The phc Quorum-Sensing System in Ralstonia solanacearum Species Complex

Abstract

Ralstonia solanacearum species complex (RSSC) strains are devastating plant pathogens distributed worldwide. The primary cell density–dependent gene expression system in RSSC strains is phc quorum sensing (QS). It regulates the expression of about 30% of all genes, including those related to cellular activity, primary and secondary metabolism, pathogenicity, and more. The phc regulatory elements encoded by the phcBSRQ operon and phcA gene play vital roles. RSSC strains use methyl 3-hydroxymyristate (3-OH MAME) or methyl 3-hydroxypalmitate (3-OH PAME) as the QS signal. Each type of RSSC strain has specificity in generating and receiving its QS signal, but their signaling pathways might not differ significantly. In this review, I describe the genetic and biochemical factors involved in QS signal input and the regulatory network and summarize control of the phc QS system, new cell–cell communications, and QS-dependent interactions with soil fungi. Expected final online publication date for the Annual Review of Microbiology, Volume 77 is September 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A study on twitching motility dynamics in Ralstonia solanacearum microcolonies by live imaging

“…A future study on this aspect is likely to reveal interesting aspects of bacterial behavior in the bacterial colony, which might be attributed to either quorum sensing and/or twitching motility. Therefore, the creation of mutation in genes such as the phcB and phcS , which is responsible for quorum sensing [27] or the pilT , which is responsible for the formation of TFP [15] in R. solanacearum F1C1 would help us gain more insights into the apparent effect that quorum sensing and/or twitching motility has upon the shape of R. solanacearum F1C1 microcolonies.…”

Development of a tomato xylem-mimicking microfluidic system to study Ralstonia pseudosolanacearum biofilm formation

“…The adhesin RadA, together with RcpA and RcpB, allowed for efficient bacterial attachment to abiotic and root surfaces, as well as contributed to bacterial fitness in tomato stems (Carter et al, 2023). Inside the tomato stems, Rps lost its flagellar motility (Meng et al, 2011;Kai, 2023) to form complex biofilm composed of EPS and extracellular DNA (Tran et al, 2016), although a subpopulation of Rps might retain motility as a means to disperse from mature biofilm. It was also speculated that the spread of Rs in xylem vessels was mainly due to its twitching motility mediated by type IV pili (Kang et al, 2002;Wairuri et al, 2012;Siri et al, 2014).…”

Positive regulation of the PhcB neighbouring regulator PrhX on expression of the type III secretion system and pathogenesis in Ralstonia solanacearum

“…In R. solanacearum , all infection steps from the soil into xylem vessels are globally controlled by the quorum‐sensing (QS) system, encoded by the phcBSR operon and phcA genes. The QS system regulates the expression of 30% of R. solanacearum genes, controlling processes including cellular activity, primary and secondary metabolism, and EPS production (Genin & Denny, 2012 ; Kai, 2023 ). The R. solanacearum QS signal has been identified as 3‐hydroxypalmitate methyl ester or 3‐hydroxymyristate methyl ester, which is biosynthesized by the methyltransferase PhcB (Flavier et al., 1997 ; Kai et al., 2015 ).…”

“…At a low cell density in soil and at the root surface at the leading edge of infection, PhcA exhibits little regulatory function, which might be optimized to survive in nutrient‐poor environmental habitats or to grow rapidly during early invasion stages. At the high cell density within host xylem vessels, PhcA exhibits abundant regulatory function, resulting in the production of multiple virulence factors and inhibition of the production of survival/invasion factors (Kai, 2023 ; Khokhani et al., 2017 ; Schell, 2000 ).…”

“…Although hrp gene expression has been demonstrated to be controlled by several regulators, such as PrhN, PrhO, PrhP, TapV, and CysB, the exact molecular mechanism remains to be fully elucidated (Hikichi et al., 2017 ; Valls et al., 2006 ). Moreover, hrp gene regulation by the PhcB–PhcA QS system remains to be fully understood (Genin & Denny, 2012 ; Kai, 2023 ). In the present study, we focused on the transcriptional regulator gene rsc2734 , hereafter named prhX , which is located 597 bp upstream of the phcB operon (Salanoubat et al., 2002 ) (Figure S1 ).…”