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Speck Disease (speck + disease)
Selected AbstractsPopulation Dynamics of Pseudomonas syringae pv. tomato Strains on Tomato Cultivars Rio Grande and Rio Grande- Pto under Field ConditionsJOURNAL OF PHYTOPATHOLOGY, Issue 4 2009David K. Willis Abstract We examined the effects of the Pto resistance locus on the population dynamics of Pseudomonas syringae pv. tomato (Pst) strains in field experiments with the nearly isogenic tomato lines Rio Grande (RG, susceptible to Pst races 0 and 1) and Rio Grande-Pto (RG-Pto, resistant to Pst race 0, susceptible to Pst race 1). Pst strain SM78-1Smr (race 0) grew well under field conditions and caused ample bacterial speck disease on susceptible RG plants. In contrast, strain DC3000 failed to establish large populations when inoculated onto field grown RG plants. Mean population sizes of SM78-1Smr were 4,5 orders of magnitude larger on RG than RG-Pto plants indicating that RG-Pto plants were highly effective in attenuating pathogen population development. Most of the sampled leaflets from RG-Pto field plots harboured small numbers of SM78-1Smr. However, population sizes SM78-1Smr as large as 105,106 CFU were found on a few leaflets. Bacteria isolated from these leaflets had phenotypes characteristic of Pst race 1 strains. In growth chamber plant assays, the bacterial strains grew well and caused typical speck lesions on RG-Pto plants. The strains appeared to be race-shift mutants of SM SM78-1Smr. Interestingly, results from DNA hybridization experiments demonstrated that the race-shift mutants were deleted for the avirulence gene, avrPto but not for avrPtoB. [source] The N-terminal region of Pseudomonas type III effector AvrPtoB elicits Pto-dependent immunity and has two distinct virulence determinantsTHE PLANT JOURNAL, Issue 4 2007Fangming Xiao Summary Resistance to bacterial speck disease in tomato is activated by the physical interaction of the host Pto kinase with either of the sequence-dissimilar type III effector proteins AvrPto or AvrPtoB (HopAB2) from Pseudomonas syringae pv. tomato. Pto-mediated immunity requires Prf, a protein with a nucleotide-binding site and leucine-rich repeats. The N-terminal 307 amino acids of AvrPtoB were previously reported to interact with the Pto kinase, and we show here that this region (AvrPtoB1-307) is sufficient for eliciting Pto/Prf-dependent immunity against P. s. pv. tomato. AvrPtoB1-307 was also found to be sufficient for a virulence activity that enhances ethylene production and increases growth of P. s. pv. tomato and severity of speck disease on susceptible tomato lines lacking either Pto or Prf. Moreover, we found that residues 308,387 of AvrPtoB are required for the previously reported ability of AvrPtoB to suppress pathogen-associated molecular patterns-induced basal defenses in Arabidopsis. Thus, the N-terminal region of AvrPtoB has two structurally distinct domains involved in different virulence-promoting mechanisms. Random and targeted mutagenesis identified five tightly clustered residues in AvrPtoB1-307 that are required for interaction with Pto and for elicitation of immunity to P. s. pv. tomato. Mutation of one of the five clustered residues abolished the ethylene-associated virulence activity of AvrPtoB1-307. However, individual mutations of the other four residues, despite abolishing interaction with Pto and avirulence activity, had no effect on AvrPtoB1-307 virulence activity. None of these mutations affected the basal defense-suppressing activity of AvrPtoB1-387. Based on sequence alignments, estimates of helical propensity, and the previously reported structure of AvrPto, we hypothesize that the Pto-interacting domains of AvrPto and AvrPtoB1-307 have structural similarity. Together, these data support a model in which AvrPtoB1-307 promotes ethylene-associated virulence by interaction not with Pto but with another unknown host protein. [source] Crystallization and preliminary crystallographic analysis of the ADP-ribosyltransferase HopU1ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2010Yan Lin Several Gram-negative pathogens of plants and animals and some eukaryotic associated bacteria use type III protein-secretion systems (T3SSs) to deliver bacterial virulence-associated `effector' proteins directly into host cells. HopU1 is a type III effector protein from the plant pathogen Pseudomonas syringae, which causes plant bacterial speck disease. HopU1 quells host immunity through ADP-ribosylation of GRP7 as a substrate. HopU1 has been reported as the first ADP-ribosyltransferase virulence protein to be identified in a plant pathogen. Although several structures of ADP-ribosyltransferases have been determined to date, no structure of an ADP-ribosyltransferase from a plant pathogen has been determined. Here, the protein expression, purification, crystallization and preliminary crystallographic analysis of HopU1 are reported. Diffracting crystals were grown by hanging-drop vapour diffusion using polyethylene glycol 10,000 as a precipitant. Native and SAD data sets were collected using native and selenomethionine-derivative HopU1 crystals. The diffraction pattern of the crystal extended to 2.7,Å resolution using synchrotron radiation. The crystals belonged to space group P43, with unit-cell parameters a = 92.6, b = 92.6, c = 101.6,Å. [source] | ||||||||||