Reference: Guo WJ, et al. (2008) Examining the specific contributions of individual Arabidopsis metallothioneins to copper distribution and metal tolerance. Plant Physiol 146(4):1697-706

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Abstract


Metallothioneins (MTs) are small cysteine-rich proteins found in various eukaryotes. Plant MTs are classified into four types based on the arrangement of cysteine residues. To determine whether all four types of plant MTs function as metal chelators, six Arabidopsis MTs (MT1a, MT2a, MT2b, MT3, MT4a, and MT4b) were expressed in the Cu- and Zn-sensitive yeast mutants, Deltacup1 and Deltazrc1Deltacot1, respectively. All four types of Arabidopsis MTs provided similar levels of Cu tolerance and accumulation to the Deltacup1 mutant. The type 4 MTs (MT4a and MT4b) conferred greater Zn tolerance and higher accumulation of Zn than other MTs to the Deltazrc1 Deltacot1 mutant. To examine the functions of MTs in plants, we studied Arabidopsis plants that lack MT1a and MT2b, two MTs that are expressed in phloem. The lack of MT1a, but not MT2b, led to a 30% decrease in Cu accumulation in roots of plants exposed to 30 microM CuSO4. Ectopic expression of MT1a RNA in the mt1a-2 mt2b-1 mutant restored Cu accumulation in roots. The mt1a-2 mt2b-1 mutant had normal metal tolerance. However, when MT-deficiency was combined with phytochelatin-deficiency, growth of the mt1a-2 mt2b-1 cad1-3 triple mutant was more sensitive to Cu and Cd compared to the cad1-3 mutant. Together these results provide direct evidence for functional contributions of MTs to plant metal homeostasis. MT1a, in particular, plays a role in Cu homeostasis in the roots under elevated Cu. Moreover, MTs and phytochelatins function cooperatively to protect plants from Cu and Cd toxicity.

Reference Type
Journal Article
Authors
Guo WJ, Meetam M, Goldsbrough PB
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