6. Equipe Integration des fonctions nutritives

Biochimie et Physiologie Moléculaire des Plantes, UMR 5004 INRA/ENSAM/CNRS/UM2, 2 place Viala, 34060 Montpellier, France

Dr. Alain Gojon, E-mail:gojon@ensam.inra.fr  

The group ” Intégration des fonctions nutritives ” is part of the Laboratory ”Biochimie et Physiologie Moléculaire des Plantes ” (INRA-ENSAM-CNRS-University) which is dedicated to plant membrane transport. The aim of the group is to understand the mechanisms of N absorption and their regulation at the whole plant level. Physiological studies conducted in the group have shown that N absorption is under the control of two types of regulation. The first type, specific for the ion, controls the uptake capacity in order to adjust N absorption to N demand of the whole plant. The second type, general to the major mineral ions, adjusts N absorption to the C nutritional status of the plant. Both pathways are complex and depend on the exchange of signals between roots and shoots. Products of N and C metabolism translocated through the phloem sap - amino acid and sugar- have been suggested to play the role of signal molecules.

In the past few years, genes encoding NO3- transporters have been isolated in Arabidopsis. A major contribution of our group has been to characterize the in vivo function of some of these transporters by functional studies using reverse genetic strategies. The group has developed unique facilities and methodologies in order to analyze N uptake and N assimilation in photosynthetically active Arabidopsis plants grown hydroponically. We have shown that at least two genes NRT1.1 and NRT2.1 encoding NO3- transporters contribute to the NO3- uptake in Arabidopsis roots. We have shown that both regulations (by N or C status, respectively) control NO3- transporter genes and modulates NO3- influx (1,2). We have characterized the complexity of these regulations. Various N treatments, together with the use of assimilatory mutants (nitrate reductase mutants) have allowed us to reveal the existence of previously unknown regulations affecting NO3- and NH4+ transporters. This includes: (i) repression of NRT1.1 expression par NIA (2), and (ii) regulation of NRT2.1 in roots by shoot signals of N limitation (3). On the other hand, we have demonstrated, for the first time, that sugars are signals regulating the expression of root ion transporter genes (1). Genetic strategies to identify new genes involved in the regulation of NO3- uptake have been initiated. In addition to a genetic screen on EMS treated lines using the G’4-3 nitrate reductase mutant of Arabidopsis as a genetic background (the screen is based on measurement of accumulation of NO3- in shoots), we have conducted another screen on T-DNA insertion collection (INRA Versailles) for new chlorate resistant mutants. These mutants are currently under investigation.

The group ”Integration des Fonctions Nutritives” has long experience in international exchange and student training. In the past 4 years the group has welcomed 4 post-doc fellows and 3 Ph.D. students coming from France, Europe or North America. Collaboration with groups worldwide are frequent and have resulted in the past 4 years in the publication of 6 joint research articles in first rank journals. More than 80 people implicated in research and/or student training are present in BPMP laboratory (”Biochimie et Physiologie moléculaire des Plantes”) that is supported by INRA, CNRS, Montpellier university and AgroM Agronomic engineer school. As a part of the University and Agronomic school the BPMP laboratory has developed a long term effort in training students. The Lab is the major partner of the Ph.D. training program ”Integrative Biology” and of the DEA training program ”Plant adaptation and development”. In addition to the numerous conferences held in the various labs and research institutes of Montpellier, the laboratory organizes two weekly seminars. One is open to the laboratory members and offers the opportunity for everyone, with emphasis on student and post-doc, to present and discuss their own work. The other is organized at the university and provides a series of research lectures to higher students.

Participating scientists:

• Alain Gojon

• Marc Lepetit

• Pascal Tillard