Overexpression of the PHO84 gene causes heavy metal accumulation and induces Ire1p-dependent unfolded protein response in Saccharomyces cerevisiae cells.

Pho84p, the protein responsible for the high-affinity uptake and transport of inorganic phosphate across the plasma membrane, is also involved in the low-affinity uptake of heavy metals in the Saccharomyces cerevisiae cells. In the present study, the effect of PHO84 overexpression upon the heavy metal accumulation by yeast cells was investigated. As PHO84 overexpression triggered the Ire1p-dependent unfolded protein response, abundant plasma membrane Pho84p could be achieved only in ire1Δ cells. Under environmental surplus, PHO84 overexpression augmented the metal accumulation by the wild type, accumulation that was exacerbated by the IRE1 deletion. The pmr1Δ cells, lacking the gene that encodes the P-type ATPase ion pump that transports Ca(2+) and Mn(2+) into the Golgi, hyperaccumulated Mn(2+) even from normal medium when overexpressing PHO84, a phenotype which is rather restricted to metal-hyperaccumulating plants.