Thylakoid ion flux-Linking photosynthetic efficiency with osmotic stress response

Abstract

The global need for dramatic increases in food and fuel over the next decades requires the rapid development of crops with enhanced photosynthetic efficiency and robustness or tolerance to environmental challenges. Recent work suggests that the dynamics (or speed) of activation and deactivation of photoprotective mechanisms of photosynthesis are critical for avoidance of photodamage and for improving the efficiency of light capture of photosynthesis. Intriguingly, the initial characterization of mutants defective in thylakoid ion transport proteins uncovered a key role for thylakoid ion flux in regulating these dynamic responses. Moreover, thylakoid ion carriers act on Ca2+ signalling, a central mediator in the osmotic stress response. Taken together, these findings strongly suggest thylakoid ion flux as a promising, perhaps pivotal, target for plant improvement, yet our knowledge of key components is far from complete. Our preliminary results suggest that additional, previously uncharacterized, proteins are involved in fine-tuning the thylakoid network of ion homeostatic mechanisms and that multiple ion flux systems cooperate towards their physiological functions. A key goal of our consortium is to develop a mathematical model which will link modifications to thylakoid ion flux with photosynthetic efficiency and hyperosmotic stress response. The model will allow for testing new strategies to improve plant yield in various environments. We will use two data sets to verify and train our model: (a) experimental data derived from Arabidopsis and tomato mutants with loss- and gain of function in thylakoid ion transport proteins and (b) data derived from tomatoes grown commercially in Spain. The project brings together an international group with complementary expertise in chloroplast biology, thylakoid ion flux, bioenergetics, spectroscopy, phenotyping, modelling, ionomics, and biochemistry. We propose to pursue the following work packages (WP): (i) complete the thylakoid ion transport protein inventory; (ii) Determine the role of thylakoid ion flux interactions in photosynthesis and hyperosmotic stress resistance; (iii) Identify the process by which thylakoid ion flux impacts the hyperosmotic stress response; (iv) Analyse thylakoid ion flux impacts on key agronomical traits in tomato; and (v) Generate a model for simulating increases to photosynthetic efficiency and salt stress resistance as a function of thylakoid ion flux.