The Role Of Superoxide Dismutase-2 In Immune Responses Of The Pea Aphid,Acyrthosiphon Pisum

Aphids are diverse sap-sucking insects that can be serious agricultural pests and vectors of plant disease.Sequencing of the pea aphid?A.pisum?genome provides the basis for genomic studies of pea aphid and other aphids.Stricking,pea aphids appear to be missing genes present in other insects'genomes.These genes are thought to be essential for insects'immune responses.ROS act as signal molecules and participate in intracellular signalings and immune responses.The superoxide dismutases?SOD?catalyze the conversion of the O₂^-to H₂O₂ and O₂,H₂O₂ and chloride ions?Cl^-?can be converted to hypochlorous acid?HOCl?.The H₂O₂ and HOCl are thought the major ROS involved in hosts'responses.Therefore,the SOD might be involved in hosts'immune responses.In this study,to evaluate the contribution of superoxide dismutases 2?SOD-2?to the pea aphids defense against microbal infection,we knocked down the SOD-2 expression and investigated the H₂O₂ level,aphid's survival,and viability of bacteria and fungus in the pea aphids after infection.The main results are as follows:1.After infected with S.aureus,P.aeruginosa and B.bassiana,the H₂O₂ levels in the pea aphids increased markedly.2.The SOD-2 mRNA level significantly up-regulated by S aureus,P aeruginosa and B bassiana infection,indicating that SOD-2 is involved in the pea aphid's defense.3.The H₂O₂ level in the pea aphid decreased significantly after the SOD-2 was silenced,and the H₂O₂ levels in the pea aphids infected with S.aureus,P.aeruginosa and B.bassiana were also significantly lower than that of the pea aphids ingected with dsGFP,suggests that the SOD-2 is responsible for H₂O₂ production in the pea aphids.4.After the silencing of SOD-2,the proliferation of S.aureus in the pea aphids was accelerated significantly,and the proliferation of P.aeruginosa and B.bassiana were increased,indicating that SOD-2 is capable to inhibit growth of bacteria and fungi in the pea aphids.5.After silencing of SOD-2,the mortality of the pea aphids was significantly higher than that of the aphids injected with dsGFP.The mortality of pea aphids infected with S.aureus was significantly higher than that of the pea aphids ingected with dsGFP.Although there was no significant difference between the mortality of the SOD-2 silenced and dsGFP injected groups after infection with B.bassiana,the mortality of SOD-2 silenced the pea aphids was higher that aphids injected with dsGFP during the second to fourth days.Conclusion:After pea aphids were infected by microorganisms,the SOD-2 catalyzes the production of H₂O₂ and thereby inhibit proliferation of microorganisms in the pea aphids.