Two circulative plant pathogens in different genera suppress anti-viral immunity in their hemipteran vectors against insect-infecting flaviviruses

Authors: LARREA-SARMIENTO, ADRIANA - Cornell University; OLMEDO-VELARDE, ALEJANDRO - Cornell University; WEST-ORTIZ, MICHAEL - Cornell University; STUEHLER, DOUGLAS - Oak Ridge Institute For Science And Education (ORISE); HOSSEINZADEH, SAEED - Cornell University; COLEMAN, AMINAH - Boyce Thompson Institute; PREISING, STEPHANIE - Cornell University; PARKER, GLENN - Cornell University; FEI, ZHANGJUN - Boyce Thompson Institute; Heck, Michelle

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 8/15/2024
Publication Date: 8/15/2024
Citation: Larrea-Sarmiento, A., Olmedo-Velarde, A., West-Ortiz, M., Stuehler, D., Hosseinzadeh, S., Coleman, A., Preising, S., Parker, G., Fei, Z., Heck, M.L. 2024. Two circulative plant pathogens in different genera suppress anti-viral immunity in their hemipteran vectors against insect-infecting flaviviruses. bioRxiv. 2024. https://doi.org/10.1101/2024.08.15.608128.
DOI: https://doi.org/10.1101/2024.08.15.608128

Interpretive Summary: The green peach aphid is a vector of over 100 plant viruses, including the economically important potato leafroll virus (PLRV) infecting potatoes. In this work, we discovered a new virus that only infects insects, specifically the green peach aphid, Myzus persicae. This particular virus, named Myzus persicae flavivirus (MpFV) only infects aphids. MpFV creates a large protein that is cut into smaller pieces, some of which help the virus make more copies of itself inside the aphid. Unlike PLRV, MpFV is passed on from parent aphids to their offspring and replicates in the aphid body, but not the aphid salivary glands. MpFV can infect other species of aphids. We found that when aphids are carrying PLRV, the aphid's anti-viral immune system is turned down and the amount of both PLRV and MpFV viruses increase inside the aphid. To generalize these findings we showed that a similar process happens in another insect, the Asian citrus psyllid, which spreads citrus greening disease. The bacterium associated with citrus greening, CLas, also turns down the psyllid immune system against a psyllid-specific flavivirus. In summary, this research reveals that some plant pathogens, specifically those that circulate in their insect vectors, can actually boost the levels of insect-specific viruses within insects, which may change how we understand the relationships between plants, insects, and the viruses that infect them. These findings open a new and unexplored avenue of research in the possible role of insect viruses in transmission of plant pathogens and/or their future use to dissect the molecular mechanisms involved in transmission.

Technical Abstract: A positive, single-stranded RNA virus member within the Flavivirus genus was identified and characterized infecting Myzus persicae. This new insect-specific virus (ISV), Myzus persicae flavivirus (MpFV), has 23,236 nucleotides in length and encodes a large polyprotein from a single open reading frame. Analysis of conserved domains showed that helicases, NS3-proteases, Fts-J methyltransferase, and an RNA-dependent RNA polymerase are present in the coded polyprotein. Aphid-infecting ISVs have been reported to interact with plant viruses within the vector, modulating its titer and manipulating aphid behavior and morphology. Small RNA (sRNA) profile analysis of the M. persicae sRNA profile demonstrated that the circulative plant virus, potato leafroll virus (PLRV), modified the aphid antiviral immunity against MpFV. Abundant sRNA reads matching MpFV were detected when aphids were fed on healthy plants, sucrose diet, and potato virus Y-infected plants. In contrast, no MpFV reads were detected in aphids that had acquired PLRV from infected plants or artificial diet sachets containing purified virions. While the titer of M. persicae densovirus (MpDNV) was previously reported to be regulated by expression of the PLRV silencing suppressor protein P0, P0 had no effect on MpFV titer in the aphid. MpFV was transmitted 100% vertically to the offspring and exhibited tissue tropisms for the body rather than the head. By artificial diet assays, other aphid species, including Aphis gossypii (cotton aphid), Schizaphis graminum (greenbug aphid), Rhopalosiphum padi (bird cherry-oat aphid), and R. maidis (corn leaf aphid), acquired the MpFV. These findings further support the idea that PLRV suppresses aphid immunity against ISVs, suggest the existence of at least two distinct pathways for PLRV-induced aphid immune system modulation. To test whether other circulative plant pathogens suppress insect anti-viral immunity against insect-specific flaviviruses, we quantified the small RNA response of Diaphorina citri, vector of “Candidatus Liberibacter asiaticus” (CLas) associated with citrus greening disease and showed that CLas also suppresses D. citri anti-viral immunity against D. citri-like flavivirus (DcLFV). These data reveal an evolutionary conserved, unexpected role for diverse circulative plant pathogens in modulating anti-viral immunity in hemipteran vectors.