a few differences. Comparedwith conservative homologous sequences of other 18 insects from different orders, it isfound that the 18S rDNA of the insects of Lepidoptera is structurally more similar to thoseof the insects of Diptera, suggesting a closer phylogenetic relationship between the twoorders. We also find that the insects of Homoptera is closer to those of Hemiptera andIsoptera is closer to that of Blattellidae inferred from the phylogenetic trees. Phylogeneticrelationship analysis also reveals that the Strepsiptera is closer to Collembola, andindicates their being an independent ancient branch in phylogeny. The thing that thephylogenetic trees generated by different conservative regions in 18S rDNA are similarsuggests that the conservative regions evolute concertedly, Furthermore, it is moreconservative in the 5' than 3' regions in the 18S rDNA, The 18S rDNA can be used as apowerful marker in high level molecular phylogeny analysis. G,T bases in the ITS1 and A,T bases in the ITS2 are abundant,which indicate thatthe ITS evolutes with base bias. The phylogenetic trees based on the sequence of ITS1 andITS2 of several insects of Lepidterptera,generated by the mothod of Neighbor Jointingindicate that ITS1 is more conservative than ITS2, the ITS1 and ITS2 can be used as themaker in different level molecular phylogenetic analysis. 28S rDNA is the longest seqencein the rDNA repeat,the bases component of bases is eqilibrium, we find several regionsare homologous and several regions are variable in 28S rDNA by being blasted inGenBank.