Figure 2.

Bacterial suppressors of silencing interfere with miRNA-mediated host defense. Bacterial infection is initially perceived by the plant cell through PAMPs, as in the recognition of flagellin by the plant receptor FLS2 illustrated here. This triggers a signaling cascade that activates transcription of primary-microRNAs (pri-miRNAs) from the plant genome, which are then processed into mature miRNAs (red line). miRNA is bound by the protein Argonaute1 (light blue) and the miRNA-Argonaute1 complex silences specific mRNAs, enhancing resistance to the pathogen (PTI). The pathogen injects numerous effector proteins (orange shapes) into the host cell in an attempt to reprogram the cell to become susceptible to the pathogen. Voinnet and colleagues [4] recently identified some of these effector proteins as bacterial suppressors of silencing (BSRs), which inhibit the miRNA pathway at multiple stages to inhibit host defense.