CHALOT, MICHEL, SYLVAIN LERAT, ARNAUD JAVELLE, DANIEL WIPF, JEAN-PIERRE JACQUOT & BERNARD BOTTON.
University Henri Poincaré, Nancy I, Faculty of Sciences, Laboratory of Forest Biology, INRA, BP 239, F-54500 Vandoeuvre Cédex, France.
Almost all knowledge about membrane transport in fungi derived from studies
with only two species : Saccharomyces cerevisiae and Neurospora
crassa. This is 0.0001% of the total estimated number of species.
Furthermore, only 0.03% of the total species of the Basidiomycetes has been
investigated for membrane transport. More recently Burgstaller postulated that
the properties of plasma membrane transport are closely associated with the
habitat and with the ecological role of filamentous fungi. The ammonium ion,
which is the most abundant compound of the inorganic nitrogenous fraction in
soil, is an important ion involved in nitrogen metabolism and can be
transported across the plasma membrane of many organisms.
NH4+ transporters have been recently characterized in
cyanobacteria, algae and plants. In symbiotic ectomycorrhizal fungi, uptake
experiments have demonstrated the existence of specific transport systems for
NH4+. The P. involutus ammonium transporter gene
has been cloned and sequenced using primers designed from yeast ammonium
transporter sequences (mep 1, 2 and 3). Sequence comparisons have shown high
homology with the mep 1, 2 and 3 genes. Using this sequence, an homologous
probe will be synthetized and will be used to screen a P. involutus cDNA
library in order to identify the gene of interest. To analyze gene expression
total RNA will be extracted from fungi grown under different nitrogen
conditions and the
transcript level will be analyzed by northern hybridization. Transporter genes
for organic nitrogenous compounds (amino acids and oligopeptides) are also
under investigation.