Molecular analysis of salt tolerance proteins

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Soil salinity is a major factor in reducing plant growth and productivity. Most crop plants are highly sensitive to salt stress that tends to cause a water deficit due to osmotic stress, and that causes several biochemical problems due to toxic excess intracellular sodium. The degree of salt tolerance of some plant species varies greatly. Sodium/Hydrogen (Na+/H+) antiporters are membrane proteins that remove salt from inside the cells of plants and yeast. Overexpression of Na+/H+ antiporters has been shown to confer improved salt tolerance in plants allowing them to grow in saltier soils. The purpose of our project is to understand how Na+/H+ antiporters work, that is, to better understand the way that they remove salt out of cells. To do this we are using a model system of yeast to study how Na+/H+ antiporters function. Yeast have Na+/H+ antiporters that are very similar to plant Na+/H+ antiporters. They are related in protein sequence and can replace each other and function normally. There are several parts to the project. In one part we are learning which regions of the protein are important in activity. We use a yeast that has its Na+/H+ antiporter deleted and return the Na+/H+ antiporter into the yeast after we make mutations in the protein. Then we study how the protein functions. In another part of the study we are producing the protein and will examine the protein structure using nuclear magnetic resonance and electron microscopy. This will give us a picture of the protein. Additionally, we will use a technique whereby we can label the Na+/H+ antiporter protein with specific tags. These allow us to identify the location of the tags on the protein and give us an idea of the topology (or structure) of the protein. Overall, the project will help us understand how the protein works, allowing us to better design proteins that can be used to improve salt tolerance in plants.