| The oriental fruit fly,Bactrocera dorsaliss(Hendel),one of the most destructive pests throughout South East Asia,causes severe economic loss to over 250 fruit crops.Phospholipase A2(PLA2)is responsible for releasing the fatty acid moiety from the sn-2 position of phospholipids.PLA2 acts in a wide array of biological processes,such as lipid digestion,cellular membrane remodeling,signal transduction,host immune defense and production of various lipid mediators.Many papers have demonstrated the important role of PLA2 in immune responses and the reproduction system.However,little is known about the function of PLA2 in the humoral immune response and reproduction system in insects.We analyzed the changes in the humoral immune response and male fertility after silencing PLA2 gene,in order to explore the regulatory mechanism of PLA2 and provide a new target and strategy for the control of B.dorsalis.1.The expression profiles of PLA2 in B.dorsalisWe obtain PLA2 sequence from B.dorsalis c DNA library.Its open reading frame is highly identical with the other insects PLA2 homology.In this study,we investigated the expression profile of PLA2 in different tissues and developmental stages in B.dorsalis,and the results showed that the transcriptional level of PLA2 was high in the egg and mature stage,and in the fat body and testis tissue.2.The PLA2 gene mediates the humoral immune responsesBacterial infection increased the expression of PLA2,and the highest degree of up-regulation appeared in the fat body.Silencing PLA2 influenced the expression of immune-related genes,including My D88 and defensin in the Toll pathway and relish and diptericin in the Imd pathway.Moreover,the expression of My D88 and defensin was down-regulated significantly in the ds-PLA2 group compared with those in the ds-egfp group when B.dorsalis was infected with L.monocytogenes and S.aureus,indicating that PLA2 was involved in the activation of the Toll pathway.Meanwhile,infection with L.monocytogenes and E.coli,which activate the Imd pathway,does not increase the m RNA levels of relish and diptericin in the ds-PLA2 group as severely as it increases those in the ds-egfp group,indicating that the Imd pathway was also repressed after silencing PLA2.Notably,the development of lipid droplets in fat body cells was influenced by silencing PLA2,implying that PLA2 affects the function of fat body tissue.These results suggest that the PLA2 gene may mediate humoral immune responses by reducing lipid storage in fat body cells in B.dorsalis.3.The PLA2 gene influences the male fertilityWe analyzed the expression of PLA2 in male after the eclosion,and the result shows the expression of PLA2 has a rapid increase before the sexually mature stage.We successfully silenced the PLA2 gene by double injection with ds-PLA2.The egg hatching rate,average number of larva per female and average number of pupa have a significant decrease after virgin females mated with the treated males.To explore the mechanism,we check the sperm viability.The total number of spermatozoa has no difference after silencing PLA2,however,the percentage of live sperm has significantly decreased after silencing PLA2.It indicates that PLA2 can influence the male fertility by decrease the sperm viability.These results indicate that PLA2 may reducing the lipid storage and sperm viability in order to mediate the humoral immune response and male fertility. |
