Molecular mechanisms underlying plant specialization in the pea aphid complex – Bugspit

We hypothesize that the proteins secreted by aphid saliva and bacterial symbionts are involved in aphids’ feeding success on specific host plants. We examined genomic sequences of many aphids that feed on different host plants to identify the salivary genes that show sequence variation depending on their host plants. We also manipulate the composition of symbionts and examine their contributions to plant specialization.

We examined a large genomic sequence dataset and identified the genes that encode salivary proteins that show sequence variation depending on the plants they are adapted to. Furthermore, we found that some salivary genes can produce multiple proteins with different sequences. The functions of those salivary genes are currently tested.
We eliminated bacterial symbionts that are frequently associated with clover feeding aphids and conducted performance tests to examine the contribution of the symbionts in aphid fitness on clover. As we did not observe significant effects of the symbionts, more aphid/symbiont lines will be examined.
Finally, to examine the activities of aphid or symbiont derived proteins in plants, we have optimised a protocol to transiently express aphid/symbiont proteins in two plant species.

The knowledge on the functions of aphid salivary proteins will help us to identify the plant factors that are targeted by those proteins. This will allow us to develop or select the crops that are less susceptible to the aphids. The knowledge on plant-aphid-symbiont interactions may be used to develop biocontrol strategies of the aphids in the field. Overall, the knowledge created by this project will contribute to protect crop production by minimizing pesticide use.

We published two review articles: one focuses on plant-insect interactions (1) and another one discusses plant-insect-microbe interactions (2). We presented our work in two international conferences and 8 national meetings.


1. Simon JC, d'Alençon E, Guy E, Jacquin-Joly E, Jaquiéry J, Nouhaud P, Peccoud J, Sugio A, Streiff R.(2015) Genomics of adaptation to host-plants in herbivorous insects. Brief Funct Genomics. pii: elv015. [Epub ahead of print]

2. Sugio A, Dubreuil G, Giron D, Simon JC. (2015) Plant-insect interactions under bacterial influence: Ecological imprications and underlying mechanisms . J. Exp. Bot. 66, 467-478

Aphids are insect pests that feed on plant phloem sap and cause feeding damages and transmission of plant pathogens. The pea aphid (Acyrthosiphon pisum) complex is consisted of multiple biotypes each of which adapted to specific legume plants (e.g. clover, pea and medicago) and cannot perform well on non-adapted legumes. However, molecular mechanisms by which the aphids specialize to certain plant species are not yet understood. Aphids use a specialized mouth part to puncture plant phloem sieve cells and suck plant nutrients. During the feeding process, aphids secrete saliva which contains various proteins that might interact with plant proteins. Indeed, some saliva proteins were shown to promote aphid colonization and some were shown to have negative impact. Another factor that is involved in plant-aphid interaction is facultative symbionts of aphids. Interestingly, the pea aphids carry various facultative symbionts and one of which, Regiella, is known to increase aphid adaptation to clover plants. This project aims to examine the roles of aphid saliva proteins and aphid symbionts in host plant adaptation. Based on the numerous studies in plant-microbe interactions, we hypothesize that aphid saliva proteins function like microbial pathogen effectors (virulence and avirulence factors). Thus, we anticipate that the saliva proteins that are involved in host adaptation process are under high evolutionary pressure and/or show biotype specific expression patterns or polymorphisms. We further hypothesize that the presence of Regiella influences the expression patterns or composition of aphid saliva proteins and alter aphid-plant interactions.
In this fundamental research project, we will integrate transcriptional and genome resequencing data to identify the salivary genes that can be involved in the host plant adaptation processes of the pea aphid. Aphid gene silencing and in planta transient gene expression will be employed to examine the roles of the saliva genes in plant-aphid interactions. In addition, we will examine the Regiella strains that do/don’t increase aphid adaptation to clover to understand the complex host adaptation mechanisms of the aphids. We will conduct transcription analysis and saliva proteomics of the pea aphids with and without the Regiella strains to identify the factors that might be required to increase aphid performance on clover. The project will advance our knowledge on the roles of aphid saliva proteins and their symbionts in host plant specialization process and will be the first step to develop benign strategies to control aphid pests in the field.