Cowpea aphid–plant interactions: endosymbionts and related salivary protein patterns

Abstract

The specificity of plant use by aphids is related to symbiont diversity of some aphid models. Aphis craccivora Koch (Hemiptera: Aphididae, Aphidini) is a well-known aphid that feeds on species of Fabaceae, but has also been recorded recently on Amaranthus species (Amaranthaceae) in Gabon (Africa). Aphis craccivora strains used in this study were originally collected from crop Vigna unguiculata L. Walp. (Fabaceae) from Togba in Benin (Africa) and Amaranthus hybridus L. from Libreville in Gabon, for a comparative study of symbionts. Saliva composition, potentially including bacterial proteins, also contributes to the phytotoxic effect of aphid attacks. Both, endosymbiont bacteria and saliva protein diversity should be targeted to investigate the feeding behavior of aphids and to explain plant–aphid interactions. Bacteria-targeted PCR was conducted on six symbionts in A. craccivora. The obligate symbiont Buchnera aphidicola Munson et al. (Enterobacteriaceae) was identified in all aphids collected. In comparison, the facultative symbiont Serratia symbiotica Moran et al. (Enterobacteriaceae) was only found in A. craccivora from Gabon, whereas Rickettsia sp. (Rickettsiaceae) was only found in aphids from Benin. Using nano-LC-MS/MS (liquid chromatography-tandem mass spectrometry), some proteins were only found in solid or soluble saliva, whereas others originated from S. symbiotica. Two of the identified proteins are involved in plant–pathogen interactions: calmodulin and elongation factor Tu. This information on endosymbionts and related salivary proteomes from A. craccivora in Gabon helps improve our understanding of aphid–plant interactions.