Abstract
When growing in its native habitat, Thlaspi goesingense can hyperaccumulate 1.2% of its shoot dry weight as nickel. We reported previously that both constitutively elevated activity of serine acetyltransferase (SAT) and concentration of glutathione (GSH) are involved in the ability of T. goesingense to tolerate nickel. A feature of SAT is its feedback inhibition by l-cysteine. To understand the role of this regulation of SAT by Cys on GSH-mediated nickel tolerance in T. goesingense, we characterized the enzymatic properties of SATs from T. goesingense. We demonstrate that all three isoforms of SAT in T. goesingense are insensitive to inhibition by Cys. Further, two amino acids (proline and alanine) in the C-terminal region of the cytosolic SAT (SAT-c) from T. goesingense are responsible for converting the enzyme from a Cys-sensitive to a Cys-insensitive form. Furthermore, the Cys-insensitive isoform of SAT-c confers elevated resistance to nickel when expressed in Escherichia coli and Arabidopsis thaliana, supporting a role for altered regulation of SAT by Cys in nickel tolerance in T. goesingense.
Highlights
Glutathione (GSH) is proposed to be an important antioxidant compound in reducing oxidative stress induced by the high concentration of nickel accumulated by the nickel hyper
X-ray absorption spectroscopy showed no significant presence of Ni-S complexes in either transgenic A. thaliana expressing targeted SAT from T. goesingense (TgSAT-m) [5] or in hydroponically or natural field-grown T. goesingense [5, 7], confirming that elevated GSH does not play a role in binding nickel directly
We hypothesize that an increased Cys insensitivity of serine acetyltransferase (SAT) in T. goesingense is a possible mechanism to account for at least part of the increased OAS production observed in T. goesingense and which we have shown leads to elevated GSH and nickel resistance [5]
Summary
Glutathione (GSH) is proposed to be an important antioxidant compound in reducing oxidative stress induced by the high concentration of nickel accumulated by the nickel hyper-. Plants transformed with the Cys-insensitive SAT genes, C268P, C268P/G270A, and TgSAT-c, and accumulating high levels of the SAT proteins showed elevated Ni2ϩ resistance, measured as either shoot or root growth, compared with the lines accumulating high levels of the Cys-sensitive AtSAT-c (Fig. 4, A and B).
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