plant surface microbiology.pdf

22 Nitrogen Transport and Metabolism in Mycorrhizal Fungi and Mycorrhizas 401
subjected to nitrogen repression in H. cylindrosporum (Fig. 2). AMT3 was
poorly regulated at this level.
Expression of AMT1 only in ammonium-limiting conditions is consistent
with a role for the high-affinity ammonium transporter in scavenging low
concentrations of ammonium. The low-affinity ammonium transporter Amt3
would be required for growth in ammonium-sufficient conditions.
In order to identify the effector(s) for nitrogen regulation in H. cylindrosporum,
the correlation coefficient for the relationship between AMT1,
AMT2, AMT3, transcript levels and N-compound amounts were calculated.
This transcriptional control is driven by intracellular Gln. Indeed, an intracel-
Fig. 2. AMT1,AMT2,AMT3,GDHA and GLNA mRNA levels in Hebeloma cylindrosporum.
Fungal colonies were grown for 10 days on cellophane-covered agar medium containing
3.78 mM ammonium as sole nitrogen source (T 0 ) and transferred to a N-free liquid medium
for 12 h (–N).Some colonies were further transferred to a 0.1,1 or 10 mM ammonium-containing
medium. Total RNA was extracted at 3, 6, 12 and 24 h from 100 mg of mycelium and
20 mg/lane were separated on 1.5 % agarose-formaldehyde gel and hybridized to the
[a- 32 P]dCTP labelled cDNA probes or 5.8S rRNA probe as loading control