[Seminars] PSB event reminder
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Thu Jun 17 09:10:01 CEST 2010
Calendar Name: seminars
Scheduled for: Thursday, June 17 2010, 11:00 - 12:30
Event text: Alain Gojon
Plant Biochemistry and Molecular Physiology
UMR 5004 Campus INRA/SupAgro Place Viala
Montpellier
FRANCE
Details: "Tranceptor-mediated nitrate signalling in Arabidopsis"
ABSTRACT
Nitrate is not only a major nitrogen source for higher
plants, but also a signal molecule governing both their
physiology and development. Nitrate per se regulates the
expression of several hundred genes in Arabidopsis
thaliana, including those of its own acquisition and
assimilation pathway. The signalling effect of nitrate
is also particularly strong on root development,
resulting in a high plasticity of the root system
architecture in response to both spatial and temporal
changes in external nitrate availability. Although the
nitrate signalling pathways remain largely unknown at
the molecular level, evidence is accumulating that the
membrane nitrate transporter NRT1.1 (CHL1) may act as a
nitrate sensor triggering transduction of the nitrate
signal. NRT1.1 was first characterized as a
dual-affinity influx carrier involved in root nitrate
acquisition from the external medium. However, knock-out
mutants for NRT1.1 (chl1 mutants) display a strongly
altered regulation by nitrate of other root nitrate
transporters (e.g. NRT2.1, Muños et al. 2004, Krouk et
al. 2006) and of root growth. Defective nitrate
signalling in chl1 plants cannot be explained by the
loss of NRT1.1 nitrate transport activity. We showed
that NRT1.1 participates in a specific nitrate
signalling pathway, involving the putative transcription
factor ANR1, and favouring preferential growth of
lateral roots in nitrate-rich patches of the external
medium (Remans et al. 2006). The actual role of NRT1.1
is to repress lateral root growth in nitrate-poor
patches by preventing auxin accumulation in lateral root
primordia and lateral root tips when the external
nitrate concentration is low. Surprisingly, the
strongest effect of NRT1.1 on auxin accumulation in
lateral roots is found in the absence of nitrate. The
mechanisms responsible for the control of local auxin
gradients in lateral roots by NRT1.1 will be discussed,
in connection with the observation that NRT1.1 may not
transport only nitrate, but also auxin. Altogether,
recent functional studies carried out by several groups
indicate that, as evidenced for the so-called yeast
transceptor proteins, NRT1.1 fulfils a dual
transport/sensing role governing several responses on
the plant to nitrate.
Muños S., Cazettes C., Fizames C., Gaymard F., Tillard
P., Lepetit M., Lejay L., Gojon A. 2004 Transcript
profiling in the chl1-5 mutant of Arabidopsis reveals a
role of the nitrate transporter NRT1.1 in the regulation
of another nitrate transporter, NRT2.1. Plant Cell 16:
2433-2447.
Krouk G., Tillard P., Gojon A. 2006 Regulation of the
high-affinity NO3- uptake system by NRT1.1-mediated NO3-
demand signaling in Arabidopsis. Plant Physiol. 142:
1075-1086.
Remans T., Nacry P., Pervent M., Filleur S., Diatloff
E., Mounier E., Tillard P., Forde B.G., Gojon A. 2006
The Arabidopsis NRT1.1 transporter participates in the
signaling pathway triggering root colonization of
nitrate-rich patches. Proc. Natl. Acad. Sci. USA 103 :
19206-19211.
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