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IN BRIEF

Effector XopD Suppresses Tissue Degeneration in Xanthomonas-Infected Tomato Leaves

Science Editor

jmach{at}aspb.org

Some plant pathogens deploy dozens of effector proteins through the type III secretion apparatus into host cells. These effectors manipulate host basal defenses and metabolism to the advantage of the pathogen, a process essential for pathogenesis (reviewed in Mudgett 2005; Grant et al., 2006). Effectors can also betray the presence of the pathogen, triggering robust plant defense responses that other proteins in the suite of effectors attempt to suppress at several key points. For example, several effectors diminish salicylic acid (SA) signaling by activating jasmonic acid signaling, which is antagonistic to the SA pathways. Pathogen type III effectors also affect host programmed cell death and ethylene signaling, suppress cell wall defenses, and perturb other defense signaling.

In the absence of pathogen recognition and effective host defense responses, plants are susceptible to pathogen colonization, which results in tissue degeneration, including chlorosis and necrotic cell death. Pathogen effectors are key to controlling the severity of host responses to infection. Kim et al. (pages 1915–1929) examined the type III effector XopD in pathogenesis of tomato by Xanthomonas campestris pathovar vesicatoria (Xcv). XopD is a Cys protease that can process the precursor of SUMO, the small ubiquitin-related modifier, or remove SUMO from other proteins. SUMO regulation is implicated in multiple responses, including repression of transcription. Consistent with this, XopD localizes to foci within the plant nucleus. The authors examined the role of XopD in Xcv pathogenesis by studying the phenotype of an Xcv strain carrying a deletion of XopD (Xcv xopD). Tomato leaves infected with Xcv xopD showed reduced pathogen growth, earlier onset of chlorosis and necrosis (see figure ), and upregulation of senescence-associated genes. Genetic removal of SA from the host plant allowed Xcv xopD to grow as well as wild-type Xcv, but did not change the premature onset of symptoms. Structure-function analysis showed that XopD nonspecific DNA binding activity, SUMO protease activity, and EAR motifs (associated with transcriptional repression) are essential to suppress symptom development late in infection. Consistent with XopD's role in modulating senescence-associated gene expression, transient expression of XopD in Nicotiana benthamiana showed that XopD could repress induction from pathogenesis-related promoters by SA and methyl jasmonate.

View larger version (44K): [in this window] [in a new window] [as a PowerPoint slide]   Tomato leaves infected with Xcv carrying wild-type XopD (top) show reduced disease symptoms compared with leaves infected with Xcv carrying a XopD deletion mutation (bottom). Leaves are shown 10 d (left) and 12 d (right) after infection. (Note: The holes were punched from the leaves for experimental sampling of bacterial titer.)

Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.108.200710

REFERENCES

Grant, S.R., Fisher, E.J., Chang, J.H., Mole, B.M., and Dangl, J.L. (2006). Subterfuge and manipulation: Type III effector proteins of phytopathogenic bacteria. Annu. Rev. Microbiol. 60: 425–449.[CrossRef][ISI][Medline]

Kim, J.-G., Taylor, K.W., Hotson, A., Keegan, M., Schmelz, E.A., and Mudgett, M.B. (2008). XopD SUMO protease affects host transcription, promotes pathogen growth, and delays symptom development in Xanthomonas-infected tomato leaves. Plant Cell 20: 1915–1929.[Abstract/Free Full Text]

Mudgett, M.B. (2005). New insights to the function of phytopathogenic bacterial type III effectors in plants. Annu. Rev. Plant Biol. 56: 509–531.[CrossRef][Medline]

Related articles in Plant Cell:

XopD SUMO Protease Affects Host Transcription, Promotes Pathogen Growth, and Delays Symptom Development in Xanthomonas-Infected Tomato Leaves

Jung-Gun Kim, Kyle W. Taylor, Andrew Hotson, Mark Keegan, Eric A. Schmelz, and Mary Beth Mudgett
Plant Cell 2008 20: 1915-1929. [Abstract] [Full Text]  

This Article Full Text (PDF) All Versions of this Article: 20/7/1731    most recent tpc.108.200710v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Google Scholar Articles by Mach, J. PubMed PubMed Citation Articles by Mach, J. Agricola Articles by Mach, J.