RESEARCH PAPER |
The plant nitrogen mobilization promoted by Colletotrichum lindemuthianum in Phaseolus leaves depends on fungus pathogenicity
1Unité de Nutrition Azotée des Plantes, UR 511, INRA, Route de Saint Cyr F-78000 Versailles, France
2Laboratoire de Phytopathologie Moléculaire, IBP, UMR 8618, Bât 630 Université Paris-Sud XI, F-91405 Orsay, France
* To whom correspondence should be addressed. E-mail: masclaux{at}versailles.inra.fr
Nitrogen plays an essential role in the nutrient relationship between plants and pathogens. Some studies report that the nitrogen-mobilizing plant metabolism that occurs during abiotic and biotic stress could be a ‘slash-and-burn’ defence strategy. In order to study nitrogen recycling and mobilization in host plants during pathogen attack and invasion, the Colletotrichum lindemuthianum/Phaseolus vulgaris interaction was used as a model. C. lindemuthianum is a hemibiotroph that causes anthracnose disease on P. vulgaris. Non-pathogenic mutants and the pathogenic wild-type strain were used to compare their effects on plant metabolism. The deleterious effects of infection were monitored by measuring changes in chlorophyll, protein, and amino acid concentrations. It was shown that amino acid composition changed depending on the plant–fungus interaction and that glutamine accumulated mainly in the leaves infected by the pathogenic strain. Glutamine accumulation correlated with the accumulation of cytosolic glutamine synthetase (GS1 
) mRNA. The most striking result was that the GS1 gene was induced in all the fungus-infected leaves, independent of the strain used for inoculation, and that GS1 expression paralleled the PAL3 and CHS defence gene expression. It is concluded that a role of GS1 in plant defence has to be considered.
Key words: Amino acids, glutamine synthetase, nitrogen remobilization, senescence
Received 6 April 2007; Revised 10 July 2007 Accepted 13 July 2007