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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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