SseF, a type III effector protein from the mammalian pathogen Salmonella enterica, requires resistance-gene-mediated signalling to activate cell death in the model plant Nicotiana benthamiana.
Type III effector proteins (T3Es) of many Gram-negative pathogenic bacteria manipulate
highly conserved cellular processes, indicating conservation in virulence mechanisms during
the infection of hosts of divergent evolutionary origin.
• In order to identify conserved effector functions, we used a cross-kingdom approach in
which we expressed selected T3Es from the mammalian pathogen Salmonella enterica in
leaves of Nicotiana benthamiana and searched for possible virulence or avirulence pheno-
• We show that the T3E SseF of S. enterica triggers hypersensitive response (HR)-like symp-
toms, a hallmark of effector-triggered immunity in plants, either when transiently expressed
in leaves of N. benthamiana by Agrobacterium tumefaciens infiltration or when delivered by
Xanthomonas campestris pv vesicatoria (Xcv) through the type III secretion system. The
ability of SseF to elicit HR-like symptoms was lost upon silencing of suppressor of G2 allele of
skp1 (SGT1), indicating that the S. enterica T3E is probably recognized by an R protein in
N. benthamiana. Xcv translocating an AvrRpt2–SseF fusion protein was restricted in multipli-
cation within leaves of N. benthamiana. Bacterial growth was not impaired but symptom
development was rather accelerated in a compatible interaction with susceptible pepper
(Capsicum annuum) plants.
• We conclude that the S. enterica T3E SseF is probably recognized by the plant immune
system in N. benthamiana, resulting in effector-triggered immunity.
Üstün, S.; Müller, P.; Palmisano, R.; Hensel, M.; Börnke, F. 2012. SseF, a type III effector protein from the mammalian pathogen Salmonella enterica, requires resistance-gene-mediated signalling to activate cell death in the model plant Nicotiana benthamiana. New Phytologist 194, 1046-1060.