Se adjunta una oferta predoctoral para trabajar en tolerancia al estrés de arroz con simbiosis con micorrízas.
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Salt tolerance in rice: involvement of potassium transport systems and interactions with arbuscular mycorrhizal fungi.
As one of the most sensitive crop to soil salinity, rice has to cope with the toxicity of sodium (Na+). Potassium (K+) uptake by root system has been described to alleviate the deleterious effect of Na+, among other molecular mechanisms (such as Na+ extrusion and reabsorption, …). Here, we aim at uncovering the role of three major K+ transport systems in rice (OsAKT1, OsHAK5, OsHAK1) and Na+ (OsHKT1;5, OsSOS1) in salt stress tolerance. Furthermore, increasing records from the literature point to the role of endomycorrhizal fungus interactions with plants and the beneficial effects of such interactions on abiotic stress tolerance. Hence, we are interested to test the role of such microorganisms in K+ and Na+ homeostasis and salt stress tolerance. The rationale of the project states that studying K+ and Na+ transport systems in rice, is highly relevant for salt stress tolerance. Moreover, considering the beneficial effects of AMF interacting with roots of the crops is highly relevant, in particular in the context of soil salinity. The present project will target a major crop using state-of-the-art knowledge on physiological, molecular and genetic processes obtained in other plant model. We aim at going into a deeper understanding of plant adaptation on one of the most severe effects of climate change. Although we will develop basic research, our project will allow to gain knowledge for the profit of applied research. Context and Motivation Rice, the most cultivated crop worldwide, is subjected to soil salinization threat owing to its cultivation habitat (high occurrence in river deltas), and is furthermore the most salt (NaCl) sensitive cereal. Excess salinity in soil leads to both osmotic and ionic stresses. The later one is mainly due to detrimental effects of Na+ on cellular metabolism. The maintenance of a high cellular K+/Na+ ratio is a common mechanism developed by plants to withstand salt stress and K+ uptake is crucial in this objective (Horie et al. 2009). Thus, overexpression of OsHAK5 enhanced rice salt tolerance by elevating the shoot K+/Na+ ratio (Yang et al. 2014). Studies aiming at identifying key determinants of plant salinity tolerance have so far rarely taken into account mycorrhizal symbiotic interactions, although beneficial effects of arbuscular mycorrhizal fungi (AMF) on the plant response to salt stress is widely acknowledged (Chandrasekaran et al. 2016; Dodd and Pérez-Alfocea 2012). Improvement of plant mineral nutrition upon mycorrhizal inoculation, including increased K+ uptake, promoting a higher K+/Na+ in the host plants, was commonly reported, but the molecular mechanisms are still to be elucidated (Chandrasekaran et al. 2016; Ruiz-Lozano et al. 2012). In rice, AMF infection naturally occurs (Nakagawa and Imaizumi-Anraku, 2015). In this species, recent studies identified AMF-dependent expression regulation of cation transport systems involved in cell/tissue Na+ sequestration upon salinity stress (Porcel et al. 2016). However, no study addressed yet the effect of AMF symbiosis on plant cell K+ uptake systems upon salt stress. The rationale of the project states that studying K+ and Na+ transport systems in rice, is highly relevant for salt stress tolerance. Moreover, considering the beneficial effects of AMF interacting with roots of the crops is highly relevant, in particular in the context of soil salinity. Scientific Objectives To go deeper into the molecular and cellular explanation, the aim of the project is to uncover the regulation of K+ and Na+ uptake in rice upon salt stress and AMF symbiosis. It will be addressed by the following items: 1. The subcellular localization of (i) the three major K+ transport systems (OsAKT1, OsHAK5, OsHAK1) and (ii) the two major Na+ transport systems (OsHKT1;5, OsSOS1) will be investigated in rice, by means of cell biology approaches. A better understanding of subcellular behaviour of these five major rice K+ and Na+ transport systems upon salinity will be monitored. Thus, we will observe potential relocalization from plasma membrane into specific compartments, their dynamics of lateral diffusion in the plane of the plasma membrane, and their constitutive cycling dynamics. Moreover, their potential polar localization will also be described. 2. Identifying the molecular components involved into the subcellular dynamics of K+ and Na+ transport systems in rice roots in response to stimuli such as salt stress. From the first item, clues will be obtained that pave the way towards identifying molecular components suspected to be involved into the subcellular localization, the lateral diffusion in the plane of the membrane, the constitutive cycling upon salinity. More specifically, molecular components involved into the endocytosis and exocytosis will be addressed. 3. The subcellular localization of K+ and Na+ transport systems in rice root cells colonized by AMF will be investigated either in mock or salt stress conditions. Methodology and Planning 1. Molecular cloning of K+ OsAKT1 channel (Li et al. 2014), the high affinity K+ transporters OsHAK5 (Yang et al. 2014) and OsHAK1 (Chen et al. 2015), the Na+ transporter OsHKT1;5 and the H+/Na+ antiporter OsSOS1 which both play a role in maintaining an K+/Na+ ratio as high as possible in rice cells (Martínez-Atienza et al. 2007; Platten et al. 2006; Ren et al. 2005). These sequences will be tagged with a fluorescent protein sequence, and the constructs used for stably rice transformation, to obtain rice transgenic lines expressing at protein level the K+ or Na+ transport systems tagged with a fluorescent protein. 2. Transgenic rice plants cultivated in hydroponics will be challenged to salinity. Cell biology approaches by means of laser scanning confocal microscopy will be used to monitor the subcellular localization, and dynamics of the constructs in root cells (Luu et al. 2012; Wudick et al. 2015). To gain into resolution, super-resolution sptPALM microscopy will be applied according to previous developments in plant cells (Hosy et al. 2015). For instance, dynamics of lateral diffusion in the plane of the plasma membrane will be observed, as well as compartmentalization in microdomains of the cell surface. 3. Rice transgenic plants will be inoculated with AMF Rhizophagus irregularis, and subcellular dynamics of constructs will be observed. We will pay attention to rice cortical cells not colonized and colonized by arbuscular structure, to observe with a high interest the potential localization of the constructs into the peri-arbuscular membrane, a specialized plant cell plasma membrane in contact with the AMF. Plants inoculated with the AMF will be salt challenged, to decipher the specific behaviour of K+ and Na+ transport systems in plant-microorganism interactions. 4. Cortical cell colonization by arbuscular structures will be estimated and a survey of the genes specifically expressed by the plant cells during their colonization will be done. Physiological parameters accounting for the salt tolerance will be monitored (K+/Na+ ratio, reactive oxygen species production, chlorophyll content, …). In the frame of the thesis, the PhD student will be trained for and by scientific research activities. The PhD student will carry out experiments on rice plants grown in greenhouses and growth chambers, in a team concerned by ion transport and adaptation to environment in cereals, within an institute focused on water and nutrient nutrition in plants. Approaches on physiology and cell biology will be used. The PhD student will be trained to presentation, report and scientific article writing. He/she will have access to a wide choice of training courses (non-mother tongue language courses (French or English), statistics, ethics, …). Overall, the thesis will make the PhD student with skills in plant molecular physiology and cell biology, ready to be hired into research institute.
The PhD student will have good background in plant biology, particularly in plant physiology and cell biology. He.she will have an interest for scientific research activities and work done in rigorous conditions.
Your profile is eligible to apply for the PhD/Doctorate program «Make Our Planet Great Again» if:
- You have a Master’s degree or you will pass a Master’s degree before August 31, 2018
- You have lived in France for less than 90 days since April 1, 2016
- You are exclusively a foreign national
How to APPLY?
Please send your CV and a letter of motivation to the following contact : email@example.com