CE13 - Biologie cellulaire, biologie du développement et de l’évolution

Lipid transport to mitochondria and contact sites formation during phosphate starvation in plants. – MiCoSLiT

How do plants adapt to nutrient-depleted environments?

The MiCoSLiT project seeks to understand how lipid remodelling occurs in plant mitochondria in response to phosphate starvation and how this remodelling impacst the global resistance of plants to this stress.

Understanding of the mechanisms involved in the adaptation of plants to phosphate-depleted environments.

Plants are organisms that are permanently subjected to numerous stresses such as high temperatures or nutrient deficiencies. Phosphate is an essential microelement for plant development, the absence of which has a considerable negative impact on agricultural yields. It is therefore important to understand how plants adapt to this stress. During phosphate deficiency, plants set up mechanisms to increase phosphate uptake from the soil and to mobilize the reserves present in the cells. In plant cells, one third of the phosphate is retained in the lipids that make up the cell membranes namely phospholipids. These lipids are therefore degraded in phosphate deficiency and replaced by galactolipids which do not contain phosphate. This process, called lipid remodeling, involves an important traffic of lipids between different compartments of the cell and is currently poorly understood since only one actor has been identified. The MiCoSLiT project aims to identify new actors involved in lipid remodeling in plants growing in phosphate-depleted environments and thus to better understand how plants can adapt and resist to this stress.

The first part of the project consists in identifying new candidates potentially involved in lipid remodeling. For this purpose, biochemical approaches based on 1) the search for partners of known proteins as well as 2) on differential analyses carried out on plants grown in the presence and absence of phosphate have been implemented. From these approaches, three candidates were selected for an advanced functional analysis, which constitutes the second part of the project. The analyses consisted firstly in constructing lines expressing or not the candidates of interest and then in studying different parameters. Thus, biochemical approaches, such as the purification of cellular compartments coupled to lipidomics, were implemented in order to study the effect of the candidates on lipids remodeling in response to phosphate deficiency. Fluorescence and electron microscopy approaches were used to study the localization of the candidates and their effect on cell ultrastructure. Finally, growth tests in a phosphate-deficient environment were used to analyze the impact of these candidates on the resistance of plants to phosphate deficiency.

The MiCoSLiT project allowed the identification of three new actors playing a role in lipid remodeling induced by phosphate deficiency. The first actor is involved in the phospholipid transport process leading to their degradation. The other two might be involved in the communication between cellular compartments to orchestrate remodeling. Thus, this project has allowed us to better understand one of the mechanisms of intracellular phosphate mobilization in plants. In the long term, these results could be used to select varieties that could better resist this nutrient stress.

The functional analyze of our three candidate proteins will highlight their roles in the lipid remodeling process occurring during phosphate starvation and their importance for plant resistance to phosphate starvation. The results will also open important perspectives about the mechanisms involved in the regulation of mitochondria contact sites formation and lipid transport processes.

Two book chapters have been written as a result of this project: one corresponding to a protocol detailing one of the techniques developed during the project and a second corresponding to the state of the art on the whole knowledge in the field of lipid transport in plants. A research paper tracing the evolutionary history of a candidate has been recently submitted. Some additional experiments have still to be performed before the publication of the functional characterization of our different candidates.

Phosphate (Pi) starvation is a frequent nutrient stress impacting crop yields. To adapt to this stress, plants exert different mechanisms to increase the uptake of extracellular Pi and to remobilize intracellular reserves. In cells, one third of the Pi is retained in phospholipids, the main components of extra-plastidial membranes. During Pi starvation, phospholipids are partially degraded to release Pi and are replaced by a non-phosphorous lipid synthesized in plastids: the digalactosyldiacylglycerol (DGDG). Thus, the synthesis and transfer of DGDG from plastids to other organelles is highly stimulated in this situation. However, the mechanisms involved in lipid remodeling remain poorly understood. DGDG transfer to mitochondria is thought to occur by non-vesicular pathways at contact sites between mitochondria and plastids. Recently, we have identified in Arabidopsis thaliana a super-complex, the MTL (Mitochondrial Transmembrane Lipoprotein) complex, involved in DGDG transfer to mitochondria during Pi starvation. Among this complex, AtMic60, a protein located in the inner membrane of mitochondria, plays an indirect role in DGDG transfer 1) by regulating contact sites formation between both mitochondrial membranes and 2) by destabilizing membranes. Only a partial decrease of DGDG transport is observed in the absence of AtMic60, suggesting that other pathways are also involved. In addition, we currently do not know how plastid-mitochondria contact sites, an important structure for lipid transport, are formed. The goal of the MiCoSLiT project is to identify keys actors involved in DGDG transport to mitochondria and/or in the formation of plastid-mitochondria contact sites in response to Pi deprivation. Our working hypothesis is that the MTL complex and other actors, which remain to be identified, are involved. First of all, a combination of three biochemical approaches will be optimized to identify new candidate proteins potentially involved in such processes. A first approach corresponds to a deep analysis of the composition and organization of the MTL complex in order 1) to better understand its functions and 2) to highlight new components putatively involved in lipid transport and/or membrane contact sites formation. Two non-targeted approaches, corresponding to the analysis of the mitochondrial proteome in response to Pi starvation and the optimization of a method to isolate plastid-mitochondria contact sites, will be performed in parallel to identify new pathways. All these approaches will be performed from A. thaliana cell cultures grown in presence and in absence of Pi to highlight candidates specifically involved in Pi-starvation response. Then, a functional analysis of a small subset of candidates will be undertaken to decipher their role(s) in the transport of lipids to mitochondria and/or in the formation of plastid-mitochondria contact sites. Finally, the involvement of these candidates in the global response of plant to Pi starvation will be studied in order to demonstrate the important role of lipid remodeling in the adaptation of plant to this situation. Impacts of the MiCoSLiT project are expected in both basic research and agricultural sciences. Indeed, the project will increase our understanding of the mechanisms involved in mitochondrial lipid transport and in the formation and regulation of contact sites between organelles, processes which remains poorly characterized, particularly in plants. In addition, by the investigation of the cellular mechanisms involved in plant response to Pi starvation, the project will open important perspectives in the development of crops presenting higher yield when grown in low-Pi soils.

Project coordination

Morgane Michaud (LABORATOIRE DE PHYSIOLOGIE CELLULAIRE ET VEGETALE)

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

LPCV LABORATOIRE DE PHYSIOLOGIE CELLULAIRE ET VEGETALE

Help of the ANR 248,664 euros
Beginning and duration of the scientific project: October 2019 - 36 Months

Useful links

Explorez notre base de projets financés

 

 

ANR makes available its datasets on funded projects, click here to find more.

Sign up for the latest news:
Subscribe to our newsletter