The LetA‐RsmYZ‐CsrA regulatory cascade, together with RpoS and PmrA, post‐transcriptionally regulates stationary phase activation of Legionella pneumophila Icm/Dot effectors

Abstract

SummaryLegionella pneumophila utilize the Icm/Dot type-IV secretion system to translocate effector proteins into host cells. Some of these effectors were shown before to be regulated at the transcriptional level by the PmrAB and CpxRA two-component systems. In addition, the stationary phase-related regulators LetA and CsrA, which are both members of the same posttranscriptional regulatory cascade, were shown to be involved in L. pneumophila virulence. In this report, we identified two small non-coding RNAs which are part of the LetA-CsrA regulatory cascade and three effector-encoding genes which are directly controlled by this regulatory system. We found that the small non-coding RNAs RsmY and RsmZ, were upregulated by LetA at stationary phase, and relieve the repression of CsrA from its target genes. The three effector-encoding genes were found to be posttranscriptionally upregulated at stationary phase and to contain CsrA regulatory elements that were found to be essential for their stationary phase activation. In addition, rsmY and rsmZ were found to be regulated by the RpoS sigma-factor and the csrA encoding gene was found to be regulated by PmrA. Our results demonstrate that L. pneumophila effectors are regulated at both the transcriptional and the post-transcriptional levels by a complicated regulatory network.

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…UvrY directly binds to the csrB and csrC promoters in vitro (63,73), yet the details of its transcription activation mechanism have not been determined. Though Csr/Rsm-inhibitory sRNAs of various species may bear little sequence identity outside the CsrA/RsmA binding sequences, their expression in most cases is highly dependent on the UvrY ortholog (73)(74)(75)(76)(77)(78)(79). Whether UvrY and its various orthologs have additional regulatory roles remains to be determined, although the GacA protein of P. aeruginosa was proposed only to regulate Rsm sRNA transcription (80).…”

“…This T4SS secretes approximately 300 effectors (207)(208)(209)(210) and is important for intracellular replication, organelle trafficking, and effector-dependent egress from the host cell (204,(211)(212)(213). CsrA regulates the expression of at least 26 of 44 tested Dot/Icm effector genes and at least three genes encoding regulatory proteins that influence Dot/Icm expression (78,214). Though many of these putative CsrA targets appear to contain multiple CsrA binding sites, in vitro CsrA binding experiments in L. pneumophila have yet to be reported.…”

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

“…LetA seems to be involved in the expression of two small regulatory RNAs (RsmY and RsmZ) that are substrates for the RNA-binding protein CsrA. As a consequence of RsmY and RsmZ binding, CsrA is released from its target mRNAs inducing the expression of transmissive traits (Rasis and Segal 2009;Sahr et al 2009;Zusman et al 2002;Molofsky and Swanson 2003). Flagellar gene expression is thought to be regulated by this CsrA-dependent pathway.…”

Large-scale identification and translocation of type IV secretion substrates by Coxiella burnetii

“…We hypothesized that similar interactions occur between Coxiella T4SS substrates and its DotF protein. In addition, in L. pneumophila, expression of some effectors is coregulated with some dot/icm genes, and the genetic elements of such regulatory circuits have been identified (16,17). Finally, it has been shown that proteins with motifs and structural features specific for eukaryotic cells are more likely to be effectors (7,14).…”