Role of AUTOphagy in plant ADAPTtation to Nitrate and Sulphate limitation in environment – AUTOADAPT

The aims are
(i) Investigate the role of autophagy in nutrient management and fluxes at the whole plant level during senescence or starvation using 15N and 34S isotope tracing on autophagy mutants and wild types and analysis by mass spectrometry (IRMS)
(ii) Investigate the proteolytic processes during leaf senescence and nitrogen/sulphur remobilisation in autophagy mutants by measuring protease activitiesin gelo and in vitro
(iii) Investigate the nature of the autophagy targets depending on starvation using LCMS proteome analysis
(iv) Investigate protein modifications like carbonylation occurring in leaves during ageing using 2D or 1D SDS Page gel separation
(v) Using Arabidopsis populations, we willl determine the natural variability of autophagy activity. Autophagic activity variations will be correlated with variations in nitrogen use efficiency and variation in leaf senescence and stress tolerance to nitrate or sulfur limitation.

Our first results show that autophagy is importante for plant tolerance to nitrate and sulphur limitation.

Perspectives will be to determine whether autophagy is selective depending on nutritive conditions. The determination of the nature of the proteins targeted by autophagy depending on conditions will help us to identified candidates physiologically important for plant adaptation to nitrate or sulphur starvations.

none at the moment

Plants have a fundamental dependence for inorganic nitrogen and sulphur and million metric tons (MMt) of nitrogenous fertilizers are added to the soil worldwide annually. Nitrogen is one of the most expensive nutrients to supply and commercial fertilizers represent the major cost in plant production. There is serious concern regarding nitrogen loss in the fields that pollutes soils and water. Incomplete capture and poor conversion of fertilizer N also causes global warming through nitrous oxide emissions. The possibility of lowering fertilizer input and breeding plants with better nitrogen remobilization efficiency has been considered to increase nitrogen use efficiency and limit nitrogen fertilizers. This difficult challenge is important to preserve the environment and improve a sustainable and performing agriculture. In addition, the ability to recycle and remobilize organic nutrients as organic nitrogen and sulphur is crucial for the adaptation of plants to fluctuating environment and for the development of new organs. Processes allowing the export and recycling of nutrient to storage organs and to seeds are the basis for crop productivity. In response to low nitrogen supply, plant leaf senescence is accelerated and nitrogen recycling and remobilisation are increased. Proteolysis is required for recycling and nutrient remobilisation during senescence. However the sequence of events and the enzymes involved in protein degradation for remobilisation are poorly known. Autophagy is likely to be a key event, allowing the trafficking of substrates and proteases to lytic vacuoles. Autophagy is an ubiquitous proteolytic process in eukaryotic cells that permits protein breakdown and amino acids recycling via a non-selective lysosomal/vacuolar proteolysis. Autophagy pathway is defined by a specific molecular machinery involving the products of ATG genes and the formation of double membrane bound lytic autophagic vacuoles, named autophagosomes. Autophagy occurs at a basal level in all eukaryotic cells. In yeast and animals, autophagy is described as essential for cell longevity by managing cell waste and regulating homeostasis. In these organisms, autophagy is also stimulated in response to stress, and especially amino acid or sugar starvation. In plants, despite a recent regain of interest for this amazing cell function due to the identification of 25 Arabidopsis AtATG genes, little is known about the molecular events underpinning autophagy processes. However, our recent data suggest a role of autophagy in plant metabolism, carbon and nitrogen management, nutrient salvage and recycling during leaf senescence and in response to N-starvation. The results obtained in our laboratory give evidences that autophagy controls N remobilisation at the whole plant level as well as protease activities in leaves. So far we know, the role of autophagy in sulphur management has never been studied. The aim of this project is to study different aspects of autophagy physiological role for nutrient recycling and seed feeding in plant in response to limited nitrate or sulphate supply. This project includes the physiological characterization of autophagy atg mutants, the analysis of the impact of autophagy on nutrient fluxes at the whole plant level, the role of autophagy in protease activities and protein turnover in leaves and seeds during maturation. To our knowledge, these aspects are unique in the today researches. Indeed, some research groups are currently investigating the role of autophagy in response to oxidative stress, drought and salinity as well as plant pathogen. However, none of these groups have our expertise to tackle and investigate the physiology and metabolism of Arabidopsis autophagic mutants in response to N- or S-supply.