Pea transcriptional and phytohormonal responses to adapted and non-adapted aphid biotypes at early stages of infestation.

Pea (Pisum sativum L.), a major legume crop, is affected by various parasites including the pea aphid (Acyrthosiphon pisum Harris). The pea aphid is composed of multiple biotypes, each one being able to feed and reproduce on one or a few legume species. To understand the pea defense mechanisms to a pea adapted and a non-adapted A. pisum biotype, we studied the early molecular responses of four pea genotypes with contrasted levels of resistance, which are controlled primarily by the ApRVII locus. We found that major defense-related phytohormones and their derivatives in pea did not show clear response to aphid infestations. Transcriptomic analyses showed that the number of differentially expressed genes (DEGs) increased over time in pea genotypes infested with pea-adapted aphids, while significantly fewer DEGs were detected in genotypes infested with non-adapted aphids. The most resistant of the four investigated pea genotypes showed the fewest DEGs to both aphid biotypes. Aphid infestation of the three other pea genotypes commonly induced down-regulation of various pathways involved in fundamental biological processes. Comparison of the transcriptional data of pea genotypes identified candidate genes potentially involved in the aphid resistance conferred by ApRVII.