The scaffolding and signalling functions of a localization factor impact polar development

Abstract

Summary In the differentiating alphaproteobacterium Caulobacter crescentus, organelle synthesis at cell poles is critical to forming different progeny after cell division. Co‐ordination of polar organelle synthesis, including pili and holdfast, and flagellum ejection, is mediated in part by the scaffolding protein PodJ. At the time of cell division, PodJ undergoes regulated processing to a short form that persists at the flagellar pole of swarmer cells. This study analyses how PodJ's role in structural and signalling protein localization impacts organelle synthesis. A PodJ mutant with an internal deletion exhibits reduced sensitivity to pili‐tropic phage ΦCbK, resulting from reduced pilA gene expression, which can be linked to altered signalling protein localization. The phage sensitivity defect of a ΔpodJ mutant can be partially suppressed by ectopic pilA expression. Induction of PodJ processing, by manipulation of podJ itself or controlled perP expression, resulted in decreased pilus biogenesis and, when coupled with a podJ mutation that reduced pilA expression, led to complete loss of phage sensitivity. As a whole, the results show that PodJ's scaffolding role for structural and signalling proteins both contribute to flagellar pole organelle development.

Identification of essential alphaproteobacterial genes reveals operational variability in conserved developmental and cell cycle systems

“…), although the reduced swim expansion may be caused in part by the cell filamentation. Many polar developmental defects in C. crescentus can be traced to impacts on CtrA (Stephens et al ., ; Skerker and Shapiro, ; Curtis et al ., ). It may be that deletion of gcrA does not significantly impact the total cell cycle but it may impact CtrA activity enough to result in the defects shown here.…”

The Sinorhizobium meliloti sensor histidine kinase CbrA contributes to free-living cell cycle regulation

“…S. meliloti null mutants for the cpdR1 gene, which in C. crescentus functions downstream of CckA to repress CtrA at the level of stability, grow as filamentous cells containing greater than a 2N genome complement ). In C. crescentus, PodJ is required for polar localization of PleC, and thus podJ mutants display defects in pilus synthesis and flagellar motility (Curtis et al, 2012;Levi & Jenal, 2006;Viollier et al, 2002). Interestingly, pleC is essential in S. meliloti, although there are two nonessential PodJ homologues: PodJ1 and PodJ2 (Fields et al, 2012).…”

Polarity and cell fate asymmetry in Caulobacter crescentus

“…The swarmer pole localization of DivL in predivisional cells also depends, to some extent, on PodJ [50]. However, cells lacking podJ frequently still localize DivL suggesting that other factors may be involved.…”