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

Plant manganese nutrition for optimal photosynthesis and growth – PlantMan

Manganese, an essential nutrient for photosynthesis and plant growth

The project aims at understanding the mechanisms that enable plant to capture manganese, an essential nutrient, from soils and bring it to the photosynthetic centers where it plays a critical role in producing dioxygen from water and convert solar energy to chemical energy for the cell.

Improve manganese nutrition to optimize plant growth

Despite the importance of manganese (Mn) for plant growth, the mechanisms allowing the uptake of this nutrient and the pathway for its incorporation into photosystem II have been the topic of only few studies. The major aim of this project is to combine complementary approaches towards a better understanding of Mn homeostasis in plants.<br />The specific aims will be (1) to determine the pathway providing Mn to photosystem II in photosynthetic cells (2) to determine the distribution and speciation of Mn in seeds and their implication for seed germination and (3) to identify new players controling Mn uptake in roots and Mn use efficiency in plants.

To study Mn homeostasis, the partners of the project will combine complementary approaches from plant molecular genetics to biophysics: Arabidopsis molecular genetics will be used to determine the integrated function of genes encoding Mn transporters, Mn binding proteins or regulators. Chlorophyll fluorescence will allow in vivo monitoring of photosystem II function. X-ray fluorecence imaging using synchrotron radiation (SXRF) or high energy particles (PIXE) will allow mapping Mn in tissues and cells. Finally, High Field electron paramagnetic resonance (HF EPR) will be used to determine Mn speciation, i.e. Mn chemical environement, in intact plant tissues.

1) Cells control strictly their internal metal concentrations. Metals are only rarely free and most often associated to proteins called chaperones. We have identified a putative Mn chaperone present in chloroplasts but also in the cytosol of plant cells.
2) Using Arabidopsis seeds as model, we have pionneered the use of High Field Electronic Paramagnetic Resonnance (HF EPR) to determine the chemical environment of Mn in intact biological samples.
3) Mn is essential for photosynthesis and Mn deficiency leads to a rapid drop in photosynthetic efficiency. A mutant screen based on chlorophyll fluorescence imaging (see Figure) allowed the identification of candidate plants displaying higher tolerance to Mn deficiency.

1) To decipher the network of Mn transporters and chaperones that allow to target Mn to photosystem 2.
2) To analyze perturbations of Mn chemical environment in seeds of mutants affected in Mn transport and their consequences on germination.
3) To identify and characterize elements that regulate Mn entry in plants.
4) To identify genes impaired in the mutants able to tolerate Mn deficiency that we have identified in the first part of the project.

Schnell Ramos M, Khodja H, Mary V, Thomine S (2013) Using µPIXE for quantitative mapping of metal concentration in Arabidopsis thaliana seeds. Front Plant Sci. 4:168. doi: 10.3389/fpls.2013.00168.
*This publication illustrates the use Particle Induced X-ray Emission with a focused beam (µPIXE) to quantify Fe and Mn distribution in Arabidopsis thaliana seeds.
Thomine S, Vert G. (2013) Iron transport in plants: better be safe than sorry. Curr Opin Plant Biol. 16(3):322-7. doi: 10.1016/j.pbi.2013.01.003.
*This review addresses the fact that Fe deficiency induces accumulation of other transition metals, including Mn, and raises the issue of specificity in metal transport.

Manganese (Mn) is an essential nutrient in plants; Mn not only acts as a cofactor for manganese dependent superoxide dismutase, as in other organisms, but it is also a crucial cofactor of the oxygen evolving complex of photosystem II. Both Mn deficiency and Mn excess in soil limit crop yield on large areas of arable land worldwide. Mn also plays a role in plant resistance to pathogens and may be more generally involved in tolerance to oxidative stress. However, Mn homeostasis has been understudied in plants.
The aim of this project is to use an integrated approach to improve our knowledge on manganese homeostasis in plants. To initiate this approach, the project will gather 3 partners with the following complementary expertises: molecular genetics of metal transport, biochemistry of metalloproteins, photosynthesis and manganese physical chemistry. The partners have previously worked on different facets of manganese homeostasis in plants. The project will use the reference plant Arabidopsis thaliana as a model. The partners will focus on two systems: (1) the photosynthetic mesophyll cell, to address the question of the intracellular mechanisms allowing manganese supply to the photosystem II, and (2) the seed to address the question of manganese storage and mobilization. In addition, the project will also investigate the regulation of Mn uptake into root cells, the role of Mn in plant reproduction and will initiate the search for the genetic determinants of Mn use efficiency. To target these questions, the PlantMan project uses a unique combination of relevant approaches: Arabidopsis molecular genetics to investigate the integrated function of genes involved in Mn homeostasis, chlorophyll fluorescence measurements to monitor the efficiency of the photosystem II; X-ray fluorescence, induced by synchrotron radiation (SXRF) or high energy particles (PIXE) to image metal concentrations in plant organs and plant cells; and High Field Electronic Paramagnetic Resonance (HF EPR) to specifically probe Mn speciation in intact plant tissues. This project pioneers the use of HF EPR in intact complex biological samples. The project is supported by a sum of preliminary results that validate the proposed approaches.
The main expected outputs of this project are (1) an improved basic knowledge of key steps in Mn homeostasis in Arabidopsis thaliana and (2) the identification of molecular mechanisms relevant for improving crop yield and their tolerance to biotic and abiotic stresses.

Project coordination

Sébastien THOMINE (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR SUD) – thomine@isv.cnrs-gif.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

CNRS CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR SUD
CEA COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES - CENTRE D'ETUDES NUCLEAIRES SACLAY
CNRS CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON

Help of the ANR 372,000 euros
Beginning and duration of the scientific project: - 36 Months

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