Genetic Diversity And Evolution About Bro Genes In Bombyx Mori Nucleopolyhedrovirus

A comparison between BmNPV T3 genome sequence published in NCBI and CQ1 genome sequenced by our laboratory revealed that there were mainly two different regions named VI, V2. In T3 genome sequence, VI has a length of 2 358bp from 16 031bp to 78 388bp, including bro-b and bro-c. V2 ranges from 12 5542bp to 12 7075bp, a fragment of 1 534bp, in which bro-d and bro-e exist. We also collected other strains including CQ2, SC, JS, GD. Taking genome DNA of CQ2, SC, JS, GD as templates respectively, through PCR, cloning and sequencing, we got the sequence information of CQ2, SC, JS, GD corresponding to VI, V2 of T3. Together with bro genes of BmNPV -T3 and -SC7 published in NCBI, we analyzed heredity diversity and evolution of 24 bro genes. The main results were as follows:1. The distribution of bro genes in different BmNPV genomesWe analyzed the distribution of bro genes in different BmNPV genomes by DNAstar. In the seven strains bro genes were located in three genome regions, and the variation of the copies of bro genes was observed. In BmNPV T3, five bro genes were distributed in three genome locations: the bro-a gene was located alone (we called this genome location region I), the bro-b and bro-c genes were adjacent to each other in a head-to-tail arrangement (we called this genome location region II) and the bro-d and bro-e genes were also in a head-to-tail arrangement (we called this genome location region III). Compared with T3 strain, loss of bro-b gene occurred in Region II from CQ1, CQ2, SC, JS isolates and loss of bro-e gene existed in Region III from GD isolate.2. Phylogenetic analysis of bro genesNeighbor-joining tree of bro genes suggested that 24 bro genes were clustered into three subgroups named A, B and C. bro-d genes belong to A subgroup, bro-a and bro-c belong to B subgroup, bro-b and bro-e belong to C subgroup. This result was consistent with previous report. In addition, a high level of sequence divergence existed between bro genes of C subgroup with those of A and B subgroups.