Authors: Peter S Solomon Richard P Oliver
Publish Date: 2001/08/15
Volume: 214, Issue: 3, Pages: 414-420
Abstract
The growth of the biotrophic pathogen Cladosporium fulvum within the tomato Lycopersicon esculentum Mill leaf is restricted to the intercellular space Previous studies from this laboratory have demonstrated that γaminobutyric acid GABA accumulates to millimolar concentrations in the apoplast during a compatible interaction We decided to further investigate the role of GABA during infection A gene encoding a required enzyme for GABA metabolism GABA transaminase Gat1 was cloned and sequenced from C fulvum The predicted protein sequence of Gat1 had high homology to other fungal GABA transaminases particularly from Aspergillus nidulans In vitro expression experiments revealed Gat1 to be strongly expressed during fungal growth on both GABA and glutamate whereas nearly no expression was evident during nitrogen starvation conditions Expression of Gat1 was also apparent during infection suggesting for the first time that C fulvum actively metabolises GABA during infection This indicates that the fungus may be utilising the GABA in the apoplast as a nutrient source Further analysis revealed that the expression of tomato glutamate decarboxylase the enzyme responsible for GABA synthesis appeared appreciably higher during a compatible interaction than in the incompatible interaction These findings imply that the infecting fungus may alter the physiology of the tomato leaf with the result that a source of nitrogen is supplied
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