The Roles Of JAK/STAT Signaling In The Immune Responses Of The Pea Aphid,Acyrthosiphon Pisum

The pea aphid Ayrthosiphon pisum is the model insect of Hemiptera.It is an important agricultural pest,which seriously harms legumes and other crops.Genome sequencing results showed that the pea aphids’ genome lacks of a large number of immune-related genes.However,the immune system of the pea aphid is still able to resist the invasion of pathogenic microorganisms effectively.JAK/STAT signaling is a signal transduction pathway composed of multiple cytokines.This pathway is widely involved in various physiological processes and plays an important role in innate immune regulation of insects.In order to investigate the roles of JAK/STAT signaling in the immune system of the pea aphid,we detected the expression of the receptor Domeless1-3,tyrosine kinase JAK,signal transducer and activator of transcription Stat92E-1 and suppressor of cytokine signaling SOCS5 after infection with different bacteria and fungus.RNA interference technology was used to knockdown expression of JAK and Stat92E-1 in pea aphids,then the aphids were infected with bacteria and fungus after confirmation of knockdown of the target genes.We investigated the aphids’ survival,viability of bacteria and fungus after infections.The main results are as follows:1.Bioinformatic analysis showed that the JAK protein of pea aphid has a band 4.1homology domain,an Src homology 2 domain,a protein tyrosine kinase and a tyrosine kinase catalytic domain,the Stat92E-1 protein of pea aphid has a STAT interaction domain,a STAT all-alpha domain,a STAT DNA binding domain,an Src homology 2 domain and a low complexity region.These domains are conserved in insects.Multiple sequence alignment and the phylogenetic tree showed that JAK and Stat92E-1 were relatively conserved,and they were closely related to their homologs reported in other insects,such as Drosophila melanogaster,Aedes aegypti and Bombyx mori.2.After infection with Gram-negative bacterium Escherichia coli,Gram-positive bacterium Staphylococcus aureus and the fungus Beauveria bassiana respectively,the expression levels of Domeless1-3,JAK,Stat92E-1 and SOCS5,which is specifically regulated by Stat92E-1,were upregulated at different time points,with significant differences compared to the control group.This indicates that the JAK/STAT signaling was activated after pathogen infections.3.After knockdown Stat92E-1,the expression trend of SOCS5 was consistent with the expression trend of Stat92E-1,indicating that the transcriptional activation of SOCS5 is regulated by Stat92E-1.4.E.coli and S.aureus were used to infect the JAK and Stat92E-1 deletion pea aphid groups.Bacterial proliferation increased significantly in pea aphid.After B.assiana infection,compared with the control group,the number of fungal spores had no significant change.5.After knockdown of JAK,the mortality rate of pea aphid was higher than the control group.When infected with E.coli and S.aureus,the survival rate of pea aphid decreased significantly compared to the control group.After infected with B.assiana,the survival rate was lower than the control group,but with no significant difference.After knockdown of Stat92E-1,and infection with E.coli and S.aureus,the survival rate of pea aphid was significantly lower than the control group,with a very significant difference.After infected with B.assiana,the survival rate decreased with no significant difference.Conclusions: JAK/STAT signaling participates in the immune defense response of the pea aphid against bacteria and fungus infections.It plays a critical role to resist the invasion of E.coli and S.aureus,but a weak role in the anti-B.assiana reaction.