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Plant Immunity Directly or Indirectly Restricts the Injection of Type III Effectors by the Pseudomonas
 

Summary: Plant Immunity Directly or Indirectly Restricts the
Injection of Type III Effectors by the Pseudomonas
syringae Type III Secretion System1[W][OA]
Emerson Crabill, Anna Joe, Anna Block, Jennifer M. van Rooyen, and James R. Alfano*
Center for Plant Science Innovation (E.C., A.J., A.B., J.M.v.R., J.R.A.), School of Biological Sciences (E.C.,
A.J., J.M.v.R.), and Department of Plant Pathology (A.B., J.R.A.), University of Nebraska, Lincoln, Nebraska
685880660
Plants perceive microorganisms by recognizing microbial molecules known as pathogen-associated molecular patterns
(PAMPs) inducing PAMP-triggered immunity (PTI) or by recognizing pathogen effectors inducing effector-triggered immunity
(ETI). The hypersensitive response (HR), a programmed cell death response associated with ETI, is known to be inhibited by
PTI. Here, we show that PTI-induced HR inhibition is due to direct or indirect restriction of the type III protein secretion
system's (T3SS) ability to inject type III effectors (T3Es). We found that the Pseudomonas syringae T3SS was restricted in its
ability to inject a T3E-adenylate cyclase (CyaA) injection reporter into PTI-induced tobacco (Nicotiana tabacum) cells. We
confirmed this restriction with a direct injection assay that monitored the in planta processing of the AvrRpt2 T3E. Virulent
P. syringae strains were able to overcome a PAMP pretreatment in tobacco or Arabidopsis (Arabidopsis thaliana) and continue to
inject a T3E-CyaA reporter into host cells. In contrast, ETI-inducing P. syringae strains were unable to overcome PTI-induced
injection restriction. A P. syringae pv tomato DC3000 mutant lacking about one-third of its T3E inventory was less capable of
injecting into PTI-induced Arabidopsis plant cells, grew poorly in planta, and did not cause disease symptoms. PTI-induced
transgenic Arabidopsis expressing the T3E HopAO1 or HopF2 allowed higher amounts of the T3E-CyaA reporter to be injected
into plant cells compared to wild-type plants. Our results show that PTI-induced HR inhibition is due to direct or indirect

  

Source: Alfan, James R. - Department of Plant Pathology, University of Nebraska-Lincoln

 

Collections: Biology and Medicine