A Study On The Molecular Evolution And Codon Bias Of Baculoviruses

The former molecular evolution of baculovriruses were focused onphylogenetic analysis based on single-gene or genomic sequences. In thisstudy, the evolutionary rate and codon bias of baculoviruses were analyzed.By comparing the differences among evolutionary rates of groups and codonusage of baculoviruses, the detailed evolutionary relationship of lepidopteranbaculoviruses and the patterns of codon bias of baculoviruses were revealed.Chapter 1 was a general introduction of baculoviral taxonomy, genomicfeatures and former researches on molecular evolution and phylogeneticanalysis. The molecular evolutionary rate and codon bias were introduced.In chapter 2, evolutionary rates and selection pressure of core genesand unique genes of lepidopteran baculoviruses were analyzed. Based on theresults, a hypothesis was postulated that GroupⅠNPV was derived of anancestral GroupⅡNPV, and the acquiring of gp64 was essential for theforming GroupⅠNPVs. Due to function overlap with gp64, F-like genes ofGroupⅠevolved under relaxed selection pressure and partially lost its fusionfunction.In chapter 3, 38 sequenced baculoviruses were used to estimate thecodon bias based on ENC (effective number of codons) values, GC content, etc. Results showed baculoviruses were divided into following two kinds: 1)The GC content of genes were low or medium, and contained only few geneswith codon bias (1～4 gene in a speicies). For this kind of baculovirus, mutation was the important cause that lead to the codon bias. 2) The GCcontent and GC content in 3rd position of synonymous codons (GC3) werehigh, and the number of genes with codon bias were more than 10％of totalgenes. For this kind of baculovirus, the selection pressure between virus andhost possiblly resulted in the codon bias. LdMNPV and OpMNPV are of highGC content and with high codon bias. Genome analysis indicated that hrf-1(host range factor 1), might be a key gene that led to the high codon bias ofthese two viruses.Finally, in chapter 4, the results were summarized and the directions forfuture research were explored.