Potato Aphid Salivary Proteome: Enhanced Salivation Using Resorcinol and Identification of Aphid Phosphoproteins

Aphids
deliver saliva into plants and acquire plant sap for their
nourishment using a specialized mouthpart or stylets. Aphid saliva
is of great importance because it contains effectors that are involved
in modulating host defense and metabolism. Although profiling aphid
salivary glands and identifying secreted proteins have been successfully
used, success in direct profiling of aphid saliva have been limited
due to scarcity of saliva collected in artificial diets. Here we present
the use of a neurostimulant, resorcinol, for inducing aphid salivation.
Saliva of potato aphids (Macrosiphum euphorbiae),
maintained on tomato, was collected in resorcinol diet. Salivary proteins
were identified using mass spectrometry and compared with the existing M. euphorbiae salivary proteome collected in water. Comparative
analysis was also performed with existing salivary proteomes from
additional aphid species. Most of the proteins identified in the resorcinol
diet were also present in the water diet and represented proteins
with a plethora of functions in addition to a large number of unknowns.
About half of the salivary proteins were not predicted for secretion
or had canonical secretion signal peptides. We also analyzed the phosphorylation
states of M. euphorbiae salivary proteins and identified
three known aphid effectors, Me_WB01635/Mp1, Me10/Mp58, and Me23 that
carry phosphorylation marks. In addition to insect proteins, tomato
host proteins were also identified in aphid saliva. Our results indicate
that aphid saliva is complex and provides a rich resource for functional
characterization of effectors.