nrt2 nitrate reductase nitrite reductase

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Phylogeny of the high affinity nitrate
transporter, NRT2 Bayesian analysis using mixed
protein models (figure 3) weakly suggests a
sister relationship between stramenopile NRT2 and
fungal NRT2. Parsimony analysis, however, weakly
supports a plant-stramenopile NRT2 clade.
Eukaryotic sequences are supported as
monophyletic with a clade (parsimony) or
paraphyletic assemblage (Bayesian) of mostly
proteobacterial sequences suggesting a possible
mitochondrial origin of the gene. NRT2 phylogeny
mostly tracks species phylogeny within the plants
and fungi represented. (Support values in figure
3 represent maximum parsimony bootstraps/Bayesian
posterior probabilities.)
nrt2 nitrate reductase
nitrite reductase
Table 1. Genomes used in this study
Table 1. Genome projects used in these analyses
Figure 5b. A putative binding site for nitrate
in NRT2
Does a recent duplication of nrt2 influence the
ecology of the ectomycorrhizal fungus, Hebeloma
helodes. The Hebeloma crustuliniforme complex
(which includes H. helodes) differs from other
Hebeloma by associating with a broader range of
hosts, by having strong molecular support for
monophyly (Aanen et al, 2000) and by possessing a
second copy of the nrt2 gene. The two copies of
nrt2 in H. helodes have experienced an elevated
ratio of non-synonymous to synonymous divergence
of nucleotide sequence in the region of a
putative binding site (Unkles et al, 2004) shown
in figure 5b, suggesting a possible
diversification in affinity for nitrate.
Acknowledgements We would like to thank Brandon
Matheny, Manfred Binder and Zhang Wang for
extensive help with molecular techniques and
phylogenetic analyses. This work is supported by
National Science Foundation.
Presented at the 5th Congress, Vienna 2006
Literature Cited Aanen, D.K., T.W. Kuyper, T
Boekhout, R.F. Hoekstra. 2000. Phylogenetic
relationships in the genus Hebeloma based on ITS1
and 2 sequences, with special emphasis on the
Hebeloma crustuliniforme complex. Mycologia,
92(2) 269-281. Jargeat, P., D. Rekangalt, M.
Verner, G. Gay, J. DeBaud, R. Marmeisse, L.
Fraissinet-Tachet. (2003). Characterisation and
expression analysis of a nitrate transporter and
nitrite reductatse genes, two members of a gene
cluster for nitrate assimilation from the
symbiotic basidiomyctete Hebeloma cylindrosporum.
Curr. Genet. 43 199-205. Montanini, B., A.R.
Viscomi, A. Bolchi, Y. Martin, J.M. Siverio, R.
Balestrini, P. Bonafante, S. Ottonello. (2006).
Functional properties and differential mode of
regulation of the nitrate transporter from a
plant symbiotic ascomycete. Biochem. J. 394
(125134). Unkles, S.E., D.A. Rouch, Y. Wang,
M.Y. Siddiqi, A.D.M. Glass, J.R. Kinghorn. 2004.
Two perfectly conserved arginine residues are
required for substrate binding in a high affinity
nitrate transporter. Proc. Nat. Acad. Sci.,
U.S.A., 101(50) 17549-1755.
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