Analysis of structure and function of the cell death regulator protein BAX INHIBITOR-1 at the interface of plant-microbe interactions

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BAX INHIBITOR-1 (BI-1) proteins are conserved regulators of stress- and pathogenesis-related cell-death in plants and animals. We found that BI-1 negatively controls cell death as well as resistance to the biotrophic powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) in barley. Over-expression of BI-1 was suitable for control of necrotrophic fungal pathogens and supported establishment of arbuscular mycorrhizal symbiosis. Recently, we obtained evidence that BI-1 is required for barley full susceptibility to Bgh. Little is known about the mechanism of BI-1 activity, but it likely regulates cellular Ca2+ concentrations. We want to investigate in detail the interaction of BI-1 over- and under-expressing Arabidopsis thaliana and barley plants with different biotrophic and necrotrophic pathogens. Ca2+ imaging in intact plants and single epidermal cells will accompany infection studies. Because we assume functional redundancy of BI-1-like proteins in Arabidopsis, we will generate multiple knock-outs and knock-downs of BI-1-like genes. To further investigate BI- 1 function, we are going to identify and functionally analyze proteins, which interact with barley BI-1 by using a split ubiquitin membrane yeast two hybrid system.