RovC - a novel type of hexameric transcriptional activator promoting type VI secretion gene expression

Abstract

Type VI secretion systems (T6SSs) are complex macromolecular injection machines which are widespread in Gram-negative bacteria. They are involved in host-cell interactions and pathogenesis, required to eliminate competing bacteria, or are important for the adaptation to environmental stress conditions. Here we identified regulatory elements controlling the T6SS4 of Yersinia pseudotuberculosis and found a novel type of hexameric transcription factor, RovC. RovC directly interacts with the T6SS4 promoter region and activates T6SS4 transcription alone or in cooperation with the LysR-type regulator RovM. A higher complexity of regulation was achieved by the nutrient-responsive global regulator CsrA, which controls rovC expression on the transcriptional and post-transcriptional level. In summary, our work unveils a central mechanism in which RovC, a novel key activator, orchestrates the expression of the T6SS weapons together with a global regulator to deploy the system in response to the availability of nutrients in the species' native environment.

The AraC‐type transcription factor TagK is a new player in the signaling cascade that induces the anti‐eukaryotic T6SS of Xanthomonas citri

“…Bacterial secretion systems are sophisticated and specialized multiprotein complexes that require energetically costly mechanisms for their biogenesis and correct assembly across the bacterial cell envelope. In line with this notion, T6SS are generally subjected to tight control at multiple levels, with regulators of gene expression, protein assembly and activity commonly encoded within the T6SS gene clusters (Knittel et al, 2020; Metzger et al, 2016; Mougous et al, 2007; Silverman et al, 2011). We have previously described the function of the X. citri T6SS as an anti‐eukaryotic weapon required for resistance to predation by the bacterivorous amoeba D. discoideum , a common inhabitant of tropical and temperate soil that may have a significant impact on the diversity of bacterial populations in the environment (Bayer‐Santos et al, 2018; Swanson et al, 1999).…”