Abstract
Argonaute (AGO) proteins are critical components of RNA silencing pathways that bind small RNAs and mediate gene silencing at their target sites. We found that Arabidopsis AGO2 is highly induced by the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Further genetic analysis demonstrated that AGO2 functions in antibacterial immunity. One abundant species of AGO2-bound small RNA is miR393b(∗), which targets a Golgi-localized SNARE gene, MEMB12. Pst infection downregulates MEMB12 in a miR393b(∗)-dependent manner. Loss of function of MEMB12, but not SYP61, another intracellular SNARE, leads to increased exocytosis of an antimicrobial pathogenesis-related protein, PR1. Overexpression of miR393b(∗) resembles memb12 mutant in resistance responses. Thus, AGO2 functions in antibacterial immunity by binding miR393b(∗) to modulate exocytosis of antimicrobial PR proteins via MEMB12. Since miR393 also contributes to antibacterial responses, miR393(∗)/miR393 represent an example of a miRNA(∗)/miRNA pair that functions in immunity through two distinct AGOs: miR393(∗) through AGO2 and miR393 through AGO1.