Four housekeeping genes including gapA, groEL, gyrA and pgi were used in order to reveal a phylogenetic relationship among Paenibacillus species. Phylogenetic analysis and end-to-end pairwise analysis were carried out using nucleotide and amino acid sequences of the housekeeping genes. A monophylogenetic clade including P. popilliae, P. thiaminolyticus and P. dendritiformis formed in all phylogenetic trees. The results in both analyses indicated that the relationship between P. larvae subsp. larvae and P. popilliae was comparatively far. The result of the end-to-end pairwise analysis also showed that, among the Paenibacillus species used in this study, the closest species to P. popilliae was P. dendritiformis.

View full abstract

Cry39Aa from Bacillus thuringiensis serovar aizawai BUN1-14 is highly toxic to the larvae of Anopheles stephensi mosquitoes, which transmit malarial parasites. We constructed a homology model of Cry39Aa toxin using the reported structure of Cry4Ba toxin (PDB file 1W99) as a template, and we identified 349KYAYWR354 as the putative loop 1 in domain II. Many studies of various Cry toxins have shown that surface-exposed loops of domain II are critical for toxicity and receptor binding. To investigate the functional role of the putative loop 1 of Cry39Aa toxin, we performed site-directed mutagenesis in the loop. The results of alanine substitutions revealed that the entire structure of loop 1, and aromatic amino acids Y350 and Y352 in particular, are essential for larvicidal activity. In contrast, the toxicities of Cry39Aa mutants with phenylalanine substitutions at these two tyrosine residues did not differ markedly from the toxicity of wild-type Cry39Aa. A competitive binding assay involving A. stephensi brush border membrane vesicles revealed that the alanine mutants showed reduced competition with wild-type Cry39Aa toxin. Our results suggest that the molecular structure of loop 1 in domain II of Cry39Aa toxin is important for toxicity and receptor binding in the midgut of A. stephensi larvae.

View full abstract

Using a cDNA microarray, we monitored global gene expression profiles in silkworm BmN4-SID1 cells after the knockdown of BmAGO1 and BmAGO2 genes. Interestingly, there was a significant overlap between the target genes up-regulated by BmAgo1 (292 out of 481) and BmAgo2 (292 out of 361). Of these, the Replicase gene of macula-like virus (BmMLV) was highly induced in both of BmAgo1- and BmAgo2-depleted cells. RT-PCR analysis confirmed that the knockdown of silkworm RNAi pathway-related genes increased the expression of the Replicase gene. These data strongly suggested that the RNAi pathway negatively regulated BmMLV proliferation in silkworm BmN4 cells.

View full abstract

About two thirds of open reading frames (orfs) predicted on Bombyx mori nucleopolyhedrovirus (BmNPV) genome were dispensable for expression of the reporter gene derived from the polyhedrin promoter in BmN cells when knocked out one at a time (Ono et al., 2012). Effects of removal of multiple genes of BmNPV and genetic interactions of the viral genes have been poorly investigated. In this study, we constructed BmNPV lacking multiple non-essential genes at the orf11-12-13-14 gene cluster and analyzed the expression of EGFP under the control of the polyhedrin gene promoter. Viruses lacking more than two genes except for the one lacking orf13 and orf14 showed distinct phenotypes compared to the single gene knockout viruses. Synergistic, compensatory, and additive relationships were observed in the genetic interaction analyses between pairs of adjacent genes in the gene cluster. In addition, the virus lacking both orf12 and orf13 but carrying the orf12 genomic region at downstream of the polyhedrin locus expressed EGFP at higher levels than the control virus BmGFP (Ono et al., 2012) although the transcription of orf12 was not changed by insertion at the different locus. This increased EGFP expression was not observed with the virus in which the defect of orf12 and orf13 was rescued with orf13 at the same position. These observations suggested that inserting orf12 at the position specifically affected expression of the reporter gene at the polyhedrin locus.

View full abstract