Skip to main page content
U.S. flag
See More

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2009 Sep;22(9):1069-80.
doi: 10.1094/MPMI-22-9-1069.

The majority of the type III effector inventory of Pseudomonas syringae pv. tomato DC3000 can suppress plant immunity

Ming Guo  1 , Fang Tian, Yashitola Wamboldt, James R Alfano
Affiliations

The majority of the type III effector inventory of Pseudomonas syringae pv. tomato DC3000 can suppress plant immunity

Ming Guo et al. Mol Plant Microbe Interact. 2009 Sep.

Abstract

The Pseudomonas syringae type III protein secretion system (T3SS) and the type III effectors it injects into plant cells are required for plant pathogenicity and the ability to elicit a hypersensitive response (HR). The HR is a programmed cell death that is associated with effector-triggered immunity (ETI). A primary function of P. syringae type III effectors appears to be the suppression of ETI and pathogen-associated molecular pattern-triggered immunity (PTI), which is induced by conserved molecules on microorganisms. We reported that seven type III effectors from P. syringae pv. tomato DC3000 were capable of suppressing an HR induced by P. fluorescens(pHIR11) and have now tested 35 DC3000 type III effectors in this assay, finding that the majority of them can suppress the HR induced by HopA1. One newly identified type III effector with particularly strong HR suppression activity was HopS2. We used the pHIR11 derivative pLN1965, which lacks hopA1, in related assays and found that a subset of the type III effectors that suppressed HopA1-induced ETI also suppressed an ETI response induced by AvrRpm1 in Arabidopsis thaliana. A. thaliana plants expressing either HopAO1 or HopF2, two type III effectors that suppressed the HopA1-induced HR, were reduced in the flagellin-induced PTI response as well as PTI induced by other PAMPs and allowed enhanced in planta growth of P. syringae. Collectively, our results suggest that the majority of DC3000 type III effectors can suppress plant immunity. Additionally, the construct pLN1965 will likely be a useful tool in determining whether other type III effectors or effectors from other types of pathogens can suppress either ETI, PTI, or both.

PubMed Disclaimer

Figures

Fig. 1
Fig. 1
The Pseudomonas syringae pv. tomato DC3000 type III effector HopS2 can suppress the HopA1-dependent hypersensitive response (HR) elicited by P. fluorescens(pHIR11). P. fluorescens(pHIR11) strains carrying a control vector, pLN1624 (pshcS2 + hopS2) containing hopS2 with its type III chaperone gene shcS2, or pLN452 (phopS2) expressing hopS2 alone were infiltrated into Nicotiana tabacum cv. Xanthi leaves at a cell density of 1 × 108 or 2 × 107 cells/ml. The leaves were evaluated for production of a HR and were photographed after 48 h. The ability of HopS2 to suppress the HopA1-dependent HR was dependent on the presence of its cognate type III chaperone ShcS2. This experiment was repeated 10 times with similar results.
Fig. 2
Fig. 2
Pseudomonas syringae type III effectors AvrRpm1 and AvrRpt2 can suppress the HopA1-dependent hypersensitive response (HR) in tobacco. P. fluorescens(pHIR11) strains carrying constructs pVSP61::avrRpm1 (pavrRpm1), pLN1906 (pavrRpt2), or a vector control were infiltrated into Nicotiana tabacum cv. Xanthi leaves. P. fluorescens(pHIR11) carrying a vector control elicits a HR at the rate of 1 × 108 and 2 × 107 cells/ml, whereas the HR is suppressed in the P. fluorescens(pHIR11) strains expressing avrRpm1 or avrRpt2, indicating that AvrRpm1 and AvrRpt2 can suppress the HopA1-dependent HR. Tobacco leaves were evaluated for the development of the HR and were photographed 48 h after infiltration.
Fig. 3
Fig. 3
Modification of the Pseudomonas fluorescens(pHIR11) system shows that a subset of type III effectors that are class I suppressors can also suppress the AvrRpm1-dependent effector-triggered immunity. A, Arabidopsis thaliana ecotype Col-0 leaves were infiltrated with P. fluorescens(pLN1965)(pavrRpm1) strains carrying an empty vector (pBBR1MCS5) or constructs that expressed different type III effectors known to suppress the HopA1-dependent hypersensitive response (HR). In each case, the type III effector was also capable of suppressing the AvrRpm1-dependent HR. B, A. thaliana ecotype Col-0 leaves were infiltrated with P. fluorescens(pLN1965)(pavrRpm1) strains carrying an empty vector (pBBR1MCS5) or constructs that expressed different type III effectors known to suppress the HopA1-dependent HR. Callose deposition induced by AvrRpm1 was suppressed in strains that expressed a type III effector known to suppress the HopA1-dependent HR. Leaves were microscopically viewed for evidence of callose deposition 16 h after infiltration.C, Callose deposits shown in B were quantified, and the average of 20 views of fields from five leaves and standard errors are shown.
Fig. 4
Fig. 4
Type III effectors belonging to the class I suppressor group can suppress callose deposition induced by pathogen-associated molecular pattern (PAMP)–triggered immunity. A, Arabidopsis thaliana ecotype Col-0 leaves were infiltrated with Pseudomonas fluorescens(pLN1965) strains carrying an empty vector (pBBR1MCS5) or constructs that expressed different type III effectors known to suppress the HopA1-dependent hypersensitive response. These type III effectors can suppress callose deposition triggered by PAMPs presented by P. fluorescens(pLN1965). Leaves were microscopically viewed for evidence of callose deposition 16 h after infiltration. B, Callose deposits shown in A were quantified, and the average of 20 views of fields from five leaves is shown. Each experiment was repeated three times with similar results, and the standard errors are indicated in the bar graphs.
Fig. 5
Fig. 5
Transgenic Arabidopsis thaliana plants expressing the HopAO1 or HopF2 type III effectors were reduced in pathogen-associated molecular pattern–triggered callose deposition. A, Callose deposition was visualized in wild-type A. thaliana Col-0 plants or in plants expressing HopAO1 hemagglutinin (HA) or HopF2-HA 16 h after treatment with flg22 or flg22At, an inactive peptide from Agrobacterium flagellin. Immunoblots were carried out using anti-HA antibody on leaf tissue samples from plants used in the experiment, to confirm that HopAO1-HA and HopF2-HA were produced. B, Callose deposition in plants depicted in A was quantified by counting the number of callose foci per field of view. C, Callose deposition induced by a DC3000 hrcC mutant (defective in the ype III protein secretion system) or a DC3000 hrcC fliR (defective in flagellar biogensis) double mutant was quantified as noted in B. The numbers of callose foci in B and C are averages of 20 fields of view (four views per leaf samples) and standard errors are shown. All experiments were repeated three times with similar results.
Fig. 6
Fig. 6
Transgenic Arabidopsis thaliana plants expressing HopAO1 or HopF2 are more susceptible to Pseudomonas syringae and a type III–defective mutant than is wild-type Arabidopsis. A, A. thaliana Col-0 plants were spray-inoculated with P. syringae pv. tomato DC3000. DC3000 was able to grow to higher levels in plants expressing HopAO1 or HopF2 than in A. thaliana Col-0. B, A. thaliana Col-0 plants were pretreated with 1 µM flg22, and after 16 h, were spray-inoculated with DC3000. Overall, the pretreatment with flg22 reduced bacterial growth comp plants ared with non-pretreated plants in A. DC3000 grew to higher levels on plants expressing HopAO1 and HopF2 than it did on A. thaliana Col-0. C, A. thaliana were spray-inoculated with a DC3000 hrcC. The growth of the DC3000 hrcC mutant was enhanced in transgenic plants expressing HopAO1 or HopF2 as compared with wild-type Col-0. In all experiments, plants were inoculated at a cell density of 2 × 108 cells/ml, and bacteria were enumerated at days 0 and 4.
See this image and copyright information in PMC

References

    1. Abramovitch RB, Martin GB. AvrPtoB: A bacterial type III effector that both elicits and suppresses programmed cell death associated with plant immunity. FEMS (Fed. Eur. Microbiol. Soc.) Microbiol. Lett. 2005;245:1–8. - PubMed
    1. Abramovitch RB, Anderson JC, Martin GB. Bacterial elicitation and evasion of plant innate immunity. Nat. Rev. Mol. Cell Bio. 2006;7:601–611. - PMC - PubMed
    1. Adam L, Somerville SC. Genetic characterization of five powdery mildew disease resistance loci in Arabidopsis thaliana. Plant J. 1996;9:341–356. - PubMed
    1. Alfano JR, Collmer A. The type III (Hrp) secretion pathway of plant pathogenic bacteria: Trafficking harpins, Avr proteins, and death. J. Bacteriol. 1997;179:5655–5662. - PMC - PubMed
    1. Alfano JR, Bauer DW, Milos TM, Collmer A. Analysis of the role of the Pseudomonas syringae pv. syringae HrpZ harpin in elicitation of the hypersensitive response in tobacco using functionally nonpolar hrpZ deletion mutants, truncated HrpZ fragments, and hrmA mutations. Mol. Microbiol. 1996;19:715–728. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources