AGO4, one of the ten AGO proteins in Arabidopsis, is involved in gene silencing at transcriptional level. The general objective of this research is to understand whether AGO4 protein plays a defense role against Myzus persicae (the green peach aphid) infestation. The green peach aphid (GPA), as a generalist sap-sucking insect, is an economically important agricultural pest, which has broad host range among 40 different plant families including important crops like potato, sugar beet, and stone fruits. Understanding the mechanism of AGO4 in the aphid resistance will help us design effective pest control strategies. This study intended to identify potential AGO4-regulated genes in response to GPA infestation. qPCR analyses were performed on GPA fed on ago4 and Col-0 plants. Genes exhibiting different expression patterns between ago4 and Col-0 were selected to study their biological functions. Among 127 aphid response genes, 25 genes were selected and bioassays were performed on 38 selected T-DNA mutant lines. ago4-1 mutant plants showed compromised resistance to GPA. Adult aphids raised on ago4-1 mutants displayed higher fecundity than those raised on wild-type plants. At5g17990, the TRYPTOPHAN BIOSYNTHESIS 1 (TRP1) gene was induced in wild-type plants but decreased in ago4-1 mutant plants after aphid infestation. Moreover, our bioassay experiment indicated that the mutant plants of TRP1 were preferred by GPA, suggesting TRP1 gene could be an aphid resistant gene, possibly regulated by AGO4.
