Document Detail

Legumes regulate Rhizobium bacteroid development and persistence by the supply of branched-chain amino acids.
MedLine Citation:
PMID:  19597156     Owner:  NLM     Status:  MEDLINE    
One of the largest contributions to biologically available nitrogen comes from the reduction of N(2) to ammonia by rhizobia in symbiosis with legumes. Plants supply dicarboxylic acids as a carbon source to bacteroids, and in return they receive ammonia. However, metabolic exchange must be more complex, because effective N(2) fixation by Rhizobium leguminosarum bv viciae bacteroids requires either one of two broad-specificity amino acid ABC transporters (Aap and Bra). It was proposed that amino acids cycle between plant and bacteroids, but the model was unconstrained because of the broad solute specificity of Aap and Bra. Here, we constrain the specificity of Bra and ectopically express heterologous transporters to demonstrate that branched-chain amino acid (LIV) transport is essential for effective N(2) fixation. This dependence of bacteroids on the plant for LIV is not due to their known down-regulation of glutamate synthesis, because ectopic expression of glutamate dehydrogenase did not rescue effective N(2) fixation. Instead, the effect is specific to LIV and is accompanied by a major reduction in transcription and activity of LIV biosynthetic enzymes. Bacteroids become symbiotic auxotrophs for LIV and depend on the plant for their supply. Bacteroids with aap bra null mutations are reduced in number, smaller, and have a lower DNA content than wild type. Plants control LIV supply to bacteroids, regulating their development and persistence. This makes it a critical control point for regulation of symbiosis.
J Prell; J P White; A Bourdes; S Bunnewell; R J Bongaerts; P S Poole
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2009-07-13
Journal Detail:
Title:  Proceedings of the National Academy of Sciences of the United States of America     Volume:  106     ISSN:  1091-6490     ISO Abbreviation:  Proc. Natl. Acad. Sci. U.S.A.     Publication Date:  2009 Jul 
Date Detail:
Created Date:  2009-08-11     Completed Date:  2009-09-28     Revised Date:  2013-06-02    
Medline Journal Info:
Nlm Unique ID:  7505876     Medline TA:  Proc Natl Acad Sci U S A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  12477-82     Citation Subset:  IM    
John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom.
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MeSH Terms
ATP-Binding Cassette Transporters / genetics,  metabolism
Amino Acids, Branched-Chain / biosynthesis,  metabolism*
Bacterial Proteins / genetics,  metabolism
Biological Transport
Biosynthetic Pathways
Host-Pathogen Interactions
Microscopy, Electron
Nitrogen Fixation / physiology
Peas / genetics,  metabolism,  microbiology*
Rhizobium leguminosarum / genetics,  physiology*,  ultrastructure
Root Nodules, Plant / genetics,  metabolism,  microbiology
Grant Support
BBS/B/02916//Biotechnology and Biological Sciences Research Council
Reg. No./Substance:
0/Amino Acids, Branched-Chain; 0/Bacterial Proteins

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