Transcriptomic screening of salivary proteins in the bean bug Riptortus pedestris

Here, we analyzed, for the first time to our knowledge, the transcriptomes of salivary glands of R. pedestris males, females and nymphs. Their transcriptomes each showed about 28,000 unigenes, in which about 40 % had the open reading frames (ORFs) and therefore the predicted proteins were obtained. Overall, their transcripts are similar with a high proportion involved in protein biosynthesis and transport, suggesting that the saliva glands produce a rich repertoire of proteins. However, nymphs still expressed thousands of genes in different levels compared to that by adults, indicating that they may use some salivary proteins with specific preferences. We found about 800 proteins with secretion signal peptides, and they are likely to be secreted from salivary glands to saliva and thus have a higher probability as effectors that regulate plant defenses. Over 20 proteins have a similarity (over 30 %) with the reported hemipteran effectors, such as catalases, peroxiredoxins, metalloproteases, calcium-binding proteins and DNases etc. How the effector candidates might modulate plant defenses was discussed. We also found hundreds of proteases, lipases and esterases in the salivary glands that are probably used to digest proteins and oils in beans. The datasets reported here represent an important first step in identifying candidate effectors of R. pedestris.