Mudgett, Mary Beth , Kim, Jung-Gun , Keegan, Mark .
Xanthomonas XopD TTSS effector is a repressor of hormone-induced transcriptional responses.
XopD, a type III effector protein from Xanthomonas campestris pv. vesicatoria (Xcv), the causal agent of bacterial spot disease on tomato and pepper, encodes a cysteine protease which cleaves small ubiquitin-related modifier (SUMO) precursors and removes SUMO from SUMO-conjugated proteins. After delivery into the plant cell, XopD localizes to subnuclear foci indicating that the major host targets are likely nuclear sumoylated protein(s). To analyze the potential role of XopD in Xcv virulence, we created a xopD null strain where the entire ORF was deleted by marker exchange mutagenesis. Interestingly, growth of the Xcv xopD deletion strain was significantly reduced in susceptible VF36 tomatoes; however leaf senescence appeared more rapidly in the infected tissue compared to leaves infected with wild type Xcv. Only the wild type gene complemented the Xcv xopD mutant phenotype. An inactive catalytic core protease mutant xopD(C470A) did not, indicating that XopD protease activity is required to suppress leaf senescence during infection. Agrobacterium-mediated transient expression of XopD in Nicotiana benthamiana repressed PDF1.2 gene transcription induced by methyl jasmonate treatment revealing that XopD can suppress gene expression in planta. We are currently testing whether XopD is altering hormone biosynthesis and/or perception by directly or indirectly regulating gene expression during infection. We will present the data from these studies and propose possible biochemical mechanisms by which XopD can delay leaf senescence. Our working hypothesize is that XopD may repress host-induced senescence to save nutrients and/or an ecological niche for the growing pathogen.
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1 - Stanford University, Biological Sciences, 371 Serra Mall, 228A Gilbert Bioscience, Stanford, CA, 94305-5020, USA
2 - Stanford University, Biological Sciences
3 - Menlo School
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM