The Diversity of Wolbachia and Other Bacterial Symbionts in Spodoptera frugiperda.

Bacterial symbionts associated with insects can be crucial in insect nutrition, metabolism, immune responses, development, and reproduction. However, the bacterial symbionts of the fall armyworm Spodoptera frugiperda remain unclear. S. frugiperda is an invasive polyphagous pest that severely damages many crops, particularly maize and wheat. Here, we investigated the infection, composition, abundance, and diversity of bacterial symbionts, especially Wolbachia, in different tissues of S. frugiperda female adults. The infection prevalence frequencies of Wolbachia in five provinces of China, namely Pu'er, Yunnan; Nanning, Guangxi; Sanya, Hainan; Yunfu, Guangdong; and Nanping, Fujian, were assessed. The results indicated that Proteobacteria, Firmicutes, and Bacteroidetes were the three most dominant bacterial phyla in S. frugiperda adults. At the genus level, the abundant microbiota, which included Enterobacter and Enterococcus, varied in abundance between tissues of S. frugiperda. Wolbachia was found in the ovaries and salivary glands of S. frugiperda adults, and was present in 33.33% of the Pu'er, Yunnan, 23.33% of the Nanning, Guangxi, and 13.33% of the Sanya, Hainan populations, but Wolbachia was absent in the Yunfu, Guangdong and Nanping, Fujian populations. Further phylogenetic analyses revealed that all of the Wolbachia strains from the different S. frugiperda populations belonged to the supergroup B and were named the wFru strain. Since there were Wolbachia strains inducing cytoplasmic incompatibility in supergroup B, these findings may provide a foundation for developing potential biocontrol techniques against S. frugiperda.

Multiple dsRNases Involved in Exogenous dsRNA Degradation of Fall Armyworm Spodoptera frugiperda.

RNAi is regarded as a promising technology for pest control. However, not all insects are sensitive to RNAi. Studies have confirmed that insect dsRNases are one of key factors affecting RNAi efficiency. In the current study, we identified four genes coding for dsRNases from the Spodoptera frugiperda genome. Spatial and temporal expression analysis showed that those dsRNases were highly expressed in the midgut and old larvae. Then a delivery method was applied for inducing efficient RNAi based on dsRNA encapsulated by liposome. Furthermore, we assessed degradation efficiency by incubation with dsRNA with gut juice or hemocoel to characterize potential roles of different SfdsRNases after suppression of SfdsRNase. The result showed that interferenced with any sfdsRNase reduced the degradation of exogenous dsRNA in midgut, interfered with sfdsRNase1 and sfdsRNase3 slowed down the degradation of exogenous dsRNA in hemolymph. Our data suggest the evolutionary expansion and multiple high activity dsRNase genes would take part in the RNAi obstinate in S. frugiperda, besides we also provide an efficient RNAi method for better use of RNAi in S. frugiperda.

Core promoter regulates the expression of cathepsin B gene in the fat body of Bombyx mori.

Bombyx mori cathepsin B (BmCatB) is involved in the programmed cell death of the fat body during B. mori metamorphosis. For a better understanding of the functional regulatory mechanism, the promoter region of BmCatB in the transcriptional regulation has been identified and analyzed in the present study. BmCatB promoter region performed by the 5' truncation or mutagenesis of EcREs was inserted in the pFA3Luc-A3RL double fluorescence expression vector to activate the fireflies luciferase (FLuc) gene. The results indicated that the dual-luciferase activity of BmCatB gene in the silkworm larval fat body is regulated by the length of promoter. Site-directed mutagenesis of EcRE experiment has shown that the EcREs are up-regulated significantly in the regulation of the BmCatB promoter. A 142bp region (-1165 to -1023) and EcREs are the mainly fat-body tissue-specificity related region and could function as a core promoter element.

Identification and functional analysis of the cathepsin D gene promoter of Bombyx mori.

The gene encoding cathepsin D of silkworm, Bombyx mori (BmCatD) is specifically expressed in the larval fat body and pupal gut, and plays an important role in the programmed cell death during metamorphosis. To identify element involved in this transcription-dependent spatial restriction, truncation and deletion of the 5' terminal from the BmCatD promoter were conducted in vivo. The recombinant AcMNPV vector (Autographa californica multiple nucleopolyhedrovirus) with a dual-luciferase quantitative assay system was used as the transfer. A 289 bp DNA sequence (-1,214 to -925) upstream of the transcriptional start site is found to be responsible for promoting tissue-specific transcription. Further analysis of a series of deletion within the 289 bp region of overlapping deletion showed that a 33 bp region (-1,071 to -1,038) sequence suppresses the ectopic expression of the BmCatD promoter. These results suggest that this 33 bp region could function as a promoter element in the tissue-specificity expression.