Molecular analysis of phosphite induced responses in Arabidopsis

Phosphite (H2PO3-) is a phosphate analog widely used to protect plants from oomycete pathogens such as Phytophthora and Phytium. Phytopthora species are prominent pathogens in agriculture, e.g. Phytopthora infestans being the causing agent of potato blight (Irish potato famine). Phytopthora cinnamomi has devastating effects (“dieback disease”) on native ecosystems with over 2000 plant species at risk in Western Australia alone. Phosphite is the only known protectant of plants and exhibits a complex mode of action. At elevated concentrations it directly inhibits the pathogen’s growth by interference with its phosphate-dependent metabolism which is paralleled in plants grown on high phosphite concentrations. At the same time it also inhibits the plant’s phosphate starvation response, e.g. the up-regulation of high-affinity phosphate transporters, and thus has constrictive effects on plant growth under low phosphate supply. In addition to these direct effects phosphite also induces some of the plant’s defence responses, e.g. treatment of plants leads to increased expression of defence genes. However, the underlying mechanism of this indirect effect is not understood. We have started to characterise the impact of phosphite on plant defence responses by analyses of gene expression and metabolic pathways. Transgenic plants have been generated that express a microbial phosphite dehydrogenase which converts phosphite into phosphate. These plants are a valuable tool to dissect direct from indirect phosphite effects