The Role Of Catalase In The Immune Responses Of The Pea Aphid,Acyrthosiphon Pisum

The pea aphid?Acyrthosiphon pisum?is the first hemimetabolous insect that genome has been published.Genomic analyses have indicated that the pea aphid has an unique immune system compared with other insects,because of the lack of many important immune-related genes.Recent studies showed that reactive oxygen species?ROS?is involved in pea aphid defense responses.However,excessive ROSs will cause oxidative damage to the organisms.Catalase?CAT?is a key antioxidant enzyme in almost all living organisms,which involved in decomposing hydrogen peroxide?H₂O₂?into oxygen?O₂?and water?H₂O?.In present research,in order to understand the role of Catalase in the immune responses of the pea aphid,we studied the relationship between ROS,catalase and pea aphids'survial by silencing catalase with RNAi.Our results show the following:1 After infected with M.luteus,the H₂O₂ levels and the catalase expression in the pea aphid increased markedly.It indicates that ROS and catalase were involved in the inmmune defense of pea aphid.2 The H₂O₂ level of the pea aphid was rised significantly after the catalase was silenced.And the H₂O₂ level of the pea aphid post Micrococcus luteus infection was also up-regulated.It suggests that the catalase can eliminate excess H₂O₂ in the pea aphid.3 After the silencing of catalase,the M.luteus introduced into the aphids multiplied slower.It may suggested that the increased H₂O₂ could inhibit the growth of M.luteus.4 After infected by M.luteus,there was no difference in survival between the pea aphids which the catalase was silenced and unsilenced.This indicates that there are other antioxidant pathways in pea aphid.5 Infected with Escherichia coli did not cause an obvious increse of H₂O₂ level in the pae aphid.Catalase siliencing had no effect on the proliferation of E.coli.This implies that the pea aphid has different strategies when dealing with M.luteus and E.coli infection.Conclusion:Catalase can protect the pea aphid from M.luteus infection.However,for E.coli infection,aphid may have other defense strategies.