Abstract
SummaryThe plant innate immune system employs plasma membrane‐localized receptors that specifically perceive pathogen/microbe‐associated molecular patterns (PAMPs/MAMPs). This induces a defence response called pattern‐triggered immunity (PTI) to fend off pathogen attack. Commensal bacteria are also exposed to potential immune recognition and must employ strategies to evade and/or suppress PTI to successfully colonize the plant. During plant infection, the flagellum has an ambiguous role, acting as both a virulence factor and also as a potent immunogen as a result of the recognition of its main building block, flagellin, by the plant pattern recognition receptors (PRRs), including FLAGELLIN SENSING2 (FLS2). Therefore, strict control of flagella synthesis is especially important for plant‐associated bacteria. Here, we show that cyclic‐di‐GMP [bis‐(3′‐5′)‐cyclic di‐guanosine monophosphate], a central regulator of bacterial lifestyle, is involved in the evasion of PTI. Elevated cyclic‐di‐GMP levels in the pathogen P seudomonas syringae pv. tomato (P to) DC3000, the opportunist P . aeruginosa PAO1 and the commensal P . protegens Pf‐5 inhibit flagellin synthesis and help the bacteria to evade FLS2‐mediated signalling in N icotiana benthamiana and A rabidopsis thaliana. Despite this, high cellular cyclic‐di‐GMP concentrations were shown to drastically reduce the virulence of P to DC3000 during plant infection. We propose that this is a result of reduced flagellar motility and/or additional pleiotropic effects of cyclic‐di‐GMP signalling on bacterial behaviour.
Highlights
Plants rely on an innate immune system consisting of passive and active defences to resist potential attack by most microbial patho-The molecular events that occur on MAMP recognition have been studied extensively, especially using the flg22/FLAGELLIN SENSING2 (FLS2) and elf18/ EF-TU RECEPTOR (EFR) perception systems
BAK1 is a key co-receptor, mediating full signal activation of downstream responses through auto- and trans-phosphorylation events (Cao et al, 2013; Schulze et al, 2010; Schwessinger et al, 2011; Sun et al, 2013; Wang et al, 2014; Yan et al, 2012).Activation of FLS2 and EFR converges on signalling pathways that share numerous downstream elements and induce an array of defence responses, including reactive oxygen species (ROS) production, callose deposition, stomatal closure and transcriptional reprogramming (Boller and Felix, 2009; Macho and Zipfel, 2014)
We show that high cdG levels in plant-associated Pseudomonas spp. suppress flagellin expression, which correlates with evasion of the FLS2
Summary
The plant innate immune system employs plasma membranelocalized receptors that perceive pathogen/microbeassociated molecular patterns (PAMPs/MAMPs). This induces a defence response called pattern-triggered immunity (PTI) to fend off pathogen attack. Commensal bacteria are exposed to potential immune recognition and must employ strategies to evade and/or suppress PTI to successfully colonize the plant. High cellular cyclic-di-GMP concentrations were shown to drastically reduce the virulence of Pto DC3000 during plant infection. We propose that this is a result of reduced flagellar motility and/or additional pleiotropic effects of cyclic-di-GMP signalling on bacterial behaviour
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
