Transcriptomic Response Of Tetranychus Urticae Embryos From Wolbachia-induced Cytoplasmic Incompatibility

Wolbachia is considered to be the most successful and widely distributed on our planet.It can regulate host reproduction and development in selfish ways.In addition,it can protect insects from pathogens,provide necessary nutrition for the host,and improve the proliferation of host stem cells.Wolbachia regulates host reproduction including cytoplasmic incompatibility,male killing,feminization and parthenogenesis.Among them,the most common is CI,which can lead to incompatibility between male and female gametes,thereby selectively eliminating non-infected host individuals and increasing the reproductive capacity of infected females in the population.Tetranychus urticae is one of the most destructive agricultural pests in the world and is also one of the main pests on many crops in China.The natural infection rate of T.urticae varies from 2.5%to 85%,and showes an increased trend year by year.In order to assess the effect of Wolbachia on the reproductive phenotype and mechanism of it’s interaction with T.urticae,we first clarified the effects of Wolbachia on the fecundity and offspring development on T.urticae.We then performed transcriptomic sequencing on one-day embryos from WU(♀WU×♂WU),WI(♀WI×♀WI)and CI(♀WU×♂WI)to screen cytoplasmic incompatibility-related host genes and pathways involved.The results are summarized as follows:Ⅰ.The effect of Wolbachia infection on the reproduction of T.urticae.We surveyed the biological indicators such as egg production and hatching rate of the two-spotted spider mite.The results showed that Wolbachia could kill some female embryos by cytoplasmic incompatibility during embryonic development,thus reducing the number of uninfected female offspring.Secondly,Wolbachia infection did not increase the egg number,but increased the proportion of female offspring and changed the sex ratio of offspring.Ⅱ.The effect of Wolbachia infection on the transcription of T.urticae embryos.By collecting eggs deposited within 24 hours from three cross combinations of WU,WI and CI for transcriptomic sequencing,we found that the number of differentially expressed genes between WI and WU was significantly lower than the other two groups.A total of 145 genes were differentially expressed between WI and WU embryos,including 84 up-regulated genes and 61 down-regulated genes in WI embryos.Wolbachia infection increased the expression of IAP(Inhibitors of apoptosis),suggesting that Wolbachia may inhibit the apoptosis of T.urticae embryos.The high expression of CtsB(Cathepsin B)indicated that WI embryos may effectively degrade yolk nutrients into lipids,which might be used by embryonic tissues for growth and differentiation.Down-regulation of GST(glutathione S-transferase)gene expression in T.urticae infected with Wolbachia indicated that the WI embryos were less resistant to oxidative stress.In addition,the down-regulation of ribosomal proteins also suggested that the translation of WI proteins may slow in the early embryonic stage.Ⅲ.The effect of cytoplasmic incompatibility on the transcription of Tetranychus urticae embryos.In this study,we identified 1613 up-regulated genes and 294 down-regulated genes specifically expressed in CI embryos.The CI embryos expressed more genes related to biological processes of cellular macromolecules including nucleotides and nucleic acids,modification of proteins like histone and peptidyl-lysine,chromatin binding and protein-DNA complex subunit organization,transcription factor activity,cell cycle,cytoskeleton tissue,cell tissue,anatomical structure and growth and development morphogenesis genes.KEGG pathway enrichment analysis showed that many genes that were specifically up-regulated in CI embryos were linked to embryo development,including RNA transcription(such as lysine degradation),and protein translation(such as ribosome biogenesis and aminoacyl-tRNA biosynthesis).KEGG pathways associated with extracellular matrix(ECM-receptor)interaction and transforming growth factor beta(TGFB)signaling pathways were also present in the up-regulated genes.Among the 294 CI-specific down-regulated genes,GO enrichment analysis showed that the genes related to metabolism and antioxidant activity.Similarly,KEGG pathways were mainly involved in energy production,carbohydrate metabolism(including glycolysis/gluconeogenesis,pentose phosphate pathway,and Butanoate metabolism)and fatty acid elongation.In summary,we clarified the reproductive effects of Wolbachia on T.urticae.We also explored the transcriptomic response of T.urticae embryos from Wolbachia-induced cytoplasmic incompatibility,which revealed cytoplasmic incompatibility-related host genes and pathways involved.The date provided a foundation for future studies aimed at understanding the mechanism of Wolbachia-induced cytoplasmic incompatibility.