A Pseudomonas syringae type III effector suppresses cell wall-based extracellular defense in susceptible Arabidopsis plants - PubMed (original) (raw)

A Pseudomonas syringae type III effector suppresses cell wall-based extracellular defense in susceptible Arabidopsis plants

Paula Hauck et al. Proc Natl Acad Sci U S A. 2003.

Abstract

Bacterial effector proteins secreted through the type III secretion system (TTSS) play a crucial role in causing plant and human diseases. Although the ability of type III effectors to trigger defense responses in resistant plants is well understood, the disease-promoting functions of type III effectors in susceptible plants are largely enigmatic. Previous microscopic studies suggest that in susceptible plants the TTSS of plant-pathogenic bacteria transports suppressors of a cell wall-based plant defense activated by the TTSS-defective hrp mutant bacteria. However, the identity of such suppressors has remained elusive. We discovered that the Pseudomonas syringae TTSS down-regulated the expression of a set of Arabidopsis genes encoding putatively secreted cell wall and defense proteins in a salicylic acid-independent manner. Transgenic expression of AvrPto repressed a similar set of host genes, compromised defense-related callose deposition in the host cell wall, and permitted substantial multiplication of an hrp mutant. AvrPto is therefore one of the long postulated suppressors of an salicylic acid-independent, cell wall-based defense that is aimed at hrp mutant bacteria.

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Figures

Fig. 1.

Fig. 1.

Bacterial populations in wild-type Col-0, ein2, and _nahG_transgenic plants. hrcC mutant growth in Col-0 (black bars),ein2 (dark gray bars), and nahG leaves (light gray bars) are shown. DC3000 growth in Col-0 (white bars) is shown for comparison.

Fig. 2.

Fig. 2.

(A) Western blot analysis of AvrPto expression in leaves of wild-type and AvrPto transgenic plants 24 h after spraying with 30 μM dexamethasone. (B) Cluster analysis of the expression profiles of 117 TTSS-regulated genes (colored bars) after DC3000 infection and transgenic expression of AvrPto. Rows I-A and I-B represent DC3000 TTSS-regulated genes from two independent biological replicates (see columns I-A and I-B in Table 2). Rows IV and V represent gene expression in AvrPto-129 and AvrPto-76 transgenic plants, respectively, 24 h after dexamethasone induction (see columns IV and V in Table 2).

Fig. 3.

Fig. 3.

(A) Portions of wild-type and AvrPto transgenic leaves stained with Aniline blue for callose (white dots in these images) after inoculation with the hrcC mutant or DC3000. (Scale bar, 100 μm.) (B) Average number of callose depositions per field of view (0.58 mm2) with SD displayed as error.

Fig. 4.

Fig. 4.

(A) hrcC mutant growth in wild-type (black bars) and AvrPto-76 plants (dark gray bars). DC3000 growth in wild-type (light gray bars) and AvrPto-76 (white bars) plants. (B) hrcC mutant growth in wild-type (black bars) and AvrPto-129 plants (dark gray bars). DC3000 growth in wild-type (light gray bars) and AvrPto-129 plants (white bars).

References

    1. Alfano, J. R. & Collmer, A. (1997) J. Bacteriol. 179 5655-5662. - PMC - PubMed
    1. Lindgren, P. B. (1997) Annu. Rev. Phytopathol. 35 129-152. - PubMed
    1. He, S. Y. (1998) Annu. Rev. Phytopathol. 36 363-392. - PubMed
    1. Cornelis, G. R. & Van Gijsegem, F. (2000) Annu. Rev. Microbiol. 54 735-774. - PubMed
    1. Buttner, D. & Bonas, U. (2002) EMBO J. 21 5313-5322. - PMC - PubMed

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