Planta

, Volume 214, Issue 3, pp 414–420

Evidence that γ-aminobutyric acid is a major nitrogen source during Cladosporium fulvum infection of tomato

  • Peter S. Solomon
  • Richard P. Oliver
Original Article

DOI: 10.1007/s004250100632

Cite this article as:
Solomon, P.S. & Oliver, R.P. Planta (2002) 214: 414. doi:10.1007/s004250100632

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 γ-aminobutyric 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.

Apoplast Cladosporium γ-Aminobutyric acid Lycopersicon (plant-pathogen interaction) Nitrogen Nutrition

Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • Peter S. Solomon
    • 1
  • Richard P. Oliver
    • 1
  1. 1.Department of Physiology, Carlsberg Laboratory, Gamle Carlsberg Vej 10, 2500 Copenhagen ValbyDenmark
  2. 2.Australian Centre for Necrotrophic Fungal Pathogens, State Agricultural Biotechnology Centre, Division of Science and Engineering, Murdoch University, Perth 6150 Western Australia, e-mail: roliver@central.murdoch.edu.au, Fax: +61-8-93606303Australia