Many strategies, one aim. How viruses manipulate hosts and vectors for transmission: Rome – Rome

The first objective of Rome is to better characterize aphid performance and feeding behavior on healthy and infected plants to identify a) the vector parameters modified for a potentially augmented transmission and b) the implicated viral determinants. The second objective of Rome strives to establish, by RNA profiling, a catalog of plant and aphid genes modified by viral infection of aphid-infested plants, thus potentially involved in transmission. The third objective of Rome is to validate some of the candidates.

Aphid performance was assessed by measuring behavior (duration of probing and phloem feeding) and fecundity. Aphids on CaMV infected plants reach phloem faster and feed longer on it on both hosts, phloem salivation is reduced, indicating that the aphids like CaMV-infected plants. However, fecundity is reduced. This appears to correlate with viral load (more viral proteins, less fecundity). Aphids on TuYV-infected arabidopsis reach on infected plants the phloem faster and feed longer, as expected for a circulative virus. However, phloem salivation is longer, which might be indicative of phloem defenses against aphids. Fecundity is unchanged, meaning that nutritive value is similar after all. On infected camelina, the effects are similar but weaker.
We identified CaMV proteins P2 and P6 as responsible for most effects, identification of TuYV proteins is still ongoing We will analyze the role of RNA silencing in plant-aphid interactions by testing arabidopsis dcl234 and rdr triple mutants infected with TuYV and CaMV.
We obtained enough material for RNA profiling by Illumina sequencing. The raw data are now available. Bioinformatic analysis of these small RNA-seq and mRNA-seq data is in progress to characterize small RNA-ome (viral and host) and transcriptome (viral and host) in plants and aphids and to identify virus-regulated plant and aphid genes (CaMV-, TuYV-specific, and co-regulated by both viruses), including aphid genes targeted by mobile (viral or plant) small RNAs or virus-regulated aphid small RNAs as well as plant genes targeted by mobile aphid small RNAs or aphid-regulated plant small RNAs.

We will analyze more in detail the role of P2 and P6 in CaMV ‘manipulation’ and identify and hopefully characterize TuYV proteins involved in host and vector modifications.
We will soon obtain a catalogue of plant and aphid genes differentially regulated in aphid-infested plants infected or not with CaMV or TuYV. These genes are potentially involved in plant-aphid interactions. Some candidates will be selected for validation and their mode of action characterized.

To come soon

Plant viruses and the vectors, especially hemipterans like aphids, that they use for plant-to-plant transmission, cause tremendous damage in agriculture. Conventional control strategies rely on insecticides to eliminate the aphids, but appearance of resistances, ecological issues and new legislation demand alternative control strategies that are more respectful of the environment and compatible with sustainable agricultural practices.
Evidence emerges that viruses manipulate plant traits, vector behavior and vector performance to optimize their transmission. Thus, research targeting plant viruses, vectors and hosts, and exploring the tritrophic interactions between them may show ways to more sustainable pest control strategies. This is the objective of our project. We want to identify the molecular mechanisms driving these interactions on all three levels, with an emphasis on their role in transmission. For this, we will study two viruses sharing the same hosts and aphid vectors, and representing the two most common transmission modes used by plant viruses, non-circulative (NC) and circulative (C) transmission. NC viruses are transmitted by binding to and being released from a specific site on the external mouthparts of vectors, whereas C viruses must traverse the intestine of their aphid vectors, cycle through the hemocoel and invade the salivary glands, before they can be inoculated with saliva when aphids feed on a new host. In a comparative study, we want to elaborate the similarities and differences between NC and C transmission and to determine whether they can be host-specific. For this, we use NC Cauliflower mosaic virus (CaMV) and C Turnip mosaic virus (TuYV) as viruses, the model plant Arabidopsis thaliana and the biofuel plant Camelina sativa as hosts for the two viruses, and the economically important pest, green peach aphid (Myzus persicae L.), as a vector transmitting both viruses. Our first objective is to confirm, by aphid performance analysis (individual growth rate, fecundity, starvation survival, arrestment, behavior), previous studies showing that these viruses do modify aphid behavior and traits in a way favorable for transmission, and analyze these traits in detail. Then we will identify and characterize virus-induced sRNAs and viral proteins involved in aphid modifications. This will be achieved by analyzing aphid performance on plants expressing the candidates stably or transiently. It is then our second objective to create, by RNA profiling, a comprehensive catalog of aphid and plant genes whose transcription is altered by viral infection and/or aphid infestation. Our third objective is to validate and characterize, by functional analysis, the host and aphid genes and pathways identified by RNA profiling and that are primarily involved in modifying plant and aphid traits in a way conducive for transmission. Taken together, this project will show which host and vector traits are modified by the viral infection for a better transmission, which viral factors provoke these changes, and which host and vector genes and pathways are targeted by the two viruses.