Functional homologs of fungal metallothionein genes from Arabidopsis.

Abstract

Metallothioneins (MTs) are cysteine-rich proteins required for heavy metal tolerance in animals and fungi. Two cDNAs encoding proteins with homology to animal and funga1 MTs have been isolated from Arabidopsis. The genes represented by these cDNAs are referred to as M7Y and MT2. When expressed in an MT-deficient (cupíA) mutant of yeast, both M77and MT2 complemented the cuplA mutation, providing a high leve1 of resistance to CuS04 and moderate resistance to CdS04. Although the MT-deficient yeast was not viable in the presence of either 300 pM CuS04 or 5 pM CdS04, cells expressing MT1 were able to grow in medium supplemented with 3 mM CuS04 and 10 pM CdS04, and those expressing MT2 grew in the presence of 3 mM CuS04 and 100 pM CdS04. In plants, MT1 mRNA was more abundant in roots and dark-grown seedlings than in leaves. In contrast, MT2 mRNA accumulated more in leaves than in either roots or darkgrown seedlings. MT2 mRNA was strongly induced in seedlings by CuS04, but only slightly by CdS04 or ZnS04. However, MT1 mRNA was induced by CuS04 in excised leaves that were submerged in medium. These results indicated that Arabidopsis MT genes are involved in copper tolerance. Plants also synthesized metal binding phytochelatins (poly[yglutamylcysteine]glycine) when exposed to heavy metals. The results presented here argue against the hypothesis that phytochelatins are the sole molecules involved in heavy metal tolerance in plants. We conclude that Arabidopsis MT1 and MT2 are functional homologs of yeast MT.

Expression of the type 2 metallothionein-like gene MT2 from Arabidopsis thaliana in Zn2+-metallothionein-deficient Synechococcus PCC 7942: putative role for MT2 in Zn2+ metabolism

“…260 bp product was recovered from an agarose gel [39], cloned into pGEX3X generating pGAMT2, and checked by sequence analysis (reaction products analysed using an Applied Biosystems 370A DNA sequence analyser). The obtained sequence was identical to the reported cDNA for MT2 [ 51 ], but both differ from the original database sequence (X62818) by a single nucleotide resulting in a codon change Ser-64 to Asn-64.…”

“…Type 1 sequences are from maize (Z. mays) [3 ], barley (H. vulgate) [31 ], wheat (T. aestivum) [421, rice (O. sativa) [EMBL U 18404], pea (P. sativum) [5], clover (T. repens) [EMBL Z26493] and M. guttatus [4]. Type 2 sequences are from clover [EMBL Z26492], broadbean (K faba) [8], soybean (G. max) [20], castorbean (R. communis) [48], kiwi fruit (A. deleciosa) [24], arabidopsis (A. thaliana) [ when expressed in a copper-sensitive CUP1-deficient mutant of yeast under the control of a constitutive promoter [51]. It was concluded that these genes are functional homologues of fungal (copper) metallothionein, but can a plant metallothionein functionally substitute for a known Zn z+ metallothionein?…”

A novel stress-inducible metallothionein-like gene from rice

“…However, the role of MT in plants has only been recently investigated upon the finding that MT-like proteins containing cysteine-rich domains may also exist in higher plants. Indeed, genes encoding MT-like proteins have been identiffed in wheat [3], maize [4], barley [5], Arabidopsis [6,7], pea [8] and soybean [9]. Evidence that MT-like proteins from plants can bind certain trace metal ions has also been noted [10], suggesting a bona fide MT nature of these proteins.…”

“…Some of the plant The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number V10404 MT-like genes have also been shown to be inducible under different environments. MT 1 and MT2, two isoforms of MT-like genes of Arabidopsis, are induced by CuSO4 [7], ids-1 of barley is induced under iron deficiency [5], Ec gene of wheat is induced by abscisic acid (ABA) [3], and LSC54 of Brassica napus is induced during leaf senescence [ 12].…”

RNA expression patterns of a type 2 metallothionein-like gene from rice

“…However, a survey of the distribution of class l MT-like gene products from pea [7], maize [5], barley [16], wheat [21], Arabidopsis [25,27], long pod bean [9], and rice [1 l, 19] shows that type 1 transcripts accumulate mainly in the underground and type 2 in the aerial portions of a plant.…”