Vector-borne pathogens are known to alter the phenotypes of their primary hosts and vectors, with implications for disease transmission as well as ecology. Here we show that a plant virus, barley yellow dwarf virus, increases the surface temperature of infected host plants (by an average of 2°C), while also significantly enhancing the thermal tolerance of its aphid vector Rhopalosiphum padi (by 8°C). This enhanced thermal tolerance, which was associated with differential upregulation of three heat-shock protein genes, allowed aphids to occupy higher and warmer regions of infected host plants when displaced from cooler regions by competition with a larger aphid species, R. maidis. Infection thereby led to an expansion of the fundamental niche of the vector. These findings show that virus effects on the thermal biology of hosts and vectors can influence their interactions with one another and with other, non-vector organisms.

Candidatus Liberibacter asiaticus (CLas), a bacterium transmitted by the Asian citrus psyllid, Diaphorina citri, is the causal agent of citrus greening disease, or Huanglongbng (HLB). Currently, vector population suppression with insecticides and tree removal are the most effective strategies for managing the HLB pathosystem. In this study, we assessed the bactericidal capabilities of 2′-deoxy-2′-fluoro-d-arabinonucleic acid antisense oligonucleotides (FANA ASO) both in vitro and in vivo by (1) confirming their capacity to penetrate insect cells, (2) silencing bacterial essential genes, and (3) quantifying reductions in bacterial titer and D. citri transmission. We confirmed that FANA ASO are able to penetrate insect cells without the use of a delivery agent. Expression of an essential gene in the D. citri endosymbiont, Wolbachia (wDi), significantly decreased by 30% following incubation with a wDi-specific FANA ASO. Viability of isolated wDi cells also decreased in response to the FANA ASO treatment. Delivery of a CLas-specific FANA ASO to infected adult D. citri in feeding assays resulted in significant silencing of a CLas essential gene. CLas relative density and transmission were significantly lower among D. citri fed FANA ASO in diet compared to untreated insects. Root infusions of a CLas-specific FANA ASO into infected Citrus trees significantly reduced CLas titer during a 30-day trial. Our results suggest that FANA ASO targeting insect-transmitted plant bacteria or insect endosymbionts may be useful tool for integrated management of agricultural pathogens.

We report on the development, evaluation, and efficient delivery of antisense oligonucleotide FANA (2′-deoxy-2′-fluoro-arabinonucleotide) RNA-targeting technology into citrus trees and potato plants for management of bacterial pathogens and arthropod pests. The FANA ASO technology is a single nucleotide strand of 20–24 nt in length that incorporates 2′F- chemically modifications of nucleotides, along with a phosphorothioate backbone and modified flanking nucleotides, in their structure called “gapmers,” produced by AUM LifeTech., Inc. These unique modified structures of FANA “triggers” enables gymnotic activity that self-delivers into cells, moving systemically in treated plants and insects, with significant suppression of their RNA targets. Reported is the FANA suppression of two plant-infecting bacterium Candidatus Liberibacter asiaticus, CLas (in citrus trees), and C. Liberibacter solanacearum, CLso (in potato and tomato). The CLas pathogen is associated with huanglongbing (a.k.a. Citrus Greening Disease), which causes severe loss of citrus trees, threatening global citrus production. The CLas bacterium is transmitted during feeding by the Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae). CLso causes Zebra-Chip disease in potato and is transmitted by the potato psyllid, Bactericera cockerelli (Hemiptera: Triozidae). Infected citrus trees or potato plants were treated with aqueous FANA solutions applied as a soil drench, root-infusion, topical spray, tree trunk injection or by absorption into cuttings, detached leaves, and leaf disks. Plants showed significant reduction of each pathogen or symptom development in response to FANA treatments. Similarly, ingestion of FANA solutions designed specifically to CLas by insects via artificial diets produced significant titer reductions in infected citrus psyllid adults that resulted in reduction of CLas transmission. The unique properties of FANA ASO solves many of the problems of stability, cell entry, and binding affinity that plagues exogenous RNAi strategies. Breakthroughs in production methods are reducing costs enabling these ASO to expand beyond medical applications into agricultural treatments. Thus, FANA ASO may provide viable treatments in the response to crop pandemics, like huanglongbing in citrus that threatens global food production.