MEDIATOR SUBUNIT16 is required for plant resistance to Turnip mosaic virus and its aphid vector

Mediator is a multiprotein complex that acts as a transcription activator or repressor in eukaryotes, depending on protein subunit and interacting partner. One of mediator’s subunits, MEDIATOR SUBUNIT16 (MED16), was previously shown to regulate ethylene (ET)/jasmonic acid (JA)-dependent defense responses against necrotrophic pathogens in Arabidopsis thaliana. In this study we show that MED16 is also required for resistance to Turnip mosaic virus (TuMV), an important pathogen of over 300 plant species, and its primary aphid vector, the green peach aphid (Myzus persicae). Using bioinformatics, qRT-PCR, Arabidopsis mutants, and epitope-tagged complementation we demonstrate that the Arabidopsis MED16 protein is cleaved and MED16-dependent defense responses are compromised in plants infected with TuMV.  NIa-Pro cleavage sites were also found in MED16 protein of Nicotiana benthamiana and Solanum lycopersicum, suggesting that during TuMV infection, NIa-Pro may target MED16 in plants to suppress downstream ethylene defenses, leading to increased aphid fecundity and virus performance.