JCJC SVSE 6 - JCJC - SVSE 6 - Génomique, génétique, bioinformatique et biologie systémique

Nutrient sensing in plants – NUTSE

Nutrient senssing in plants

The general goal of this project is to identify the mecanisms used by plant to perceive their mineral environment. <br />

Nitrate transport and sensing in plants

The mineral nutrition of most terrestrial organisms (bacteria, fungi, plants) relies on the uptake of inorganic ions from the soil. However, the availability of these ions dramatically fluctuates in both time and space. To face this constraint, all organisms are able to develop a wide range of adaptive responses triggered by sensing systems that perceive the external nutrient availability. The identification of these sensing systems has a strategic importance at both fundamental and applied levels to unravel and manipulate the molecular mechanisms involved in tolerance to nutrient stress. Until recently, our knowledge about mineral nutrient sensors in eukaryotes has mostly been limited to yeast. However, our findings in Arabidopsis thaliana prompted us to propose that NRT1.1 transporter, initially characterized as an uptake system in the roots, also acted as a NO3- sensor. We showed that NRT1.1 triggers specific signaling pathways governing both physiological and developmental responses of A. thaliana to NO3-, and plays in particular a key role in the NO3- regulation of root development. Following our initial report, the hypothesis that NRT1.1 directly participates in NO3- sensing has received a strong validation from studies performed by other groups. <br />A central question remained unresolved. For all transporters/sensors identified, there is presently no clue on how these proteins can transform the external concentration of a nutrient into a signal transduced into the cell. We have recently made a major advance on this point, and proposed a model for the signalling mechanism responsible for NO3- sensing by NRT1.1. We found that NRT1.1 not only transports NO3- but also auxin. Auxin transport by NRT1.1 is inhibited by NO3-, suggesting that the signal transduced by NRT1.1 is a modification of auxin trafic in root cells. <br /> The general goal of this project is to expand the study of this highly novel mechanism by initiating totally new approaches.

These approaches are defined by three main considerations:
1) NRT1-1 belongs to the NRT1/PTR family (53 members in Arabidopsis) but to date, very little is known about the function of the different members of this family, and nothing has been published on the putative involvement of other PTR transporters in NO3- sensing. Therefore, a systematic approach in heterologous system (xenopus oocytes and yeast) will be set up to find additional NO3-/auxin -transporters in NRT1 family.
2) Nothing is known about the molecular bases of the capability of NRT1.1 to transport both NO3- and auxin and to act as a nitrate sensor. A structure-function analysis will then be developed (in oocytes, yeast and plant cell culture) to delineate the specific domains or residues conferring to NRT1.1 its unique functional properties.
3) In planta functional characterization will be carried out on genes identified in 1) and on genes known to interact with NRT1.1 (CIPKs and CBLs). For that purpose, KO mutants will be isolated and nitrate dependent root development will be analyzed. For the most interesting candidates, in depth characterization will be performed: expression pattern, sub-cellular localization and production of double mutants. We will aim in particular to get mutated versions of NRT1.1 with specific features (dominant negative or permeant only to either NO3- or auxin) that will be highly valuable to further investigate the sensing mechanism of this transporter in planta.
Through the combination of these complementary strategies, the overall project is designed as an integrative approach to elucidate the role of a new family of nutrient sensors in plants, and to understand how their dual hormone/nutrient substrate specificity can be a molecular basis of the nutritional control of plant development.

The first results are analyzed.

Through the combination of these complementary strategies, the overall project is designed as an integrative approach to elucidate the role of a new family of nutrient sensors in plants, and to understand how their dual hormone/nutrient substrate specificity can be molecular bases of the nutritional control of plant development. It will benefit from very strong implication in international collaborations (VIB, Universities of Nottingham and Prague), and will be tightly coordinated with another project in the group focused on the link between NRT1.1 and other auxin import/export system (PIN, PGP, AUX/LAX).
Although this project clearly defines a new direction for the team where heterologous expression systems and structure/function analysis approaches were not yet present, it also includes the integration of these approaches with those conducted in planta by the other scientists of the group. As detailed below, functional expression in heterologous systems will provide new basic knowledge on the functional specificities of the NRT1 proteins, but will also generate molecular and genetic tools to investigate the mechanisms of their action in planta. The long term viability of the project is ensured because we will be able to set back the results in a larger context with the other projects of the group to understand the integrative role of NRT1.1 and other candidates, in the way plants sense their mineral environment and react to optimize their nutrition and development.

The results that will be generated by this project will be published in high-impact peer-reviewed journals publishing basic research results, as it has been constantly done for nearly 12 years now for the various projects of Benoit Lacombe (h-index: 16; 2

The mineral nutrition of most terrestrial organisms (bacteria, fungi, plants) relies on the uptake of inorganic ions from the soil. However, the availability of these ions dramatically fluctuates in both time and space. To face this constraint, all organisms are able to develop a wide range of adaptive responses triggered by sensing systems that perceive the external nutrient availability. The identification of these sensing systems has a strategic importance at both fundamental and applied levels to unravel and manipulate the molecular mechanisms involved in tolerance to nutrient stress. Until recently, our knowledge about mineral nutrient sensors in eukaryotes has mostly been limited to yeast. However, our findings in Arabidopsis thaliana prompted us to propose that the NRT1.1 (formerly CHL1) nitrate (NO3-) transporter, initially characterized as an uptake system in the roots, also acted as a NO3- sensor. We showed that NRT1.1 triggers specific signaling pathways governing both physiological and developmental responses of A. thaliana to NO3-, and plays in particular a key role in the NO3- regulation of root development. Following our initial report, the hypothesis that NRT1.1 directly participates in NO3- sensing has received a strong validation from studies performed by other groups in France, Taiwan and UK.
A central question remained unresolved. For all transporters/sensors identified, there is presently no clue on how these proteins can transform the external concentration of a nutrient into a signal transduced into the cell. In collaboration with two Belgian and Swedish groups (VIB Gent and University Umea), we have recently made a major advance on this point, and proposed a model for the signalling mechanism responsible for NO3- sensing by NRT1.1. We found that NRT1.1 not only transports NO3- but also auxin. Auxin transport by NRT1.1 is inhibited by NO3-, suggesting that the signal transduced by NRT1.1 is a modification of auxin trafic in root cells.
The general goal of this project is to expand the study of this highly novel mechanism by initiating totally new approaches.
These approaches are defined by three main considerations:
1) NRT1-1 belongs to the NRT1/PTR family (53 members in Arabidopsis) but to date, very little is known about the function of the different members of this family, and nothing has been published on the putative involvement of other PTR transporters in NO3- sensing. Therefore, a systematic approach in heterologous system (xenopus oocytes and yeast) will be set up to find additional NO3-/auxin -transporters in NRT1 family.
2) Nothing is known about the molecular bases of the capability of NRT1.1 to transport both NO3- and auxin and to act as a nitrate sensor. A structure-function analysis will then be developed (in oocytes, yeast and plant cell culture) to delineate the specific domains or residues conferring to NRT1.1 its unique functional properties.
3) In planta functional characterization will be carried out on genes identified in 1) and on genes known to interact with NRT1.1 (CIPKs and CBLs). For that purpose, KO mutants will be isolated and nitrate dependent root development will be analyzed. For the most interesting candidates, in depth characterization will be performed: expression pattern, sub-cellular localization and production of double mutants. We will aim in particular to get mutated versions of NRT1.1 with specific features (dominant negative or permeant only to either NO3- or auxin) that will be highly valuable to further investigate the sensing mechanism of this transporter in planta.
Through the combination of these complementary strategies, the overall project is designed as an integrative approach to elucidate the role of a new family of nutrient sensors in plants, and to understand how their dual hormone/nutrient substrate specificity can be a molecular basis of the nutritional control of plant development.

Project coordinator

Monsieur Benoit Lacombe (INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - CENTRE DE MONTPELLIER) – benoit.lacombe@supagro.inra.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

BPMP INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - CENTRE DE MONTPELLIER

Help of the ANR 286,000 euros
Beginning and duration of the scientific project: January 2012 - 48 Months

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