Document Detail

Characterization of a Ralstonia solanacearum operon required for polygalacturonate degradation and uptake of galacturonic acid.
MedLine Citation:
PMID:  12795379     Owner:  NLM     Status:  MEDLINE    
The bacterial wilt pathogen Ralstonia solanacearum produces three extracellular polygalacturonases (PGs): PehA, PehB, and PehC. All three PGs hydrolyze pectin's polygalacturonic acid backbone, but each releases different reaction products. PehA and PehB contribute significantly to pathogen virulence, probably by facilitating root invasion and colonization. To determine the collective contribution of PGs to virulence and saprophytic survival, we cloned, characterized, and mutated the R. solanacearum pehC gene, which encodes a distinctive monogalacturonate-releasing exo-PG. The virulence of a pehC mutant on tomato was indistinguishable from that of its wild-type parent; thus, this exo-PG alone does not contribute significantly to wilt pathogenesis. Unexpectedly, a completely PG-deficient triple pehA/B/C mutant was slightly more virulent than a pehA/B mutant. PehC may degrade galacturonide elicitors of host defense, thereby protecting the pathogen from plant antimicrobial responses. A galacturonate transporter gene, exuT, is immediately downstream of pehC and the two genes are co-transcribed. It has been hypothesized that galacturonic acid released by PGs from plant cell walls nourishes bacteria during pathogenesis. To separate the pectolytic and nutrient-generating roles of the PGs, we made an exuT mutant, which still produces all three isozymes of PG but cannot uptake PG degradation products. This exuT mutant had wild-type virulence on tomato, demonstrating that metabolism of galacturonic acid does not contribute significantly to bacterial success inside the plant.
Enid T González; Caitilyn Allen
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Molecular plant-microbe interactions : MPMI     Volume:  16     ISSN:  0894-0282     ISO Abbreviation:  Mol. Plant Microbe Interact.     Publication Date:  2003 Jun 
Date Detail:
Created Date:  2003-06-10     Completed Date:  2003-09-26     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  9107902     Medline TA:  Mol Plant Microbe Interact     Country:  United States    
Other Details:
Languages:  eng     Pagination:  536-44     Citation Subset:  IM    
Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison 53706, USA.
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MeSH Terms
Amino Acid Sequence
Bacterial Proteins / genetics*,  metabolism
DNA, Bacterial / chemistry,  genetics,  isolation & purification
Glycoside Hydrolases / genetics*,  metabolism
Gram-Negative Aerobic Rods and Cocci / genetics*,  metabolism,  pathogenicity
Hexuronic Acids / metabolism*
Membrane Proteins / genetics,  metabolism
Molecular Sequence Data
Operon / genetics*
Pectins / metabolism*
Sequence Analysis, DNA
Grant Support
Reg. No./Substance:
0/Bacterial Proteins; 0/DNA, Bacterial; 0/ExuT protein, bacteria; 0/Hexuronic Acids; 0/Membrane Proteins; 0/Pectins; 14982-50-4/galacturonic acid; 9046-38-2/polygalacturonic acid; EC 3.2.1.-/Glycoside Hydrolases; EC

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