The Salmonella effector protein SpvC, a phosphothreonine lyase is functional in plant cells

Abstract

Salmonella is one of the most prominent causes of food poisoning and growing evidence indicates that contaminated fruits and vegetables are an increasing concern for human health. Successful infection demands the suppression of the host immune system, which is often achieved via injection of bacterial effector proteins into host cells. In this report we present the function of Salmonella effector protein in plant cell, supporting the new concept of trans-kingdom competence of this bacterium. We screened a range of Salmonella Typhimurium effector proteins for interference with plant immunity. Among these, the phosphothreonine lyase SpvC attenuated the induction of immunity-related genes when present in plant cells. Using in vitro and in vivo systems we show that this effector protein interacts with and dephosphorylates activated Arabidopsis Mitogen-activated Protein Kinase 6 (MPK6), thereby inhibiting defense signaling. Moreover, the requirement of Salmonella SpvC was shown by the decreased proliferation of the ΔspvC mutant in Arabidopsis plants. These results suggest that some Salmonella effector proteins could have a conserved function during proliferation in different hosts. The fact that Salmonella and other Enterobacteriaceae use plants as hosts strongly suggests that plants represent a much larger reservoir for animal pathogens than so far estimated.

Salmonella Persistence in Tomatoes Requires a Distinct Set of Metabolic Functions Identified by Transposon Insertion Sequencing

“…SPI-1 and SPI-2 may also be needed to subvert immunity, which may become more important as more bacterial cell numbers are invading and therefore activating the plant's immune response. While Salmonella effectors were shown to be functional when directly transformed into cell wall-less plant protoplasts (22), it is not clear how they are delivered across the plant cell wall.…”

“…Strains lacking SPI-1 and SPI-2 T3SSs had reduced proliferation in Arabidopsis thaliana leaves, failed to suppress the plant immune response against bacteria, and were required for the chlorotic appearance of plants (22). The effector spvC carried by the virulence plasmid suppressed inducible plant defenses when it was directly transformed into Arabidopsis protoplasts (22). Salmonella strains lacking SPI-1 T3SS induced a stronger response from plants, suggesting that this pathogenicity island represses plant immunity (23).…”

“…While the contribution of the Salmonella genes that generally impact animal virulence was characterized during the attachment and colonization of alfalfa sprouts (6), the involvement of the more dedicated virulence-related functions, such as type III secretion systems (T3SS), and their regulators encoded on the Salmonella pathogenicity islands (SPIs) remains controversial. Strains lacking SPI-1 and SPI-2 T3SSs had reduced proliferation in Arabidopsis thaliana leaves, failed to suppress the plant immune response against bacteria, and were required for the chlorotic appearance of plants (22). The effector spvC carried by the virulence plasmid suppressed inducible plant defenses when it was directly transformed into Arabidopsis protoplasts (22).…”

Molecular Mechanisms Used by Salmonella to Evade the Immune System

“…(Mazurkiewicz et al, 2008). Interestingly, during the interaction of Salmonella with the plant model Arabidopsis, SpvC interacts with and dephosphorylates activated MAPK6 to inhibit defence signalling (Neumann et al, 2014). This suggests that some Salmonella effector proteins could have a conserved function during proliferation in different hosts.…”

Meeting report: Adaptation and communication of bacterial pathogens

“…4). 35 Stephane Genin (Laboratoire des Interactions Plantes-Microorganismes, Castanet-Tolosan, France) presented an evolution experiment in which the phenotypic and genotypic changes happening to the broad-host range quarantine plant pathogenic bacterium Ralstonia solanacearum during its adaptation to tolerant, resistant or susceptible plant hosts, was followed for 350 generations. New isolates were then tested in challenge experiments against the ancestor in different hosts.…”