PROTEOMPLANTSALTSTRS · Proteomics of plant responses to salt stress

Final Activity Report Summary - PROTEOMPLANTSALTSTRS (Proteomics of plant responses to salt stress)

In the coming years, climate change is predicted to have a significant impact on crop productivity globally. Climate change will not only involve a general warming worldwide but will lead to more extremes of climate such as heat waves and periods of flooding and drought. Increase in drought will lead to a greater need for irrigation, which, if poorly managed can cause soils to be contaminated with salt. Rising sea levels and increasing frequencies of storms will give rise to contamination of low lying agricultural land. Thus, salinity in soils is a major global problem and is one that is of growing importance. Globally, around 20% of all land is affected by salinity, up to 50% of irrigated land. The annual cost of this is estimated to be at least €10 billion, with this being expected to rise in the coming decades. This, combined with the growing world population, makes this vital that we increase our understanding of how plants respond to such stress. The need to ensure on-going food security in the face of changing climates is widely recognised as a major concern and is prominent amongst the recently defined EU priorities. Photosynthesis is well established to be the primary target of many forms of environmental stress, including salinity. This project, undertaken by Dr. Piotr Stepien in collaboration with Dr Giles Johnson at the University of Manchester, UK, investigated the extent to which the regulation mechanisms of photosynthesis contribute to resistance to damage in plants exposed to salt stress. The aim was to identify factors that might contribute to stress tolerance which could ultimately be breed into crop plants. Although photosynthesis is essential to life, it is widely recognised that the photosynthetic apparatus of plants can actually harm the leaf. If too much light is absorbed, photosynthesis can be a major source of a group of highly damaging substances called reactive oxygen species (ROS). These are produced in particular when plants are exposed to stress conditions such as salinity or drought which can give rise to imbalances in the leaves metabolism. ROS, including for example hydrogen peroxide, are highly reactive and can cause widespread damage to cells, destroying membranes, proteins and DNA. To prevent such damage, there are a number of enzymatic processes in chloroplast to scavenge ROS. Unfortunately these are highly energetically expensive, requiring the synthesis of high concentrations of antioxidants and antioxidant enzymes. An alternative strategy, placing less of a metabolic burden on plants, would be to avoid the production of ROS in the first place. This project investigated novel mechanisms to achieve this through regulation of photosynthesis. This study examined the effects of salt stress on the regulation of photosynthesis in two model plant species. Thale cress (Arabidopsis thaliana) is a common weed species that is widely used as a model plant in studies of plant genetics. A closely related species, salt cress (Thellungiella halophila) is found growing in salt rich soils, for example in parts of China. A number of studies have previously examined the responses of thale cress to salt. This has the advantage of being a well studied model system with a wealth of molecular and genetic information, however, as found here, its usefulness in salt tolerance studies, is limited by the fact that Arabidopsis is rather a salt sensitive. Salt cress, in contrast, is very salt tolerant. It is also tolerant of other environmental stresses, such as drought and low temperature. However, because it is a close relative of thale cress, sharing most of the same genes, it can be studied using many of the tools that have already been developed for its sensitive relative. In particular, a comparative approach studying both species has the potential to identify key characteristics that might be transferred between species to enhance stress tolerance. The work undertaken in this project demonstrated thale cress to exhibit severe symptoms of stress upon exposure to even moderate salinity, and, at higher concentrations of salt, to rapidly die.

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