The Effects of Polyphosphate on SPX Domains in Dictyostelium Discoideum
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Phosphorus is an atom taken up by cells as inorganic phosphate (Pi). The mechanism behind how cells measure cellular Pi levels is not well understood. SPX domains are positively charged helical bundles located at the N-termini of phosphate transporters, PolyP polymerase vacuolar transporter chaperone proteins, and phosphate signaling proteins. SPX domains have been shown to sense inositol polyphosphate signaling molecules in plants and yeast. These proteins are conserved in eukaryotes and affect polyphosphate synthesis, phosphate transport, and phosphate starvation. The genome of the simple eukaryote Dictyostelium discoideum encodes five predicted uncharacterized SPX domains. Using this knowledge a homologous recombination gene knockout for SPX 2 containing a Blasticidin resistance gene as a selectable marker was created. After validating the genotype of the knockout the associated phenotypes were elucidated. The SPX 2- cells exhibited a lack of aggregation upon exposure to 150 μM PolyP. SPX 2- fruiting bodies had longer stalks, smaller spore heads, and more mounds than wild-type. SPX 2- cells also had slightly higher motility rates. As polyphosphate and SPX domains are conserved across eukaryotes, anything learned about these areas can be applied to other organisms in areas such as Pi transport and starvation responses.
Watson, Jacob Basil (2017). The Effects of Polyphosphate on SPX Domains in Dictyostelium Discoideum. Undergraduate Research Scholars Program. Available electronically from