Minisymposium 22: Phytoremediation

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Abs # M2203: Isolation and characterization of a unique arsenate reductase from the arsenic hyperaccumulating fern Pteris vittata

Presenter:	Ellis, Danielle       Contact Presenter
Authors	Ellis, Danielle  (A)   Gumaelius, Luke  (A)   Indriolo, Emily  (A)   Banks, Jo Ann  (A)   Salt, David E (A)
Affiliations:	(A): Purdue University

Pteris vittata sporophytes hyperaccumulate arsenic to 1-2% of their dry weight. Like the sporophyte, the gametophyte was found to reduce arsenate (As(V)) to arsenite (As(III)) and store arsenic as free As(III). Here we report the isolation of an arsenate reductase gene (PvACR2) from gametophytes that can suppress the arsenate sensitivity and arsenic hyper-accumulation phenotypes of Saccharomyces cerevisiae lacking the arsenate reductase gene ScACR2. Recombinant PvACR2 protein has in vitro arsenate reductase activity similar to ScACR2. While PvACR2 and ScACR2 show similarities to the CDC25 protein tyrosine phosphatases, ScACR2 and PvACR2 lack phosphatase activity. In contrast, Arath;CDC25, an Arabidopsis thaliana homolog of PvACR2 was found to have arsenate reductase and phosphatase activities. PvACR2 is the first reported plant arsenate reductase that lacks phosphatase activity. CDC25 protein tyrosine phosphatases and arsenate reductases have a conserved HCX5R motif that defines the active site. PvACR2 is unique in that the arginine of this motif, previously shown to be essential for phosphatase and reductase activity, is replaced with a serine. Steady-state levels of PvACR2 expression in gametophytes were found to be similar in the absence and presence of arsenate while total arsenate reductase activity in P. vittata gametophytes was found to be constitutive and unaffected by arsenate, consistent with other known metal hyperaccumulation mechanisms in plants. The unusual active site of PvACR2 and the arsenate reductase activities of cell free extracts correlate with the ability of P. vittata to hyperaccumulate arsenite, suggesting that PvACR2 may play an important role in this process.